A planetary gearbox cycloidal drive or cycloidal rate reducer is a system for reducing the speed of an input shaft by a particular ratio. Cycloidal acceleration reducers can handle fairly high ratios in small sizes. [1]

The input shaft drives an eccentric bearing that in turn drives the cycloidal disc in an eccentric, cycloidal motion. The perimeter of the disc is targeted at a stationary ring equipment and has a series of result shaft pins or rollers positioned through the facial skin of the disc. These result shaft pins straight drive the result shaft as the cycloidal disc rotates. The radial motion of the disc is not translated to the result shaft.