Abstract: A drive for opening and closing air flow control devices, such as ventilation curtains, in a poultry house or the like includes a ball screw drive which is automatically disengaged during a power failure to allow the air flow control devices to drop open partially or fully. Upon restoration of power, the air flow control device is automatically restored to a set position. A digital controller receives inputs from a thermostat and/or pressure sensor which cause periodic actuation of a gear motor that rotates the ball screw and thereby moves a block to which one or more ventilation curtains are attached by means of lifting cables. An electromagnetically actuated brake is attached to the motor which holds its output shaft in position during normal operation.