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Mouse Trap Cars: Adjusting Gearing

January 20, 2012

Gearing determines how far and how fast a mousetrap racer will travel. Learn about various ways to adjust and tweak the gearing of a mousetrap powered vehicle.

The gearing of a mousetrap car determines the acceleration and the travel distance. Gearing can be adjusted to increase and/or decrease the pulling force, the torque, the travel distance, and the acceleration of a mousetrap powered vehicle. With all mousetrap cars the gearing is controlled by the length of the lever arm and/or by the ratio of the drive axle and drive wheel set-up. Most record-setting long distance mousetrap vehicles are geared so that they have the smallest possible energy consumption rate or power output in order to maximize the pulling distance and decrease the force of friction. Smaller power outputs produce less wasted energy and have greater efficiency than larger power outputs. The amount of energy released by using a short lever arm or a long lever arm is the same but the length of the lever arm will determine the rate at which the energy is consumed called power output.

Adjusting the Gearing

If you place your mousetrap racer on the ground and the vehicle does not move or starts to move but needs more acceleration then the problem is that your mousetrap vehicle needs more torque or force at the drive wheels.

Increase the torque by any of the following:

  • shorten the length of the lever arm
  • using a smaller diameter drive wheels, or
  • increase the diameter of the drive axle

Tape Method

If you cannot change the lever arm length without a lot of reconstruction of your mousetrap vehicle then try increasing the diameter of the drive axle with tape. The idea here is to wrap tape around the drive axle and change the axle-to-wheel ratio and increase the torque delivered to the drive wheels.

step #1: Remove the original axle hook.

step #2: Starting in the center of the axle and carefully wind tape around the axle to build up the axle diameter.

step #3: Reattach the axle hook and then test the mousetrap racer. If more torque is still need after testing then add more tape as described above.

bonus tip: layers of tape can be removed to make a series of gears or a transmission on the axle so as to change the pulling force in steps.

Wheels and Axles

By changing the size of the drive wheel(s) you can speed-up or slow-down your mousetrap vehicle. Larger drive wheels will have a greater travel distance per each turn compared to smaller drive wheel. It would make sense to use a super huge drive wheel so for each turn of this massive drive wheel the mousetrap vehicle will travel an incredible distance. But as the size of the drive wheel increase, more torque is also required to start and keep the wheel turning. At some point a drive wheel can become so large that there is not enough force from the mouse trap to keep the wheel turning. With speed-trap racers smaller wheels will have a shorter travel distance per turn but will be much easier to accelerate and will require less pulling force to achieve the same acceleration as a larger wheel. Smaller drive wheels should be used on speed-trap racer in order to increase the acceleration and larger drive wheels should be used on long-distance travelers to cover more linear distance per rotation.

The diameter of the axle compared to the diameter of the wheel is also very important. The smaller the diameter of the drive axle in comparison to the diameter of the drive wheel the more force that will be required to accelerate the vehicle but the greater the distance of travel per rotation. This axle-to-wheel ratio is part of a mousetrap vehicle's gearing that needs to be understood in order to build the perfect mousetrap racer. For a long distance mousetrap racer a large diameter drive wheel with a small diameter drive axle is desired. For speed trap racers a smaller diameter drive wheel with a larger diameter drive axle is desired.

It is always important to understand the relationships between variables but never over exaggerate any one concept. The ideal size for an ultra big wheel on a long distance mousetrap racer seams to be somewhere between 10 and 15 inches. And the ideal size for a drive wheel on a speed-trap racer seams to be between 2 and 3 inches but no more than 4 inches.

bonus tip: speed-trap racers have a short lever arm, smaller diameter drive wheels, and a larger diameter drive axle in comparison to a long-distance racer.

bonus tip: long-distance racers have a longer lever arm, larger diameter drive wheels, and a smaller diameter drive axle in comparison to a speed-trap racer.

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