7. Gears and Gearmotors

If you take an ordinary DC motor from a hobby shop and apply power to its leads, you’ll see that the shaft rotates quickly—hundreds or thousands of rotations per minute. But if you attach a significant load to the shaft, it may not turn at all. This is a frequent problem for makers building motorized systems: The motor rotates at high speed but can’t exert the necessary amount of torque.

A common solution is to buy special motors called gearmotors. A gearmotor is an integrated combination of an electric motor and a gear. The gear increases the torque delivered to the load and reduces the motor’s speed. Now the problem is to select the right gearmotor. Should you buy the 6:1 spur gearmotor or the 26:1 planetary gearmotor? ...

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