Problem Statement:

1. Design, build, test, and race a transportation vehicle (called a Mousetrap Racecar).

1. Use a standard mousetrap.
2. Car cannot have manufactured wheels.
3. Car must be made at home.
4. Car must use found or scrounged materials.

• Car must be built sturdy enough to make multiple runs over the starting line.
• Car may be built for speed (velocity) or distance (velocity* time).
• F(Force)=M(mass)*A(acceleration) therefore the mousetrap provides a standard unit of force (F=1) and if my design is heavier, the acceleration will decrease which equals lower speed. If my design is lighter, the acceleration will increase which equals a higher speed. To make my car go farther, I need to keep force (F=1) acting throughout a longer period of time because V(velocity)*T(time)=D(distance).
• My design objective will be to try to maximize the period of time that the spring force of the mousetrap acts upon the wheels.

• I predict that the lighter my car is the farther it will go.

1. I have started searching for my materials by looking at old toys. I located an old Erector set that still has many mechanical brackets and parts. I found some old computer CD-ROMs. I went to Giant and bought a mousetrap. I also bought Epoxy and some string. I raided my mother’s sewing box and found some spools and I pulled all of the thread off of them. I asked my dad for help when using Epoxy and drilling holes.
2. I drew my first designs (Figure 1 — First Design and Concept). I drew my first design using 3 wheels because it is lighter and sturdier than 4 wheel designs.




Figure 1 — First Design and Concept

3. I decided to use old CD-ROMs for my wheels. My first problem was that the middle holes ire too large (Figure 2 — Wheels made from CD-ROMs). Because of that, I looked through an old Erector set and found 2 gears. I centered the gears and I glued them in place with 5 minute Epoxy (which takes 3 hours to get hard).




Figure 2 — Wheels made from CD-ROMs

4. While waiting for the wheels to dry, I decided to find out how far the mousetrap spring traveled (Figure 3 — Distance Traveled By Mousetrap Lever). I will use this information to size my pulley string.
   
   




Figure 3 — Distance Traveled By Mousetrap Lever




5. I performed an experiment to see how far the string would be pulled when the mousetrap was set off and moved through a half-circle (Figure 4 — Distance Traveled by String Attached to Lever).







Figure 4 — Distance Traveled by String Attached to Lever




6. I then built a frame for my car (Figure 5 — Frame Layout). It’s called a ladder frame because it looks like a ladder. I first used screws to bolt it together to see if everything fit. After final fitting (Figure 6 — Final Layout of Mousetrap Car), I removed the screws and used pop rivets to securely fasten everything together. I received help with the pop rivet gun from my dad.




Figure 5 — Frame Layout



Figure 6 — Final Layout of Mousetrap Car




7. To make the rear axle and pulley, I cut 2 rubber grommets so that they would fit inside a small spool (Figure 7 — Rear Axle, Pulley, and Grommets). I pushed the axle into the grommets exactly halfway. I measured it to 28 millimeters on each side of the axle so it would be exactly in the center. Then I used Epoxy to attach the pieces together so they would not move around (Figure 8 — Pulley and Axle Assembly after Epoxy Glue).




Figure 7 — Rear Axle, Pulley, and Grommets



Figure 8 — Pulley and Axle Assembly after Epoxy Glue




8. I assembled our front wheel (Figure 9 — Front Wheel Assembly). The axle diameter was too small for the spool’s internal diameter. I epoxied 2 #10 washers to the spool so the axle would not slip around as much.




Figure 9 — Front Wheel Assembly




9. I measured the mousetrap to make sure it was going to be in the centerline of the car. I drilled 2 holes in the mousetrap. Again I used pop rivets to attach the trap to the vehicle. Then I cut a length of string, and attached it to the lever arm on the mousetrap. (Figure 10 — Mousetrap Positioning).




Figure 10 — Mousetrap Positioning




10. I attached the front wheel (Figure 9 — Front Wheel Assembly) and the rear pulley assembly (Figure 7 — Rear Axle, Pulley, and Grommets) to the frame of the car. I completed the final pop riveting and then I epoxied the front wheel assembly to prevent the axle from sliding.
11. I applied Epoxy to all of the pop rivet joints (Figure 11 — Detail of Front of Car Showing Epoxy) because of a problem, that the rear cross frame was moving.




Figure 11 — Detail of Front of Car Showing Epoxy




12. I attached the rear wheels to the car (Figure 12 — Top View of Vehicle) and my dad cut a notch in the pulley to secure the string. The vehicle was now complete and ready for its first test run.




Figure 12 — Top View of Vehicle

February 27, 2000

13. I began my runs. I used a hallway in my house on a regular wood floor (Figure 13 - Starting Line). I set up a starting line so the cars would all start in the same place. I used a Synchrotimer® X-1000 stopwatch, which was capable of measuring to 1/100 of a second. My dad operated the stopwatch so I could set off my car and measure distances.







Figure 13 - Starting Line




14. We began our runs (Figure 14 — Test Runs). I made ten runs because I could figure out the average and minimizing errors in timing, measuring distances, and errors in the mousetrap’s spring. I figured out my average speed by D(distance)/T(time). The car’s average speed was 92.1 cm/s.




Figure 14 — Test Runs

15. I found some problems in the Test Run (Figure 14 — Test Runs). The first problem I saw was the string wrapped around the axle sometimes. Another problem was the string came off the wheels and didn’t come off the spool. The other problem I saw was the wheels didn’t have enough friction. To solve these problems, I have to figure out a way to keep the string in the center of the mousetrap lever. To fix the friction problem, I will try adding a softer material, which has more friction, like a rubber band.




Figure 15 — Rubber Bands

16. I ran the car after fixing the mistakes (Figure 16 — Second Trial Run). The string kept catching on the spool, so my dad cut a larger hole in it. It worked much better. The average speed improved.




Figure 16 — Second Trial Run

17. I put an entire can of play-do on the back of the car (Figure 17 — Play-Do) to see if my hypothesis was correct. It was correct because it went much slower, but it also went much farther(Figure 18 — Test Runs with Heavier Weight).



 

 

Figure 17 — Play-Do

Problem:

1. Dropped Mousetrap Racecar and broke rear wheel in half (Figure 19 — Broken Wheel).

Materials (Figure 20 — Repaired Broken Wheel):

1. Quickset Epoxy
2. CD-ROM
3. Axle Hub
4. Screw
5. Allen Wrench
6. Diagonal Cutters
7. Plastic

1. I removed broken wheel and screw with Allen Wrench.
2. I used Diagonal Cutters to cut through and remove old Epoxy in axle hub although I got some help because I was not strong enough.
3. I mixed up Epoxy according to directions.
4. I then placed axle hub on plastic so it will not stick to other surfaces.
5. Then I attached axle hub to CD-ROM using Epoxy.
6. I waited 3 hours for Epoxy to dry.

1. Although the wheels worked, I’m going for a longer distance by adding larger wheels.

Figure 19 — Broken Wheel

Figure 20 — Repaired Broken Wheel

Problem:

1. Racecar didn’t go as far as it could because the back drive wheels are too small.

1. Quickset Epoxy
2. Plastic Plates
3. Back wheels
4. Drill

1. I measured the plates to find the center.



2. I drilled a hole in the plate.
3. I then applied Epoxy to the plastic plate and attached the wheels.



4. I waited 3 hours for the Epoxy to dry.

1. The wheels were larger (Figure 21 — Wheels) and could go farther than the small wheels with the same amount of force. They still spin and I can’t find any rubber bands, which will fit over the wheels.

Problem:

1. Racecar didn’t have as much traction because of the plastic plates.

1. Wrench
2. Play-Doh (Figure 22 — Play-Doh)
3. Car
4. Screws
5. Erector-Set pieces

1. I attached an Erector piece to the back of my car with a wrench, bolts, and screws.
2. I then placed purple play-doh to the back of the car.

1. The car works better but it is still spinning too much.

Figure 22 — Play-Doh

Problem:

1. The racecar’s wheels are spinning out of control although they are better because of the play-doh.

1. Car
2. Electrical Tape

1. I attached the electrical tape (Figure 23 — Electrical Tape) to the wheels of the car.

1. The car is much better but it is popping wheelies, which are losing energy.

Figure 23 — Electrical Tape

Problem:

1. The car is popping wheelies and losing energy because of them.

1. Play-Doh
2. Car

1. I removed about 1/2 of the play-doh (Figure 24 — Less Play-Doh).
   
   

1. The car goes farther and faster because of more energy added to the car instead of the wheels.

Figure 24 — Less Play-Doh

Problem:

1. Wheels are sliding back and forth across the axle because they are too loose so they must be tightened.

Materials:

1. Allen Wrench

2. Car

Procedure

1. I tightened the screws on car wheels and then got my dad to tighten them even more.

2. Rerun car ().

Conclusion:

1. It helped the wheels go straight but they are very slow.

Problem:

1. The racecar goes very slow which is probably because now there is too much weight on the car.

Materials:

1. Car

2. Play-Doh

Procedure:

1. I removed play-doh from back of car so it would go faster.

2. Rerun Car (Figure 26 - Trial Run 2)

Conclusion:

1. The smaller weight helped the car move faster so my car is done (Figure 27 - Final Car).

Figure 26 - Trial Run 2

Figure 27 - Final Car