Abstract: A planetary drive system especially useful in the transmission of high torques is disclosed. An internal ring gear is fixed to a base on which a rotator is mounted. A plurality of planet gears mounted on the rotator engage the ring gear. A driven sun gear imparts translational motion to the planet gears relative to the fixed ring gear, thereby driving the rotator. The planet gears and sun gear are mounted to permit radial movement with respect to the ring gear so that the sun gear and planet gears are self-centering, and lack of perfect roundness of the ring gear can be accommodated.