Patent ID: 8632436

Claim:
A motor assembly of a surgical tool, comprising a motor having a motor shaft and a gear train driven by the motor, the gear train comprising: an output shaft; a fixed ring gear; a cover; a movable ring gear installed inside the cover; and a multi-stage planetary gear set, each stage comprising a sun gear, a carrier, and planet gears mounted on one side of the carrier and in mesh with the sun gear and one of the fixed ring gear and the movable ring gear, wherein the movable ring gear has inner teeth formed on an inner peripheral surface and one of the carriers has outer teeth formed on an outer peripheral surface; the movable ring gear is movable between a first position where the movable ring gear is engaged with an non-rotatable relative to the cover and is disengaged from said one carrier, whereby the gear train has a higher gear reduction ratio, and a second position where the movable ring gear is disengaged from the cover and is engaged with and rotatable with said one carrier and the planet gears adjacent to the other side of said one carrier whereby the gear train has a lower gear reduction ratio; and wherein the gear train includes a mounting bracket which is fixed to the motor and the fixed ring gear is fixed to the mounting bracket by a snap fit connection.