A planetary gearbox identifies a gear system in which a number of ‘world’ gears rotate around a central ‘sun’ gear. Typically, a planet carrier is driven by the insight torque which rotates the planets around a set outer ring (sometimes known as the annulus). This in turn drives sunlight gear which then supplies the output torque. However there are types of the additional combinations, such as the sun gear being fixed and the ring providing output torque.

The main advantage of planetary gearboxes are their high power transmission efficiencies. Typicially this can be around just 3% per stage. Additional to the, the high effiency is certainly delivered regardless of the compact style giving a sizable torque to size/weight ratio. Some of this is thanks to the load sharing that occurs across the multiple planet gears.