Grinder Gearworks

Have you tried sticking a plastic wheel straight onto a motor shaft to create a race car? The first thing you’ll find is that the shaft is usually so slick that it doesn’t stay attached to the wheel without a ton of glue. And IF you’re able to attach the wheel to the motor firmly, it usually doesn’t have enough ‘oomph’ to turn the wheel without a push-start. The trouble is that you’ve got too much speed and not enough torque at the wheel.

The motor will generate the certain amount of power, but you can use that power in different ways. For example, a fan needs to be turning at high speed to be of any use, so it makes sense to simply strap a propeller onto the shaft and power up the motor. However, if you need a motor shaft to spin more slowly and with more ‘oomph’, then you need to add a couple of gears to help you do this.

When we build these race cars with college students, we made larger versions that could really transport them across the parking lot. Only instead of a tiny hobby motor turning the pinion (the gear attached to the motor shaft) as we’re going to do in our experiment here, the students powered their ride-on cars with a battery-powered drill they had to hold while riding it across the floor.

The biggest challenge students faced was selecting the gears. Depending on the student’s weight and rolling friction of the wheels, they would need to find the right gear combo for their car. The main thing to keep in mind is that you always trade speed for torque (twisting motion).

In the case with gears, the power is always the same (from the drill), but we slowed the rotation speed way down to increase the amount of torque (how much ‘oomph’ a wheel had to turn) in order to get it rolling. We’re going to experiment with this idea by creating our own geared race cars. Are you ready?

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