21planetary gearing

Planetary gearing, also known as epicyclic gearing, is an unusual-looking system of gears that allows you to significantly change the gear ratio within a limited space. It’s very common in the real world; you can find it in bicycles, car transmissions, differentials, all kinds of toys, and even mechanical pencil sharpeners.

A planetary gear system, as shown in Figure 21-1, consists of four elements:

image A single gear in the center called the sun gear.

image Two or more gears called planet gears that rotate around the sun gear.

An element ...

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