front stage of a planetary gear reducer and the rear stage of a cycloid gear reducer. The rotation of the first deceleration via the input shaft is transferred from the gear on the input shaft to the planetary gear. The planetary gear is connected to the crankshaft, and the second deceleration is driven by the rotation of the crankshaft to drive the cycloid wheel for eccentric motion. After the crankshaft is rotated for 1 week, the cycloid wheel will rotate one tooth in the opposite direction to the movement of the crankshaft.