Introduction to FSR Design 2014
Technical Introduction
for
New Teams
Pat Clarke 2014 ©
Introduction to FSR Design 2014
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Introduction to FSR Design 2014
Introduction:
This presentation is specifically written to introduce students, involved
in Formula Student Russia for the first time, to the practical aspects of
designing a suitable car.
It does not tell you how to design the vehicle, nor does it attempt to
influence your design decisions.
The intent is to help guide teams to build a safe car, one that will pass
through tech inspection and will permit the team to take part in all
events, both static and dynamic, in a competitive manner.
Please note that any illustrations in this presentation are just that,
illustrations!
Some are exaggerated in order to better explain some topic.
They should not be scaled or used in the design of a Formula Student
car in any way other than as examples.
The Rules for Formula Student change from time to time. This manual
was written in 2014 and represents the rules as they stand at that time.
Pat Clarke
OH!
Pat Clarke will take any responsibility for any loss or injury suffered to
any person whilst building or driving a Formula Student car after
following some of the guidelines given in this manual.
© JP Clarke 2014
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Introduction to FSR Design 2014
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Introduction to FSR Design 2014
Contents:
3.
7.
8.
10.
11.
13.
14.
17.
19.
21.
27.
39.
46.
51.
53.
55.
59.
60.
67.
74.
77.
80.
88.
94.
108.
119.
126.
151.
162.
166.
Introduction
The Intent of Formula Student Russia
Recommended Books
The Rules
Project Management
Murphy’s Law
Design Decision Stage
Interpreting the Rules
The Challenge Reduced to Basics
Tyre Choice
Technical Terms Explained
Roll Centres
Steering Effects on Suspension Geometry
Force Based Roll Centres
Anti Roll Design
Pitch and Squat
Overall Design of the Car
Special Parts
Designing the Suspension Geometry
The Engine
Final Drive and Differential
Design of the Chassis
Mounting the Suspension and Wheels
Building the Chassis
Bodywork Fabrication
Threaded Fasteners
Workshop and Hand Tools
Using Electrical Tools
Simple Electrical Diagnosis
Supplemental Information
167. How To Write a Design Report
171. Roll Centres: Myth and Reality
183. Reading a Dyno Chart
185. Cockpit Control Forces
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Introduction to FSR Design 2014
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Introduction to FSR Design 2014
First Question.
What are you trying to achieve?
Before you start your Formula Student project, you need a plan!
This is where a team must face its limitations. There is nothing worse
than trying to achieve more than the team’s capabilities!
That is a sure fire path to disappointment!
Remember the old saying...
‘If you fail to plan, you plan to fail’!
The Intent of Formula Student
Formula Student was introduced to enhance the skills of young
graduate engineers by giving them a ‘Real Life’ challenge.
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It is a Design Competition.
It is not a Racecar competition.
It is part of your education
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Introduction to FSR Design 2014
Words of Wisdom
Carroll Smith, famous race car engineer said...
“We are seeing engineers who can calculate all the
stresses and strains in a threaded fastener, but
don’t know which way to turn the wrench”!
Carroll was a race engineer most famous for
preparing the Ford GTs that dominated Le Mans in
the 1960s. Later he was a champion of FSAE and
recruited most of the current crop of Chief Judges
This is the first of Several ‘Words of Wisdom’.
Note, all wisdom related to Formula Student does not come from Race
car engineers!
A FSI teams should have the Carroll Smith ‘To win’ series of books in
their reference library!
And while speaking of books, every team member
should have their personal copy of ‘Learn and
Compete’, the Formula Student primer written by
many of the Senior Design Judges.
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Introduction to FSR Design 2014
So, the challenge is to design a car for production.
The car is designed and then built as a proof of concept.
At the Competition the design is then statically judged to determine
which is the best and most suitable for a production car.
The car is thoroughly inspected to ensure it meets all rules and safety
requirements. (Tech Inspection or Scrutineering)
Finally, once the car has been determined as being safe and in
compliance with the rules, it’s performance is then demonstrated in the
various Dynamic Events.
Although all students eagerly anticipate driving their cars, FSR is not
primarily about the Dynamic Events.
The Dynamic Events are the Proof of Concept.
So, if the competition is primarily about Design, then a Design Plan
must be drawn up.
This plan and the running report on its progress becomes the basis of
the Design Report.
We can read about the Design Report later in the supplemental part of
this manual.
NOTES:
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Introduction to FSR Design 2014
Second Question.
Where do you start?
With the Rulebook! First, you must read and
understand the rules! All the rules!
It might seem like the rule book is a huge
complicated document, but it really is quite
logical.
Many useful things about the design of a
Formula Student car can be gleaned from the
rulebook!
If a car is brought to an event and it cannot
pass Technical Scrutiny, it simply will not be
permitted to compete in the Dynamic Events!
You may think this is unfair, however, they
are the rules of the game and apply to all
teams.
NOTES:
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Introduction to FSR Design 2014
Project Management
The biggest single challenge in Formula Student is Managing the
Project. If the entire project is not complete, then the entire years work
by the team may have been wasted.
Every year we see disappointed students bring an unfinished or
untested car to the competition. Don’t be one of them!
Project Management is a hugely important facet of Formula Student
and also in life. It is beyond the scope of this course to cover Project
Management, but I would urge you to pursue training in this area.
There are several free on-line seminars teaching Project Management
available.
Avoid the temptation to modify the design after the ‘Design Freeze’
deadline.
Every team member will learn as they go and there is a huge
temptation to add this new knowledge to the car. Unless it can be
seamlessly done, bright new ideas should be saved for the next car!
It takes a strong project manager to ensure this happens.
And remember the words of George Santayana!
Words of Wisdom
George Santayana, Spanish philosopher
wrote...
“Those who cannot remember the past
are condemned to repeat it"
George Santayana was a philosopher,
essayist, poet, and novelist.
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Introduction to FSR Design 2014
Team Leader
It is imperative to set project deadlines and then to meet them.
The car must be finished a month before the competition to allow for
testing, tuning and driver training and the repairs and remanufacturing
that will inevitably follow!
Formula Student is no place for democracy! The Team Leader (singular)
must be a strong and decisive character who has the respect of his
team. His word must be law.
Every successful Formula team I ever saw had such a leader!
It is all too easy for a team to democratise itself into mediocrity! I have
seen that happen too!
Every team member learns as the process evolves. They begin to
understand more about what they are doing and so will often come up
with great new ideas to make the car better.
The team leader must moderate this enthusiasm, only permitting
whatever ‘improvements’ can be incorporated seamlessly into the
project. Otherwise these great new ideas should be put aside for next
years car. It is also the responsibility of the team leader to ensure the
team are working within their capabilities. We have seen some
wonderful unfinished cars at Formula Student when the team ran out of
time, money or inspiration.
Don’t laugh at the graph
shown here! It shows a
(somewhat cynical)
graphical representation of
the dynamics within a
Formula Student team.
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Introduction to FSR Design 2014
A Word of Warning
I would like to introduce you to a gentleman who will do his utmost to
derail your project!
He ‘sees’ everything you do!
He never blinks, he never sleeps, he is always ready to intervene.
He does his best work when you are at your worst!
Only careful planning, constant vigilance, record keeping and common
sens will keep him at bay and frustrate his efforts.
His name is Murphy! Edward Aloysius Murphy.
Major Ed Murphy, aerospace engineering
auditor wrote...
“Whatever can go wrong, will go wrong!"
Better known as ‘Murphy’s Law’
Edward Aloysius Murphy, Jr. (1918 – 1990) was
an American aerospace engineer who worked
on safety-critical systems on the rocket sled
team as part of the US Astronaut program.
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Introduction to FSR Design 2014
NOTES:
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Introduction to FSR Design 2014
The Car Design Decision Stage
Before the team even start on their design, they need to decide on two
items
1. What tyres they will use, and
2. What engine they will use.
If the team is located in a country where it may be difficult to source
suitable engines and tyres, then a concentrated effort must be made to
source them (the engine in particular) prior to commencing Design.
The team then need to make their own copies of the various templates
used in Formula Student, The foot-well and cockpit templates and the
‘Percy’ manikin.
At the event, if the car does not accept these templates, it will not be
permitted to compete in the Dynamic Events.
‘Percy’
Cockpit
Foot-well
Note, the Percy model and ALL the drivers must pass Technical
assessment regarding Roll hoop clearance etc. If one driver fails this or
the 5 second egress test, he (or she) will not be permitted to drive at the
event.
Before starting design, the team should assess all aspects of the car
such as power, weight, weight distribution, C/G position as far as
possible. This should be managed from the first day of the project.
Weight is critical and cannot be overcome with ‘more power’ as some
teams think. Excess weight slows the car in cornering and braking as
well as in acceleration.
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Introduction to FSR Design 2014
Words of Wisdom
Ron Tauranac, Champion Formula 1
Designer says...
“Nothing weighs less than nothing”!
Ron Tauranac A.O. designed and built the
1966 and 1967 World championship
Brabham cars as well as innumerable
championships in lower formulae won by
Brabham and RALT cars.
Ron Tauranac is the Patron of FSAEA.
What does Ron T. mean by this?
Simply, if something serves no good function on the car or doesn’t need
to be there, then it shouldn’t be left off!
We so often see things on cars that add nothing but mass. That includes
structures or components that are either too large, over engineered or
simply not needed.
Teams need to think very hard about the advantages if they decide to
add heavy components like superchargers, ABS systems or even fire
suppression systems.
Fancy bodywork, especially in fibreglass and aerodynamic appendages
should also come under review.
Judges are very critical of heavy cars. There is no reason for any 600cc
four cylinder car to weigh much more than 200Kg and a single cylinder
car should weigh less than 170Kg! Even for a new team!
Teams often think an extra 10 or 15Kg will not make much difference.
I ask them to consider what the effect would be if I asked them to drive
with two bowling balls on their lap!
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Introduction to FSR Design 2014
Early Design Decisions.
Before starting on the car, all the following things should be considered
and entered into the equation as each has a significant effect on the
final design!
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Engine choice.
Wheel size choice.
Tyre choice.
Cockpit and foot-well templates.
Percy and all drivers.
Front impact structure.
Side impact structure.
Front and rear roll hoops.
Steering wheel.
Pedal box.
Steering Rack position.
An approximation of the suspension mounting points.
How to Interpret the Rules
The Formula Student rules are printed in a straightforward document
and must be complied with. This is not Formula One where every
loophole is exploited and teams bring lawyers to every race.
Simply, you abide by the rules or you don’t drive!
There is an appeals process where a team can lodge a number of points
which they lose if the appeal is lost.
Not many appeals are won, so as a result, there are very few appeals!
However, there are advantages to be had by fully understanding what
the rules actually say!
If a team has any doubt about a rule or its intent, they should contact
the organiser for a ruling.
Opinions stated on FSAE.com don’t count!
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Introduction to FSR Design 2014
For Instance...
What does the 50mm wheel travel rule mean?
Does it mean a minimum of 25mm ground clearance?
Well, maybe it does, but there is no rule that requires 25mm ground
clearance, but there is a rule that prohibits any part of the car coming
in contact with the track surface except the tyres.
So, ground clearance should be set at 25mm+ in most cases.
But, if your car had some advanced suspension system, say an ‘active
ride system’, there is no rule stopping you from running the car at 1mm
ground clearance as long as you can avoid track contact!
Sometimes the rules will give you a hint to where some performance
can be gained, but before you can determine this you need to
understand what the rules are all about.
Some are for safety, and they are absolute. Don’t mess with them.
Other rules are Formula Rules and this is where some advantage may
be found.
An example of this is the 20mm intake restrictor. This is an absolute
maximum dimension with no tolerance. It will be checked with a go/no
go gauge at the competition and if it is even .001mm oversize, it will
fail tech. Note it must also be round, not oval or some other shape and
it is also singular. This means you can only have one, even of you are
running a twin engine car, which is quite legal if within the 610cc
capacity limit.
However, there is no rule prohibiting a converging/diverging venturi
through the restrictor to recover some of the lost flow. Nor is there a
rule prohibiting a plenum after the restrictor to minimise its effect.
So, it is important to understand the rules and the intent of the rules if
they are to be used to your best advantage, but remember, violation of
the intent of a rule is seen as violating the rule itself!
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Introduction to FSR Design 2014
The Formula Student challenge reduced to basics
In its most basic form, the solution to designing a fast car is reduced to
a simple physics problem.
You are being asked. ‘Using only the
forces generated at the tyre contact
patch, accelerate a mass (the car) from
here, back to here via the race course in
the shortest time possible, using the
least amount of fuel’!
If we look at it as simply a physics problem, we need some...
Words of Wisdom
from the world’s most famous physicist.
Sir Isaac Newton outlined three Laws of Motion that
all Engineers should be familiar with and all relate to
‘Accelerating that Mass around the race course’
Newton’s First Law of Motion
“The velocity of a body remains constant unless that body is acted upon
by an external force”
Paraphrased, this relates to our car as follows...
“The car will continue in a straight line unless we apply some force to
turn it” or “The car will sit there stationary unless we apply some force
to move it” or “The car will fly off the road in a corner unless we apply
some force to turn it”.
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Introduction to FSR Design 2014
Newton’s Second Law of Motion
“The acceleration ‘a’ of a body is parallel and directly proportional to
the net force ‘F’ and inversely proportional to the mass ‘m’”.
This is usually expressed as:
F = ma
When we relate this to our car, it means that to increase the ‘a’ (in any
direction), we must either reduce the ‘m’, increase the ‘F’ or preferably
do both!
It is very important to understand this!
Newton’s Third Law of Motion
“The mutual forces of action and reaction between two bodies are
equal, opposite and collinear”.
This is usually written “Every action has an equal and opposite
reaction”.
How this relates to our car is simple, the harder we push (the ‘F’)
and the lighter it is (the ‘m’), the faster it will go (‘a’)!
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Introduction to FSR Design 2014
Tyre Choice
What do we ‘push against’ to make our car go, stop and turn?
Ignoring aerodynamic devices for the time being, the only thing we can
‘push against’ is the grip generated at the four tyre contact points!
So, the most important performance decision when designing your car
is not the choice of engine but the choice of tyre!
Ideally, the tyre would be chosen based on the results of testing in the
TTC program.
But in the real world, for an inexperienced team the tyre choice order
should be...
1. Any dedicated FSAE tyre
2. Any other racing slick tyre
3. Any other racing treaded tyre
9. Any high performance road tyre
No, that is not a misprint! Road tyres should only be chosen as an
absolute last resort!
1. Dedicated FSAE tyres.
Hoosier is the most popular Formula Student tyre now that Goodyear
have withdrawn from the market, so there is lots of knowledge
available about this tyre. Other companies make FSAE tyres
A team will need three sets of slick tyres and one set of ‘wet’ tyres!
Slick tyre
Treaded ‘wet’ tyre
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Introduction to FSR Design 2014
You will destroy one set when
setting up the car, trying to find the
optimum toe and camber settings!
Once the car is set up, you need a
set to practice and train the drivers
and another new set for the event.
Plus ‘wets’ (grooved tyres)
mounted on rims in case it rains!
Note, at Formula Student Germany,
it always ‘rains’ on the figure
eight event!
Other Racing Tyres
Slick tyres for some other racing formula are the next option! Be careful
if choosing tyres designed for sprint and hill-climb events. These are
designed to offer maximum grip from cold and so are easily damaged
in longer distance events such as a Formula Student endurance run.
Race tyres for ‘spec formulas’ are compromised in the other direction.
Because there is no tyre competition, the contracted supplier makes
very conservative tyres which are often quite hard and long wearing
(read ‘slow’).
It is worthwhile contacting tyre companies directly, especially if they
have a competition division. Remember, tyre companies need
development engineers, so a bright young student who has an
understanding of tyres might gain a career opportunity!
Race tyres designed for modified road cars are also a poor choice as the
carcase will be stiff enough to support a heavy (greater than 1000Kg)
street car and so will be far too stiff for a sub 300Kg Formula Student
car.
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Introduction to FSR Design 2014
9. Street Tyres
As a last option, a team can use street tyres.
The disadvantages would be...
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Much lower grip.
Excessive carcase stiffness.
Much higher weight, especially in the steel belt.
This greatly increases the rotational inertia.
The advantages would be...
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Lower cost
Longer life
Easy availability
No need for additional ‘wet’ tyres.
Why do I recommend a 13” wheel for new teams?
There are several reasons...

The choice of tyres is greater.

There is more room inside the wheel for brakes and
suspension components.

A 13” wheel permits a better load path for the suspension
and braking forces to be fed into the chassis.
NOTES:
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Introduction to FSR Design 2014
Wheel Parameters
There are standards for wheel
parameters and teams considering
making their own wheels should be
aware of them.
I recommend that chassis and
suspension design should be around
a ‘standard’ wheel design as
‘custom wheels are rare and
expensive!
‘Sporty’ alloy wheels may look nice,
but in reality are often much
heavier than standard pressed steel
road car wheels.
Choosing a ‘standard’ wheel
dictates several vehicle parameters.
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Wheel Diameter and bead width
Wheel offset.
Wheel stud number and PCD.
Centre spigot diameter.
It may also dictate such things as brake calliper placement and steering
arm location, so if the team decide to use an ‘over the counter’ wheel, it
should be chosen prior to design of the suspension and steering
commencing.
Some more advice about wheels.
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Wheel compliance is a major contributor to dynamic
camber loss.
The wheel should be centred on a spigot, not by the
taper on the wheel nuts.
All wheel and tyre assemblies should be balanced to
prevent unbalance forces upsetting the tyre contact patch.
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Introduction to FSR Design 2014
Tire Testing Consortium
In 2005, a group of teams and FSAE Mentors set up the FSAE TTC.
The FSAE TTC is a volunteer managed organization
who pool financial resources to obtain high quality
tire data.
The TTC’s role is to organize and conduct tyre tests,
and distribute the data to all participating teams.
The TTC Coordinator, Dr. Ed Kasprzak can be
contacted at...
edward.kasprzak@millikenresearch.com
Membership of the TTC (US$500) is worthwhile, not just for the data
available about FSAE tyres, but it is an incredible education about how
tyres are made and tested.
Looking after tyres.
Race tyres are expensive, can be difficult to obtain and are critical to
your car’s performance, so it makes sense to look after them properly.
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Between uses, deflate the tyres and store them in a cool dry
place, in a sealed garbage bin liner if possible.
Store them away from sunlight and ozone sources such as
electric motors, compressors, welders etc.
Avoid contaminating the tread surface with oil, fuel or other
substances
Ensure the air used for inflation is dry.
To avoid picking up contamination, use tyre covers when
rolling the car around on its race tyres, especially when they
are hot.
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Introduction to FSR Design 2014
Revisiting F=ma relative to tyres
‘F’ comes from the tyre grip so we should do all we can to enhance that,
‘m’, mass in tyres generates rotational inertia, so the weight of tyres is
important.
Steel belted radial street tyres are heavy and much of that weight is
located at the outer periphery of the tyre, the steel belt, so the polar
moment of inertia within the wheel and tyre assembly is very high!
Another reason to avoid such tyres if at all possible.
‘Polar moment of Inertia’ is usually used in the context of yaw inertia in
the entire vehicle, but PMI should also be considered within the car!
The illustrations below show the practical effect of reducing PMI.
Two barbells are being swung, the first with the weights at the outside
of the bar, the second has the weights moved closer to the rotational
axis, i.e. reduced PMI.
It is easy to see the lower barbell is easier to control than the top one.
Keeping this principle in mind when designing every aspect of the car
will ensure the tyres have their best chance of ensuring a
manoeuvrable car with minimum tyre stress.
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Introduction to FSR Design 2014
Explanation of Technical Terms
It is important to be able to ‘talk the talk’ when discussing chassis
design parameters with team mates, judges and other engineers.
Wheelbase
Wheelbase describes the distance between the centre of the front and
rear wheels when viewed from the side. It is usual, but not compulsory,
that the wheelbase is the same on both sides of the car.
There is a rules minimum for the wheelbase on Formula Student cars,
which usually have a short wheelbase.
Track
Track refers to the distance, centre to centre, between the front or rear
wheels. It is not the total width.
On a Formula Student car, the rear track is usually narrower than the
front, but this difference is covered by a rule.
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Introduction to FSR Design 2014
Camber (Static)
Camber is the angle, expressed in degrees, at which the tyre is
presented to the ground.
In race cars, camber is usually set ‘negative’, that is the tyres are closer
together at the top than at the bottom.
Track testing will help a team determine optimum camber by
measuring tread temperature across the tread.
The usual camber range
used in Formula Student
is typically from
0⁰ to -2⁰.
Steering Axis Inclination (SAI)
SAI, also called ‘KPI’ (Kingpin inclination’) is the angle of the axis about
which the wheel steers when viewed from the front expressed in
degrees. It is primarily a stability parameter, centring the steering when
exiting a corner.
SAI moves camber in a positive direction when the wheel is steered.
Because of this and the light weight of a Formula Student car, very little
SAI is required.
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Introduction to FSR Design 2014
Scrub Radius
Scrub radius, sometimes called ’Steering offset’ is the offset of the
centre of the contact patch from an extension of the steering axis,
measured at ground level. It is expressed in mm.
A small amount of positive offset is desirable in a lightweight car in
order to give steering feel feedback to the driver.
Tyre distortion may
cause scrub radius to
go negative when
Cornering. This is
not a desirable
condition.
Caster
Caster is the angle of the steering axis when viewed from the side.
It is expressed in degrees. It should always be ‘positive’, that is the top
ball joint trails behind the bottom one.
Caster is a stability parameter and a typical Formula Student car would
have between 2⁰ and 8⁰ positive caster.
Caster will also affect wheel
camber when the car is steered.
The camber will move towards
positive when the wheel is
turned out and towards
negative when the wheel
is turned in.
Chassis engineers use this
effect to their advantage!
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Introduction to FSR Design 2014
Caster Trail
Sometimes the choice of caster angle for kinematic reasons may result
in excessively heavy steering effort. This effect can be minimised by
moving the axle ahead of the steering axis, thus reducing the ‘trail’ and
therefore the steering effort required.
It is sometimes called ‘caster offset’
or ‘spindle offset’.
Toe In and Toe Out
‘Toe’ refers to the difference in width measured at the front and rear of
either pair of wheels at axle height.
‘Toe-out’ means the front measurement is greater than the rear, and
‘toe-in’ is the opposite. The illustration shows toe-in.
Toe is usually expressed in mm, or less frequently, in degrees and
minutes.
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Introduction to FSR Design 2014
Bump and Roll Steer
Bump and Roll Steer is a condition where the wheel steers as the
suspension articulates. It can affect the front or rear of the car.
It is caused by an incompatibility between the suspension geometry
and the steering or toe control linkage geometry.
Bump steer makes the car unstable when cornering, braking and
accelerating. More on Bump Steer later in this manual.
Ackermann
Ackermann is (usually incorrectly) used to describe any mechanism or
articulation of the steering linkage used to change the toe setting as
the wheels are steered. It might be more properly called ‘Dynamic Toe
Change’.
Ackermann is said to be ‘positive’ when the toe out increases or the toe
in decreases with steering. ‘Negative’ Ackermann is where the toe out
decreases or toe in increases with steering.
Formula Student cars usually benefit from a strong positive Ackermann
geometry as this helps with the rapid steering changes needed in a
Formula Student event.
Testing whilst monitoring tyre temperatures can help determine the
optimum Ackermann for any given car.
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Introduction to FSR Design 2014
Ackermann
The following illustrations show how positive Ackermann geometry increases the front wheel toe-out as the car is steered.
With the steering turned to the right, it can be seen that the inner (RH)
wheel has turned through a greater angle than the outside (LH) wheel.
When Ackermann effect is combined with the effect of Caster and SAI,
this will materially affect a diagonal weight transfer in the car when
the steering is turned.
In turn, this can affect the teams choice of differential!
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Introduction to FSR Design 2014
Rear Toe Control
Inadequate control of rear wheel toe angle leads to a fundamentally
poor handling car that is very difficult to drive.
It is one of the major design errors seen repeatedly on Formula Student
cars.
Usually, a ‘Z arm’ or a separate toe link is used to control rear toe.
For this control to be effective, the reaction must be spread over as
wide a base as is practical, another argument in favour of 13” wheels!
The illustration below shows common rear toe control errors.
In both cases the rear toe base is insufficient. Toe change forces in the
RH example are fed in bending into the control arm.
The LH example will also result in bump steer.
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Introduction to FSR Design 2014
Dynamic Camber Change
Usually the suspension geometry is designed to change the camber
angle as the suspension articulates. This ‘camber gain’ is to cancel the
effect of ‘camber loss’ as the chassis rolls under the effect of lateral
force when cornering.
Camber Change in Bump
Note, the virtual swing axle length shortens as the wheel moves in
bump, so the generation of negative camber increases with wheel
travel. A good argument to limit wheel travel!
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Introduction to FSR Design 2014
Camber Change in Droop
The negative camber reduces at a decreasing rate when the suspension
moves into droop and the virtual swing axle gets longer.
So, the dilemma facing the suspension designer is to try keep the tyres
virtually upright under braking and accelerating when the car dives or
squats, but to try avoid the outside wheel going into positive camber
when the car rolls under the influence of lateral force whilst cornering.
Words of Wisdom
Champion Formula 1 designer Colin Chapman
wrote...
“Any suspension can be made to work as
long as you don’t let it”!
Chapman’s Lotus cars won the World Championship
on seven occasions as well as the Indianapolis 500.
At the most basic level, this is best achieved by limiting suspension
travel to restrict the amount of camber change.
This is what Chapman meant when he made his statement.
But remember, there is a Formula Student rule about minimum
suspension travel!
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Introduction to FSR Design 2014
Swing Axles
This illustration is included to show what is meant by ‘swing axle
length’.
Camber Dilemma
At the front, the wheels should be straight up and down when braking
and in negative camber when the chassis rolls.
Usually, the opposite happens but a saving grace is the camber gain as
a result of caster effect.
At the rear, the wheels should be straight up and down when braking
or accelerating and in negative camber when the chassis rolls.
There is no caster effect at the rear to help!
To Solve the Dilemma
The rules require a minimum of 50mm useful suspension travel. How
much camber change can that limited travel produce?
Suspension travel should be limited to the minimum amount required
to be legal at Tech Inspection.
Can this limited travel keep the camber angles within the operating
parameters of the chosen tyre. TTC data will help determine this.
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Introduction to FSR Design 2014
Roll Stiffness
The most effective way to control camber loss caused by chassis roll,
that is to inhibit the roll in the first place.
There are several ways to accomplish this.
1.
2.
3.
4.
Lower the vehicle C/G.
Raise the Roll Axis.
Increase the spring rate.
Use anti roll devices.
It is far better to lower the C/G than to raise the roll axis.
As the axis rises above ground, the lateral forces generated in cornering
tend to cause the car to ‘pole vault’ over the outside contact point.
This is referred to as ‘jacking’ and is very detrimental to roadholding
and the drivers confidence level.
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Introduction to FSR Design 2014
Santayana and Jacking
The secret to understanding Jorge Santayana’s advice is to learn from
the mistakes of others. Some teams never do!
Triumph Spitfire in 1962
Formula SAE car in 2006
44 years later, yet the same design error made!
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Introduction to FSR Design 2014
Roll Centres
When a car rolls in a corner under the influence of lateral force, it is
said to be ‘rolling about its roll axis’
The front and rear suspension linkages define the ends of this axis.
The centre of mass is invariably above this axis and the distance above
it is called the ‘moment arm’ or more simply, the ‘lever’ that pulls the
car over when a lateral force is applied at the C/G.
Below are three views of our hypothetical race car.
Front view
Rear view
Side view
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Introduction to FSR Design 2014
Finding the Front Kinematic Roll Centre
Finding the geometric roll centre starts by extending the centreline of
the top wishbone.
Next, extend the centreline of the lower wishbone until the lines
intersect. This intersection is called the ‘Instant centre’. This is the
virtual pivot point of a swing axle reflecting the wheel movement.
Finally, from the centre of the tyre contact patch, draw a line back to
the instant centre. Where this line crosses the car centreline is the
location of the front kinematic Roll Centre.
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Introduction to FSR Design 2014
Strictly speaking, we should also draw lines on the other side of the car.
Where the contact patch to I/C lines intersect, this is where the
geometric roll centre is located, but because our car is symmetrical, we
can skip this second step.
As you will see, it is impossible to keep the R/C static, but designers try
to keep the movement to a minimum.
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Finding the Rear Kinematic Roll Centre
Follow the same procedure at the rear of the car.
R/C
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The usual convention is to have the rear R/C higher than the front,
sloping the Roll Axis down at the front. This imparts a slight understeer
tendency to the car.
The Resultant Roll Axis
Nominally, the Roll Axis between the front and rear R/Cs is the axis
around which the chassis will rotate when subjected to lateral force
whilst cornering.
Note this car has a rearward weight bias, primarily because the
Power-train is mounted behind the driver.
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Introduction to FSR Design 2014
Roll Centre Migration with Chassis Movement.
In bump, the Roll Centre
usually falls by more than the
amount of the bump travel.
In droop, the Roll Centre
usually rises by more than the
amount of the bump travel.
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Introduction to FSR Design 2014
Roll Centre Migration in Roll
In roll, the R/C will migrate to one side.
At this stage, looking at the picture, you should be asking yourself some
questions about kinematic roll centres!
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Introduction to FSR Design 2014
Steering Effects on Suspension Geometry
Effect of SAI Taken in Isolation



Both wheels go into positive camber and the chassis height
is jacked up when the car is steered in either direction.
The inner suspension points are raised, the amount of this
movement depends on the SAI angle, the scrub radius and the
Steering Input.
The countering effect of gravity becomes a self centring force
on the steering system.
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Introduction to FSR Design 2014
The Effect of Caster Taken in Isolation




The loaded outside wheel goes into negative camber and
lifts the inner suspension mounting points.
The inside wheel goes into positive camber and lowers the
inner suspension mounting points.
This imparts a torque to the chassis causing a diagonal
weight transfer.
The magnitude of this torque depends on the caster angle,
the scrub radius and the steering input.
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Introduction to FSR Design 2014
Effect of SAI and Caster in Combination




The outside wheel goes into negative camber, moderated by
the SAI effect and lifts the inner chassis suspension points
The inner wheel goes into positive camber, increased by the
caster effect and lowers the inner chassis points.
This imparts a torque to the chassis, causing a diagonal weight
transfer.
The magnitude of this torque depends on the SAI, Caster, Scrub
Radius and steering input.
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Introduction to FSR Design 2014
Effect of Steering Input on the Front R/C
This is different to the attitude taken by the car when there is a lateral
load on the chassis.
Droop limitation has caused the inside wheel to lift, moving C/G
inboard and the ‘real’ R/C to the outside contact patch.
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Introduction to FSR Design 2014
Summation
All this kinematic stuff might be very interesting and a mathematical
challenge to the Chassis Designer, but in truth, it doesn't mean very
much once the car is in motion.
We have seen that any force applied to the chassis is seen to change the
apparent position of the Roll Axis.
In recent years, this has seen suspension designers adopting the theory
of ‘Force Based’ Roll Centres. Unless one can visualise the forces and
vectors involved it can be difficult to grasp the subject.
The next two pages cover the subject briefly, but for a deeper
understanding I urge you to read Bill Mitchells paper on Force Based
Roll Centres that I have reproduced later in this manual.
In the mean time, the old idea of a Kinematic Roll axis is still a very
good basis for design, but this only goes to show the importance of
getting the car finished in time to test and tune it.
Perfect theory doesn't always give perfect results!
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Introduction to FSR Design 2014
Force Based Roll Centres
It is not the intention of to get too deep into FBRCs in this manual. I will
leave that to Bill Mitchell and limit this explanation to simple terms.
As mentioned earlier, there is a very significant movement of the kinematic R/C away from the C/G.
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Introduction to FSR Design 2014
This illustrates the forces vectors and magnitudes reacted in the car
whilst cornering.
By carefully analysing these forces, software like ADAMS (Automated
Dynamic Analysis of Mechanical Systems), a multibody dynamics
simulation program, can determine the relative motions and determine
a ‘null point’ in the structure.
This ‘Null Point’ is the actual Roll Centre, determined by forces not by
kinematics. It is ‘instantaneous’ meaning that any change in the inputs
will instantly change it.
In other words, it is a spectre, a fleeting shadow that can never be
nailed down.
Maybe that explains the fascination?
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Introduction to FSR Design 2014
Anti Roll Design
Chassis roll can be resisted by using a stiff suspension spring rate.
This can be adjusted by using stiff springs, or if pull-rod or pushrod
linkages are used, by selection of a suitable multiplication rate on the
bell cranks.
It is important to recognise that the important figure is ‘wheel rate’ not
spring rate, that is the spring force as seen at the wheel.
If using linkages, the designer can chose between a progressive,
digressive or linear wheel rate. This means the spring rate can be
mechanically made to rise or fall in rate as well as there being no rate
change in a linear system.
I would suggest a linear to rising rate at the front and for traction
reasons, a linear to falling rate in the rear.
Anti Roll Devices
These are usually springs or torsion bars arranges to resist roll whilst
contributing nothing to the wheel rate.
Usually they are a ‘U’ shaped torsion bar, but may well be a ‘T’ shaped
bar or even a compressed gas or hydraulic mechanism.
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Introduction to FSR Design 2014
Anti Roll Systems
‘U’ tyre Anti Roll Bar.
Each end of the ‘U’ is connected
to the suspension members by
links and the main bar pivots on
the chassis.
Chassis roll thus causes the ARB
to twist resisting the roll motion.
‘T’ Type Anti Roll Bar
Each end of the ‘T’ top are connected to the
bell cranks whilst the leg of the T is anchored to
the chassis but can pivot freely in a fore and aft
direction only.
Chassis roll thus causes either the leg of the ‘T’
to twist or the arm of the ‘T’ to bend, thus
resisting the roll motion.
Hydraulic Anti Roll System
Two hydraulic actuators are cross
connected via two accumulators.
The accumulators have compressed
gas over the fluid.
Chassis roll displaces the fluid
which is resisted by the gas pressure.
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Introduction to FSR Design 2014
Pitch and Squat
A car will not only roll about its Roll Axis, it will also pitch about its
Pitch Axis. We see this as ‘dive’ when the car is braking and as ‘squat’
when the car accelerates.
Control of pitch can be handled kinematically in a similar way to roll, by
suitable location of the pitch centre or by locating the C/G as low as
possible.
‘Anti Dive’ geometry can be adopted in the front suspension and ‘Anti
Squat’ geometry adopted at the rear to minimise or eliminate dynamic
chassis pitch.
Anti-Dive Geometry
Anti-dive geometry can be introduced
by inclining the chassis mounts of the
front top A-arms.
This inclination can be shimmed for
adjustment.
excessive Anti-dive will
reduce driver feedback
through the steering.
Front
of car
Anti-squat Geometry
Anti squat geometry can be introduced by inclining the chassis mounts
of the rear A-arms. These can be shimmed for adjustment. Excessive
anti-squat can have a detrimental effect on traction.
Front of car
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Introduction to FSR Design 2014
Anti Dive/Squat Kinematic Calculations
Drawing a from each contact patch, through the instant centres, where
this line crosses the vertical height of the C/G determines the
percentage of anti dive or anti squat geometry.
In the example shown above, the percentage of anti-dive is 50% and
the percentage of anti-squat is 100%.
Exceeding 100% of anti-squat or anti-dive will cause them to become
‘pro-lift’!
Mechanical Pitch Control
It is possible to use the ARB to introduce an element of physical
anti- dive or anti-squat. This is done by introducing a spring or bump
rubber to partially inhibit the free rotation of the ARB during pitch
movements.
The illustration here (courtesy of
OptimumG) shows a system
where a third spring and
damper on the ftont T-bar ARB
to inhibit dive under braking
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Introduction to FSR Design 2014
Monoshock Suspension
Some designers try to combine the ride springing with pitch springing
by using a sIngle spring ‘Monoshock’ system as illustrated below.
Monoshock
ARB
This results in a decrease in parts count and therefore less weight,
however, combining Roll, Pitch and Ride in a single mechanism makes
setup adjustments very difficult as it is impossible to adjust any one
parameter without affecting others.
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NOTES:
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Actual Design of the Car
We will assume that as an inexperienced team, you intend to build a
simple, straightforward space-frame car with double A-arm suspension
and the recommended 13” wheels.
Note, several aspects of the chassis design are laid down in the rule
book and these must be complied with.
Suspension System
Before suggesting a ‘suspension design’, the team should have
determined what suspension units and other special parts like uprights
and callipers, they can source.
First decision, pushrod, pull-rod or direct acting suspension? Each have
their benefits and drawbacks, such as...
Pushrod
Pull-rod
Advantages
Disadvantages
Bell crank permits easy changes of
wheel rate. Damper rate changes
with spring rate.
Bell crank and damper units mounted
high in the car raise the c/g
Pushrod permits quick changes in
ride height without disturbing spring
rate.
Additional parts count and complication add weight and opportunities for
failure
High mounting makes the spring and
dampers accessible for adjustment.
Ride loads passed in buckling through
the pushrod.
Bell crank permits easy changes of
wheel rate. Damper rate changes
with spring rate.
Low mounting makes the spring and
dampers inaccessible for adjustment.
Pull-rod permits quick changes in ride
height without disturbing spring
rate.
Additional parts count and complication add weight and opportunities for
failure
Bellc rank and damper units mounted
low in the car lower the c/g
Due to the inclination angle of the upper A-arm, desirable geometry may be
difficult to attain.
Ride loads passed in tension through
the pull rod resist buckling.
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Introduction to FSR Design 2014
Direct
Acting
Advantages
Disadvantages
Simple mounting, low complication.
One less node required in chassis.
Ride height or corner weights can not
be adjusted without changing spring
preload
Low parts count reduces weight and
should improve reliability
Ride rate is usually digressive and this
requires progressive springs to
Overcome.
Outboard mounting makes for ease
of accessibility.
Ride rate can only be adjusted by
changing springs.
An option not often seen, but
one that offers some potential
benefits, is a direct acting
suspension using rocking beam
upper A-Arms, as shown.
Special Parts
Dampers:
Most inexperienced teams opt for mountain bike spring/shock units.
With the exceptions mentioned below, bike shocks are not a good
choice for the following reasons.

The damping rates are unsuitable for car use, even those with
‘adjustable damping’.

Invariably, no two are the same, so it is difficult to get a
matched set.

They tend to suffer from stiction and high hysteresis, making
them difficult to tune.
The exception is the Cane Creek (Ohlins) damper. These are very high
quality and can be ordered with damping rates suitable for a Formula
Student car, however, they are not cheap!
Other suitable quality dampers are available from companies like Koni,
Sachs, Penske and Ohlins.
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Introduction to FSR Design 2014
Uprights:
Most teams make their own uprights, either sheet steel weldments or
machined from billet aluminium.
Uprights can be bought from specialist companies making parts for
racing. These are an option worth considering, however such a choice
places some restrictions on the suspension design as compromises need
to be made.
However, these uprights can be ordered with hubs and bearings and
with a brake disk and calliper and may be worth considering if an
inexperienced team lack the skills, knowledge or ability to make their
own.
Later in this manual I will show you how to make a simple welded
upright assembly.
Brakes:
I have seen teams make their own callipers, but I see that as a luxury
only viable for teams with lots of members who can contribute the
design and manufacture time required.
It is sensible to buy your callipers, master cylinders and brake balance
assemblies from companies like Wilwood in the US, AP in the UK or
Brembo in Italy. These companies offer good discounts to Formula
Student teams.
Teams can make their own rotors (discs) or can buy them in. Karts are a
good source of suitably sized ventilated cast iron brake discs.
Rod Ends:
Suitable rod ends can be sourced from Aurora in Chicago, who offer a
50% discount to Formula Student teams.
Rod ends should be used appropriately and the threaded shanks should
never be loaded in bending!
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Introduction to FSR Design 2014
Uprights
Front uprights come in two styles with either ‘live’ or ‘dead’ stub axles.
‘Live’ axles rotate within the upright with the wheel, the bearings being
located in the upright. The hub and wheel rotate together on the
stationary ‘dead’ axle with the bearings located in the hub.
The live axle solution offers the stiffer installation. Rear uprights always
have ‘live’ quarter axles, driven by the drive-shafts.
Live front upright
on a Formula 3 car
Front
Rear
Fabricated sheet steel uprights.
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Introduction to FSR Design 2014
Fabricating uprights
Sheet steel, cut and folded
Tack welded
Finished upright on the car
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A pair of front uprights machined
from aluminium billet and heat
treated.
Front upright with live axle,
brake disc and calliper.
Front upright with dead
axle, showing wheel hub
and bearings.
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Introduction to FSR Design 2014
Another potential source of
uprights is ATV vehicles
(Quad bikes)’
These examples are from
Yamaha, but other makes
are similar.
Small FWD cars invariably have McPherson strut front suspension
which is unsuitable for adaptation to a Formula Student car.
However, the rotating elements inside the ‘knuckle’ or upright can be
utilised at the front and rear of the car.
It may well be that the original FWD drive-shafts can be adapted for
use at the rear of a Formula Student car.
If a team decide to use suspension and steering components from a
production vehicle of some kind, then this decision must be made
before the chassis is designed! Otherwise it will be virtually impossible
to feed the suspension, steering and suspension forces into nodes in the
chassis.
The Compliance Monster will like that, the Design Judges will not!
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NOTES:
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Introduction to FSR Design 2014
Designing the Suspension Geometry
For a first year car, the most straightforward
suspension system to employ is a SLA/Double
wishbone design.
At first glance, there seems to be as many
variations in geometry as variations in a
In reality, the Rules limit the combinations.
The foot-well template virtually mandates a low mounted steering
rack.
It also sets the width of the chassis at the front.
The track width is limited by the need to drive between cones in the
chicanes.
When all the parameters over which the Designer has no control are
considered, the choices diminish.
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Rear Suspension
First, draw in the bottom rear wishbone.
This should be drawn parallel to the ground and pick up on the chassis
near a node.
Making the bottom wishbone parallel to the ground will minimise track
variation (scrub) as the suspension moves.
The wishbone should be as low as possible.
Picking a theoretical roll centre of +50mm, we mark that on the vertical
centreline.
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Introduction to FSR Design 2014
Draw a line from the centre of the contact patch to where it intersects
an extension of the bottom wishbone centreline .
This intersection becomes the static ‘Instant Centre’ determining the
‘Virtual Swing Axle’ length.
As a rough guide, this should be equal to the rear track width or a little
VSA Length
Now it gets tricky! From the I/C point, draw a line through the upper
inner wishbone pivot to the upper ball joint on the upright.
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Introduction to FSR Design 2014
By experimenting with the position and length of the top wishbone, the
desired amount of camber gain can be found.
About 1° camber gain per inch (25mm) of suspension travel is a
reasonable starting point
Adding some more complications.
Rear steer moment can be reduced by reducing the ‘Rear Scrub Radius’,
this effectively reduces the ‘lever arm’ trying to steer the rear wheel.
Zero scrub radius here is a good number!
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The drive shafts should also be parallel to the ground in order to reduce
changes in length as the suspension articulates.
Keeping the drive shafts straight also reduces any potential power loss
and heat generation in the universal joints.
This sets the position of the final drive in the chassis.
Because the drive shafts are shorter than the VSA, there is a need to
adapt to the changing length as the suspension operates.
The best solution is to use ‘tripod’ joints at one or both ends of the
shafts.
Tripod life is actually increased as the spider moves within the cup,
thereby reducing ‘brinelling’ at the contact points.
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Front Suspension
Front suspension geometry design is similar to the rear, but with a
lower roll centre and with steer effect camber changes.
Front suspension design follows the same principles. In this case, the
roll centre is at a nominal 25mm and the VSA (Virtual Swing Arm)
length is slightly longer.
This results in less camber gain as the suspension articulates, but this is
partially offset by the Camber change caused by Caster when the
steering is operated.
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Steering Geometry
Incorporating the steering mechanism at the front is similar to
incorporating the drive axles at the rear... with one big difference!
At the rear we were able to accommodate any difference between the
driveshaft geometry and the VSA by allowing plunge in the tripod
joints.
At the front any clash between the steering geometry and the
suspension geometry will result in the wheels steering as the
suspension articulates.
This is called ‘bump steer’ or ‘roll steer’. It is an undesirable thing and
should be eliminated as much as possible.
A major complication arises because the VSA changes with suspension
movement whilst the steering geometry remains virtually static.
Expect to spend a significant amount of time experimenting with the
steering geometry in order to reduce Bump Steer to an absolute
minimum!
Parameters that affect bump
steer are...
• Rack position
• Tie rod length
• Steering arm length
• Upright design
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Introduction to FSR Design 2014
Engine
Apart from the acceleration event, Formula Student is a ‘handling
competition’ not a ‘horsepower competition’.
In the Autocross and Endurance events, full throttle is only used only
about 10% to 15% of the time.
It follows that the engine should not have a ‘peaky’ power band, should
have progressive and predictable throttle response and these days,
should be relatively economical.
So, it follows that almost any four cycle engine with a capacity less than
610cc will be suitable, but for an inexperienced team, there is a lot to be
said for the traditional choice of a 600cc inline 4 motorcycle engine.
Single cylinder engines are becoming very popular and their use can
save 50Kg or more in the final vehicle weight.
But singles tend to have a ‘snatchy’ power delivery and are more
difficult to drive for inexperienced drivers.
The cockpit templates have resulted in wide chassis, so there is no
frontal area benefit to using a narrow single cylinder engine, and in the
wide chassis, it may be more difficult to mount the engine whilst
retaining good chassis stiffness.
A word of warning about second hand 450cc motocross engines!
These engines are designed for competition use and so have a short
service life. An engine bought from a used motocross bike is probably
close to the end of it’s life and the cost of a rebuild added to the initial
cost of the engine may well exceed the cost of a new engine. This may
well be why the bike was broken up for spares in the first place.
On the other hand, there is no shortage of crashed 600cc sports-bikes
as their rider’s enthusiasm was not matched by their talent.
The engines from these wrecks (when checked as ‘OK’) make excellent
Formula Student power plants!
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Advantages and Disadvantages of EngineTypes
Advantages
450/500cc Single
600cc i4
Disadvantages
Lighter weight.
Short engine service life.
Simple intake and exhaust
systems save more weight
Second hand engines
usually worn out.
Usually more economical
than 600cc engines.
‘Stab’ torque requires some
strong (heavy) driveline
components
Better service accessibility
when the engine is
installed.
‘Snatchy’ power delivery at
low RPM makes them
difficult to drive by
inexperienced drivers.
Easier to acquire. More
used engines available.
Weigh much more than
single cylinder engines.
Engines have a long service
life.
More complicated intake
and exhaust systems.
Easier to mount in wide FS
Chassis.
Les economical than single
cylinder engines.
Easier to drive by
inexperienced drivers.
Poorer accessibility to
engine and ancillaries .
Notice, in the table above I have made no mention of ‘power’!
Both types of engine make adequate power for Formula Student.
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Intake Restrictor
Formula Student rules require
a 20mm intake restrictor.
It is permitted to ’streamline’ the
airflow through the restrictor.
Exhaust System
The exhaust system on a single engine is a somewhat simple task with
the only variables being exhaust pipe diameter and length.
Four cylinder engines pose a significantly greater challenge.
A well designed exhaust system will help improve engine power.
A tip for inexperienced engine tuners is that a with a 4-2-1 exhaust
manifold will help suppress the torque flat spot that typically occurs at
about 75% of peak power RPM with a 4-1 manifold.
The Formula Student rules limit the permitted noise output to 110dba
and a car that exceeds this level will not be permitted to compete in the
dynamic events.
For single cylinder engines, a source of lightweight exhaust silencers
worth investigating is the list of FIM homologated silencers for
Speedway Motorcycles.
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Final Drive and Differential
Most Formula Student cars are fitted
with a differential to balance the rear
wheel speeds whilst cornering.
There are options available as
follows...



A simple open differential as used in most small cars.
A limited slip differential sourced from companies like Torsen,
Quaife or Drexler.
A limited slip differential sourced from a production vehicle
or ATV.
There is also the option of a ‘spool’ drive (locked rear drive).
Open Differential
This is an easy solution, using
differential gears from virtually
any small car.
It permits good differential
performance and will permit the
car to drive freely in corners.
The disadvantages are...

Diagonal weight transfer or lateral cornering forces can cause
a loss of traction on one wheel. This in turn will lead to a total
lock of traction.

A single inboard rear brake cannot be used.
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Introduction to FSR Design 2014
Limited Slip Differentials
There are three general types of LSD.
1.
2.
3.
Salisbury (clutch pack) type
Helical (Torsen type)
Cam and pawl, as used in some ATVs.
There are also viscous coupled differentials, but I would not recommend
one for Formula Student use.
Helical LSD by GKN
There is another option, the ‘Spool Drive’
Spool Drive
Spool
A ‘spool’ is a simple solid shaft that takes the place of a differential assembly. In other words, the wheels are locked together with no differential action.
It is a cheap and reliable solution and the induced understeer can be
tuned out. This is another reason the car should be finished early to
allow chassis setup and driver experience to suit the spool.
Advantages of a spool include...




A weight reduction of several kilograms.
Reduced rotational inertia.
Significant cost saving.
The ability to safely use a single inboard rear brake.
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By now, the team should have made some firm decisions about their
car.
Hopefully, they have decided to...






Build a simple space-frame chassis!
Use 13” wheels!
Designed a suitable suspension system!
Chosen an engine.
Chosen a differential.
Frozen the ideals.
Now it is time to build a car!
Designing the Chassis
First point to remember is there are several Formula Student rules
governing the chassis that must be obeyed. They include...




Front and side impact structures.
Front and rear roll hoop construction.
Steering wheel position.
Chassis templates.
So, with these things in mind, let us go about some actual chassis
design.
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Remember, earlier in this manual we stated the basic task?
“Using only the forces generated by the tyres, to accelerate the mass
(the car) from here, back to here via the racecourse, in the shortest time
whilst using the least amount of fuel”
If we can imagine the car as a 300kg mass, centred at the C/G, and
force arms extending from the C/G to each of the tyre contact patches,
then we can envisage the most simple model of the car.
This simplified example allows
a visualisation of the forces
involved in accelerating the
mass around the course.
If we push the mass in any
direction, we can easily see
how that affects the forces
seen at the contact patches.
If we push too hard to one side or the other, we will push the c/g
outside the support envelope and the structure will fall over. Unless you
have lots of drivers to use up, that is an area of experimentation you
should avoid!
The obvious solution would be to make the base area bigger by
increasing the track width. The problem with that solution is the need
the car to be narrow enough to be fast through the slaloms that are
part of a Formula Student course.
A better solution is to
lower the C/G.
This illustration shows how
the reaction force angle is
similar to widening the
track in the example shown
above.
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Words of Wisdom
Champion Formula One designer Gordon Murray
said...
“All things being equal, the car with the
lowest centre of gravity will win”.
Murray designed the Brabham and McLaren cars
that won six World Championships as well as the
McLaren sports car that won the LeMans 24 hour
race twice.
Unlike some previous ‘Words of Wisdom”, there is absolutely no
mystery about what Gordon Murray is telling us.
So, let’s take Gordon’s advice and lower the C/G as much
as possible. We can start by physically lowering the car
as far as we can on the suspension. How low can we go?
Remember, there are two rules that
affect this decision!
1. The 50mm travel rule.
2. The ‘no ground contact’ rule.
The Formula Student rules dictate a 50mm suspension travel rule,
25mm in bump and 25mm in droop. If ground contact is to be avoided
in a full bump situation, then common sense dictates that the ground
clearance should be greater than 25mm.
How much more?
That is for the designer to decide, a classic design dilemma!
My suggestion would be at least 5mm more to allow for tyre
deformation, track surface irregularities and compliance in chassis and
suspension.
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At the start you don’t really know where every thing in the car goes,
but you now know where the bottom of the chassis, the bottom tube.
Call it the ‘Reference Plane’ just like they do in Formula 1!
Inside the chassis, the two heaviest things you need to accommodate
are the power-train and the driver.
Both should be carried as low as possible.
Other heavy components like the battery and fuel tank should be
mounted as low as possible (low C/G) and as close to the vehicle centre
as possible (low PMI)
Lowering the Driver
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A Significant lowering of the vehicle C/G can be achieved by reclining
the driver and lowering him to the floor.
This is an actual design drawing from a successful team showing the
lengths they have gone to in lowering the driver.
There are other benefits to lowering the driver...

The height of the main roll hoop can be lowered, safing weight
and keeping the C/G low.

The load path for the safety harness mounts can be more
direct, and...

A triangular space opens up behind the driver that is suitable
for locating the fuel tank.
There are imitations to lowering the driver...

The front hoop must be higher than the steering wheel.

The front hoop size is effectively set by the foot-well template.

The driver’s eye line must be above the
front roll hoop. This must be kept in
mind for all drivers!
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Optimising the chassis cockpit area
Moving the main roll hoop forward and leaning it back by the
permissible 10⁰ allows the hoop to be shorter whilst still maintaining
the required 50mm clearance above the drivers helmet as well as
shortening the length of the heavy tubes in the side impact structure.
The front hoop can also be inclined by up to 10⁰ which permits further
shortening of the side impact structure. The SIS must be constructed
according to the rules and is part of the design task.
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The final cockpit ‘hard point’ to concentrate on is the pedal mounting
box. The rules require this to accept a drivers input of 200kg without
deflection or failure. Again, this is part of the design task!
Remember that Newton told us that every action has an equal and
opposite reaction, so the 200kg load on the brake pedal must also be
reacted by the seat back, where the driver is being pushed back into it!
The geometry of the master cylinder is important. The brakes should
have a linear to rising geometry. Falling rate geometry gives poor
feedback to the driver.
Flexible pedal mounting is seen as very poor design by the Formula
Student judges!
Finally, no part of the pedal system is permitted to be forward of the
rear face of the front bulkhead.
Cockpit Foot-well Template
The template must pass unhindered through the chassis to 400mm
from the face of the pedals. There is a clearance slot for the steering
column. Only the steering wheel may be removed for the test.
400mm
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At Tech Inspection, the chassis will be tested for cockpit size by using
the two templates mentioned in the rules. If the templates can not be
inserted, the car will not be permitted to compete in the dynamic
events!
This rule has a very significant effect on the design of the steering
system.
Some teams have tried to use the ‘loophole’ fitting the steering rack
into the 100mm clearance allowance, but if the mechanism impedes
the drivers operation of the controls (all the drivers!) then the car will
not pass technical inspection!
So, where can you put the steering mechanism?
Simply stated, it must be above, below or ahead of the template swept
area. This rule has set a significant challenge to design a steering
system with adequate geometry, little compliance and smooth
operation.
Side Effects of Poorly Designed Steering Systems.




Bump steer, the unintended steering of one or both wheels
when a bump is encountered.
Roll steer, the unintended steering of one or both wheels when
the chassis rolls in cornering.
Bump and Roll steer can occur at either end of the chassis
‘Stiction’. This is a term combining ‘sticky’ and ‘friction’, used to
describe a ‘grabby’ operation in a mechanism.
The foot well template has caused severe complications to the design of
a ‘sanitary’ steering system design which is then further complicated by
the short wheelbase most designers choose.
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Mounting the Suspension and Wheels
There are three items of discussion here...



How do you mount the wheels to the chassis?
How do you transfer the wheel forces to the chassis?
How do you maintain appropriate wheel geometry?
At the front of the chassis, the usual (and recommended) solution is to
use a double A-arm suspension system.
This is a ‘four bar mechanism’ the design of which poses a challenge for
the designer.
The operation of this mechanism must generate appropriate wheel
geometry control and the chassis links of the mechanism must be able
to resist the forces with minimal compliance and without failure.
How does the Designer determine the optimal suspension link lengths
and angles to ensure correct geometry?
The next illustration might give a clue!
Note, they are all different! There is no one correct design!
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Each of the Designs shown are the result of a designer’s idea of the of
the range and rate of camber change within the permitted range of
wheel travel.
In truth, if the wheel travel is limited to 50mm or a little more, there
will be minimal camber change unless an unusually short VSAL is
chosen.
Very short VSALs (or even Swing Axles) cause their own problems!


Excessive camber change in bump and droop will negatively
affect braking and accelerating performance
The angularity of the suspension arms means the wheel forces
must be reacted into the chassis over a very narrow vertical
base.
Infinite VSA
-
No Camber change in
operation
Short VSA
-
Some Camber change
in operation
Swing Axle
-
Extreme Camber
change in operation.
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Kinematic Roll Centre for Each Example
Some things to note about the previous
samples.
As the VSA gets shorter, the R/C gets
higher.
A higher R/C (closer to the C/G) resists
chassis roll but increases the jacking
forces.
Most teams use a dedicated software program to design their
suspension. I recommend the OptimumK kinematics solution.
Before designing the suspension, the design team must understand the
potentially very large forces that will be fed into the chassis.
This is very important to understand because a
steering or suspension failure can cause a serious
accident!
The greatest forces are delivered from the brakes to
the front of the chassis. A lack of understanding of
brake torque resulted in this failed upright!
(Note also the compliant mounting of the steering
arm).
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The Brake Torque forces, added to the forward weight transfer force
must be carried by the front suspension arms, particularly the lower
one. The designer should ensure the pickup points are located close to
chassis nodes in order to avoid excessive compliance.
There is no point in designing specific suspension geometry if excess
compliance in the suspension components, the chassis or the pickup
points permit uncontrolled wheel movement.
Excess compliance is a monster that will undermine all aspects of the
design!
Stiffness and Strength
So, the structure must be...




Geometrically acceptable.
Strong enough to bear the loads.
Stiff enough to resist deflection, and
Light.
That is a pretty tall order!
Remember this?
The arrows show the most direct
load paths from the C/G to the
contact patches.
Any deviation from these straight lines introduces an opportunity for
compliance to degrade the structure.
I understand ‘straight’ load paths are impossible to attain, but the
designer should always keep this ideal in mind.
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Words of Wisdom
More words of wisdom from Colin Chapman,
Lotus F1 designer.
“Simplify, then add lightness”
This is a dictum that all young engineers should
strive to adopt!
As young engineers, you should relish the challenge of designing...



A lightweight and stiff structure for the chassis.
Light and rigid suspension uprights and arms.
A non compliant way of matching the suspension to the
chassis, which moves without ‘stiction’, all whilst maintaining
appropriate wheel geometry.
In Nature, the stiffest 2D structure is a triangle and the stiffest 3D
structure is a tetrahedron.
Where possible, a space-frame chassis should consist of interconnected
tetrahedrons and the loads should be applied at the nodes!
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Building the Chassis
Material Selection
I have stated this before, but it is worth repeating. AS4130 steel tube is
not needed to make a winning Formula Student car!
4130 or ‘chrome moly’ tube is a nice product and if aviation certified,
has exceptionally high production standards. It is available in a large
range of sizes and gauges and is very expensive.
1018 or 1020 CDS (cold drawn seamless) tube is much cheaper and
much more readily available, although the number of sizes and gauges
may not be as great as 4130,
The advantage 4130 has over 1020, size for size, is in its ultimate yield
strength but the stiffness of both steels is essentially the same.
Short of a major crash, it is unlikely your chassis will even explore the
ultimate strength of either steel types, but the chassis should be
designed for stiffness and in this area there is little difference.
There are some areas of the chassis where the thinner wall tube
available in 4130 may offer some weight saving, but with many of the
tubes, roll hoops and supports, side impact structure, front bulkhead
etc, having a minimum wall thickness laid out in the rules, the weight
saving in the entire chassis will be minimal.
Special welding techniques are required for 4130 and this is especially
true of thin-wall tubing.
So again, my recommendation for an inexperienced team is simple CDS
mild steel tubing.
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To avoid distortion when welding, the construction should take place on
a table with a heavy flat surface and there should be some fixture or jig
to hold the tubes in place.
The tubes can be pre-cut or the tubes can be prepared as they are
required. The tubes are then placed in the jig. Slight adjustments can be
made by filing and when a satisfactory fit is obtained the tubes can be
tack welded in place, ready for full welding later on. Do not complete
the welds as the tubes are fitted as this will cause the structure to
distort excessively.
Remember, it is not the actual position of the tubes that is important
(within 5mm) but the location of the suspension, steering, engine and
drive-train locations need to be located within 2mm of their designed
position.
Remember, suspension clevises can be shimmed into place, so this
should be taken into account in construction.
Shown here is one form of jig
with the main roll hoop in place.
This illustration shows a different
type of jig. This has been cut from
sheet steel and assembled ‘egg crate’
style.
On the following pages, we will
follow a team as they build their car
in this jig.
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If the team is using just a flat table, it makes sense to weld the
flat planes of the chassis first.
Note, in this chassis, the team have opted to use some square
section tubing. There are disadvantages and advantages to
making the chassis from square tube.
Disadvantages:



For any given tube size, square tube will weigh about 1/3 more than
round tube of the same wall thickness.
Square tubing is not as resistant to torsional loads as round tube.
Brackets welded to square tube may cause ‘panting’ or ‘lozenging’ of
the tube when forces are applied.
Advantages:





Square tubing is easier to cut and make accurate tube to tube joints.
Square tubing is easier to cut and make accurate tube to tube joints.
Square tubing is easier to cut and make accurate tube to tube joints.
It is easier to attach brackets and panels to a square tube structure.
Square tube resists bending loads better than round tube, so this must
be kept in mind when planning load paths.
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Here, the base plane has of the chassis has been assembled and welded
in the jig. Triangulation in the floor and the rear bulkhead has been
fabricated and tack welded in place.
The front hoop and foot-well structure has been tack welded in place.
The main roll hoop is in place and connected to the rear bulkhead.
Note, this chassis is not compliant with 2013 Formula Student rules.
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Usually, the welding can not be completed until the chassis has been
removed from the jig. This is because the jig makes some parts of the
chassis inaccessible to the welder.
Note:
In this illustration, the welder is using a TIG (Tungsten Inert Gas)
welder, which requires a skilled operator for best results.
For an inexperienced team making a mild steel chassis, a MIG (Metal
Inert Gas) welder (often called a ‘Wire welder’) is easier to master and
will give acceptable results.
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The rear bulkhead, showing
the machined differential
mounting brackets.
Detail of pedals integrated
into front box.
Note the holes in the bottom
rails that permit adjustment
of the pedals.
No part of the pedal
assembly, including master
cylinders and brake lines, can
protrude farther forward
than the rear face of the front
bulkhead at any time.
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These master cylinders protrude into the front bulkhead as shown by
the red line. They are not Rules compliant!
These master cylinders protrude into the front bulkhead as shown by
the red line. An error like this may well not be able to be corrected at
the competition and the car would not be permitted to compete.
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Detail of a suspension bracket.
The tapered spacers allow for small suspension geometry adjustments.
Test fitting of the engine and differential assembly (below).
Although the sump protrudes below the floor of the engine bay, it is still
above the level of the cockpit floor and therefore is technically legal.
However, a protruding sump like this is very vulnerable if there are
bumps on or near the course.
Sump damage will oil down the course and make you very unpopular
with the organisers and your fellow competitors!
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Painting the chassis.
Note the painter is not using personal protection equipment!
The painted chassis.
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Complete car assembly prior to disassembly and painting. This permits
small corrections to be made to the chassis prior to painting.
Note, the firewall between the engine bay and cockpit is not fitted in
this picture!
FS Fires do Happen!
Firewall fitted to chassis.
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The firewall must be made from fire resistant material!
The driver must be protected from heat, flame, steam, fluids etc, up to
the level of their neck.
Aluminium tape, as illustrated here, can
only be used to seal small gaps, less than
3mm, in the firewall.
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Modelled complete chassis.
Completed car viewed from above, showing aerodynamic under tray.
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Modelled view of the rear of the car.
Rear view of completed car. Compare with last picture.
This car has a single inboard rear brake, operating across a limited slip
(Torsen type) differential.
The team should consider the operation of the differential if the brakes
are applied while the car is turning!
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Front view of assembled car.
The latest rules require a diagonal brace in the front bulkhead if the
impact attenuator is smaller than the overall size of the bulkhead.
Note that some fluid has been spilled on the tread area of the front
tyre. This can significantly degrade the performance of the tyres .
Modelled view of steering, front suspension and pedal assembly.
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Bodywork
Fabrication
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This team made an ‘egg-crate’ model of their car using MDF (particle
board) cut and fitted together as shown.
The nose cone and left and right side pods were made separately.
These structures are called ‘bucks’.
Cloth was then stretched over the three bucks and glued in place.
This was then painted with a varnish to tighten it and render it
waterproof.
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The buck was then filled with a simple water based plaster.
When filled, the buck was sanded to shape.
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The bucks were painted to seal the plaster and then sanded to give a
smooth finish.
The smoothed and sanded buck is then suitable to be used to make a
bodywork mould.
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The bucks were then coated with a release agent so they could be used
to make bodywork moulds.
The team laid fibreglass mat and resin over the buck.
This was reinforced with stiffening webs and permitted to cure.
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The bucks are then cut out of the mould, leaving the mould ready for
the bodywork lay-up.
Fibreglass bodywork taken from the mould. The colour is moulded in
the gel-coat.
A coat of clear lacquer gives the finished bodywork a gloss finish.
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An Alternate Way to Make Bodywork.
First, the bodywork needs to be modelled in a 3D CAD Program like
SolidWorks.
Once the required volume is determined, expanded polystyrene
(‘Styrofoam’) blocks can be bought from building suppliers. It is used as
insulation in buildings.
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Using data from the CAD program, this foam can be milled to shape on
a NC Mill. Note, this is a very messy operation and breathing protection
MUST be worn.
Note the mess!
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When the parts are milled, they are glued together to make the buck.
The buck is then coated with polyester body filler. When this has cured,
it can be smoothed and sanded to a fine finish.
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When the buck is finished and sealed, it can be used to lay up the
bodywork on it rather than making a female mould. This will result in a
less professional finish, but saves the step of making a mould.
This team are laying up carbon cloth.
The carbon is then treated with epoxy and placed in a vacuum bag to
cure. This ensures the finished bodywork is dense and free of voids.
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When the carbon is cured it has this matte grey look. After it is trimmed,
it is given a coat of lacquer to protect it and enhance its appearance.
The finished item.
Note, the same styrofoam and carbon method can be used to make
aerofoil sections for wings!
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Threaded Fasteners
There are several Formula Student rules concerning fasteners and
fastener locking systems.
Some common sense should be used when choosing fasteners for the
project. Careful selection of sizes means fewer tools will be needed to
work on it. That might not sound important, but when something goes
wrong in the heat of competition, you will appreciate this advice!
Do not set some arbitrary rule like, “Our car is going to be fully metric”,
because sometimes the best fastener for the job is not metric! Proof of
this is that metric fasteners are not used in critical locations on Airbus
aircraft!
Similarly, there is no need for left handed threads on the car! Instead of
making tie rods and pushrods as ‘turnbuckles’ with left and right hand
threads, giving a coarse adjustment, consider using two different Right
Hand threads instead. This will give a much finer ‘vernier’ type
adjustment in length.
Thread Locking
Thread locking is advisable on all fasteners on a Formula Student car.
This is because the vibrations inherent in a FS car will quickly loosen
fasteners and this can quickly lead to a DNF.
In the case of some fasteners, those the Tech Inspectors consider
‘critical’, thread locking is mandatory. The following illustrations show
the accepted methods of thread locking’.
Note, anaerobic thread locking fluids (such as ’Locktite’) are not
acceptable in the mandated areas under Formula Student rules.
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Permitted Forms of Thread Locking
Lock wire
Castle nut and split pin
Lock wire and seal
Various Tab Washers
Nylock Nuts
Jam nuts (only on rod ends)
Note, all these are mechanical forms of thread locking that can be
easily identified at Technical Inspection without the need for
disassembly.
Other similar forms of thread locking may be acceptable, but check
with the Tech Inspectors first.
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Prohibited Methods of Thread Locking
Thread locking fluids
Lock Washers
Spot Welding.
PAL Nuts
Formula Student cars, which typically have the engine bolted directly
into the chassis, suffer from significant vibration. This can loosen
fasteners, leading to a potential DNF.
Lock Wiring
In aviation, the solution to this problem is to use lock wire, which
makes it the recommended method of thread locking on
Formula Student cars.
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Prohibited Fasteners in Critical Locations
Flat head, countersunk and button head fasteners are not permitted in
areas of the car deemed ‘safety critical’ such as brake and steering
Systems, Harness mounting etc.
Fasteners in question.
Example of the use of an unapproved countersunk screw to retain a
suspension clevis.
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Countersunk cap screws used to retain the steering wheel. This is not permitted.
Countersunk button head screws used to mount the steering column support.
This is not permitted
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Workshop Environment
and
Hand Tools
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Warning Signs:
A warning sign indicates a hazard. In most countries warning signs take
the shape of an equilateral triangle with a thick black border and a
yellow background. The most common types of warning signs are
illustrated below.
Escape and Advise Signs:
Escape signs show the way out of a dangerous situation, such as fire.
Advise signs are used to improve working safety and are located in
areas where the usage of safety equipment, such as gloves or safety
glasses, is required
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Environmental Issues
A workshop has a significant effect on the environment.
The diagram illustrates the different environmentally relevant aspects.
An important aspect is the treatment of waste water! Among other
things it can be contaminated with petrol, oil and heavy metals such as
copper, lead, nickel, cadmium, tin and zinc.
Local regulations should be observed before discharging waste water
into the sewerage system!
Spilled oil should be cleaned up immediately.
Engine oil, coolant, brake fluid should be contained and disposed of
appropriately, as should old batteries.
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Tools
A tool is a device that provides a mechanical or mental advantage in
accomplishing work on a machine.
‘Hand tools’ are devices for doing a particular job. They do not use a
motor, but are powered solely by the person using it. Examples are
almost endless, from general tools like the hammer to specific tools like
micrometers, torque wrench or vernier calipers.
Tools that use a motor, such as a drill motor or grinder, are called
‘Power tools’
The most common hand tools used when working on a Formuls Student
car are shown below.
If working on the engine or transmission, some special service tools
may be needed, as will a workshop manual for the power-train being
worked on!
Do not uses damaged hand tools!
They can cause serious injury as well as
damage to the work piece.
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More Hand Tools
Electrical Tools
Specialised electrical tools are needed when working on a Formula
Student car.
Later in this manual, I will cover electrical troubleshooting and use of
these electrical tools.
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Using Hand Tools
Incorrect use of tools or use of the incorrect tools can cause physical
injury as well as damage to the components being worked on.
Damaged tools should be repaired or replaced and never used due
to their potential to cause injury.
Safety Precautions:



Tools that show evidence of damage should to be replaced!
Don´t carry tools in your pocket as this can lead to injury!
Always wear eye protection in the workshop, even when you
think you don’t need to!
Correct use of wrenches.
Correct
Incorrect
Incorrect
Always ensure the wrench or
spanner is the correct size for
the bolt or nut being turned.
Correct use of screwdrivers.
Correct
Incorrect
Always ensure the screwdriver is
the correct width and thickness
for the screw being turned.
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Torque wrench
A Torque Wrench is a wrench
handle with a device built into it
for precisely measuring the
amount of torque (or twist) being
applied to a nut or bolt.
In many situations it is necessary
to put just the right amount of
torque on a fastener.
Too little torque will not secure the
part properly and too much torque
can cause damage or binding of
rotating parts.
There are two basic designs for a Torque Wrench: A bar/dial design
that has a pointer parallel to the main shaft of the wrench and
indicates that amount of torque being applied in foot-pounds or
Newton meters and an internal spring-loaded version that will allow on
the amount of specified torque to be applied and then will make a
clicking sound to indicate that the right value has been reached.
A Torque Wrench is a precision tool that has been calibrated at the
manufacturer to deliver exactly the correct value. To maintain that
precision it is necessary to use them and maintain them carefully. When
you are tightening a fastener, keep an even turning speed. Do not stop
mid stroke and ratchet the wrench a little bit. The force needed to
overcome friction will give you an incorrect torque reading.
When you are finished using a spring loaded Torque Wrench, return the
wrench to the lowest setting on the handle and relax the tension on the
internal spring.
If you do not relax the internal spring you are effectively stretching it
out of calibration.
Do not to drop a Torque Wrench. It can break or it will probably need to
be recalibrated.
Do not use a ratchet head Torque Wrench as a normal ratchet wrench.
Torque wrenches are precision tools and should be treated as such.
Do not use a Torque Wrench to undo fasteners.
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Using a Torque Wrench
Torque, in this instance, is the measure of how tight a nut or bolt needs
to be. It was once opined that there were three torque levels:
White knuckles, grit your teeth, and break wind.
This is usually followed by a fourth… the bolt snapping off!
You can be more precise with a torque wrench, a special tool that
measures how much rotational force you’re is being applied to a bolt.
There are two types: The beam type with a pointer indicating how tight
the nut or bolt is, and the click type which uses a calibrated clutch
(usually set by turning the handle to the desired torque setting).
Both work well, although the beam type is usually less expensive.
Torque is measured in foot-pounds or Newton-meters.
Really small bolts are measured in inch-pounds or Newton-centimeters,
don’t confuse the two.
When using a torque wrench, be sure the nut or bolt is clean.
The specifications will tell you whether it should be dry or lubricated.
With critical bolts (like engine connecting rods) there should be no
guesswork—refer to a detailed shop manual. These bolts may require
an additional tool, an angle gauge.
For other fasteners (suspension mountings, wheel nuts, switch panels)
some general guidelines are in the next illustration.
Note that these are for the bolt-shaft diameter,
not the measurement across the flats on the bolt head.
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What is ‘Torque’?
The gravity acting on an object 1kg in mass is referred to as 1kg.f.
1kg.f is referred to as 9.8N (Newton) but can usually be rounded up to
10N.
The examples below show the effect of leverage on the tightening
torque of threaded fasteners.
In the first example, 10 kg of force is applied to the end of the wrench .
The length of the wrench is 10cm.
The resulting tightening torque of the bolt therefore is 10Nm.
If the wrench is two times longer and the applied force remains the
same, the resulting tightening torque is two times higher (20Nm)
Tightening torques are usually indicated in the unit of Nm.
When parts of your car are mounted using bolts and nuts, it is
important that they are tightened to the specified torque.
For measurement of tightening torque the usage of a torque wrench is
required.
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Grades of Fastener and the Appropriate Torque Setting
There are many different grades of bolts and nuts. The most common
are listed in the table below.
Note that each nut property class listed can support the bolt proof
strength load.
The bolts and nuts most commonly used on Formula Student cars are
classified according to JIS (Japanese Industrial Standard).
This is because that is the standard used by the engines that are commonly used. A number stamped on each bolt has a given tightening
torque which can be found out by looking at the chart.
Note, bolts and nuts without an id. number should be tightened to the
lower torque setting.
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Various Threaded Fasteners
There are other threaded fasteners typically used in Formula Student
cars.
The thread diameter of a metric fastener is specified in millimeters
(mm) prefixed by the capital letter M, as in "M6" for a 6 mm diameter
screw.
The pitch of metric threads varies according to the diameter.
Some examples: a M3 thread has a 0.5 mm pitch, M4: 0.7 mm, M6: 1
mm, M8: 1.25mm, M10-12: 1.5 mm, M14-16: 2 mm, M18-22: 2.5 mm.
The diameter of a metric screw is the outer diameter of the thread. The
tapped hole (or nut) into which the screw fits, has an internal diameter
which is the size of the screw minus the pitch of the thread. Thus, an
M6 screw, which has a pitch of 1 mm, is made by threading a 6 mm
shaft and the nut or threaded hole is made by tapping threads in a 5
mm hole.
Metric screw threads are also available in ‘fine pitch’ versions, sometimes several pitches for one diameter (example: M18/fine in 1, 1.5 and
2 mm pitches).
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Taps and Dies
Taps and dies are tools used for the cutting of screw threads in metal
parts.
The tap is used to cut a female thread on the inside surface of a predrilled hole. The three taps shown here are of different types.
The bottom tap has the thread going
all the way to the end of the tap and
is called a bottoming tap; it will tap
to the bottom of the hole.
The middle tap is an intermediate tap
where the thread tapers off before the bottom.
The top tap is a taper tap where the thread has an even more
pronounced taper towards the end of the tap. This taper allows the tap
to ease into the freshly drilled hole in a gradual cutting action, relieving
the cutting pressure on the first few teeth of the tap.
To use it, a hole is drilled that is the minor diameter for that sized tap.
This is the equivalent of the blank size (major diameter), less thread
depth.
The order of usage when hand tapping is to use the taper tap first, the
intermediate next (if the material is hard and it is felt that the tap is still
working too hard), and finally the bottoming tap is used to get the full
form of the thread for the full depth of the hole.
The die cuts a male thread on a
preformed cylindrical rod. To use it
a cylindrical blank, which is usually
slightly undersize of the required
diameter, is machined with a slight
taper (chamfer) at the threaded
end. This chamfer allows the die to ease onto the blank before it cuts a
sufficient thread to pull itself along.
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Cutting Threads
Unlike drills, taps and dies cannot automatically remove the chips created by their operation.
A tap/die cannot cut its threads with a single rotation because this will
create long chips that will not clear and thus will jam the tap, possibly
causing it to break.
Because of this, the proper procedure is to cut the threads between 1/2
and 2/3 of a turn (180° to 240° of rotation), then back the tap/die
(reverse turning direction of the wrench) for about 60⁰ until the chips
created by the cutting action are broken by the back edges of the cutters.
It may be necessary to periodically remove the tap completely to clear
the chips from the tool and the hole, especially when a ‘blind’ (closed
bottom) hole is being threaded.
During the cutting process, cutting oil should be applied to the tap/die
on regular basis.
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Removal of a Broken Bolt:
Using a punch:
In case of a broken bolt, tightened only with a small torque or on bolts
with a large diameter you can try to use a punch to turn out the bolt.
Using a screw extractor (‘Easyout’):
Another method is to use a screw extractor. In this case a hole has to be
drilled into the screw.
A spanner attached to the end of the screw extractor helps to remove
the bolt easily.
Using another bolt:
It is also possible to use another bolt remove the broken bolt.
Drill and tap a hole in the centre of the broken bolt.
A new bolt is threaded into the hole and the broken bolt is extracted.
It is necessary to use a LH threaded bolt to extract a RH threaded bolt
and vice versa.
After the broken bolt is extracted, use a tap to clean up the thread.
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Washers, Pins and Keys
Washer:
A washer is a thin disk with a hole, usually in the middle. It is normally
used to support the load of a threaded fastener.
Washers are also used to prevent damage to the contacting surface of a
bolt or nut that may occur when it is tightened.
Other uses are as a spacer, spring (wave washers) and locking device to
prevent looseness that may result from vibration.
Pins:
Pins (split pins, roll pins, tapered pins) are used to prevent rotation or
slipping off.
Keys:
Shafts and Hubs are usually fastened together by means of keys.
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Bearings
A bearing is a component used to reduce friction in a machine.
Bearings may be classified broadly according to the motion they allow
and according to their principle of operation.
Bearing loads
Bearings typically have to deal with two
kinds of loading, radial and axial (thrust).
Depending on where the bearing is being used, it may see all radial
loading, all axial loading or a combination of both.
The bearings in the alternator and the pulley in fig. 1, face only a radial
load. In this case, most of the load comes from the tension in the belt
connecting the two pulleys.
The bearing in fig. 2 is like the one in a barstool. It is loaded purely in
thrust, and the entire load comes from the weight of the person sitting
on the stool.
The bearing in fig. 3 is like the one in the
hub of the car wheel. This bearing has to
support both a radial load and an axial
load.
The radial load comes from the weight of
the car, the axial load comes from the
cornering forces when the car goes around
a turn.
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Types of Bearings
There are many types of bearings, each used for different purposes.
These include ball bearings, roller bearings, ball thrust bearings, roller
thrust bearings and tapered roller thrust bearings.
Ball Bearings:
Ball bearings can handle both radial and thrust loads, and are usually
found in applications where the load is relatively small.
In a ball bearing, the load is transmitted from the outer
race to the ball, and from the ball to the inner race.
Since the ball is a sphere, it only contacts the inner and
outer race at a very small point, which helps it spin
very smoothly. But it also means that there is not very
much contact area holding that load, so if the bearing
is overloaded the balls can deform or the race they run
in can be damaged, thus ruining the bearing.
Roller bearings:
Roller bearings are used in applications like pulleys, where they can
absorb heavier radial loads.
In these bearings, the roller is a cylinder, so the
contact between the inner and outer race is not a
point but a line. This spreads the load out over a
larger area, allowing the bearing to handle much
greater loads than a ball bearing.
However, this type of bearing is not designed to
handle much axial loading.
A variation of this type of bearing, called a needle bearing, uses
cylinders with a very small diameter. This allows the bearing to fit into
tight places.
Roller thrust bearings:
Roller thrust bearings can support large radial and axial loads. They are
often found in gear sets like car transmissions, between gears and
between the housing and the rotating shafts. The helical gears used in
most transmissions have angled teeth. This causes an axial load that
must be supported by a bearing.
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Tapered roller bearings:
Tapered roller bearings can support large
radial and large axial loads. Tapered
roller bearings are used in car hubs,
where they are usually mounted in pairs
facing opposite directions so that they
can handle thrust in both directions.
Plain Bearings:
A plain bearing is the simplest type of bearing, comprising just
a bearing surface and no rolling elements. Therefore the journal (i.e.,
the part of the shaft in contact with the bearing) slides over the bearing
surface. The simplest example of a plain bearing is a shaft rotating in a
hole. Plain bearings require a regular lubrication supply to prevent
them overheating.
Plain bearings are used a radial
application in engines as
crankshaft main bearings and con
rod big end bearings.
An axial plain bearing can often be
found supporting end movement in
the crankshaft caused by pressure
from the clutch assembly.
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Reading a Vernier Caliper
A caliper is a device used in the metalworking field of mechanical
engineering, to measure the distance between two symmetrically
opposing sides.
After the measurement is taken the distance can be read by applying
the caliper on a ruler or between the jaws of a Vernier caliper.
Vernier calipers can measure internal dimensions (using the uppermost
jaws in the picture at right), external dimensions using the pictured
lower jaws, and depending on the manufacturer, depth measurements
by the use of a probe that is attached to the movable head and slides
along the centre of the body. This probe is slender and can get into
deep grooves that may prove difficult for other measuring tools.
The vernier scales will often include both metric and imperial
measurements on the upper and lower part of the scale.
The vernier scale lets one read more precisely from an evenly divided
straight or circular measurement scale. It is fitted with a sliding
secondary scale that is used to indicate where the measurement lies
when it is in-between two of the marks on the main scale.
The indicating scale is constructed so that when its zero point is
coincident with the start of the data scale, its gradations are at a
slightly smaller spacing than those on the data scale and so do not
coincide with any on the data scale.
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When a measurement is taken with calipers, the measure is read off a
finely marked data scale ( the ‘fixed’ scale, in the diagram).
The measure taken will usually be between two of the smallest gradations on this scale. The indicating scale (‘vernier’ in the diagram) is used
to provide an even finer additional level of precision without resorting
to estimation.
When a length is measured the zero point on the indicating scale is the
actual point of measurement, however this is likely to be between two
data scale points. The indicator scale measurement which corresponds
to the best-aligned pair of indicator & data gradations yields the value
of the finer additional precision digit.
On instruments using decimal measure, as shown in the diagram, the
indicating scale would have 10 gradations covering the same length as
9 on the data scale.
Correct and Incorrect usage of the Vernier Caliper
Figures A, B and C show the examples of the correct way of measuring
outside diameter, inside diameter and depth.
Figures D, E and F show common errors made when using a caliper.
Precautions:


Clean all the measuring surfaces and the surfaces to be
measured.
Check the measuring surfaces for wear.
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Measuring with a Micrometer
A micrometer is a widely used device for precisely measuring thickness
of blocks, outer and inner diameters of shafts and depths of slots.
Micrometers have several advantages over other types of measuring
instruments like the Vernier Caliper since they are easier to use and
their readouts are consistent.
There are three types of micrometers based on their application:



External micrometer
Internal micrometer
Depth micrometer
An external micrometer is typically used to measure wires, spheres,
shafts and blocks. An internal micrometer is used to measure the
opening of holes and a depth micrometer typically measures depths of
slots and steps.
The precision of a micrometer is achieved by a using a fine pitch screw
mechanism. The spindle of an ordinary metric micrometer has 2 threads
per millimeter, and thus one complete revolution moves the spindle
through a distance of 0.5 millimeter.
The longitudinal line on the frame is graduated with 1 millimeter
divisions and 0.5 millimeter subdivisions.
The thimble has 50 graduations, each being 0.01 millimeter
(one-hundredth of a millimeter).
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To read a metric micrometer, note the number of millimeter divisions
visible on the scale of the sleeve and add the total to the particular division on the thimble which coincides with the axial line on the sleeve.
Suppose that the thimble were screwed out so that graduation 5, and
one additional 0.5 subdivision were visible and that graduation 28 on
the thimble coincided with the axial line on the sleeve.
The reading then would be 5.00 +0.5 +0.28 = 5.78 mm.
Some micrometers are provided with a vernier scale on the sleeve in
addition to the regular graduations to permit measurements within
0.002 millimeter to be made.
Micrometers of this type are read as follows:
First determine the number of whole millimeters (if any) and the
number of hundredths of a millimeter, as with an ordinary micrometer,
and then find a line on the sleeve vernier scale which exactly coincides
with one on the thimble.
The number of this coinciding vernier line represents the number of two
-thousandths of a millimeter to be added to the reading already obtained.
Thus, for example, a measurement of 2.958 millimeters would be
obtained by reading 2.5 millimeters on the sleeve, adding 0.45
millimeter read from the thimble and then adding 0.008 millimeter as
determined by the vernier.
Note:
0.01 millimeter = 0.000393 inch, and 0.002 millimeter = 0.000078 inch
(78 millionths). Therefore, metric micrometers provide smaller
measuring increments than comparable imperial micrometers because
the smallest graduation of an ordinary Imperial micrometer is 0.001
inch; the vernier type has graduations down to 0.0001 inch.
When using either a metric or imperial micrometer without a vernier,
smaller readings than those graduated may of course be obtained by
visual interpolation between graduations.
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Using a Dial Indicator
Dial indicators are instruments used to accurately measure a ‘small’
distance. They may also be known as a Dial gauge.
The definition of ‘small’ obviously depends on the observer, however a
range between 1mm and 50mm is typical with a travel of 10mm being
common.
They typically consist of a graduated dial and needle to record the minor increments, with a smaller embedded dial and needle to record the
number of needle rotations on the main dial.
They may be graduated to record measurements of between 0.01mm
down to 0.001mm for more accurate usage. The probe (or plunger)
moves perpendicular to the object being tested by either retracting or
extending from the indicators body.
The dial face can be rotated to any position, this is used to orient the
face towards the user as well
as set the zero point.
There will also be some means
of incorporating limit
indicators (the two tabs visible
in the image, at 90 and 10
respectively), these limit tabs
may be rotated around the dial
face to any required position.
The tip of the probe may be interchanged with a range of shapes and
sizes depending on application.
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Feeler Gauges, Thread Gauges and ‘Plastic Guages’
A feeler gauge is a simple tool used to measure
thicknesses. Feeler gauges are used for
measuring the clearance between two parts.
They consist of a number of small lengths of
steel of different thicknesses with measurements marked on each piece. They are flexible
enough that, even if they are all on the same
hinge, several can be stacked together to gauge
intermediate values. It's common to have two
sets for imperial units and metric measurements
although the pictured set has both measurements recorded on each blade.
A similar device with wires of specific diameter instead of flat blades is
used to set the gap in spark plugs to the correct size; this is done by
increasing or decreasing the gap until the gauge of the correct size just
fits inside the gap. Insert a thickness gauge into the clearance to be
measured. If the gauge can be pulled out with approximately 500 to
600g force, the clearance is the same as the gauge thickness stamped
onto the gauge.
Thread Gauge
Thread gauges, also referred to as pitch
gauges, are used to measure the pitch or lead
of screw threads.
Plastic Gauge
Plastic gauges (‘Plastigage’) are used to measure the thickness of thrust
and/or plain bearings. The part is assembled with the Plastigage in
place. The part is then dissembled and the width of the flattened
Plastigage is measured against a master scale to
determine the bearing clearance.
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Using Electrical Tools
Most inexperienced Formula Student teams suffer from electrical
problems of one type or another. Here we will talk about the tools
needed and how you should use them
Along the way we will try to teach you some of the fundamentals of
low voltage electrical diagnosis and repair.
Jumper Wires
A simple jumper wire can be a very useful tool when diagnosing an
electrical problem. A jumper wire, when used in conjunction with the
wiring diagram, provides a quick way to check the operation of a circuit
by bypassing specific sections of wiring, switches or components.
By eliminating parts of the circuit, or by applying voltage and/or
ground directly to the load, you can often isolate the exact location of
a problem.
Warning:

To prevent circuit damage from an accidental short to ground, only
use a fused jumper wire, heavy enough to load you are operating.

Never by-pass the load. This will create a short to ground and
probably burn the circuit.
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Using a Digital Multimeter
A Digital Multimeter (DMM) is the best measurement tool for general
electrical diagnosis.
The advantages to using a DMM over an analog meter are...
Ease of use:
Auto ranging meters self adjust to the range needed for a specific
measurement. This is particular helpful when measuring resistance values.
Accuracy:
Because of the high internal resistance (or high impedance) of
most DMM`s, the accuracy of the meter is increased. The small
power supplies that are built into many Engine Control Modules
(ECU) or the voltage produced by the Lambda Sensor will be
affected by the load placed from the voltmeter.
If the voltmeter draws to much current (low internal resistance),
the circuit voltage to be pulled low, causing the measurement to
be inaccurate. Since most DMM´s have at least 10M of resistance built in , their affect on the circuit voltage is minimal.
Durability:
Most good quality meters can withstand a substantial amount of
shock without damage. Try to get one with a rubber housing,
because you will drop it!
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Long battery life:
Batteries can last in excess of 200 service hours on DMM´s. Most new
ones have an automatic shut off feature.
Many good quality DMM´s have additional features that can be helpful
when diagnosing difficult problems.
Min-Max:
Holds in memory a maximum or minimum voltage or amperage value
measured over a period of time. This is extremely helpful to identify a
problem such as an intermittent B+ or ground connection.
Analog Bar Graph:
Most digital display refresh or update at about two times per
second. However, some electrical problems, (especially ECU
controlled circuits), can be sensitive to electrical signal changes that
happen in a time as short as 100msec.
In the past you would need to use an oscilloscope to identify these
problems. With an Analog bar graph feature, some DMM`s can show a
voltage change happening up to 50 times a second.
Because there are so many features on some of these meters, develop
the habit of double checking which scale and what value is being
measured. This will tell you if you are looking at Volts, Ohms, Hertz, %
Duty Cycle, or if the Min-Max function is in operation.
I can heartily recommend Fluke brand DMMs!
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Digital Voltmeter
The most frequently used feature of a DMM is the voltmeter.
A voltmeter is useful to determine if there is voltage present at specific
points in the circuit when diagnosing open circuit problems.
By applying a logical series voltage measurement procedure, it can also
be used to quickly isolate the location of any high circuit resistance
problem.
Measuring Open Circuit Voltage or Pin Voltage:
This inspection can be made by back probing the terminal or from the
front with the connector disconnected.
If you have to probe from the front of the connector, avoid inserting the
test probe into a female terminal. This is because the terminal can be
damaged resulting in a poor connection when the circuit is
reconnected.
1.
2.
Connect the negative probe to ground at the component
ground terminal or to a known good ground point.
Connect the positive probe to the pin you want to inspect.
If the meter is auto ranging, fix the display to show only one decimal
point. If the meter is non auto ranging, use the 20V range.
Remember that an open circuit voltage measurement tells you only if
there is a connection to B+. It does not tell you how much resistance
there is in the connection or circuit.
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Voltage Drop Measurement:
A voltage drop measurement is taken dynamically while the circuit is in
operation. This is the most accurate way to detect a problem resistance
in higher amperage (above 3A) circuits.
In these circuits, even a load of 1W (caused by a small resistance) can
have a big effect on the voltage available to the main load.
Because the test is done while the circuit is operating, factors such as
the amount of current flow and the heat generated should be taken
into account.
Connect the voltmeter in parallel to the part of the circuit you want to
check by back-probing the connector.
Remember the load should be getting about the same as battery
voltage while the circuit is operating.
1.
2.
3.
Turn the circuit ON.
Connect the positive and negative probes in parallel to the
component or section of the circuit to check.
A reading of 0 volts can indicate two different conditions.

There is no resistance (load) in the part of the circuit you are
checking, or,

The circuit is OFF or open and there is no current flow
If there is a significant voltage (greater than .2V) measured between
the ground side of the load and the earth post of the battery, this
indicates a high resistance in the earth circuit.
This is a very common source of electrical problems.
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Measuring Resistance (Ohms)
An ohmmeter measures the amount of electrical resistance between
two points. The digital ohmmeter has several significant advantages
over its analog counterpart:

Easier to read, the sweep doesn't go backwards

The zero point resets automatically

Extreme accuracy
If using the meter in ‘auto ranging’ mode, be sure to look at the units
(KΩ or Ω) at the side of the display or on the range selection knob.
When connecting an ohmmeter, ensure that the circuit or
component is isolated from parallel branches or other voltage sources.
Most good quality meters are forgiving when accidentally connected to
voltage. Usually the worst damage done is to blow the internal DMM
fuse. Be warned though, those special fuses can be very expensive.
Never test an Engine Control Module (ECU) with an ohmmeter. The
measurement made will be inconclusive at best and could cause
damage.
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Digital Ammeter
Because electric specifications are usually given in volts, the ammeter is
not frequently used as a tool in automotive electrical diagnosis.
It can, however, be a very effective tool.
If a component in a circuit is particularly difficult to access such as the
fuel pump, a current measurement of the circuit can be a good
indicator of that circuit's condition.
An Ammeter is connected in series and allows a check the amount of
current a component is drawing.
Because the ammeter is connected in series, it is necessary to break the
circuit. The ammeter is typically used in:


Starting and charging system inspection.
Diagnosing parasitic load problems.
A parasitic load can drain the battery whilst the system is
unattended.
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Types of Digital Ammeters
Series Ammeter:
A series ammeter is the type of meter that is built into every DMM. This
meter is designed to measure relatively small levels of current flow
(below 10A). Most DMMs measure in milliamps (mA) or Amps (A).
Before connecting the meter into the circuit, make sure the circuit draw
is within the range the meter can handle, i.e. don't use it to measure
starter draw or loaded alternator output.
It is a good practice to initially set the meter to the highest range
available and lower the range while the current is being measured.
Most ammeters are fuse protected to prevent damage from short to
ground or overload conditions. The series type ammeter is best suited
for measuring current flows below 1A. The current should be turned off
before the circuit is broken and the Ammeter connected.
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Clamp Types ammeter:
Clamp Type Ammeters are used on high current circuits like starting or
charging systems. A ‘Clamp probe’ is also available as an accessory that
can be plugged into any DMM to allow it to measure high current.
These battery powered inductive ammeters) measure the current
flow by sensing the strength of the magnetic field produced around the
wire while current flow is present. The clamp then converts this
amperage reading into a voltage which is read with the DMM set to
measure mV.
Due to a lack of accuracy when measuring below 1A, these accessories
are best suited for any measurement except normal parasitic loads.
Inductive current clamps can not read very small amounts of current,
but the signal can be increased by wrapping the conductor several
times through the clamp. The resultant reading then needs to be
divided by the number of conductor wraps.
Fluke Digital Multimeter with optional Current clamp.
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Diode Check
In the past, an ohmmeter was commonly used to check diodes. The
operation of the diode could be verified by checking for continuity in
one direction and for no continuity in the other. However, the voltage
that a digital ohmmeter uses to make its resistance measurement is
usually less than 0.2V. This low voltage is not enough to ‘forward bias’
the diode, so the diode will show no continuity (‘OL’) in either direction.
Most good quality Digital Multimeters have a diode check function.
This function will tell you the forward bias voltage drop of the diode,
i.e. the amount of voltage required to turn the diode ON so that current
will flow through it. For the silicon diodes used in automotive
applications, this voltage should be around 0.5V.
Some low priced meter's diode check function does not measure the
forward bias voltage drop. Instead these meters simply raise the
voltage used by the ohmmeter to allow you to check for continuity in
one direction and no continuity in the other. The number on the display
is not the voltage drop.
Use the diode check function to check the condition of a diode. Besides
in the alternator, diodes are used frequently in the wiring harness to
provide circuit isolation. Look for about 0.5V with the diode check
function.
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Simple
Electrical Diagnosis
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Pat’s Law of Electrical Diagnosis.
Part One:
The voltage after the load must be virtually Zero.
Part Two:
If the voltage is not virtually Zero, then read Part
One again!
Ohm’s Law
Forget the fancy formulas!
All you need to remember is that...
1.
2.
Ohms (R) divided by Volts (V) is the
current in Amps, and...
Volts multiplied by Amps is Watts!
A Simple Short Circuit Tester
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Using the Short Finder
Short
Short fixed
Hopefully these simple hints will help Mechanical Engineers fix small
electrical problems.
It is not the intent of the author to make the reader an ‘electrical
expert’, that is beyond the scope of this course.
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Supplemental
Information
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How to write a Design Report
I have been a Design Judge at many different FSAE and Formula
Student events for many years. The first task for the Design Judge is to
read the Design Reports (DRs) in order to understand what the teams
are submitting to the competition and to understand their design reasoning. This means for some events we read more than 100 DRs!.
This task can be both a joy and a pain!
When a team submit a nice, succinct DR, explaining their aims and
expressing their achievements with all the logic behind the decisions
and this is backed up with nice clear drawings that let me have a good
look at the car structure, reading the DR is a joy.
Such a DR makes a Judge look forward to seeing the car and meeting
the team and gives him a positive feeling prior to the competition.
Having read the DRs for most events, regretfully I have to say that less
than 25% are what I consider an appropriate document and probably
only 10% from each competition are considered excellent!
Some are way over-length, exceeding the allowable 8 pages and many
not including the requisite three view drawings. Some have no drawings at all! Many are corrupted .pdf files.
Incidentally, the way the Judges deal with over-length reviews is to
read the first 8 pages and ignore the rest, so all that hard work was for
little reward!
Where time allows we may comment on general impression but we
simply cannot, as volunteers, read hundreds of pages per Report.
Counting to 8 is not that difficult.
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Usually, when assessing places in the Design event, the moderators will
take the Judges initial report sheet, the Spec Sheet and the Design
Report into account, so a poor DR has the ability to negatively affect
the Design Score twice, first with the judges and then with the
moderators. It is considered a ‘mortal sin’ is to have a Design Report
that does not agree with the Spec Sheet!
So, here are some words of advice about how a team should prepare
their Design Report.
Firstly, you must obey the Rules. They differ slightly between
competitions so be very careful before submitting the same DR to
different events.
Next, understand what you are trying to achieve. The DR is not a
promotional document, it is a briefing document from one group of
engineers (the team) to another group of engineers (the judges).
Remember, the judges have read many DRs so please don’t patronise
them with banal statements.
You are allowed four pages of text, so don't waste them!
Write out your design aims and how you were going to address them.
Then write about what you actually achieved and what changes you
were forced to make along the way. Explain the reasons behind your
choices (not necessarily technical choices) and how you justify that
reasoning.
The judges are really interested in what you are doing and can see
through “marketing” type language.
The obligatory 3 view drawings are critical. Use only black line
drawings on white, not solid modelling screen dumps. Make the
drawings as clear and concise as possible and at a pretty high
resolution, no rastering or jpeg artefacts.
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Judges hate low definition, muddy diagrams when the rules call for
‘drawings’ and penalties will be applied.
One drawing per page, big as you can get it and do not forget the title
box: front elevation, side elevation and plan view.
These are not just pictures of your car but technical illustrations so the
judges can see what you have done. We don't want to see the body or
driver or the fancy team logo on the steering wheel. You can use
pop-ups in the drawing to highlight items and there should be sufficient
dimensioning that we can see the scale. Don't clutter the drawing with
excess detail or dimensioning!
Don’t be afraid to remove or cut away part of stuff like wheels to give
the judge a better view.
Make sure the drawing is complete (by that I mean we don't want to
see components hovering in space with no visible means of support!)
On the free page, I would recommend a really good isometric drawing
of the car! Where essential tables or graphs to support the main text
(and referenced from within the text) are required they live on the
optional page. ‘Standard’ dyno power plots, timelines and non related
stuff is really wasting valuable space in the DR.
If you want to show things like torsional or beam testing, then include a
photograph. We don't need to see pictures of the car in action, the
team members or the equipment in your workshop!
Do not waste a page on a fancy cover or contents page. Don't use
columns in the Report because it becomes too difficult to read on a
laptop or iPad.
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So, to finish...
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8 pages, no more!
Put the team name and car number on the head of the first page.
You should have no trouble filling the report with content the judges
want to read. Most likely you will have to cut some stuff out!
We judges aren't getting any younger, so a nice open font is nice.
Try Arial in 11 point.
NOTES:
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Roll Centre Myths and Reality
by Wm. C. Mitchell (2007)
Bill Mitchell is the author of ‘Racing by the Numbers’
The Roll Centre
‘Roll Centre’ is the most misunderstood term in vehicle dynamics.
A fairly simple concept - how much lateral force applied at the tyre
contact patch is transformed into vertical force - has generated a
remarkable number of myths.
The ‘roll centre’ is a simple measure, derived from symmetric
production car design, extrapolated to asymmetric racing cars, which
overwhelmed the
underlying reality. The very name ‘roll centre’
implies much more than it delivers.
Tyres generate forces which produce lateral and longitudinal
acceleration. This process involves complex concepts ranging from
molecular adhesion to the conformity of a soft tyre to an irregular road
surface.
But the result is simple: a force in the plane of the road surface and a
vertical force perpendicular to the road surface.
The best analogy, due to tire author Paul Haney, involves a broom.
If you hold the handle of the broom low it may glide over a washer
lying on the ground. If you raise the handle it becomes harder to push
but there is more vertical force pushing the bristles into the ground and
more likely to dislodge that washer.
The reality of this analogy is the angle of the broom handle, not the
height of the end. Cut the broom handle in half but maintain the angle
and the effect is the same: the height of the end is irrelevant.
‘Roll centre’ is a measure of the height of the broom handle, not the
angle.
Reality is the angles of the resulting forces.
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The History
Most of vehicle dynamics theory was developed around production cars
simply because there were many more production car engineers than
racing engineers (and there still are).
Production car suspensions are usually symmetric with the centre of
gravity near the centreline of the car.
Production cars are rarely subject to large lateral forces (outside of
racing applications).
Few drivers use more than 0.3g even in emergency situations.
Consequently production car analysis is usually limited to low lateral
forces.
Under this assumption chassis roll and subsequent suspension
movement can be ignored and the roll centre is treated as a static
point.
Good vehicle dynamics texts, including Dixon and Gillespie, mention
this.
The roll centre height is a useful concept because it defines the moment
arm - the distance from roll centre to centre of gravity - acting to
overturn the car.
John C. Dixon writes: “… the roll centre is a very useful idea, because
the roll-centre height concisely summarizes the effect of the links.
With known roll-centre heights it is easy to calculate the roll angle and
the load transfer at each of the front and rear axles.”
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Illustration 1: The moment arm is the distance from RC to CG
The Kinematic Instant Centre
Kinematic analysis gives us the four bar theory of movement which
defines instant centres of motion.
Applied to the double wishbone suspension four-bar theory establishes
an instant centre.
The four bars are the two wishbones, the chassis, and the upright/hub/
wheel/tyre assembly.
The upright/hub/wheel/tyre assembly rotates about this instant centre.
This is a very useful concept because it explains camber change
(for small displacements).
We will later show it also explains jacking force. The instant centre
corresponds to the end of the broom handle in the earlier analogy.
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Instant Centre
Illustration 2: The Kinematic Instant centre
The Kinematic Roll Centre
The familiar roll centre, shown in Illustration 1, is the intersection of
lines drawn from the suspension instant centres to the tyre contact
patches.
This is an application of 4-bar theory applied twice.
The second application treats the theoretical lines from the kinematic
instant centres to the tyre contact patches as solid links.
The other two links are the chassis (connecting the two instant centres)
and the ground. The instant centre of this mechanism gives the rotation
point which minimizes tread change in reaction to chassis roll.
This would be important if we were rolling the chassis in the shop
where every bit of scrub would be expressed with the same screech you
hear in car parks.
But we are dealing with moving vehicles where tread change becomes
a small toe change. The kinematic roll centre is easily drawn (in two
dimensions) and understood but analysing the resulting movement is
complex and leads to myths which are often wrong.
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Why a Roll Center?
Important vehicle dynamics quantities including the loads on individual
tyres, the chassis roll angle and roll couple depend on overturning
moment.
This depends on the forces operating through the suspension links and
is measured by the roll centre.
As Dixon says “… the roll-centre height may be used as a summary of
the load transfer characteristics of a suspension found by a detailed
suspension analysis, or as the input specification for a simple handling
simulation.” [1]
Load transfer, jacking forces and overturning moment are forces and
moments, not kinematics.
Thus we should address the problem through forces and moments
rather than kinematics.
This leads to the ‘Force-Based roll centre’.
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Force Based Roll Centre
This is calculated by solving a series of force and moment equations
usually expressed as a matrix.
In two dimensions it is a 3x3 matrix.
In three dimensions it is a 6x6 matrix.
In the simple two dimensional case the kinematic roll centre is identical
to the force-based roll centre for symmetric suspensions.
For more complex cases we use the Force Application Point, which is the
point on the line between the instant centre and the tyre contact patch
under the centre of gravity.
For a symmetric suspension with the CG on the centreline of the vehicle,
the FAPs are identical to the kinematic roll centre.
For an asymmetric suspension, and most symmetric suspensions
became asymmetric when the chassis rolls, we have distinct FAPs for
each side of the suspension.
Force Application Points
Illustration 3: The FAP or Force Application Points
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Determining a Force-Based Roll Centre height requires knowledge of
how the tyre force is distributed between the two tyres.
This is unfortunate because it introduces an unknown variable.
But it is easier to analyse the vertical movement of the FAP, which is
always under the CG for each side of the car, than the kinematic roll
centre, which moves vertically and laterally.
Force Based R/C
Kinematic R/C
Illustration 4: The Kinematic and Force-Based Roll Centres.
The FAPs and the Force-Based Roll Centre are important. The Kinematic
Roll Centre is of little value.
But the roll centre is a convenience, not a necessity. Dixon writes “With
detailed computer simulations that consider the forces in the individual
suspension links it is not necessary to use the roll-centre concept.”
The SAE Definition
SAE defines the roll centre as “The point in the transverse vertical plane
through any pair of wheel centres at which lateral forces may be applied to the sprung mass without producing suspension roll”. [2].
This sounds like a committee of academics compromising on a single
valid expression with minimal meaning.
Note that this really defines a height rather than a point since there is
no reference to lateral location. The roll centre is often assumed to be
on the centreline of the vehicle. Placing it under the CG would make
more sense.
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The Force-Based Roll Centre in 3 Dimensions
In the three dimensions most of us live in, the force-based roll centre
yields a 6x6 matrix.
Few of us can visualize a 6x6 matrix let alone it’s inverse. But with a
little work we can understand what we need to know. Determining the
instant centre is a bit more complex because we must construct lines
through the A-arms in the vertical transverse plane of the tire contact
point.
Often the ball joints will not be on this line. But once we understand the
concept and leaving the mathematical details to our ever-present
computer, the instant centre can be determined.
But there are five links from upright to chassis: the four A-arms plus the
steering tie-rod.
Some force, and more than many people expect, goes through the
tie-rod. This contributes to the roll moment.
The amount of contribution depends on where the tie-rod projected
crosses the instant centre axis which connects the standard instant centre with the side-view instant centre. But since the steering tie-rod is
usually aimed near the IC axis the effect of the tie-rod is usually small.
Those interested in the precise details may consult SAE paper 2006-013617.
But for most working engineers can ignore the difference (as long as
they understand what they are ignoring).
For the necessary sixth equation we consider a vertical force at the tyre
contact patch which is often called the jacking force. As an alternative
we can calculate the force going through the spring.
This ignores the compression of the spring as well as the contribution of
dampers, anti-roll bars and third springs.
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What We Need to Know
The crucial concept is the FAP rather than the Kinematic Roll Centre.
This has the advantage that an independent suspension yields independent analysis. We can study each side independently.
This is nice. The disadvantage is that we need to know the distribution
of force between the tyres. With a symmetric car the left and right FAPs
are at the same point and the distribution of force drops out of the
equation (though we still need it to calculate net jacking force).
Stability results when the FAP-CG moment arm remains constant as the
vehicle rolls.
The chassis “takes a set” rather than constantly seeking a new
equilibrium.
This can be expressed by minimizing the lateral movement of the KRC
as the vehicle rolls. But this is an artefact: there are more direct ways to
calculate this; namely with the change in FAP height resulting from
ride. It should be one-to-one.
(An easier way to visualize this is from the viewpoint of the chassis
rather than the world. The FAP point should be constant as the wheels
and tires move up and down.)
Confounding the Confusion
Everything we have written about lateral forces and the roll centre applies to longitudinal forces and the pitch centre.
The principles and the analysis are identical except cars symmetric front
-to-rear are extremely rare and sometimes longitudinal forces are generated at the axle rather than the ground.
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But engineers usually discuss anti-dive and anti-squat in percentage
whereas few discuss lateral forces as an anti-roll percentage.
Some even discuss acceleration as an angle rather than a percentage.
The use of common terms would eliminate a lot of confusion while
emphasizing the common elements.
Myth #1
The Kinematic Roll Centre
Several myths exist about keeping the kinematic roll centre in a certain
area. i.e.

It should not be under the inside tyre or not near the outside tyre.

It should be within the tyres and not in the infield.
Based on the analysis above, I know of no validity to any of these
theories.
Myth #2
The Roll Centre should not go through the ground plane.
When the chassis moves to place the instant centres near the ground
the kinematic roll centre moves rapidly laterally. When one IC is above
ground and one below ground the KRC is outside the track.
Before I understood the limited role of the KRC I thought this was bad.
One way to avoid it is to keep the ICs either above or below ground.
“Mea Culpa” (as the Romans said) or “My Bad” as the current
generation say. Formula Students occasionally present this theory and I
have to explain why it is invalid while acknowledging my guilt in their
error. Whoops!
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Myth #3:
The distance from the kinematic roll centre to the CG is the moment
arm.
If you believe in the kinematic roll centre it is easy to consider the
distance to the CG as a moment arm. A long distance from KRC to CG
produces lots of chassis roll. The problem is that this line is not
perpendicular to the lateral force. The FAPs, defined as being under the
CG, yield a moment arm perpendicular to the lateral force.
The distance from FAP to CG is a valid moment arm.
Myth #4
The Chassis Rolls about the Roll Axis
The chassis moves in reaction to a lateral force: it does not roll about a
point or axis. The movement includes chassis roll as well as vertical
movement.
The kinematic roll centre concept clearly describes the roll yet neglects
jacking force, which might be small for symmetric cases where both
tyres contribute equal lateral force.
But for racing cars the majority of the lateral force comes from the
outside tyre. In some instances the inside tyre may even be off the
ground!
Dixon writes “ … many authors introduce the roll-axis as an axis about
which the vehicle actually rolls during cornering, the roll axis being the
line joining the front and rear roll-centres.
When a vehicle is actually moving on a road, the concept of a kinematic
roll axis is difficult to justify in a precise way, especially for large lateral
accelerations.
Therefore the idea of the vehicle rolling about such an axis, although
useful as a qualitative idea, should be treated rather cautiously, except
in the special case of a stationary vehicle subject to loads in the
laboratory.” [1]
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Summary
The Roll Centre is important but you have to separate reality from
myth. Kinematics are easy to visualize and that aids understanding.
But forces move the race car!
References
1. Tyres, Suspension and Handling, John C. Dixon, Cambridge
University Press (1991)
2. Vehicle Dynamics Terminology, SAE J670e, SAE, 1952, last revised
1976
3. Racing by the Numbers, Wm. C. Mitchell Software, 125 E. Plaza
Drive, Suite 117, Mooresville, NC 28115 USA
Pat’s Note...
Sadly, we lost Bill Mitchell in 2014, a great loss to the FS/FSAE
community.
R.I.P Bill.
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Reading a Dyno Chart
A ‘dyno chart’ is a 2D representation of an engine’s horsepower and
torque over the engine’s speed range, as measured by a device called a
dynamometer.
Most dynamometers either connect to the engine output shaft, or use a
roller that bears against the rear tyres. The latter is usually called a
chassis dynamometer.
Torque is a moment of force, acting at a distance, trying to rotate
something.
When trying to twist the cap off a jar or turning off a tap, you are
applying torque, whether the cap gives way or not, i.e. no movement is
involved.
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A similar example might be turning a Torque wrench, set at 150Nm on a
bolt tightened to 200Nm until it clicks. Nothing happens, but a torque is
being applied!
Horsepower is a measurement of actual work done in a given time, so if
the wrench was set at 250Nm, some motion would occur before the
torque wrench clicked odd. Some work was done!
It was originally stated as the force needed to move 550 pounds one
foot in one second, or 33,000 pounds one foot in one minute.
Some dyno charts are calibrated in horsepower and pounds/feet of
torque; countries using the metric system use kilowatts (kW) or PS
(metric horsepower) and Newton-meters (Nm) for torque.
While the units of measure change, the fundamentals remain the same:
you’re trying to use these lines on a chart to understand the engine
output.
Power = force x distance ÷ time. In any measurement of distance and
time, like a quarter-mile (400m) time and top speed, horsepower is
going to be the determining factor.
But we don’t drive our cars at peak power or peak torque all of the
time. What we need to do is look at the shape of a engine’s horsepower
and torque curves and that’s where a dyno chart is invaluable.
A good rule of thumb states ‘Flat torque curves and wide power-bands
make for great street cars; steep torque curves and narrow powerbands are usually best suited for racing’.
A good FS engine falls somewhere in between.
Alternately, shade in the areas under the engine’s torque and power
curves with a highlighter. The greater the total shaded area under
them, the more likely you’ll enjoy the drive.
Of course, the gear ratios need to be matched to the engine output in
order to take the greatest advantage of the power available, but that is
a topic for another day.
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Cockpit Control Forces
I look forward to Formula Student competitions, not only for the
obvious reasons (you get to see a lot of neat, different cars, and talk to
a lot of incredibly bright engineering students), but also because it is
the one time of year when all the Design Judges, Tech volunteers, Rules
Committee members and the other visionary individuals who make FS
what it is, are gathered together.
We use this opportunity to talk over ideas face to face and gain a better
view of the ‘Big Picture’ so to speak.
One of the topics that came up over dinner one evening, was
sub-system robustness, or how strong does a steering/brake/
accelerator/gearshift (you pick one) system really need to be?
This is a topic which all Formula Student volunteers (Design Judges &
Scrutineers in particular) are sensitive to because we have, on occasion,
actually broken student built cars.
Make no mistake about it, when this happens, we feel very badly that
we have broken something which students have put long hard hours of
design/build/test time into.
However, we are also quick to point out that we would much rather see
the suspect part break standing still, rather than out on the track where
someone (be it a student driver, or worse yet, an innocent spectator)
could be injured or worse.
Unfortunately, some students get upset and feel that they are being
unfairly singled out, because: “We tested that __ (insert one: brake
pedal, steering shaft, accelerator pedal, gear shift, etc) beyond reasonable limits and it didn’t break for us.”
This article will look at each of the different sub-systems that a driver
exerts force to operate and help you determine what the reasonable
forces for normal operation are.
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It is not my intention to tell you how to design your car. This is just one
example of how to go about designing a reasonably robust car.
This article will (hopefully) help you identify what level of forces your
car should be able to withstand without driver induced damage.
When determining how strong any sub-system really needs to be, a
common saying we use in motorsports is: ‘Never underestimate the
strength of a scared driver’!
Steering System
There are two types of steering forces we will discuss.
The first will be steering wheel torque, or how
much force can a driver put into the steering system through ‘normal’
actuation of the steering wheel.
The second steering system force we will talk about is lateral (radial)
force, or how much can a driver pull up, down, or sideways on the
steering wheel column.
We will not discuss axial force imparted during the dynamics of a collision. Axial analysis is beyond the scope of this article.
First, let’s look at the most common types of steering system failures in
Formula Student cars.
A recurring problem we see is a lack of proper steering column support.
When a steering wheel can be
firmly pulled up, down or sideways
and the Design Judge or Scrutineer
can detect noticeable compliance,
you definitely have a problem.
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This is usually due to the fact that the steering column only has one
support, and the support (usually a metal sleeve) does not support the
shaft over a sufficient length.
A better design would have two supports per shaft.
The farther apart the supports are, the less compliance there will be in
the finished assembly.
We also see all types of bearings/sleeves supporting the shaft, ranging
from very well engineered radial ball bearings, to all types of bushings
made from all types of materials, to nothing more than a metal sleeve
substantially bigger than the steering shaft (with all of the excess compliance that comes with that sloppy
design!).
We also see all types of steering
shaft couplers and u-joints which
are under-designed, worn out,
improperly installed or simply should
never be used in a steering system in
the first place.
The most common type of coupler failure we see is the notorious shaft
in a metal sleeve with a cross drilled hole with a pin/bolt through it.
Typically the shaft is not hardened, the hole is too big, or the holes
don’t line up properly. This results in a sacrifice of adequate cross
sectional area, which causes a shearing failure or at the very least, lots
of extra compliance.
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Steering System Torque / Force
So, how much torque/force does your steering system normally see,
and how much torque/force should it reasonably be able to withstand?
Normal steering operating torque/forces depend on a number of
variables. You can build a 135 kg car with very narrow, high pressure
tyres, at zero scrub radius, with zero KPI, and zero caster, lots of
steering ratio and the steering input force will be very small indeed,
maybe as small as 1.3-2.7 Nm.
This car would be hopeless to drive competitively as it would have a
‘dead’ feel and give the driver no feedback to his steering inputs.
The opposite extreme would be a very heavy car with wide, low
pressure tyres, lots of scrub radius, lots of KPI, caster, and a low steering ratio.
You better start working out now if you are going to drive that car for
any distance…
The best suspension/steering geometry for the tyres you have chosen,
for use in a lightweight FS car, will result in reasonable steering forces,
which a driver can maintain for at least thirty minutes of non-stop
driving at race speed.
Typically we see the above average Formula Student cars at
somewhere around 4-11 Nm. of steering effort needed at a standstill.
Of course, that torque load will drop as the car starts rolling.
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A note in passing:
One of the tests we sometimes conduct during engineering design
judging is to lift the front of the car off the ground and check for
steering wheel effort.
The best cars will be able to twirl the steering wheel from lock to lock
with one little finger…
One of the Design Judges, Steve Lyman, was kind enough to send along
the following data.
This is static measured torque data he has acquired over the years
using a Sensor Development hand wheel torque sensor:




Autokraft Midget — 6.0 Nm. 380mm steering wheel.
Lola T332 — — — — 5.5-8.5 Nm. 318mm steering wheel.
Lotus 20 — — — — 4.0-4.5 Nm. 330mm steering wheel.
Lola T190 — — — — 6.0-7.5 Nm. 318mm steering wheel.
Production cars from the automotive OEMs have steering torque
specifications of 175 Nm. yield with 240 Nm. minimum ultimate
strength.
Rest easy, we will not be testing or requiring you to achieve these levels
of robustness on your Formula Student car.
These are specifications set by car manufacturers designed for dealing
with unusual customer use, and as protection from liability lawsuits.
In discussing these types of steering torque loads with formula race car
designers & builders from around the world we are all in clear
agreement that your car should never have the steering shaft or
steering rack break… no matter how much force the driver puts into it!
For the purposes of this article, we decided to determine what
maximum steering torque limits are reasonable.
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We instrumented a Formula Student car with a 254mm diameter
steering wheel, in order to assess how much peak torque a driver could
transmit to the steering column while seated in the car.
This force varies depending on how far the steering wheel is away from
the driver’s chest.
We tested with arms fully extended (Extended), arms at mid reach
(Mid), and then with the wheel held close to the chest (Close).
The closer to the chest, the greater the torque the drivers could
generate.
See the chart below for peak steering torque forces generated.
All test subjects with the exception of one were average college
engineering students between the ages of 19 and 23. No ‘body builder’
types volunteered for the test.
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Most Formula Student cars have the steering wheel positioned 300mm
to 450mm away from the driver’s chest (mid span of your total forward
reach).
It is reasonable to conclude that any well constructed FS car should be
able to withstand a minimum of 100-135 Nm. Of torque/force applied
at the steering wheel with no steering system failure.
We often also see silly undersized wheels, similar to Nintendo and other
PC game controllers. You never see a ‘real’ race car with such a tiny
wheel and there are good reasons for
this.
A second issue is the use of
carbon fibre for steering wheels.
Is it appropriate without a metal
armature? How is the steering torque
reacted into the wheel assembly?
What about the potential fracture of
the wheel in an accident, leaving razor
sharp edges to hurt the drivers hands?
Steering System Lateral (Radial) Forces
Steering system lateral (radial) forces are relatively small when the car
is on the track running at speed. However, that does not relieve you of
the responsibility to mount your steering wheel and column in a
workmanship like fashion.
Any steering wheel/column should be able to withstand at least a 660N
lateral (radial) force without failing.
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Braking System
What pedal force should you be designing for under normal on-track
conditions?
This number varies according to driver preference. Some drivers like a
pedal force as low as 110 N force per G of stopping force. That would
result in a fairly sensitive brake system.
Other drivers prefer a brake pedal effort of 440 N force per G of
stopping force (or higher).
A brake system with a pedal effort that high might be difficult to
modulate, and might not give the driver the ultimate control over the
car that he would like.
A note in passing:
Some engineers specify pedal force at lock-up, as opposed to pedal
effort per G force. Either answer is acceptable. Just be clear in how you
have specified your brake system.
Pedal geometry is also important. When the pedal goes ‘over centre’
the rate falls and the feedback to the driver is confusing, but that is a
subject for another article.
We see brake pedals and brake pedal mounts fail all too often.
Here is my statement...
“Your brake system should be so robust, that the driver cannot break it
by pushing on the pedal… with any amount of force he can generate”!
As one Design Judge is fond of saying: “When everything else on the car
has failed, the brakes should be the last thing still working.”
He also pointed out that any brake pedal mount he has ever designed
and built was so strong that the master cylinder pushrods would buckle
before the pedal broke!
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An average adult male can leg press 225-270 Kg.
For this article, let’s use the upper number, which means that one leg
can exert 1330 N force on the brake pedal, under normal circumstances.
Add a 10% safety factor and I will respectfully suggest that your brake
system should be able to withstand a 1500 N force with no damage to
your brakes. (The FS Rules now require a minimum force of 2000 N.)
You also have to react that force.
A failed seat mount can cause ‘brake failure’ and seat compliance (even
a foam insert) may limit the amount of pressure that can be applied.
Similarly, compliance in the pedal box/mounting can limit ultimate
pressure.
Something that worries me a little is the ‘adjustable’ pedal boxes we
see. Some are going to fail under high pedal pressure.
Another potential problem is that the driver may ‘pull’ on the steering
wheel as he applies high brake pressure (See earlier comments on
carbon steering wheels).
In talking to a lot of different professional (race) car builders we are all
in agreement that 1470 N force is the absolute bottom end of the brake
force threshold you should be designing and building to.
Anything you build should be robust enough to take at least that
amount of force.
Again, remember: Never underestimate the strength of a scared driver!
Finally
There are some requirements in the rule book for minimum forces the
brake pedal system should accept without failure, a rule introduced after the original publication of this document. This does not diminish the
importance of the recommendations contained here.
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