Patent ID: 7717820

Claim:
A planet gear speed reducer comprising: a casing having a receiving space defined therein for receiving an output shaft and an input shaft, a first annular groove and a second annular groove respectively defined in a front end and middle section in the casing, a first bearing and a second bearing respectively and securely received in the first annular groove and the second annular groove, wherein the output shaft and the input shaft are longitudinally connected to each other; the output shaft including a planet gear arm and a drive axle concentrically and longitudinally extending the planet gear arm, the drive axle extending through the front end of the casing for driving an apparatus that needs a high torsion, the first bearing and the second bearing respectively and securely sleeved on the drive axle and the planet gear arm, the planet gear arm being cylindrical and having multiple planet gears rotatably mounted thereon by pivots, each plant gear engaged to a gear ring that is formed on an inner periphery of the casing, the planet gear arm having a bottom corresponding to the drive axle and a cavity defined in the bottom for securely received a third bearing, an annular protrusion inward extending from an inner periphery of the planet gear arm; and the input shaft having a sun gear axle concentrically extending therefrom and engaged to the multiple planet gears on the planet gear arm, a fourth bearing securely sleeved on a heel of the sun gear axle and an outer periphery of the fourth bearing securely received within annular protrusion, a stub concentrically and longitudinally extending from a free end of the sun gear axle and securely received in the third bearing.