Abstract: A drive system for a rotary device, such as an automotive alternator compensates for and dampens the effect of sudden bidirectional rotational velocity variations of the pulley caused by sudden acceleration and deceleration of an internal combustion engine without using a one-way clutch. The drive system in one aspect comprises an axially movable cam member rotatably supported on a hub that is connected to the alternator shaft and that is journaled within the pulley. The cam member is coupled to the pulley by splines so that it rotates with the pulley while affording axial movement. Springs urge the cam member into engagement with a cam follower on the hub. Upon sudden acceleration or deceleration of the pulley, the cam member rotates angularly relative to the cam follower and moves axially to compress the springs, which exert a restoring force on the cam member and cam follower to eliminate their relative angular rotation.