cable 15 applies a force to the wheel which opposes the spring force the traversing wheel 17 is fixed to the vehicle 10 regulation of the cable speed will result in a regulation of the height of the traversing wheel 16 as will be obvious to those skilled in the art fig2 is a block diagram illustrating the improved apparatus of the present invention for controlling the cable drive of fig1 as illustrated the cable drum 13 has its shaft 14 coupled to motor 19 which may be for example a separately excited dc motor the motor is driven from a motor driver 30 which may be a double converter control of dc motors using converters is well known in the art see for example thyristor phase controlled converters and cyclo converters by b p pelly john wiley amp sons 1971 particularly page 13 et seq such control is also disclosed in harwood 39 s control of electric motors by ralph a miller master john wiley and sons 1970 in the illustrated embodiment there is shown a power input 31 which will be single or 3 phase ac power which in the converter of the motor driver is rectified in a controlled manner in accordance with the control input on.