Abstract: A drive unit for vibrating machines such as shakers or vibrating screens includes a box structure enclosing a fixed shaft having an eccentrically positioned rotor thereon. The distance of the rotor from the shaft can be varied thereby varying the amount of throw. The box structure may be mounted either vertically or horizontally to effect either vertical or horizontal motion to the device to be vibrated. The position of the box can be varied between horizontal and vertical to provide a combined motion to the driven machine.