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:
A single gear in the center called the sun gear.
Two or more gears called planet gears that rotate around the sun gear.
An element ...