The Evel Knievel of ENG 2000

Final Report

Group 6

Name Student Number E-mail Address Gordon Klein 208014573 frosty55@yorku.ca

Navjeet Singh Sarai 206943179 nsarai@yorku.ca Chris Kurulasuriya 206518229 cfern85@yorku.ca Mark Vincent Tee 208189888 mvt@yorku.ca

For Prof. Eshrat Arjomandi

Engineering 2000 (Winter)

April 6, 2007

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

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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.

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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

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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.

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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. Explosive powered car (possibly rocket propelled)

2. Car propelled by a launcher

3. Glider design

4. Compressed water

5. Elastic powered car

6. 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.

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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.

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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

46cm

30o

L-bracket with bolt

Rat trap

Fibre board siding

Fibre board base

Spindle

12cm

AccelerationRod / Arm

1" Bolt

Elastic constraintrod

L-bracket with bolt

Rat trap

AccelerationRod / Arm

Fibre board siding

1" Bolt

Fibre board base

16cm

12cm

46cm

30o

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

Hardboard base Hardboard base

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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.

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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

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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.

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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:

Travelling time: vfy = viy + at t = (vfy – viy) / ay vfy = 0 at the halflife of the projectile, so

t = 2(-viy) / ay � total time of flight

Distance traveled: dx = vixt + 1/2axt^2 No forces act horizontally on the car (ignoring air friction) ax = 0 � projectile motion so, dx = vixt + 0

Substituting t from earlier, dx = vix * (2(-viy) / ay) 5m = -2vixviy / ay

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 (-5*-9.8) / 2(0.25) = v^2 (-10*-9.8) = v^2

98m^2/s^2 = v^2

v = 9.89 m/s

vi

15o

vf

Ay = 9.8m/s/s Ax = 0m/s/s

Fg

dx = 5m

(halflife)

Vy = 0m/s

- 11 -

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 = 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.

Rwheels

Rspindle

Pulley

Rarm

Tspindle

Ft

Twheels

FA

Trat

Ft

- 12 -

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 � circumference of drive axle 25cm / 4.71cm = 5.3 rotations

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.

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Experimental Data and Testing

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

Test Parameters Qualitative Results Maximum Speed

Rod length: 8cm (min) Trap position: Back Full extension of trap

Wheels spun out Car did not travel in straight line

0.5 m/s

Rod length: 12cm Trap position: Back Full extension of trap

Wheels spun in beginning. Traction for last 1/3 of trap motion

1 m/s

Rod length: 30cm (max) Trap position: Back Full extension of trap

Wheels gripped Didn’t accelerate for first half of trap motion

1 m/s

Rod length: 30cm (max) Trap position: Front Full extension of trap

Wheels gripped for most of flight Full acceleration for entire motion of trap

4 m/s

Rod length: 12cm Trap position: Front Full extension of trap Enhanced wheel grips

Wheels spun slightly in beginning Greater acceleration, but less period of time Mouse trap glided sooner

3 m/s

Rod length: 30cm (max) Trap position: Front Full extension of trap Enhanced + cleaned wheel grips Elastic Band Augments Weighted Front

Wheels did not slip at all. Car accelerated sharply at the beginning Glided for 1.5m before braking automatically Best test scenario

7 m/s

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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 Rat Trap 2 x $0.99 Mouse Traps (Used only in earliest prototype) $1.99 Hardboard 2 x $0.79 L-Brackets 15 x $0.10 Nuts and Bolts 4 x $0.29 Wire grommets (Never used in design) $1.00 Kite string (1m long piece) $3.00 Zackz Wheels and Rubber Grips $2.00 Steel Axles / Acceleration arm (Found on side of road) $3.00 Lego Pulley $0.25 Teflon tape (15cm long piece) $1.00 Metal block for front weight (Borrowed from machine shop) $0.25 Piece of coat hanger 10 x $0.15 Elastic Bands

Subtotal: $23.20 GST/PST: $ 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.

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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

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Project Timeline / Gantt Chart

- 17 -

AON Logic Diagram

- 18 -

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.

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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.

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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.

- 22 -

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