Abstract: A drive suitable for a door or gate operator mechanism has a motor (1) and a gear box (5). The gear box (5) has a drive disengaging means (29) therein which can be pulled by a chord (7) to effect drive engagement of the motor (1) with the gear box (5). When the chord (7) is next pulled drive disengagement of the motor (1) with the gear box (5) is provided. The arrangement permits a door or gate which is driven by the operator to be manually opened in the event of power failure. The mechanical advantage of the gearbox (5) and the motor (1) on the door or gate is such that the gate cannot be manually opened without the drive being disengaged.

Abstract: A door operator for an overhead garage door having a reversible electric motor and a gear train driving the door. Limit stops are provided, one for the "up" limit and another for the "down" limit. Each of the limit stops is independently zero setable to cut off current to the motor at a pre-selected position.

Abstract: A door is provided having an automatic opening means for the door and a key locking facility for mechanically locking the door in a door closed position and electric circuit means connected with the motor means to sense a change in the electrical operating conditions of the motor above that which is normal for operation of the motor and to remove the above normal power thereby supplied to the motor in such circumstances.The sensing means preferably comprises a means which switches off the power once the electrical operating conditions are sensed above that which is normal and whereby it returns the power some time later and should the motor then reexperience electrical operating conditions above that which is normal the sensing means will again switch off the power to the motor.The sensing means desirably comprise a bimetallic cut out switch means.