Mousetrap Vehicle

Overview
Mousetrap Vehicle is a car that you must design to go forward x amount of meters and come back to its original starting point.You will be allowed two un-modified mousetraps which means that the mousetraps must have all the original parts.

How it Works
The mousetraps are mounted on the car. When the mousetraps are triggered, they pull their killbar, which is attached to a string, attached to the axle, attached to wheels. The pulling of the killbar pulls the string. So, if you wind the string around the axle, when the string is pulled, it will spin the axle, turning the wheels, propelling the car.

How to Make it Work
There are three easy designs to get it to come back:

Method 1

One mousetrap on each axle: you wind one mousetrap up and as it goes down it winds the other mousetrap up to pull it back. Normally to do this model you need to add a bar to your mousetrap to make it have more leverage to make it go the x amount of meters.

Also you need to have the string come off of the axle or you will start to head back towards the x amount of meters mark. However, you then are stuck with the problem of not having to wind up a mousetrap on the way back, which means less resistance, which needs a brake, or you'll overshoot the starting point.

Method 2

Two mousetraps on one axle with the other axle having a piece of rubber that gets stretched as you go the x amount of meters and will send it back to the beginning. Also normally you need to add a bar to your mousetrap to make it have more leverage to make it go the x amount of meters.

Method 3

The last model, thought to be the easiest, is to have two mousetraps connected to the axle and you wind it some amount of times and than wrap it around a pin on the axle and continue wrapping it the opposite way that you started. The number of times you wrap it depends on the circumference of the wheels. Standard 12 cm CD's need to have the string wound around 19 times each way. Normally you need to add a bar to your mousetrap to make it have more leverage to make it go the x amount of meters. In this case, you need double the length of the bar of the first model (on the first model, there are two bars).

An alternative to a brake is to attach two nuts to your axle and squeeze them really really tightly around your string. (You need tools for this; you can't get it by hand.) You need to make sure that when the mousetrap is fully unwound, the string has no slack at all. This way, when the mousetrap finishes unwinding after a run, the string will stop the axle, stopping the car.

Number of Turns
To figure out the number of winds needed, all you must do is get the circumference of your wheels that are being driven and divide the distance by circumference. Round up if you don't want a 1000 point penalty! However, due to inertia, testing is HIGHLY RECOMMENDED to find the number of winds. Some vehicles need more or less than others, even with wheels of the same size.

Standard 12 cm CD's need to be wound 19 times to hit 7.16 meters. However, this is MATHEMATICAL and is no substitute for REAL TESTING. When testing however, the mathematical number of winds is useful to use as a starting point.

Tips
CD's or vinyl records are common wheel ideas. Rubber bands can be placed around CD's to add traction.

While it is true that the distance you're aiming for (in 2010) is between 7 and 8 meters, you should NOT aim for 7.5 meters unless your vehicle's accuracy is off frequently. If you have an accurate vehicle, you should aim for somewhere in the 7.2 or 7.3 range to minimize distance, and thus minimize time, while still allowing room for a bit of error. After all, if every vehicle performs as well as yours, but all of the others go out 7.5 meters, and yours goes out 7.2, you have won the event on time score. However, if your vehicle is highly inaccurate, then it is best to aim for around 8, as a 50 point penalty is much better than an 1000 point penalty.

For string, fishing wire works quite well. Sewing thread breaks fairly easily. It is best to have thin string so that the thickness of the string doesn't interfere with winding the string.

When using the third method, it is best to move the mousetraps as far from the driving wheels as possible. This enables you to maximize the length of the string being wound. It is not practical to use a bar more than 34 cm (in 2010) as that is how large the distance between axles can be. The reason is that if the end of the bar ends up outside the axle (relative to the center of the car), the string must extend back to the axle to wind around it, so any additional string is wasted. Therefore, unless placing your mousetraps outside the non-driving axle, the maximum string length that can actually be would around the driving axle is around 70 cm.

When you wind the string, lock the mousetrap, hold the string tightly (you don't want any slack on the string around the axle), and turn the axle in the opposite direction that you want it to go. If you are using the third method, then you want to wind the trip back first, so you would spin the axle forward, wind around the pin, and spin the axle backward.