Metal Gearmotor works once a day


I bought a subsea gripper from Blue Robotics and it included a 34:1 Metal Gearmotor 25Dx52L mm HP 12V from Pololu. The recommended operating parameters are 9-18V, peak current 6 A and and 3.3V PWM signal (1500-1900 μs to open, 1100-1470 μs to close).

The motor only has 3 wires: red, black and yellow for the PWM signal. I connected the red and black to a 12V and 3A power supply and I am using an Mbed microcontroller to sent a 3.3V PWM signal. The circuit is very simple.

I can see from the oscilloscope that my μ-controller sends a correct PWM signal and I can see that the signal is reaching the yellow wire at the motor. I also verified with a multimeter that the red and black wires at the motor get the voltage that the power supply is sending. So everything looks good and it should rotate but it doesn’t.

It rotated in total 5 times so far in the 30 times I tried to test it. So this is what bothers me, because if the current sensor that is connected to the motor was broken, or the motor itself then it wouldn’t work at all. But instead it rotates sometimes.

Can anyone guess what’s the issue?


Hello, Harris.

Unfortunately, I do not have any immediate suggestions about what might be going wrong with your Blue Robotics gripper. We do not know what other electronics are used in the gripper though, so I suggest trying to contact Blue Robotics to see if they can help.

- Patrick

Ok thanks.

One thing I am thinking is that when working with multiple power sources, it is important to make sure they share a common ground connection. So you should make sure that there is a wire from the microcontroller’s ground to the motor’s ground. Not sure this is the problem but might be.

To test your servo motor it might be easiest to use a servo driver with PWM and it’s own battery supply after you remove it from the processor unit.
It’s possible the servo pwm needs to be closer to 4 to 6 v to work properly.