In an orbiting gear drive (planetary gear set), several gears are evenly distributed between an internally toothed and an externally toothed gear. The gears move on a concentric circular path.

Planetary gears are of great importance in many areas of mechanical engineering and are versatile. They transmit high power and achieve high ratios and speeds with a favorable mass inertia ratio. As the number of planetary gears increases, the load distribution increases, and thus the transferable torque, allowing planetary gear sets to transmit very high torques with high efficiency even in compact designs.