Abstract: A propulsion system for a manually-operated mobility device includes a hand rim configured to receive a propulsion force from a user of the manually-operated mobility device, a wheel hub fixedly attached to a wheel for the manually-operated mobility device, and a planetary gear system including a sun gear, a ring gear, and one or more planetary gears disposed between the sun gear and the ring gear. The one or more planetary gears are supported by a planet carrier. One of the sun gear and the ring gear is fixedly coupled to the hand rim and the other of the sun gear and the ring gear is fixedly coupled to the wheel hub.