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How to Calculate Gear Spur on a DC Motor

The spur gear is adjacent to the pinion gear, which sits directly on the motor shaft. The spur gear's relationship to the pinion gear is significant in that the ratio of one to the other determines the vehicle's performance. Learn how to calculate the size of the spur gear to better understand how your vehicle will handle.

Things You'll Need

Spur gear
Marker
Safety pin

Instructions

- 1
  Mark one of the teeth on the spur gear with the marker to indicate the first tooth you will consider in your calculation.
- 2
  Open the safety pin, then press it between the teeth with the marked tooth underneath it.
- 3
  Rotate the gear counterclockwise while counting the number of clicks you hear as you pass the safety pin over the teeth.
- 4
  Use the total number of teeth on the spur gear to determine the gear ratio between the spur gear and the pinion. For example, if the spur gear has 36 teeth and the pinion gear has 6, then you're running a ratio of 6:1. This means that for every rotation of the spur gear, the pinion gear turns 6 times.

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