>>back and forth motion of agitation<< apply torque in bursts, let the inertia help you. start turning the drum and contents stay in place, while drum turns,

>>back and forth motion of agitation<< apply torque in bursts, let the inertia help you. start turning the drum and contents stay in place, while drum turns, until contents match speed. then stop torque , so the drum slows suddenly and contents continue to spin until they slow down. the drum doesnt change direction, only the direction of momentum, and the mass transfering the force does