A tiltable bed is provided with a set of toothed chains and a control system therefor so that the chains are moved along the length of the bed at a linear speed which corresponds to the linear speed of movement of the bed relative to the ground and independent of the rate of movement of ground engaging means directed to move that bed along the ground: thereby there is no strain put on a cotton module engaged and caused to traverse the length of such bed by those moving chains while being lifted or lowered during adverse traction conditions.
