Putting wheels on a mousetrap car can be difficult. The trick is to get the string to pull at the correct speed. There are two types of wheels on a mousetrap car: drive wheels and nondrive wheels. Each has a different way of attaching to the body. Making sure the axles are turning freely is important. Proper construction of the wheels and axles will help assure the car performs as planned.
Attach the nondrive wheels. The front wheels are usually the nondrive wheels. These wheels are not powered. The force of the mousetrap car going forward makes them turn. If using two front wheels, attach these wheels by gluing one end of the axle to one wheel; allow to dry. Slide the end of the axle without the wheel through the holes in the body designed to hold the front axle. Make sure the axle turns freely and does not wobble. Glue the second front wheel to the axle and allow to dry. If using a single front wheel, slide the axle through one side of the support, add an O-ring, pass the axle through the front wheel, add the second O-ring, and then slide the axle through the other end of the support. Adjust the O-rings by sliding them close to the wheel. They are used to hold the wheel in place and to keep it from turning. The front axle should turn freely in the supports.
Install the drive wheels. Putting the drive wheels on the mousetrap starts out the same way as putting on the nondrive wheels. Start by attaching one end of the axle to a wheel and glue to secure. Slide the axle through the supports on the body. Glue on the other wheel and wait for the glue to dry. Add the hook to the centre of the axle and glue in place. The opening of the hook should face away from the mousetrap. Wait for the glue to dry before proceeding to Step 3.
Use the string and tie one end to the mousetrap's swing or snapping arm. This can be secured with glue if desired. Tie a loop in the other end of the string. The loop should be small, and it should not be tied with a slip knot. It should loop over the hook on the axle and fit securely. Allow enough string to wind around the axle several times. Start with 12 inches and make adjustments if necessary. To load the mousetrap, wind the drive wheels in the opposite direction from the direction in which the wheels should turn. As the string tightens, the arm of the mousetrap should move closer to set position.
Add traction to the wheels if necessary by gluing rubber bands or balloon pieces to the edge of the rear wheels. This will prevent slippage on smooth surfaces.
Use large wheels for distance and small wheels for speed. Adjust string length to add or remove power.
Make sure the wheels turn freely. Be careful when loading the car. The string can break and the mousetrap can suddenly close on hands and fingers.