An electric motor acts through a gear train to rotate an output shaft in one direction while a torsion spring rotates the shaft in the opposite direction when the motor is de-energized. When the output shaft stops abruptly at a limit position after being rotated by the spring, a lost-motion drive connection permits the output gear of the drive train to rotate relative to the shaft in order to dissipate kinetic energy through the gear train and to avoid impact loading of the gear train and the motor.