Polulu Low Voltage Motor Controller Issue


I am using the Low Voltage Dual Serial Motor Controller with a Tamiya Twin Motor Gearbox on an Arduino platform. I have the Serin line connected to Pin 3 and RST line connected to Pin 4 of the arduino (digital Pins). I am powering the motors with 2AA batteries.

I am able to reset the motor on power-up and send serial commands to run the motors (backwards or forwards). However, if I try to set the motor speed to anything greater than 10 (out of 127), the motor controller stalls and the lights go out. At this point, I can tell that the arduino is still running since I continue to see debug prints on the console.

At a speed setting of 10, I am able to run the motors without load for considerable periods of time. At speed settings of 11 to 13 the motors run for a few secs then the controller shuts off. At higher speed settings, I see a brief flash of the leds and controller shut off.

The controller is rated at 5A per motor, I doubt the motors are drawing anything close when free running without load. I believe Tamiya specs mention draw of around 150mA when free running and 2A when stalled.

Do I have a bad controller chip? Any help with diagnosing the stall issue will be greatly appreciated.


What you are describing sounds like a power or noise issue. The Tamiya motors are especially noisy, so you should add some 0.1 uF capacitors across the motor terminals for noise suppression. The noise might also be interfering with the controller’s reset line, so you might want to add some capacitance to that.

- Ben

Hi Ben,

Thanks for the quick response. I seem to be able to run the motors at full speed when I leave the RST line open, (I believe it is tied high internally), occasionally some stalls but it seems to recover the next time I set motor speed.

Please explain, “add capacitance to the reset line…”, what kind of capacitor/value and where should it be connected?

The exact type/value of the capacitor shouldn’t matter much; you’re looking for something that can keep the reset pin value from fluctuating in response to noise. I recommend trying something from 0.1 to a few uF connected between the reset pin and ground. Also, have you tried driving the reset line high from your Arduino (rather than relying on the internal pull-up)? Here’s a thread you might find helpful about a similar issue:

- Ben

I thought I was driving the reset pin from the Arduino… guess I was wrong. Moving the RST line from Pin 4 to Pin 13 of the Arduino which has a built in 1K resistor seems to have fixed the problem.

Thanks much for your help!

I took all connections to the reset line off, and that seemed to fix the problem.