In the coupling of bi-directional, non-freewheeling-type DC motors (24,25) to the pulling spool (23) of a canopy (11) deployment strap (21,22) and to a take-up roller (15), ratchet gears (26,27) 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 (11) 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 die spool keeps it from spinning freely when not engaged by the motor. Winding motors can be protected against excessive power use by measuring the level of drawn current with a digital ammeter. If the current exceeds a threshold level of operation, a timer is started. As soon as a given absolute safe period of operation is surpassed, a breaker switch is tripped interrupting the motor power supply. A plural number of trip points can be programmed into the device.