A cycloidal drive or cycloidal velocity reducer is a mechanism for reducing the swiftness of an insight shaft by a certain ratio. Cycloidal velocity reducers are capable of fairly high ratios in planetary gearbox compact sizes. [1]
The input shaft drives an eccentric bearing that in turn drives the cycloidal disc in an eccentric, cycloidal movement. The perimeter of this disc is geared to a stationary ring equipment and has a series of output shaft pins or rollers positioned through the facial skin of the disc. These result shaft pins directly drive the result shaft as the cycloidal disc rotates. The 
radial movement of the disc isn’t translated to the output shaft.