disclosed is a coupling for the connection of a drive motor to a still camera to facilitate automated cocking and actuation of the camera . the coupling has two major portions one of which rotates with a drive motor and the other of which rotates with the film transport advance drum . one of the portions will be a cam and the other portion a cam biassing device such that under low torque loads being transmitted from the drive motor to the film transport advance drum , the two portions rotate together . when the film has been wound , the film transport advance drum stops suddenly increasing the torque transmitted between the still moving motor and the transport advance drum . when the torque reaches a preset maximum amount , the cam biassing device slips relative to the cam and actually drives itself in a reverse direction . an additional apparatus is provided which free - wheels in the normal direction and couples movement in a reverse direction to a shutter release mechanism which insures that the picture is taken while the film transport advance drum is motionless . specific embodiments showing the motor powering either the cam or the cam biassing device are disclosed .