A cycloidal drive or cycloidal acceleration reducer is a mechanism for reducing the velocity of an input shaft by a particular ratio. Cycloidal velocity reducers can handle relatively high ratios in small sizes. 
The input shaft drives an eccentric bearing that subsequently drives the cycloidal disc within an eccentric, cycloidal movement. The perimeter of this disc is geared to a stationary ring equipment and has a group of result shaft pins or rollers placed through the face of the disc. These result shaft pins straight drive the output shaft as the cycloidal disc rotates. The radial motion of the disc isn’t planetary gearbox translated to the output shaft.