Simple Planetary

By Spencer Connor

Despite being “simple”, planetary drives have some properties that give them a wide variety of use cases. This is largely driven from the fact that, unlike simple compound gear trains, there are three rotations which can each be either fixed, an input, or an output. This means by fixing each of them three different gear ratios can be created. Additionally, it can function as a rotational summing device in three configurations although due to the unequal gear ratios there is a multiplier difference between the inputs that must be accounted for. Technically only a single planetary gear is necessary, but they are often found with three which balances and allows for higher loading. When using multiple planet gears their are additional restrictions on the number of teeth between the three gears.