A gear transmission comprises an internal gear, an external gear, a first gear, a crankshaft, a two-stage gear and a second gear. The first gear is affixed to an end of the crankshaft, which eccentrically rotates one of the internal gear and the external gear. The two-stage gear comprises a center gear and an outer-toothed ring gear. The center gear meshes with the first gear. The outer-toothed ring gear surrounds the first gear. The second gear meshes with the outer-toothed ring gear and transmits torque from a motor to the two-stage gear. The two-stage gear is configured such that the center gear and the outer-toothed ring gear are each at least partially disposed in a common plane that crosses the rotational axis of the gear transmission.