On one motor channel, going backwards is not possible

I recently tried to operate my bidirectional motor controller: pololu.com/catalog/product/2502 with an arduino.
The fowards direction on the M1 and M2 channels works fine.
The backwards direciton on the M1 works, but not the M2!

It is not a motor problem as I have swapped the motors around and I get the exact same problem on the same channel.
Why could this be?

Thank you in advance

I recently saw this symptom with the MC33926 Dual Controller shield and an Arduino UNO. I tracked it down to some interference with the LiquidCrystal library. When I stripped the LCD code back out of the sketch, the motor controller behaved as I expected. (The red/green motor direction LEDs on the controller helped me to track this down!)

I was going to try using I2C for the LCD, but I’ve though more about my project, and I’ll be moving into the Mega R3 instead. I’m hoping that I can avoid the problem by adding the LCD display on it’s own “port”, since I have already put in a fair amount of work for the display code.

I’m very happy with the MC33926 shield. I hope you’ll post a bit more about what you think of yours.


Hello, Tombombadilly.

Could you tell me more about your setup? Which Arduino are you using? Do you have anything else connected in your setup? Could you post pictures of your setup that clearly show the connections? Are you using the demo code included with the VNH5019 motor shield library? If not, could you post the simplest version of your code that demonstrates the problem?

- Grant