Abstract: A powered hinge for adjusting the position of inclination of a vehicle's seatbacks has a planetary gear train in which are fixed to the vehicle a pair of bifurcated internal gears between which is coaxially supported for relative bidirectional rotation a driven internal gear attached to the seatback and driven by the second of a pair of compounded external gears, the first of which is bifurcated axially and disposed on either side of the second to form a satellite which is driven eccentrically with rolling, planetary motion within the fixed pair of internal gears by means of an eccentric cam rotated bidirectionally by, e.g., a shaft driven by an electric motor. The gearing, in which the number of teeth in corresponding external and internal gear pairs differs by only about one tooth, permits extremely large gear train values to be achieved within a very compact package and the use of relatively low-torque electric motors.