A planetary gearbox refers to a gear system in which one or more ‘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 referred to as the annulus). Therefore drives the sun gear which then provides the output torque. Nevertheless Zthere are examples of the additional combinations, like the sun gear being fixed and the ring providing output torque.

The main benefit of planetary gearboxes are their high power transmission efficiencies. Typicially this could be around just 3% per stage. Additional to this, the high effiency is delivered regardless of the compact design giving a large torque to size/weight ratio. A few of this is thanks to the load sharing occurring across the multiple planet gears.