Abstract: This power transmission has a steerable yoke mounted for pivoting about an axis coaxial with an input or output shaft. The steerable yoke can be pivoted in either direction with equal torque regardless of rotation of the shaft. Two balanced drive trains interconnect the input and output of the transmission. Each drive train includes a ring gear, a planetary gear and a sun gear. The two planetary gears are interconnected by a spider which is free to pivot and compensate for motion of the steerable yoke. The spider assures that advance of one planetary gear drive equals recession of the other planetary gear drive. Since the two drive trains are equivalent and contra-rotating, torques are balanced.