Mousetrap Vehicle

Mousetrap Vehicle is a building event in which teams build a vehicle powered by one or two mousetraps. The vehicle must be capable of traveling down a straight track as quickly as possible, and stopping as close to the finish line as possible. It will be a Division C event for the 2018 season, and has been an event in both Division B and Division C in the past.



How It Works
The mousetrap is mounted on the car. Most often (but not always), a long dowel-like rod is attached to the mousetrap, so that when the mousetrap is triggered, the rod is pulled on, which is attached to a string, which is attached to the axle, which is attached to wheels. The pulling of the rod 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.

Building
Building materials you can use vary greatly, depending on your level of skill. Experienced builders might use light balsa in pre-designed arrangements. You could probably find kits available in most hobby stores that can educate you on how a mousetrap vehicle works. The kits will most likely be make of balsa wood, but some kits are available made of plastic (careful examination should be used to ensure that these kits don't have pre-made mousetraps or illegal methods) made for home experiments. Many ways can be used to build a mousetrap vehicle, but it is suggested that you go to the Mousetrap Vehicle Forum for tips and information.

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. However, due to inertia, you must test a lot to find out how many winds your string needs to go around the axle initially. Some vehicles need more or less than others, even with wheels of the same size. Careful attention should be taken to ensure that the track doesn't have any debris on it, or it could affect your mousetrap vehicle. This may not affect you, but high-caliber teams should take every detail to attention to ensure a winning score.

Adjusting the Vehicle
To reach the next level, the vehicle's design should be adjusted to better fit a variety of properties. There is no single strategy that will yield a perfect vehicle, and adjusting one element to fix one property of the vehicle may cause a negative change in another property; this is all part of the design process. All of the following tips require testing to reach the vehicle's full potential.

Making Your Car Go the Distance
If, for some reason, your car can't travel the minimum 8.5 meters, try these tips (note:if your car isn't moving at all, look at the next section, as you most likely need more power).


 * Make your drive axle thinner, this will allow you to wind your string around the axle more times, and thus your car will go farther.
 * Make your drive wheels larger; wheels with a larger circumference will travel more with each rotation.
 * Make your drive string longer (note that this also entails that you make your lever arm longer, and you may also have to increase the distance between the two axles so you don't have string just hanging).
 * Make your car lighter.

Making Your Car Faster
Making the car travel quickly is an important factor in the score. Follow these tips (note that they are opposite of the distance tips, so you will need to find a balance between the distance you can travel and speed; you will generally want to just be able to make the distance with a little wiggle room).
 * Thicken the axle: wrap some tape radially around the axle; it may be surprising as to how much faster this makes your car. This also helps if the vehicle isn't moving at all.
 * Use smaller wheels, they need less force to complete a rotation.
 * Decrease the vehicle's weight

Making Your Car Accurate
Another factor into the score is the accuracy of the stopping point of the car. It is common to include a braking system in mousetrap vehicles. Especially common are wingnut systems. See the brakes used in the previous event "Scrambler" for an example, or the picture in the link in the next section below.

Making Your Car Go Straight
In the 2013 competition, any vehicle that leaves the 0.75m track will be placed in the second tier. Therefore, traveling straight is important. If you cannot build the axles to be exactly parallel, then there are some other options. One commonly used solution is to build the car in two halves. The front axle will be part of the front half, and the rear axle will be attached to the back half. The two halves of the vehicle are connected together with a bolt that runs to the middle. Here is a modified example of this method. To adjust the path of the vehicle, simply loosen the bolt, turn the front half, and lock it in place by tightening the bolt again. Now you can adjust how straight or arched the path of the vehicle is.

Note that the picture is from the event Battery Buggy, and electricity is not allowed in Mousetrap Vehicle!

General Tips

 * 1) CD's or vinyl records are common wheel ideas. Rubber bands or balloons can be placed around CD's to add traction.Also, good wheels can be found at a local hobby store. Airplane wheels are often light and come in a variety of sizes. The only problem is they can sometimes be reasonably expensive.
 * 2) If possible, try to test on a surface similar to the one that you will encounter at the competition. Testing on tile and then competing on hardwood will affect your vehicle's performance. Best way is to test on multiple surfaces, and keep data for each one. Also, the importance of clean floors cannot be emphasized enough: the results will be varied if the floors are dusty or have small pieces of trash on them.
 * 3) Possible places to practice can be:
 * 4) a school gym
 * 5) cafeteria
 * 6) hallways
 * 7) For string, Kevlar 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.
 * 8) When building, it may be 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.
 * 9) When winding 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.

Resources

 * Several sections of the Scrambler wiki