Since I wanted it to go fast, I made the car as light as possible. If the car is light, it will take less force and energy to make it move. I made my car out of balsa wood, which is an extremely light type of wood. I made the frame square, in order to give the car a lot of stability. I also positioned the mousetrap as far away from the driving axle as possible so there could be a lot of string to make the car go farther.
My mousetrap car's wheels are made from CDs. Thinner wheels mean less weight, and that makes the wheels easy to move without a lot of force. The CDs are also pretty big, which means that they cover a lot of distance per rotation. This makes the car go far and helps with the speed because of the wheels size and weight.
To put the wheels on the mousetrap car, I had to attach them to the axles. I couldn't just glue the CDs to the axle because they wouldn't have enough support and they probably wouldn't stay. So, I used bottle caps and glued two on either side of each CD to ensure that they CDs would be stable. However, it was imperative that the axle was in the center of the CDs. Otherwise, the rotation would be uneven and throw off the balance of the car.
Another thing I added to the wheels was balloons around the edges of the back wheels. I cut strips of balloons and put them around the outer edges of the CDs. The balloons help the wheels have traction, so they don't slip.
The axles of my mousetrap car are made from thick plastic straws. I considered having wood axles, but then I realized that if my axles and frame were wood, the two components would create more friction than plastic axles. To make the car go faster, I added bottle caps covered in duct tape to the back axle to make the axle bigger. This made the car go a lot faster.
My first lever was made out of a thick plastic straw that had a hole at the end. I attached one end of the string to the hole with a toothpick, and the other end I wrapped around the thick part of the axle.
Later, I realized that if I made the lever longer, it would make the car go farther. I then made a second lever out of another thick plastic straw attached to a wood pole. This made the car go farther than the first lever.
On the side of the bottom part of the lever, I cut a slot so the mousetrap could fit in it. So, when the mousetrap snapped back, the lever moved with it.
The string of the mousetrap car is extremely important, since the car wouldn't move without it. I used fishing line to function as the string in my car. The string of my car isn't actually permanently fixed to any part of the car itself. With my final lever, one end of the string is threaded through the hole in the wooden pole part of the lever. It stays there because it is tied to a toothpick on the other side of the pole.
The other end of the string is wrapped around the large part of the axle that was created using bottle caps and duct tape. When I first tried winding the string, I had a hard time because the string kept sliding off of the axle. To fix that, I added little pieces of toothpicks around one side of the bottle caps to prevent the string from sliding off. On the other side, I had one large piece of toothpick that I hooked the other end of the string around. This was designed so that when the mousetrap car ran, the end of the string would fall off of the large piece of toothpick.
However, after testing the car several times, I realized that sometimes the string fell off of the toothpick piece and sometimes it didn't. This was a problem because if the string didn't fall off, it would turn in the opposite direction and cause the wheels to stop. So, instead of hooking the end knot of the string around the large piece of toothpick, I hooked it around one of the smaller pieces that were originally meant to prevent the string from slipping off of the bottle caps. This solution was effective, and the string almost always fell off of the piece of toothpick, so the mousetrap car went far.