Home >> Toys >> Toy Vehicles

How to Make a Mouse Trap Car Efficient

Many middle school students and hobby enthusiasts make toy cars that are propelled by a mousetrap. These vehicles are typically made from household materials or parts found at a hardware store, and often are not terribly efficient. A perfectly efficient mouse trap car would convert 100 percent of the potential energy in the mousetrap spring into rotational energy to spin the wheels, but some energy is lost to friction in the axles, slipping and wobbling wheels, and other factors. You can improve these deficiencies with a few quick fixes to minimize or eliminate costly energy losses.

Things You'll Need

4 rubber bands
3 wire coat hangers
Ruler
Level
Epoxy adhesive
4 compact discs

Instructions

- 1
  Cut out the long, straight portion of two coat hangers with tin snips to use as wheel axles. Replace the pen tube axles commonly used in mousetrap cars with the coat-hanger wire. The moment of inertia is (m)(r²) for a hollow-shelled cylinder and 1/2(m)(r²) for a solid cylinder, assuming the masses are equal. Using the solid coat-hanger wire is therefore more efficient because it less rotational force will be required to turn the axles.
- 2
  Cut out the long, straight portion of a third coat hanger with tin snips. Use it to extend the rotation of the mousetrap arm. Use epoxy adhesive to glue the third length of coat hanger wire to the mousetrap bar so that the radius of motion is extended. This means that more string or wire can be wound around the rear axle, resulting in a greater range. You will need to use a longer string than before, because you have extended the range of motion.
- 3
  Straighten the wheels using a level and a ruler. This will reduce or eliminate the wobble in the wheels that appears when they are aligned by only eyesight. Make sure that the distance between each pair of wheels is equal at each radian; that is, the distance between the wheels should match up at 12 o'clock, 6 o'clock, 3 o'clock and 9 o'clock.
- 4
  Wrap a rubber band around each wheel to serve as a tire so that the wheels will not slip as the torque from the mousetrap is applied to the axle.
- 5
  Use wheels that are as balanced as possible. Compact discs work well because they were designed to rotate without wobble, and they all have a convenient hole exactly in their center of mass.

Toy Vehicles