Abstract: A conveyor is shown having an endless material transporting member running between an idler sprocket at one end and a drive sprocket at the other, both supported in a frame of the conveyor. A drive motor is used to drive the drive sprocket, and hence the conveyor. A controlling device for the motor is provided having a pivotally mounted slack sensing lever having a first rest position spaced apart beneath an upper flight of the endless material transporting member. A counterweight, resting on a stop urges the lever in position. The lever is fixed to a pivot pin, which has a trip lever attached. Upon slack in the chain deflecting the slack sensing lever, the pivot pin rotates moving the trip lever which in turn activates a microswitch controlling the motor. Upon sufficient deflection, the motor will be de-activated.