A tarpaulin cover system includes a drive unit for moving the tarpaulin, selectively into covering and uncovering positions. The drive unit comprises first and second drive sprockets and. a rotatable actuator sprocket with all of the sprockets spaced, from and out of contact with each other. An idler sprocket is provided between the actuator sprocket and the drive sprockets. Ail of the sprockets are interconnected by a chain engaged with teeth with the chain extending partially around each sprocket whereby rotation of the actuator sprocket causes the drive sprockets to move in the intended directions.. This motion is transmitted to drive pulleys which drive cables to control the position of the tarpaulin.