A cycloidal drive or cycloidal quickness reducer is a mechanism for reducing the velocity of an input shaft by a particular ratio. Cycloidal quickness reducers can handle relatively high ratios in compact sizes. 
The input shaft drives an eccentric bearing that in turn drives the cycloidal disc in an eccentric, cycloidal movement. The perimeter of the disc is targeted at a planetary gearbox stationary ring gear and has a series of output 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 translated to the result shaft.