A cycloidal drive or cycloidal swiftness reducer is a planetary gearbox mechanism for reducing the acceleration of an input shaft by a certain ratio. Cycloidal swiftness reducers can handle relatively high ratios in small sizes. [1]
The input shaft drives an eccentric bearing that subsequently drives the cycloidal disc in an eccentric, cycloidal movement. The perimeter of the disc is targeted at a stationary ring gear and has a series of result shaft pins or rollers placed through the face of the disc. These result shaft pins directly drive the result shaft 
as the cycloidal disc rotates. The radial motion of the disc isn’t translated to the output shaft.