You also need to take into consideration the size of the wire gauge going out to the motor from the positioner, if the wire gauge is too small the DC voltage at the motor will drop.

AWG* for most installations should be a #12 gauge, a smaller gauge can be used for short runs of up to 25 feet, but the bigger the power wires the less DC voltage drop there will be, you must remember that the DC current will always be the same (lets say 4 amps) but the DC voltage can vary, if the power wires are too small and too long the DC voltage can drop too much and your motor will slow down.

At 50 feet a #12 gauge wire will loose .64 volts at 4 amps draw, a #16 gauge wire at 50 feet will drop 1.6 volts, a #20 at 50 feet will drop 4 volts, so you can see that the larger wire will drop less.

Here is a calculator to help with how big a wire would be needed for the less voltage loss on your system.

Code:
http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=33.31&voltage=36&phase=dc&noofconductor=1&distance=50&distanceunit=feet&amperes=4&x=45&y=13
Most "C" band siamese ribbon cable has a #16 conductor for the motor, this would work out OK for runs under 50 feet or so, anything longer and I would recommend a separate set of larger conductors for the motor.

*AWG = American Wire Gauge, the smaller the number the larger the diameter of the conductor, so a #16 is smaller then a #12, the larger diameter conductor will have less DC voltage loss on a longer run.