There are several keys to building a
mousetrap powered car. If you are building one of these for competition, there are a few questions you need to
keep in mind. What kind of race is it,
distance or
speed? What kind of
modifications are allowed? What materials are allowed? How long do you have to build the thing?
First, a description of how these things work.
Generally speaking, a string of some sort is wound around the back
axle. This string is pulled by the mousetrap arm to spin the back axle and provide
locomotion. Most races that I have heard of allow some basic modifications to the mousetrap, such as cutting the arm, removing excess wood, or other
cosmetic changes. Let's assume that the spring is the only thing that must remain
constant.
The first thing to consider is the type of the race. If it is for the greatest distance, then a longer arm should be used. If it is for speed, a shorter one. All other variables being constant, a longer arm will provide greater distance with less speed, while a shorter arm will provide greater speed with less distance. To create an arm out of the mousetrap, my preferred way is to unbend the existing arm of death and straighten the copper wire. Pay attention, and don't cut the wrong side of the arm, or you'll ruin the mousetrap. I'm only saying this because I've seen it happen. Now you've got your power plant. If you're going to add length to the arm, make sure the arm is rigid. Any flex in the arm, and you'll lose precious energy that you'll need to make this thing move.
The next step is to decide on the body. The basic way is to attach two long pieces of something to the sides of the mousetrap, and then affix axles to those long pieces.
| |
| | affix axle here
|_____|
| |
|mouse|
|trap |
|_____|
| |
| |
| | affix axle here
You could also get more complex, such as putting the mousetrap inside of a model car or something else equally crazy. The mousetrap arm should wind towards whatever axle is the one you want to power. If the car is going to be RWD, then the arm at rest should be towards the front axle.
Next up is wheels. My favorite wheels for these cars are CDs. They're lightweight, perfectly round, free (use those AOL ones), and large in diameter. The only problem with CDs are the large holes in the middle, which can make mounting small axles difficult. The best solution is to drill holes slightly smaller than the axle in rubber stoppers, and then put the stoppers in the holes in the CD. Attach your axle to the body using something that spins freely. I usually use a small section of copper or brass tubing with metal axles, and then lubricate the whole shebang with powdered graphite.
Now, making the thing move. You're going to need a lot of string. Use something fairly light, but strong. Fishing line will work, but after a few runs, it gets a really bad memory and won't want to wind up correctly. I usually use some sort of nylon cord. Now for some guesswork. If the race is for distance, this next part is especially important. Figure out the distance from the mousetrap arm at rest to the axle. This doesn't have to be exact. Then, you're going to want about 3 times that much string. This is so your car can roll a bit. If you put the same length of string as from the end of the arm to the axle, once your arm stops moving, so does your car. These things can build up a good bit of momentum, so you want to make sure you put some extra string on there so it can keep rolling. Tie one end around your mousetrap arm and the other around the axle. Make sure the knot doesn't slip around the axle! This is a bad thing.
For speed cars, you're going to have to do some test runs to decide how long your arm and string are going to be. Ideally, you should peak at speed about 3/4ths down the track. Then, you should be able to coast the rest of the way. When you're doing this, don't cut the arm immediately. Just move the knot of the string up and down on the arm.
Make sure everything is properly lubricated. That's it, you're ready to race.
This is my personal experience. YMMV.