Varying motor speed using the VNH5019 motor shield

We are using the VNH5019 motor shield to control two motors on a vehicle. The voltages are well within the spec ranges (12V-13V supply from battery and 5A-8A per motor) so I do not think that is a problem. The issue we are having is that the vehicle is not tracking in a straight line. There can be MANY variables causing this from wheel size to wiring… What makes me think it is a motor controller issue is when we have corrected the issue using a scalar multiplier (roughly .785 applied to M2 speed) it will veer to both sides(left and right) which means that the power supplied to the motors are not constant somewhere I think. If it was a wiring issue or a tire circumference issue then it should be constant but our problem, and the only variance aside from the motors them selves (which when connected directly to the battery have no difference to speak of), that I can think of would be the motor controller. Do you have any suggestion or any idea of what could be our problem? The problem persists in both directions. Any help would be appreciated.


Hi, Justin.

I don’t exactly know what is wrong but maybe someone else will chime in with an idea. Are the motors you are using 5A-8A free running? That might be too much for this motor driver to handle, because when a motor starts or change direction it can draw more than the stall current of the motor. What is the stall current of your motors? Do you have an oscilloscope you can use to monitor the battery voltage while it is driving? Also, what kind of battery are you using? In general, it is hard to drive straight, especially with open-loop control. I would suggest adding encoders or some other mechanism to provide feedback.

- Ryan