Literature Review
Human Powered Delta Trike
S13-45-TRKE
Saluki Engineering Company
Southern Illinois University Carbondale
Mechanical Engineering and Energy Processes
Cory Tuttle (PM)
Jarod Peyton
Dylan Polus
Cory Schueller
Daniel Unes
ctuttle@siu.edu
jarod.peyton@siu.edu
dpolus@siu.edu
cory21@siu.edu
danunes@siu.edu
Faculty Technical Advisor: Dr. Marek Szary
February 26, 2013
1
Table of Contents
Introduction (DP) .......................................................................................................................................... 3
Current Designs (CT) ..................................................................................................................................... 4
Frame Design(JP) .......................................................................................................................................... 5
Steering (JP) .................................................................................................................................................. 7
Suspension (DP)............................................................................................................................................ 9
Drivetrain (CS) ............................................................................................................................................ 11
Brakes (DU) ................................................................................................................................................. 15
Wheels and Spokes (CT) ............................................................................................................................. 17
Hubs (CT)..................................................................................................................................................... 20
Component Materials (DP) ........................................................................................................................ 21
References (CT)........................................................................................................................................... 23
List of Figures
Fig. 1: Positive Caster ............................................................................................................................ 8
Fig. 2: Positive Camber ......................................................................................................................... 8
Fig. 3: Ackermann Steering ................................................................................................................... 9
Fig. 5: Chain and Sprocket................................................................................................................... 11
Fig. 6: Derailleur .................................................................................................................................. 11
Fig. 7: Timing Belt and Sprocket ......................................................................................................... 13
Fig. 8: Internal Gear Hub ..................................................................................................................... 13
Fig. 9: Universal Driveshaft ................................................................................................................. 14
Fig. 10: Hydraulic Disc Brake ............................................................................................................... 15
Fig. 11: Mechanical Rim Brake ............................................................................................................ 16
Fig. 12: Spoke, nipple, and rim arrangement...................................................................................... 16
Fig. 13: Geometry of a Spoke .............................................................................................................. 16
Fig. 14 Geometry of a Spoke: .............................................................................................................. 20
Fig. 15 In-plane spoke length: ............................................................................................................. 21
Fig. 16 Spoke Lacings: ......................................................................................................................... 21
Fig. 17 Spoke Lacing Effects: ............................................................................................................... 21
2
List of Tables
Table 1: Existing Trike Designs .............................................................................................................. 6
Table 2: Trike Prices .............................................................................................................................. 6
Table 3: Trike Frame Weights and Materials ........................................................................................ 7
Table 4: Trike Turning Radii .................................................................................................................. 8
Table 5: Trike Turning Radii .................................................................................................................. 8
Table 6: Foldable Trikes ........................................................................................................................ 9
Table 7: Drivetrain Components and Prices ....................................................................................... 14
Table 8: Strength of Spokes of Various Materials............................................................................... 20
Table 9: Front Hub Comparison .......................................................................................................... 22
Table 10: Rear Hub Comparison ......................................................................................................... 22
Table 11: Generator Types and Efficiencies ....................................................................................... 21
Table 12: Material Properties ............................................................................................................. 21
Table 13: Material Properties Continued ........................................................................................... 22
Table 14: Tubing Prices ....................................................................................................................... 22
3
Introduction
All around the globe there are people who enjoy riding tricycles. Tricycles come in many
different styles and designs. The three most common designs are the upright style, recumbent delta,
and the recumbent tadpole. The upright style is the original design with the diamond frame and the two
wide spaced wheels in the back. The Recumbent delta design resembles the upright design in that it has
one wheel in front and two in the back. The features that separate the recumbent delta from the
upright are the overall length, seating, and steering. With the recumbent delta design the driver sits at a
much lower distance from the ground and pedals with his or her feet in front of them, making the trike
longer in length. A lot of the recumbent delta steering designs stray away from the traditional handle
bars and replace them with two separate handles that are located on both sides of the driver. The other
design of a tricycle is the recumbent tadpole. The recumbent tadpole resembles the recumbent delta in
that they both have a low stance and require the driver to pedal with his or feet in front of themselves.
The difference with the tadpole design is that there are two wheels in front and one wheel in the back.
This design allows for a more stable design when turning. There are plenty of styles of each design; the
problem is that the tricycles tend to be heavy and very expensive.
The purpose of this report is to compare current trike designs and their subsystems to analyze
and design a trike which is less burdensome to the costumer’s wallet and lighter on the legs. Analysis of
subsystems will include frame design, steering, drivetrain, component materials, suspension, brakes,
and wheel design.
4
Current Designs
The range of trike designs that are currently available varies widely from heavy to light and
come in many variations of creature comforts such as the ability to fold and suspension. The table below
shows these characteristics for a few popular trike models.
Table 1: Existing Trike Designs
Trike
2013 KMX
Typhoon [32]
TerraTrike Rover
Nexus [32]
Catrike 700 [32]
Catrike RS Trike
[32]
HP Velo
Scorpion FS [32]
SteinTrike Wild
One [37]
Challenge Allize
[7]
Weight
Sup. (lbs)
300
Wheel
Base (in)
41.0
Wheel
Track (in)
29.50
Suspension
No
Low
Profile
Yes
Seat
Angle (°)
-
Weight
(lbs)
-
350
42.0
29.25
No
No
50-65
42
250
275
45.0
41.5
27.50
29.00
No
Yes
Yes
Yes
27
39-47
33
38
286
43
30
No
Yes
32-41
39
-
43
29
Yes
Yes
-
34
285
46
30
Yes
Yes
31-38
39
Catrike is the market leader with their lightweight trikes. Catrike employs quality components
from Shimano and boasts frames designed, modeled, and analyzed through Solid Works. The trikes are
precision cut in a warehouse and welded together by technicians in the most refined and finished way
on the trike market, making Catrike synonymous with the term tadpole trike. TerraTrike has a fair bit of
catching up to do inorder to be competitive with Catrike. TerraTrike’s designs are simple, square tubing
is welded and painted and there almost no attention to aesthetics or performance. As a result of the
forementioned conditions TerraTrikes are some of the heaviest trikes that exist on the market. The Alize
trike by Challenge Bikes sits in the middle with a moderate weight and healthy supported weight.
However, what sets this trike apart is the aesthetics and the incorporation of many creature comforts,
such as the ability to fold for transportation and suspension. Trike prices vary as widely as the
specifications do, and as a result a customer may cut certain features to stay within a budget. The table
below shows a comparison of prices between the models listed above.
Table 2: Trike Prices
Trike
Price ($)
Typhoon
1100
Rover Nexus
1100
700
2750
RS Trike
2750
Scorpion FS
4390
Wild One
3895
Allize
4800
5
Frame Design
There are many different frames that have been built in the trike section of human powered
vehicles (HPV). This section will discuss in detail the types that have been put to market and are
available to the everyday consumer. In the private sector there have been a multitude of designs but
these are specialty builds, a user has an idea and just uses trial and error to determine what design
works best for their specific objective. These types will not be discussed further because they haven’t
been engineered to provide a mass market consideration. The designs that will be focused on are ones
that have went into production, trikes that can be readily bought by any user.
The most popular style is a mono-tube design. The frame is comprised of a single main tube and
the components all mount off this central tube. There have been straight tube designs where the user
sits up high on top of the frame and curved designs where the user sits down in the frame and is a far
superior design because of the much lower center of gravity that can be achieved. If the bike has a high
center of gravity it will be harder to keep the trike stable at speed, this is because the higher the load is
away from the center of mass of the machine it will create a moment about that center and therefore
make the trike unstable. The lowered center of gravity design gives the trike the ability to maintain
better tire grip in cornering situations. Because there is no moment created about the center of mass of
the trike when cornering at speed.
If the center of gravity is considered the zero position then if the rider is a distance, d, away
from that position it will create a torque, , about that position. Where F is the force of the rider, m,
multiplied by the force of gravity, the acceleration, a.
Table 3: Trike Frame Weights and Materials
Trike
CatTrike 700
TerraTrike Sportster Pro
Steintrikes Roadshark
I.C.E. Trikes Vortex
CarbonTrikes Race
Innesenti Sport
Frame Weight
33 lbs. [6]
37 lbs. [32]
35.2 lbs. [36]
32.33 lbs. [22]
23.1 lbs. [5]
34 lbs. [17]
Frame Material
Unspecified Aluminum
6061-T6 Heat Treated Aluminum
ST52BK Steel
4130 Chromoly
Carbon Composite
Carbon Composite
There are trikes that have a perimeter frame, more like a car, where the user sits in between the
frame rails. This setup is good for creating a lowered center of gravity for the user and trike which, as
stated earlier, helps keep traction and the force on the wheels. The drawback to this style of frame is
weight, it has more material than the monotube designs and therefore more weight. Also the drive
system on these designs is more complex because there is no frame in the middle of the trike for the
drive chain to run against so it must run closer to the user. One example of this style of trike is the Masa
Slingshot trike. It was developed in the 1970's and had a few issues with safety. If the user was
peddling at speed and a foot slipped off the pedals the wheels were so far forward the users feet were
in danger of being sucked under the cross member that connected the front wheels together.
Position of the wheels is the next largest design difference. The most popular style is to have
two wheels in the front to do the steering and one in the back to do the driving. At the same time there
are several designs that use two wheels in the back as drive wheels and one in the front to steer. Both
designs have their place. If the user wants to cruise along on level ground and not have to deal with
6
sharp turns or high speed cornering then one front wheel doing the steering would be sufficient. When
the inertial force of the trike is greater than the force of friction that is working against the tire when the
user tries to turn the one steer wheel the trike will continue along its original path and will not turn until
the velocity slows and the force of the trike reduces to below the force of friction between the tire and
the ground. Having two drive wheels is also not the most efficient use of user input in a trike. Splitting
the input force between two tires requires more energy because you have twice the number of chains,
pulleys and sprockets to absorb energy.
Table 4: Trike Turning Radii
Trike
Delta Trikes X1
Greenspeed Anura
Hase Kettwiesel Comfort
Turning Radius
12’[11]
11‘ 10“ [18]
Left-10’ 10” Right-11’ 6” [21]
Two wheels to do the steering at the front of the trike creates the most efficient use of user
input energy in a trike design. The driving force only has losses in one drive setup eliminating nearly half
of the parasitic loss that happens when components must be added to distribute energy across a
system. Two steering tires also increase the friction factor to maintain good steering and
maneuverability capabilities. This design is so popular even some motor powered trike companies have
adopted this design
Table 5: Trike Turning Radii
Trike
Catrike 700
I.C.E. Vortex
Greenspeed X5
Turning Radius
9’ 2” [6]
9’ [22]
12’ [19]
Suspension in a trike design is mostly driven by the purpose of the trike. If a trike is designed to
be used in road race situations where the riding area is consistent and meant to be ridden at high
speeds then it is unlikely that trike will have suspension, because it would add weight and therefore
increase the amount of user input force it would require to go as fast as a lighter bike. If the design of
the trike is for a more rugged are such as off road riding then the suspension will be a very important
feature of the bike because of the inconsistent riding surface the suspension will absorb the vibrations
coming thru the wheels. In a two front wheel steer design the front wheels will be connected to the
frame with two A-arms having two connections each at the frame and one at the wheel, making two
triangles parallel with each other. This design keeps the wheels moving only in a vertical plane which
compresses a shock and dampens vibrations. For the rear wheel a swing arm design is the most
popular, where the rear wheel is connected to the frame only at one point and that point is the pivot
then a shock is used to create a triangle. When the swing arm is cycled it works the shock to give
vibration damping.
Any of the above combinations can be combined to create a trike and many of them currently
on the market are foldable. This means that the trike itself has joints and disconnects so that it can be
folded into and onto itself to create a much more convenient way of transporting a trike. This ultimately
7
will increase the cost of a design and the weight of the trike because of the extra systems needed to
keep the strength of the design while being able to fold it up as well.
Table 6: Foldable Trikes
Manufacturer
Greenspeed
Evolve Trikes
Trident Trikes
Model
GT 3 Series II [18]
Evolve [14]
Trident [33]
Steering
All trikes have some type of steering in the following text the different types and combinations
that are available in the marketplace will be discussed and compared. Trikes with two front wheels are
split into two types, those that lean in the corners and those that do not. The other style of trike with
one front wheel uses only that one wheel to steer without taking advantage of leaning the trike. This is
mostly due to the fact that leaning a trike in a turn creates even more of an angular force on the tires
and with the limited traction of one steering tire it would not react as well as a design utilizing two front
wheels. Trikes that do have this one front wheel design are used more for what the industry calls
cruising in which the user drives the vehicle at low speeds and isn't concerned with speed but comfort.
When designing a steering system many factors need to be included. Bump steer, camber and castor
change through the cycling of the suspension, toe adjustments and clearance all have their own set of
tolerances that must be calculated.
Bump steer is an effect that happens when the suspension is cycled the steering system design
doesn't have the same radius as the radius the a-arms move on and therefore will push the wheel off of
its intended axis. This effect can only be reduced by reducing the length of the link that moves with the
a-arms and pushes or pulls on the spindle. This link is known as a tie rod because it ties the mechanism
that the user inputs the steering into and ties that motion to the motion of the wheels.
Castor is the angle that the suspension mounting points create. When a design has positive
castor that means the angle that the mounting point makes is less than 90 degrees from 0. Positive
castor helps to keep the wheel traveling in a straight line. This is because with the bottom mounting
point in a suspension leading tire it cannot move about freely. If a negative castor situation was
produced then the tire isn't being led but doing the leading and therefore is free to track in a direction
that isn't led by user input. This design would be very unstable because it would take input from the
surfaces that it rides on more easily than from the user.
8
Fig. 1: Positive Caster
Camber is the angle of the tire. From a straight on point of view a tire that is perpendicular with the
ground would have 0 degrees of camber. If the tire has negative camber then the slope of the line that
runs through the center of the tire will move from the negative x direction to the positive x direction and
having positive camber will have the slope staring in the positive x direction and move to the negative.
Fig. 2: Positive Camber
Toe is where the tires point in a different direction than the centerline of the vehicle is traveling.
This is often the only adjustment that is designed into a suspension system because the camber and the
castor do not affect the tracking of the vehicle only how the vehicle rolls and how the suspension affects
traction. Toe in is a situation where the tire is pointing inward of the direction that the vehicle center is
pointing and toe out is the opposite situation.
When two tires steer they move on an arc. Since the two tires are a set distance apart this will
cause the outside tire to have a larger turning radius and therefore the distance that it has to travel is
longer than the inside tire, this pulls the outside tire towards the inside, which is called scrubbing.
Ackermann steering geometry takes care of this situation. The Ackermann geometry changes the
mounting points of the steering system to give the outside tire a smaller radius than the inside tire
during a turn so that it will not scrub.
9
Fig. 3: Ackermann Steering
The diagram on the left shows how the mounting points on an Ackermann design are moved to
change the turning radius during a turn. The left diagram shows how the centers of the turning radiuses
are at the same point which means there will be no tire scrub.
Leaning a tire that has a radial profile will make the vehicle move in the direction of the lean.
This is because of the change in the radius of the tire where it comes into contact with the ground.
When the center of mass moves and the effects of friction, gravity, and torque change direction, it
creates a circular path for the vehicle to travel. As a result the center of mass moves, then an inertial
force is then applied to the tires at the contact patch. As the speed increases then the ability for the
vehicle to lean also increases because of the increase in force on the tires.
Suspension
For the human powered delta trike there is a plethora of ways to attach the suspension. The
most common form of suspension is the rear swing arm design. This type of suspension can be attached
in a variety of ways. In most designs the rear swing arm is connected to the frame at a pivot point,
allowing the up and down travel of the rear tire. Also connecting the rear swing arm is the shock itself.
The shock is placed above the pivot point at the top of the swing arm and behind or below the seat. This
type of design for the rear suspension allows for a lot of travel which would give the rider a smooth ride
when traveling over bumps and holes. Also with this design, the rider usually has the ability to adjust the
stiffness of the shock allowing the rider to customize the riding experience. There are also cons to this
type of rear suspension. The first is that the some of the rider’s power that he/she is inputting into the
crank can be absorbed by the shock causing the rider to put forth more effort. This can be fixed by the
type of shock absorber that is place on the bike. Another con to this design is that it will add extra
weight to the tricycle.
10
Fig. 4: Rear swing arm suspensions
The rear swing arm is not the only option for connecting a rear suspension to the human
powered delta trike. Another design is to have a pivoting seat. This design consists of the seat being
attached to the frame at two points. The front attachment point would be the pivot point, which would
allow the seat to rock back and forth around this point. The rear attachment point would be the shock
absorber connecting the rear of the seat to the frame. This shock absorber would cushion the travel of
the seat which is pivoting around the front attachment point. The cons to this design are the amount of
travel and added weight. The shock absorber attached to the seat would not allow for much travel,
especially when compared to the swing arm design. This limited amount of travel for the shock would
cause the rider to experience a rougher ride.
Another design for the suspension is to have a rear swing arm attached to the frame and have
the shocks be a part of the seat stays. There are two versions of this type of design, one with multiple
shocks and the other with a single shock. The multiple shock design would include a rear swing arm that
is connected to the frame at a pivot point behind the seat. This swing arm would have two seat stays
that rise up from the point of the rear axle to the back of the seat. These seat stays would have a shock
absorber in the middle of each of them. This would absorb the shock created when hitting a bump or
hole in the road. The single shock design would be a rear swing arm that is connected to the frame at a
single pivot point. This swing arm would have two seat stays that came up from the rear axle point and
connected together right above the tire. After the point of connection, a single seat stay would project
up and connect to a shock absorber that would connect the seat to the seat stay.
11
Drivetrain
The only way to transmit power to the wheels is through some sort of drivetrain. Various
different drivetrains are possible with variables such as wear, maintenance, availability, and complexity
to consider.
Chain and Sprocket
The roller chain and sprocket system is composed of a few different components. It requires at
least two sprockets, a roller chain, and some kind of pedal for the user to apply torque to. The torque
that is applied to the pedal is transferred using the roller chain from one sprocket to the sprocket that
requires the torque. The simple chain and sprocket setup is show below in figure 5.
Fig. 5: Chain and Sprocket
If different gearing is required the set up will become a bit more complicated. This requires a derailleur
which allows the different gearings. The derailleur consists of multiple sprockets of different diameters
attached to one another, and a mechanism that moves the roller chain from one sprocket to another. As
the roller chain moves from a smaller diameter sprocket to a larger diameter sprocket the gear ratio
decreases. Figure 6 shows the derailleur that allows different gearing in the chain and sprocket design.
Fig. 6: Derailleur
The roller chain and sprocket poses many positives and negatives compared to other driveline
options. Some of the positive attributes associated with this system consists of the ease of the design
12
and construction of the roller chain and sprocket. This is the conventional drivetrain for most cycles that
are built. Since the roller chain and sprocket are the conventional drivetrain method for cycles it also
makes all the parts necessary to construct the system very easily accessible and much cheaper than
other methods. Table 7 below shows the prices and weights of different drivetrain parts. Two separate
brands are considered and compared.
Table 7: Drivetrain Components and Prices
Brand
SRAM X.9 Rear Derailleur 2012
SRAM PG-970 9-speed MTB Cassette
SRAM PC-951 9-speed Chain
SRAM Apex Crankset w/ GXP 2011
Shimano XT M772 Shadow 9 Speed (derailleur)
Shimano XT M770 9 Speed Cassette
Shimano SLX HG61 9 Speed Cassette
(alternative)
Shimano XT CN-HG93 9 Speed Chain
Shimano Deore M521 Crank With Octalink BB
Cost ($) speed
weight(g)
97.00
9
215
45.99
9
321
22.99
9
303
99.98
890
84.98
9
235
86.98
9
300
49.98
9
330
32.98
59.98
9
9
304
1058
Due to the systems simplicity, it also makes it much easier to incorporate into complex designs.
Although all of these things would help the overall design of the project, there are many things about
the roller chain and sprocket set up that would be considered to be negatives in the overall design of the
system. In trike design the weight is a major factor, and a chain and sprocket set up would add
substantial amount of weight to the design. Another downfall of the chain and sprocket would be the
maintenance requirement. For the system to operate at maximum efficiency it is required that the chain
and sprocket stay properly lubricated and cleaned. If it is not properly maintained the efficiency is
dramatically decreased. Due to required maintenance the chain and sprocket system would have to be
located in a position that is easily accessible for removal and maintenance reasons. This setup also runs
into possible safety issues. The roller chain and sprocket is an external drivetrain system, which leaves
opportunity for injury in the system. A body part or article of clothing can easily be caught in between
the roller chain and sprocket. This requires for further steps to be taken to insure that the user is
completely safe while operating any device that has the chain and sprocket close to the user. According
to a study done by engineers at Johns Hopkins University, a chain drive bicycle has an efficiency of up to
98.6 percent if in the right conditions. Engineers at Johns Hopkins also determined that the higher the
tension on the chain the more the efficiency will rise. If the conditions that the system is tested in are
not adequate, the efficiency can drop as low as 81 percent. With this being said the maintenance must
be properly taken care of to insure efficiency.
Timing Belt
Timing belt drivetrain is similar to the design of the roller chain and sprocket, but with different
components. The drivetrain consists of a toothed timing belt that is run from one sprocket to another to
transmit torque from the input pedal to the desired output. The set up for a simple timing belt drivetrain
is similar to the chain and sprocket, and can be seen in figure 7 on the next page.
13
Fig. 7: Timing Belt and Sprocket
Although the setup of the timing belt and the conventional chain and sprocket is very similar, the way of
changing gears differs greatly. The timing belt is required to use an internal gear hub, as opposed to the
derailleur that a traditional chain and sprocket setup uses. The internal gear hub is shown below in
figure 8.
Fig. 8: Internal Gear Hub
The timing belt drivetrain only has a few negatives about it but these things can pose major
problems when attempting to integrate it into a design. For the most part timing belts come in standard
sizes, so the design would have to be engineered around the drivetrain as opposed to engineering the
drivetrain around the design. This would cause major problems in the design and would most likely
cause many problems later in the project. The cost of the timing belt drive train becomes much higher
when a multiple geared system is required. This requires an internal gear hub, which by itself will drive
the overall price of a project way up. According to the Bike Surgeon located in Carbondale IL, a reliable
internal gear hub can cost anywhere from 200-300 dollars. Although the timing belt and internal hub
would increase the price of the design there are many positives that can be found. The internal gear hub
requires little to no maintenance, and the timing belt used will not rust. The internal gear hub also
allows the user to change gears while at rest, as opposed to having to be moving for the gears to
change. The weight of the system is low so it will not affect the overall design of a project. Other positive
things about the timing belt drivetrain would be the safety and quietness of the system. The timing belt
and gear hub make virtually no noise which makes the ride much more comfortable. The safety while
using the timing belt also increases with respect to the chain and sprocket. The U.S. department of
14
energy states that timing belts have consistent efficiencies of 98 percent, and over a wide load range.
The timing belt and sprocket will also operate at the high efficiency through wet or oily environments. If
timing belts are installed properly they require little maintenance or retensioning.
Universal Driveshaft
A universal drive shaft uses a shaft as opposed to a chain or some type of belt to transfer power
from the pedals to the wheels. The universal drive shaft uses bevel which allow the axis to be shifted by
90 degrees. The shifting of the axis allows the shaft to transmit the power horizontally along the frame
of the cycle. The universal drive shaft was at one time only for the transmission of power through a one
gear system, but due to technology in internal gear hubs universal drive shafts can now consist of
several gear inputs. A simple universal drive shaft is shown below in figure 9.
Fig. 9: Universal Driveshaft
The weight and the cost of are a couple of the main problems associated with the universal
driveshaft. Due to the complexity of the gear workings and the material they are often made out of the
weight is much higher compared to other types of drivetrains. Since the universal driveshaft is only able
to travel with one gearing, it is required to have an internal gear hub to change gears. This will greatly
increase the cost of the design, but also has some positives that are included with an internal gear hub.
The internal gear hub along with the universal driveshaft requires little to no maintenance, and allows
the changing of gears while stopped or in reverse. They are also very dependable and should have no
problem with failures while riding the cycle. This in turn makes it very safe to ride since there will be no
failures with the drivetrain. This setup will also produce little to no noise while operating, so the ride
then becomes more comfortable. Dynamic Bicycles claim that their universal drive shaft operates at
over 90 percent efficiency. They also claim that the universal drive shaft is able to operate consistently
at a high efficiency through any conditions with minimal maintenance.
Front Wheel Drive
All of these options can be adapted to both front and rear wheel drive vehicles. Both options
bring negatives and positives to a project. The rear wheel drive option allows a simpler integration into a
design. Although applying it to a design is easier, it requires a longer driveline, which can add more
weight into a project. The front wheel drive option is a bit tougher to integrate into a design but allows a
more compact drivetrain since the area of torque input is very close to the desired area of the output.
Most of the time the front wheel drive option requires having a rear wheel steering system. This is often
15
more difficult and unusual to implement into a vehicle design. With this being said the choice of either
front wheel or rear wheel drive depends on the specifications of the project.
Brakes
In any tricycle, not only does the driver need to accelerate the vehicle, but he must also apply
force to stop it. There are many different ways to slow a rolling wheel, and there are many different
types of brakes that can be bought off the shelf, normally used in bicycles. The regular cyclist has choices
to slow down his vehicle: the normal recreational bicycle uses a very simple, cheap and effective design
with rim brakes, which can be applied by a number of different mechanisms that all essentially perform
the same action where a caliper pulls rubber pads against rim of the wheel; a bike the requires more
endurance, such as a touring or mountain bike will often use disc brakes that has a metal disk, fixed to
the wheel hub, and a caliper pulls shut on this disk, which in turn is slowed, therefor slowing the vehicle;
some BMX bikes will be outfitted with no braking mechanisms at all, and rely on the rider to skid his
shoe along the ground or against the treads of the tire between the back fork and seat, which acts as a
spoon brake, the simplest of options, where a pad is applied with a downward force on the top of the
tire to cause friction to slow the wheel. Any of these braking mechanisms can be implemented with a
mechanical cable, or a hydraulic system.
Fig. 10: Hydraulic Disc Brake
16
Fig. 11: Mechanical Rim Brake
The first choice in any design is always to go with the cheapest, lightest option that can meet the
performance standards; but, the wheels of delta tricycle have a number of dissimilarities from its 2wheeled cousin that make the standard options difficult to choose from. First and foremost, the trike
does not use a standard bicycle fork on the front wheels, rather the wheels are supported by strong
cantilever arms, therefor a custom mount will be necessary, as most brakes our designed for a fork
attached from both sides. Other differences from a bike include that there are three wheels as opposed
to two and the weight of the system, and its center of gravity. A bicycle can be made very lightweight
and the rider makes the system’s center of gravity very high off of the ground, having a back brake is
crucial so that the rider does not flip over with a sudden front brake; a tricycle has a lower COG so that
front braking is more applicable. In addition, the extra wheel and the dissimilarity of the rear to the front
wheel mounting makes it plausible that two different types of brakes be used on a tricycle.
Weighing the options, there are certain advantages that come out of each system. While having
no brakes would indeed increase the acceleration and overall simplicity of the trike, a decision in the
favor of safety and existing brakes would probably in the best interest of any design. The spoon brake is
an outdated design, and while simplicity reigns with the spoon option, it can be very ineffective when
exposed to dirt, mud or water and has been seen to wear out a tire rather quickly. With either of the
two remaining choices, the brakes require custom parts will need to be created to mount either rim
brake calipers or disc brakes on the front wheels. In the battle between front or back brakes, logic
dictates that as the more the vehicle slows down, the momentum of the trike and user is going to be
acting more toward the front of the vehicle, reducing the effectiveness of the back brake. One
advantage of the back brake, though, is that in the event of a sudden front-brake stop, the momentum
could cause the vehicle to flip over the front axis, posing a danger to the rider and trike itself. It seems
that a combination of both front and back brakes are needed for an effective tricycle; with this option
there could be a combination of disc and rim brakes on either the front or back wheels.
17
Wheels and Spokes
Wheels are responsible for supporting the vehicle, transferring power to the pavement, and
keeping the rider in a turn when necessary. Observably, the most common form of the wheel for an
HPDT is the spoked bicycle wheel. This is because these wheels are designed to carry loads equivalent to
a cyclist and gear while maintaining a low weight. While other wheel options have been implemented
they are not common due to large cost to benefit ratios. Thus, it is important to note the qualities of
spoked wheels for use in such applications.
The spoked wheel was designed to be strongest in the radial
direction and maintains that design goal by running spokes from the
outer rim to the inner hub of the wheel. These spokes are then put
in tension by rotating the nipple in order to draw the spoke into the
rim. The average bicycle wheel has 36 spokes laced from the rim to
two sides of the hub. This gives 18 spokes per side all in tension. As
the wheel goes around the rim deflects slightly where it meets the
pavement which causes a relief in tension on the bottom spokes.
The net effect is that the hub and bicycle end up “hanging” from the
upper spokes still in tension, which is why the wheel is most resilient
under radial loading. A spoked wheel in a laterally loaded situation
does not have as much force available from the tension of the spoke
as a wheel in a radially loaded case does to counteracting the force
of the pavement on the wheel. The force in the Y-direction, 𝐹𝑦 , is
the force available to hold the rim centered between the flanges of
the hub as shown below in eq.2 and figure 13.
𝑒𝑞. 1. )
𝐹𝑥 = 𝐹𝑐𝑜𝑠 𝐿)
𝑒𝑞. 2. )
𝐹𝑦 = 𝐹𝑠𝑖𝑛 𝐿)
Fig. 13: Geometry of a Spoke
Fig. 12: Spoke, nipple, and
rim arrangement. 1) Spoke
2) Nipple 3) Rim
18
Spokes come in many varieties varying in shape, diameter, and material. The standard for spoke
measurement is to reference the spoke diameter instead of using the old term “gauge.” Table 8 gives a
quick comparison of spoke materials and their Maximum Supported Weights (MSW) as well as the
respective strains.
Table 8: Strength of Spokes of Various Materials
Spokes
Steel
Aluminum
Composite (CF)
†Assuming
‡Assuming
Tensile (MPa)
1269
310.0
4150
E (GPa)
200
68.9
231
ρ (g/m3)
7.92
2.70
1.78
MSW† (N)
2551
623
8244
ε‡ (mm/m)
2.2
6.4
1.9
smallest spoke diameter available (1.6mm)
890 N (200 lbf) loading on one spoke
Steel offers the advantage being the cheapest material to acquire while maintaining a high MSW
to strain ratio. With this advantage comes the burden of steels relatively high density resulting in spokes
with more mass not only contributing to a higher weight but also an increase in inertia. Aluminum offers
a relief from the burden of high densities however, as a result is only capable of supporting roughly one
quarter of the weight of steel. At 6.4 mm/m aluminum is also the material with the most amount of
deflection. The carbon fiber composite seems to yield the best results for spoke applications. Carbon
fiber has the lowest density of the three leading to the lightest spokes possible and yet supports almost
four times the load of steel while maintaining the lowest strain ratio of the three.
A rim is needed in order to keep all these spokes together and aligned. That rim’s stiffness can
be approximated by eq. 3.
𝑒𝑞. 3. )
𝑘=
𝑁𝑠 𝐸𝑠 𝐷𝑠2 cos2 𝛼
(𝐿 )
16𝑅𝑟
𝑒𝑓𝑓
Fig. 14: Geometry of a Spoke
19
Where 𝑁𝑠 is the number of spokes, 𝐸𝑠 is the spoke modulus of elasticity, 𝐷𝑠 is the diameter of
the spokes, 𝐿𝑒𝑓𝑓 is the effective length of the spoke (spoke length – distance threaded into nipple). In
order to know the length of the spoke one must know what lacing pattern is being used as eq. 4 shows.
𝑒𝑞. 4. )
Fig. 15: In-plane spoke length
𝑙 = √𝑑2 + 𝑟12 + 𝑟22 − 2𝑟1 𝑟2 cos 𝑎
Fig. 16: Spoke Lacings
Where 𝑑 is the distance from the center of the hub to the hub flange, 𝑟1 is the radius from the
center of the axle to the circle on which the spoke holes lie, 𝑟2 is the inside radius of the rim, and 𝑎 is
defined by the number of spoke crossings divided by the number of spokes on one side multiplied by
360°. Figure 17 shows the various types of spoke lacing for a bicycle wheel with the most common being
2x, 3x, and 4x. Spoke lacing means that any one spoke traced from hub to rim will cross exactly n other
spokes. The effect of increasing the number of spoke crossings is easily distinguished in figure 6 below.
Fig. 17: Spoke Lacing Effects
20
Wheels laced with less spoke crossings are stiffer, according to figure 6, which makes sense due
to the angle of the spoke with respect to the hub flange circumference being closer to normal; this
allows more force to be counteracted by the tension in the spokes.
Hubs
The wheel hub is what transfers weight but allows rotation through bearings and an axle. The
quality of construction, weight, and price can all be factors for one hub or another making it’s way into a
design. Hubs come in many varieties ranging from weatherproof ceramic bearings held in cartridges and
carbon fiber shells to plain steel with loose bearings held in place with a cone shaped axle. Table 9
shows these attribute for various front hub layouts.
Table 9: Front Hub Comparison
Front Hub†
Shimano SLX (15mm)
Shimano Deore XT
Circus Monkey MDW
Cannondale Lefty IS
Cannondale Lefty SL
Chris King ISO 20mm
Price ($)
60
40
70
170
180
190
Weight (g)
190
235
130
106
100
207
Performance††
7
6
4
8
8
9
†20mm
††Out
Thru-Axle unless noted
of 10 based on build quality and components used
Table 10: Rear Hub Comparison
Rear Hub
Shimano SLX
Shimano Deore XT
SRAM 406
SRAM X.9
††Out
Price ($)
50
70
35
80
Weight (g)
450
-
Performance††
8
8.5
7
9
of 10 based on build quality and components used
Table 10 illustrates the same points as table 9 but for rear hub considerations. Through axle
hubs have a larger diameter hollow axle that runs through the inner bearing race allowing the
distribution of more force without bending as readily as the axles in hubs whose axles are only large
enough to fit a quick release bar. Hubs like the Circus Monkey MDW are appealing due to their low
weight and low cost but the bearings that come with them are not suitable for all weather purposes.
While at the other end of the spectrum the Chris King hubs boast fully sealed ceramic bearings and the
longest expected life out of the bunch, but that quality is the cause for a price tag near two hundred
dollars each.
Electricity generation can also be achieved through the hub. Hub generators come at a higher
cost than the friction based bottle dynamos which rub on the sidewall of the tire in order to cause
rotation. The hub generator offers better efficiency when converting kinetic energy to electricity and
less resistance when rolling while the bottle dynamo offers ease of setup and completely resistance free
riding when disengaged. Table 4 on the next pages illustrates the differences between various brands
and type of dynamos.
21
Table 11: Generator Types and Efficiencies
Generator
Hub Generator
Schmidt SONdelux
Shimano DH-3N72
Shimano NX-30
BIOLOGIC Joule 3
Dynamo
AXA HR
Price ($)
272
130
50
150
40
Weight (g) Efficiency (%)
390
64
680
53
720
49
355
73
230
<40
The standard for USB power connections is 5 V at 500 mW which yields 2.5 W; lighting will
consume additional power. Some generators, like the Schmidt, output only 3 W while some claim an
output as high as 6 W, like the AXA HR dynamo. The use of a generator on a trike is not a new concept;
in fact, the GT-Series from Greenspeed comes ready for a 6-V or 12-V hub generator. Most trike
manufacturers that exist today do not sell trikes with built in generators due to the cost.
Component Materials
In order to make a lighter weight delta trike, the components need to be made of a lighter
material that is of equal or greater strength. These components consist of the handle bars, fenders, seat
frame, and seat stays. It is required to know the mechanical properties of the materials that have been
used and the ones that will be used on this project. With this information, the different types of
materials can be analyzed and compared in order to determine the proper material to use. The known
materials used for these components are 4130 chromoly steel, aluminum (6061-T6, 7005-T6), titanium,
and carbon fiber. These materials are shown in comparison in the tables below:
Table 12: Material Properties
Material
4130
chromoly
steel
Aluminum
6061-T6
Aluminum
7005-T6
Titanium
Standard
Carbon
Fiber
E [GPa]
G [GPa]
Ult.
Tensile
Strength
[MPa]
Ult.
Comp.
Strength
[MPa]
Major
Poisson’s
Ratio
[MPa]
Yield
Strength
[MPa]
Density
(kg/m3)
190-210
-
670
-
0.27-0.3
360.6
7900
68.9
26
300
-
.33
241
2700
72.0
26.9
510-538
-
0.330
434-476
2800
110
41
950
970
0.342
-
4500
70
5
600
570
0.10
-
1740
22
Table 13: Material Properties Continued
Symbol
Longitudinal
Modulus
Transverse
Modulus
In Plane
Shear
Modulus
In Plane
Shear
Strength
Units
Std. CF
Std. CF
Fabric
Steel
Al
E1
GPa
17
19.1
207
72
E2
GPa
17
19.1
207
72
G12
GPa
33
30
80
25
S
MPa
260
310
-
-
Other than the mechanical properties, the price of these materials is also a factor. The prices of
these materials are shown in comparison in the table below.
Table 14: Tubing Prices
Tube Material (0.25”x0.035” OD 1’ Length)
4130 Chromoly Steel
Aluminum 6061-T6
Aluminum 7005-T6
Titanium
Standard Carbon Fiber Fabric (24”)
Price
$7.60
$2.29
$11.60
$21.25
$29.75
23
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