In the coupling of bi-directional, non-freewheeling-type DC motors to the pulling spool of a canopy deployment strap and to a take-up roller, ratchet gears assure automatic alignment and synchronization of the deployment and retraction mechanisms. The reverse direction rotation of the unwinding motor can be uninhibited through the slipping of its ratchet gear when the winding motor is slow to take up the pulling strap or the tarp being wound thereon. The slipping provides sufficient slack to accommodate changes of spool and roller diameters as more material is successively wound thereon. A friction brake acting against a flange of the spool keeps it from spinning freely when not engaged by the motor.