The Evel Knievel of ENG 2000
Final Report
Group 6
Name
Gordon Klein
Navjeet Singh Sarai
Chris Kurulasuriya
Mark Vincent Tee
Student Number
208014573
206943179
206518229
208189888
For Prof. Eshrat Arjomandi
Engineering 2000 (Winter)
April 6, 2007
E-mail Address
frosty55@yorku.ca
nsarai@yorku.ca
cfern85@yorku.ca
mvt@yorku.ca
Abstract
The “Evel Knievel of Eng 2000” project was a competitive project between six groups in
York University’s 2006-2007 ENG2000 class. The purpose of the project was to design a
vehicle which, without the aid of commercial batteries, can jump off a 15 degree incline
and land on a target 5m away. The design had to be aerodynamic, aesthetically pleasing,
had to travel exactly 5m, and had to cost in its entirety a total of $25 or less.
The report discusses several different methods of propulsion that Group 6 considered,
including explosion, compressed gas, elastic bands, and a number of designs that were
banned from the competition. The design group 6 settled on was a rat trap augmented
with elastic bands. A string was strung from a rod attached to the rat trap’s arm, through a
pulley to the drive wheels. The pulling force of the rat trap pushed the car forwards. This
design was picked because it was believed that it had enough power to accomplish the
project goals, and was a controllable, environmentally friendly form of energy.
The report shows calculations which demonstrate that the car needed to accelerate to
~10m/s to launch the correct distance, and that a force of 5.0N applied over 2.0m was
sufficient to accomplish that. Then it discusses the forces behind the car, and shows how
the torque applied by the mouse trap is related to the applied force that pushes the rat trap
forward.
Experiments and testing showed that the car accelerated best when the rat trap was placed
at the front, a 30cm rod was attached to the rat trap arm, and a small weight was applied
to the front of the car. The best test results accelerated the car to 7m/s, which was still
lower then the necessary amount of 10m/s.
Our design remained approximately on budget, costing a total of $26.45 after taxes. The
design went over-budget when some last minute changes had to be done just before
demonstrations.
The report discusses our project timeline, work breakdown structure, and AON logic
diagram which describe our project management and schedule. We made fairly steady
progress on our car, but only fully implemented one prototype which became our final
design.
The rat trap car design does not have any impacts on the environment since there are no
emissions from the car while it is being used. Safety issues due to the snapping of the rat
trap were discovered, and care had to be taken to ensure the safety of the group members.
Demonstrations were held on the roof top of one of York’s parking garages. The weather
was sufficiently calm that it did not influence the results of the demonstration. The rat
trap car failed to perform to specification. This was in part because the tires were slipping
on the ramp, and also because the rat trap did not have enough power to propel the car
with enough force. Design improvements like limiting the weight of the car and using
multiple rat traps are discussed at the end of the report.
Table of Contents
Introduction....................................................................................................................... 1
Background Information ................................................................................................. 2
Vehicle Design ................................................................................................................... 4
Design Possibilities......................................................................................................... 4
Explosive (Rocket) Powered Car............................................................................................ 4
Launcher Powered Car ........................................................................................................... 4
Glider ...................................................................................................................................... 5
Compressed Water Powered Car ............................................................................................ 5
Elastic Band Powered Car ...................................................................................................... 5
Our Design ...................................................................................................................... 6
Body Design ........................................................................................................................... 6
Propulsion System .................................................................................................................. 8
Implementation ............................................................................................................... 10
Experimental Data and Testing..................................................................................... 13
Final Budget Details........................................................................................................ 14
Work Breakdown Structure .......................................................................................... 15
Project Timeline / Gantt Chart...................................................................................... 16
AON Logic Diagram ....................................................................................................... 17
Risk Analysis ................................................................................................................... 18
Environmental / Safety Issues........................................................................................ 19
Analysis of Demonstration ............................................................................................. 19
References ........................................................................................................................ 22
Introduction
The “Evel Knievel of Eng 2000” was an innovative, competitive project which combined
both the presentation and engineering skills of the 2006-2007 engineering students at
York. The groups were assigned to make a car under an allotted budget of $25 which
could launch off a ramp and hit a target 5 meters away from the ramp. There were six
different groups participating in this project.
A target called the “green zone” was supposed to be placed in the center of the target,
with bonus points allotted to cars that can land in this green zone, but no cars hit the
target, so the green zone was never used.
Ramp specifications:
Width: 40cm
Length: 1.83m
Incline: 15 degrees
Target specifications:
Distance from ramp: 5m
Width: 1m
Height: 1m
The cars were allowed (and encouraged) to use alternative sources of power. The only
power source that was not allowed was commercial electrical sources like batteries.
Commercial products were allowed to be used, but entire car kits were not.
The demonstration was an elimination style competition, where cars that hit the target
advanced to the next round. Each round the target was placed 2m further away from the
ramp. This implied that the car designs had to be capable not only of launching off the
ramp, but launching in a controlled manner, so that the distance could be calibrated.
-1-
Background Information
A “mouse trap racer” is a vehicle that uses the
potential energy that can be stored in a mouse
trap to propel it forward. It is a design that many
high-schools use as an experimental project in
science classes. Many bright students have
thought up clever ways of extracting every joule
out of a standard mouse trap and propelling a
car forward. It is a tried, tested and true
technology.
There are a number of variations on the typical mouse trap
racer. There are elastic band powered cars, rubber band
powered planes and boats, and balloon powered racers. One
website that specializes in all of these hobby projects is a
website called “DocFizzix.com” (see References section).
This website sells plans, kits and specially machined parts for
use in mouse trap cars and elastic band cars, but they only
ship to the United States. Mouse trap cars are designed to
travel in a straight line, and the aim of the game is either to
get the greatest acceleration, or cruise for the longest
distance.
Since the design uses a mouse trap, weight is the number one
most important aspect of the design. Mouse traps themselves
hold little potential energy, so to get the greatest speed the
mass must be as low as possible. Most of DocFizzix’s
designs are made out of balsa wood, and use a clever
combination of gears and pulleys to extract as much power
-2-
out of the mouse trap as possible. In most high-school classes, the typical choices for
wheels are CDs, since they are cheap, extremely light, and easily accessible. However,
CDs have almost no traction on the ground, which is a common problem in these designs.
One feature that is common to almost all of the mouse trap designs on DocFizzix’s
website is that they all have an “acceleration rod”. This rod is attached to the mouse trap
and changes the force/time ratio applied by the mouse trap. The trap transfers the same
amount of potential energy in the end, but the rod causes the mouse trap to take a longer
time to do it. The result is less force over a longer period of time, to give the car more
time to accelerate to its maximum speed. The acceleration rod is the solution to the
traction problems of the wheels. We decided to incorporate this into our design,
anticipating that the rat trap would have issues releasing its potential energy too fast.
Usually in mouse trap competitions the only project constraint is that you must use a
single regulation mouse trap to power your vehicle. In this project, any kind of power
source could be used, so while the mouse trap design was the basis for our project, we
deviated from it and selected more powerful forms of propulsion than a mouse trap – a rat
trap. This will be discussed later in the report.
-3-
Vehicle Design
Design Possibilities
There are several options that were considered as possible designs that could meet the
project’s constraints and goals. The following design concepts were considered while
conducting our research:
1.
2.
3.
4.
5.
6.
Explosive powered car (possibly rocket propelled)
Car propelled by a launcher
Glider design
Compressed water
Elastic powered car
Mouse / Rat trap powered car
Evaluating the available choices, certain designs were rejected due to constraint
limitations and assumptions made by the team.
Explosive (Rocket) Powered Car
The explosive or rocket powered car was omitted early in the evaluation process. It was
omitted because it was found to be too dangerous. Initially the information given to the
group implied that the demonstrations were going to be conducted indoors. The fumes
released by the rocket, as well as the general danger of a rocket powered projectile which
could go out of control caused us to dismiss the idea of an explosive rocket propelled car.
Launcher Powered Car
The next idea was to have a launcher for the car and propel it across the ramp. A launcher
has the benefit of having the car’s power source be external from the car itself. There
were many ideas that would allow the car not only to be launched the necessary distance,
but also launched in a very measurable and calibrated way. However, a launcher violated
one of the constraints of the project. The project specifications were revised early on in
the project to forbid launcher powered cars. Since it was forbidden to have a launcher for
the car this idea was dismissed in the early stages.
-4-
Glider
The glider design had very good advantages as it provided a way to allow the vehicle to
make use of lift from the air as it flew. The car would need considerably less power to
propel it off the ramp, which would have made it easier to get to the target from the initial
launch. However, to accomplish a glider design, the design had to have wings. Similar to
the launcher design, the project specification was revised to forbid wings on the car under
the pretense that the car was supposed to be a land vehicle, and not an air vehicle. Since
we were not allowed to have wings on the car the glider design was dismissed.
Compressed Water Powered Car
The compressed water car was a very possible option. The water was environmentally
friendly, reusable, and the pressure could be calibrated for the right amount of power.
However, just like the rocket powered car, we originally thought that the demonstrations
were going to be performed indoors the compressed water car would make a mess of the
area it was launched in. We also found that compressed water power cars were very
difficult to control after the car has been launched. The car was very erratic when it was
in the air, and it was difficult to land the car right side up. We eventually decided that the
compressed water power car was not the best way to accomplish the project goals.
Elastic Band Powered Car
Next the elastic powered car was evaluated. We concluded that elastic power would not
give enough power at all to get off the ramp, so once again this idea was also dismissed.
The final choice that was left is the mousetrap or rat trap powered car. Our research
which will be discussed later in this report showed that it was possible to use a mouse or
rat trap to propel a car 5 meters in under one second. A rat trap was chosen over a mouse
trap to provide more power. We decided on this design because we had seen examples of
the design successfully built, and the designs we saw accelerated in a very controlled
manner. Our final design and the building processes are discussed in the following
section.
-5-
Our Design
Body Design
Our vehicle is a modification of the typical “mouse trap car”, where the power of a
mouse trap is harnessed to spin the front drive wheels and cause the car to accelerate. In
our design, we replaced the mouse trap with a larger, more powerful rat trap. The arm of
the rat trap is connected to a string, which is in turn connected to the drive wheels on the
car. The pulling force of the rat trap applies torque to the wheels and accelerates the car.
A more detailed view of how the forces work in the car is discussed in the
Implementation section of the report.
The following figure is a schematic of the design of the car from the top view; this has
been changed from our previous design, both designs are shown in the following figure.
16cm
16cm
12cm
1" Bolt
L-bracket with bolt
L-bracket with bolt
Rat trap
12cm
Rat trap
1" Bolt
46cm
46cm
Acceleration
Rod / Arm
Elastic constraint
rod
Spindle
Fibre board siding
Fibrebase
board base
Hardboard
Fibre board siding
Fibre board
Hardboard
basebase
30o
30o
Acceleration
Rod / Arm
Added front weight
Figure 1: Schematics of original design (shown on left) and new design (on the right).
The base of the car is 46x16cms and made out of 1/8” hardboard. The rat trap was
attached to the base using 1” bolts and nuts, spaced with a few centimeters of gap
-6-
between the siding and the rat trap. This allowed the base to be very strong and ensures
that the rat trap will not move in any direction even if a great amount of force is applied
to it.
The sidings were attached to the body using stainless steel L-brackets, fastened with nuts
and bolts. This makes the sides adjustable, while still being securely attached to the car.
The sides could be easily replaced if necessary.
The side panels were oriented in such a way as to minimize air drag. The wings run in the
same direction as the motion of the car, cutting through the air. The side panel is designed
so that the incoming air to the front will cause as little drag as possible and the air that the
flaps do interact with will be pushed off the top of the vehicle.
In Figure 1 it is illustrated that there were several changes made to the original design.
First the entire rat trap was moved towards the front of the car. The weight of the rat trap
closer to the drive wheels helped reduce the slipping we experienced on the drive wheels,
which is discussed in more detail in our Experimental Data and Testing section.
The second change that was made was the elastic bands. Elastics were attached to the rat
trap and tied to a rod mounted on the base, called the elastic constraint rod. The rod was
made out of a bent coat-hanger, and supported all of the additional force applied by the
elastic bands.
A front weight was added to give the wheels added traction. The downward weight
centered over the wheels would prevent the wheels from spinning out of control during
the car’s acceleration while the rat trap was closing.
Finally a spindle was added to wrap the string around, in order to give the wheels more
torque. The propulsion of the vehicle is discussed in the next section.
-7-
Propulsion System
The following figure illustrates the mechanical system which is used to accelerate the car
forward.
Figure 2: Mechanical system overview.
A string is attached to a rod glued to the rat trap’s arm. The string is threaded through a
pulley at the back of the car, and fed through, under the mouse trap, to the front drive
wheels and wrapped around the spindle attached to the front axle. As the string is wound,
the rat trap and acceleration rod is pulled back, and the front wheels are wound
backwards. This stores potential energy in the rat trap. When the car is released, the rat
trap starts to close, applying tension force from the arm through the pulley onto the
-8-
spindle. This force applies a torque to the front drive axles which accelerates the car
forward.
The motion of the axle spinning will be in the forwards direction as illustrated on the
figure above. The pulley is an important part of the design, even though the force exerted
from the arm would be perpendicular to the axles regardless of the direction of the force.
The pulley allowed the acceleration arm to pull the longest distance of string through the
spindle. If the puller were not in place, half of the motion of the acceleration arm would
not result in pulling force, but instead in simply wrapping the string around the drive
axle. The pulley allows the rat trap to be offset a greater distance from the spindle, which
uses the rat trap more efficiently, and reduces the size of the body.
The elastic bands that were added to provide additional power are shown in yellow.
These elastic bands provided additional force along with the rat trap’s spring assembly.
The elastic bands were stretched only for the first half of the rat trap’s motion, giving the
car a quick starting acceleration, and a slower acceleration near the end. Our testing
showed that this addition gave the car better acceleration and overall increased the final
velocity of the car when it reached the top of the ramp.
The revisions to our design improved the force and overall acceleration of the rat trap car.
-9-
Implementation
Our design requires the car to travel a minimum of 5m when it reaches the end of the
ramp. Using projectile-motion calculations, we can determine the speed the car must be
traveling to achieve this distance:
(halflife)
Vy = 0m/s
vi
vf
o
15
dx = 5m
Ay = 9.8m/s/s Ax = 0m/s/s
Fg
Travelling time:
Substituting t from earlier,
vfy = viy + at
t = (vfy – viy) / ay
dx = vix * (2(-viy) / ay)
5m = -2vixviy / ay
vfy = 0 at the halflife of the projectile, so
t = 2(-viy) / ay
total time of flight
Distance traveled:
5m = -2vcos(15)vsin(15) / ay
-5 / 2cos(15)sin(15) = v^2 / ay
(-5ay) / 2cos(15)sin(15) = v^2
ay = -9.8 m/s^2
due to gravity
dx = vixt + 1/2axt^2
(-5*-9.8) / 2(0.25) = v^2
(-10*-9.8) = v^2
No forces act horizontally on the car (ignoring air friction)
98m^2/s^2 = v^2
ax = 0
so, dx = vixt + 0
v = 9.89 m/s
projectile motion
- 10 -
So as a rough measurement, our car must be traveling ~10m/s when it launches off the
ramp. The following is a diagram of the forces present while the rat trap is activated
Trat
Ft
Rarm
Pulley
Tspindle
Rwheels
FA
Rspindle
Ft
Twheels
Trat = Fixed constant. The rat trap delivers a fixed amount of torque.
The difference in radius from the spindle to the wheels alters the amount of force the
torque delivers to the car.
FT = Trat / Rarm
Tspindle = FT Rspindle
Tspindle = Twheels because they are glued together.
FA = Force applied due to torque on wheels (assuming the tires don’t slip)
= Twheels / Rwheels
Combining the above formulas:
FA = FT Rspindle / Rwheels
So it is clear that the torque supplied by the rat trap (causing a tension force on the string)
can be converted into torque on the wheels, which is converted into a pulling force that
moves the car. The pulling force is different from the tension force by a ratio of the radius
of the spindle to the radius of the wheels.
If this force is enough, however, is dependant on a number of other variables.
- 11 -
An empirical measurement of our car in its best configuration shows that there is around
25cm of string that passes through the pulley from the beginning to the end of the rattrap
arm’s movement. This string is wrapped around the spindle on the drive axle, which is
1.5cm in diameter. We can use this information to determine how many rotations the
drive axle will make.
pi * d = c = 4.71cm
25cm / 4.71cm = 5.3 rotations
circumference of drive axle
And the wheels are approximately 12cm in diameter, so
5.3 rotations * pi * 0.12cm = 1.992m
We can comfortably say that the car will accelerate for about 2.0m, at which point the
rattrap will be closed and the car will glide, losing speed.
How fast does the car have to constantly accelerate to reach 10m/s in 2.0m?
Constant acceleration formula (5)
(x - xo) = 2.0m
v = vf = 10m/s
v0 = 0m/s (the car begins stopped)
a=?
2 = (10^2 – 0^2) / 2a
2(2a) = 100
a = 100 / 4 = 25m/s/s
The car must accelerate at 25m/s/s for 2.0m.
F = ma = 0.300kg * 25m/s/s = 5.0N
Using the same car setup as was described above; we came up with the following
measurements for our car:
Rwheels = 12cm = 0.06m
Rspindle = 0.75cm = 0.0075m
Rarm = 30cm
FT = 8N
FA = FT Rspindle / Rwheels = 8N(0.0075m / 0.06m) = 1N
The applied force was only 1/5th the force needed to get the car up to speed. This explains
why in our demonstration the car did not launch off the ramp, but only rolled up it and
fell off the end.
- 12 -
Experimental Data and Testing
Test Parameters
Rod length: 8cm (min)
Trap position: Back
Full extension of trap
Rod length: 12cm
Trap position: Back
Full extension of trap
Rod length: 30cm (max)
Trap position: Back
Full extension of trap
Rod length: 30cm (max)
Trap position: Front
Full extension of trap
Rod length: 12cm
Trap position: Front
Full extension of trap
Enhanced wheel grips
Rod length: 30cm (max)
Trap position: Front
Full extension of trap
Enhanced + cleaned wheel grips
Elastic Band Augments
Weighted Front
Qualitative Results
Maximum
Speed
Wheels spun out
Car did not travel in straight line
0.5 m/s
Wheels spun in beginning.
Traction for last 1/3 of trap motion
1 m/s
Wheels gripped
Didn’t accelerate for first half of trap motion
1 m/s
Wheels gripped for most of flight
Full acceleration for entire motion of trap
4 m/s
Wheels spun slightly in beginning
Greater acceleration, but less period of time
Mouse trap glided sooner
3 m/s
Wheels did not slip at all.
Car accelerated sharply at the beginning
Glided for 1.5m before braking automatically
7 m/s
Best test scenario
Our initial testing showed that without the acceleration rod, at a distance of 8cm (the size
of the rat trap kill arm itself) was completely insufficient. The wheels spun out
completely, the car did not travel in a straight line, and the forward velocity it did reach
was practically an accident. It was clear that there are a number of parameters that we
could change, so in our testing we decided which configuration of those parameters gave
the best results. All of our augments to the design were intended to either increase the
traction, or increase the power of the car, since those were the two biggest problems we
encountered during testing.
We found that putting the rat trap at the front of the car helped improve the traction. We
also found that putting strips of rubber on the wheels provided far better traction then our
previous method of putting rubber bands around the wheels. When the strips were clean,
it provided unparalleled traction far superior to the rubber bands.
A 30cm acceleration rod (the maximum allowed by the design) also provided the best
transfer of energy. Finally, adding weight to the front of the trap and augmenting the
- 13 -
mouse trap with elastic bands provided more power and better traction to the wheels.,
since our, resulting ultimately in our best test case.
Our test cases, however, showed that even traveling in a straight line the mouse trap did
not get up to the speeds we calculated that we would need. It is clear that on a ramp these
speeds be even lower. While our testing showed that our design was successful in the
scope of a traditional mouse trap race, it did not meet the criteria of this project.
Final Budget Details
$2.99
2 x $0.99
$1.99
2 x $0.79
15 x $0.10
4 x $0.29
$1.00
$3.00
$2.00
$3.00
$0.25
$1.00
$0.25
10 x $0.15
Rat Trap
Mouse Traps
Hardboard
L-Brackets
Nuts and Bolts
Wire grommets
Kite string
Zackz Wheels and Rubber Grips
Steel Axles / Acceleration arm
Lego Pulley
Teflon tape
Metal block for front weight
Piece of coat hanger
Elastic Bands
(Used only in earliest prototype)
(Never used in design)
(1m long piece)
(Found on side of road)
(15cm long piece)
(Borrowed from machine shop)
Subtotal:
GST/PST:
$23.20
$ 3.25
Total:
$26.45
Our final project cost was $1.45 over-budget as a result of taxes. However, some of the
materials we bought, like the wire grommets, never got used in the design. Our project
had to undergo some quick revisions just before demonstration day, adding elastic bands
and anchoring them with a piece of a coat hanger, which also increased our expected
cost.
- 14 -
Work Breakdown Structure
Evel Knievel of ENG2000 Project
I. Design
A. Researching for Potential Designs
1. Brainstorming
2. Advantages and Disadvantages
B. Design Decision
1. Rat trap car
II. Building Rat Trap Car
A. Materials
1. Hardboard, nuts, bolts, brackets
2. Rat trap, Acceleration rod, drive axle, string, pulley
3. Hand drill, saw, other tools
B. Assembly
1. Cut the hardboard
2. Drill holes on rat trap and board
3. Assemble the main body together.
4. Attach acceleration rod to rat trap
5. Mount rat trap, pulley system, wheels and drive axle
6. Thread the car for actual testing
III. Testing
A. Performing Test Runs
1. Flat Ground
2. CB 121 Angled Floor
B. Analysis of Test Run Results
1. Insufficient force
2. Not enough traction
C. Design Optimizations and Revisions
1.Addition of Elastic Bands
2. Addition of Weight in Front for Traction
3. Wheels Selection
- 15 -
Project Timeline / Gantt Chart
- 16 -
AON Logic Diagram
- 17 -
Risk Analysis
We identified the following risk events during the entirety of our project:
1. Rat Trap – The rat trap is capable of delivering enough force to seriously injure
a person’s finger. If one of our group members were injured, it would delay the
project since somebody would have to take over the work they were doing.
Severity: MEDIUM. Although the victim of the rat trap would be injured, this
event would not seriously deter the project from moving forward. Another group
member would take on the work the original member was doing.
Likelihood: MEDIUM. Since we were constantly dealing with the rat trap’s arm,
sometimes more than one person at the same time, the risk was always present.
Response: Accept/Reduce. The rat trap is the heart and soul of the car, and we
could not do without it, and the use of PPE would be too cumbersome and inhibit
project development. Care was simply taken in handling the rat trap, and all group
members were informed of the risks. No one was hurt from the rat trap.
2. Machinery Safety and Equipment – for constructing the car, we needed to use saws,
drills and other power tools; and if not properly used, there is a risk of injury to
the team members.
Severity: HIGH. Saws, drills and power tools could easily cause permanent, even
life threatening injury if not used properly. It was also possible to damage our
building materials with improper drilling/cutting, which could result in the project
going over budget.
Likelihood: LOW. Using the safety equipment provided with the tools, and with
common sense, this risk is reasonably low. The risk was gone after construction
of the large parts of the car was finished.
Response: Transfer/Reduce. The most dangerous cutting will be performed by
the student machine shop assistant on duty at York and we made sure we used
proper personal protective equipment like gloves and goggles whenever we used
the saw and drill.
3. Material Damage – there is always the risk of breaking or ruining some of the parts in
our project, during testing, or as a result of an oversight by one of our group
members, material could be damaged which would cause the project to go over
budget, and delay it while new materials were being purchased.
Severity: HIGH. Breaking of a critical or expensive component like the wheels or
the body at the time of testing would set the project back tremendously
Likelihood: MEDIUM. An oversight by one of the group members, or a failure
during testing was always possible throughout the lifetime of the project.
Response: Reduce: We ensured we had spare material on hand in case they failed
unexpectedly, and designed our car so that components could be swapped out.
- 18 -
Environmental / Safety Issues
Since our car is not powered by any chemical means, and does not emit any gases or
liquids, there are no environmental concerns related to our design.
There are a number of safety issues related to this project. Saws, drills and other power
tools needed to be used to assemble the car, and proper personal protective equipment
had to be used. In one case, a saw broke in half while it was being used. Pieces of metal
had to be cut using jigsaw, which caused shards of metal to fly in all directions. Nobody
was hurt during construction, but without gloves and goggles there may have been a
greater risk.
The rat trap itself posed a hazard as well. When fully wound back, the rat trap had
enough power that if it were to slip and snap shut, it can break fingers. Special care had to
be taken to ensure that nobody ever had their fingers in the path of the rat trap while it
was engaged.
The frame itself also had sharp corners, which can be dangerous when the car is moving
at fast speeds (and being caught by the catcher at the end of the test run). We rounded the
corners of the car to make it safer to catch for the final test run.
Analysis of Demonstration
The ramp was made out of plywood, and smoothed at the bottom using a piece of
aluminum sheet metal. The demonstration was done on the roof of one of the school’s
parking lots. There were minor winds, but no precipitation. It was cool, but above zero
degrees Celsius outside. All of these factors we believe did not have an affect on the
overall outcome of the demonstration.
- 19 -
Trial 1
The car’s wheels spun at the bottom of the
ramp and the car traveled approximately
halfway up the ramp. It did not make it to
the top of the ramp, and did not reach the
5m target.
We believe that the car did not have
proper traction on this run. The ramp had
dust and debris on it, which we believe compromised the traction on the wheels and
stopped them from gripping the ramp.
Trial 2
The second trail was more successful
than the first. We started the car on the
ramp itself, instead of on the sheet
metal. The rat car’s wheels still slipped,
but they gripped better than the first trial
and the car made it off the ramp. The
car, however, simply fell off the end of
the ramp without traveling any recordable distance. The car did not reach the 5m target.
Conclusions
Even though the wheels did not have complete grip on the ramp, it is clear that the rat
trap car would not have flown 5m to its destination target. The trap, even when
augmented with elastic bands, simply did not have enough power to propel the car off the
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ramp with the speed needed to reach the target. Overall, the demonstration was not a
success.
There are a number of changes to our design which may help to improve the car’s
performance. The car’s materials should have been lighter. Our original assumptions
implied that the car would weigh less than 300 grams, but our car weighed in at as much
as 700 grams. The main concern originally was that the car would break when it hit the
ground, so strong parts were used as the materials for the car, but in hindsight, car could
have used much lighter and weaker materials and still survived.
The rat trap itself could have been replaced with a dual rat trap system, where two or
more traps were used at the same time to provide more power to the car. A dual system
was considered in the early stages of the project, but eventually dismissed due to its
complexity, but in hindsight it may have been a better option to explore then augmenting
the rat trap with elastic bands.
Finally, it is clear that a major problem with the design was traction on the wheels. It is
conceivable that using different treads or differently shaped wheels might have given the
car better traction on the ramp. However, it seems apparent that the entire design of using
a set of drive wheels to propel the car may not be a realizable idea at all. The drive
wheels simply do not get enough traction on the ground (especially when the car’s weight
is minimized) to propel it with the force needed to accelerate it up to 10 m/s. Perhaps a
different design that incorporated a much longer approach would have been more
successful, but an approach that was shorter than the ramp itself was clearly insufficient.
While the design succeeded in doing what it was designed to do, it did not accomplish the
goals of the project. More revisions are needed to the design to have it accomplish the
project goals.
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References
DocFizzix – Mousetrap Cars, Boats and Racers
http://www.mousetrap-cars.com/mousetrap/mousetrap_teacher_resources.htm
Photographs of Mousetrap Cars from Billings Senior High, MT. USA
http://senior.billings.k12.mt.us/mouset/fall98/index.htm
Halliday, Resnick, Walker, Fundamentals of Physics (7th Edition).
USA: John Wiley and Sons, 2005
Constant Acceleration Forumlas:
http://selland.boisestate.edu/jbrennan/physics/notes/Motion/constant_acceleration_formulas.htm
Projectile Motion Simulator (to test the calculations):
http://galileo.phys.virginia.edu/classes/109N/more_stuff/Applets/ProjectileMotion/jarapplet.html
Torque – Wikipedia
http://en.wikipedia.org/wiki/Torque
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