One motor slowing down (stopping)

General discussion of using Roboclaw motor controllers
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felix
Posts: 18
Joined: Thu Dec 03, 2020 8:08 am

One motor slowing down (stopping)

Post by felix » Thu Dec 10, 2020 12:37 am

Hi,
I'm working on a heavy (80kg) robot. It has 4 wheels (differential drive), each one with its one motor and encoder.
I'm using 2 roboclaws 2x60A to control them (one for the front wheels, one for the rear wheels).
I'm commanding the roboclaws from a Jetson Xavier AGX developper kit (embedded computer running linux, similar to a Raspberry Pi but far more powerfull). I'm using the python API to communicate with the roboclaws from within a ROS node.

The problem I have, is that sometimes, one wheel, always the right rear one, seems to "block" (more precisely, it turns very slowly (I think driven only by the movement of the robot) while the other ones still turn at normal speed).

My first idea was some error in my code, but I always send exactly the same commands at the 2 roboclaws, so it seems very unlikely that this is the problem.

Do you have any idea were the issue might come from? Or what tests I can do to gather useful data to find the solution?

Thanks a lot in advance
Felix

PS : please find attached the code of my roboclaw ROS node.
roboclaw_node.zip
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Basicmicro Support
Posts: 1518
Joined: Thu Feb 26, 2015 9:45 pm

Re: One motor slowing down (stopping)

Post by Basicmicro Support » Thu Dec 10, 2020 1:43 pm

The symptom is what I would expect if there is a false over current. This is usually caused by too low a current blanking window. The default of 5.4% is too low for larger motors. Open General Settings and adjust the value to between 8 an 10%. Remember to Write Settings using the device menu, and then retest. Once you have a good enough value you will no longer have the problem with that wheel.

The M2 channel is more susceptible to motor noise because it's current reading is taken second during each PWM pulse so it will always be closer to the falling edge, which is actually noisier than the rising edge of the PWM.

felix
Posts: 18
Joined: Thu Dec 03, 2020 8:08 am

Re: One motor slowing down (stopping)

Post by felix » Fri Dec 11, 2020 8:40 am

Hi,
thanks a lot.
I Just changed it to 15%, I will try it in the field on Monday morning.
I keep you updated.

Best regards
Felix

felix
Posts: 18
Joined: Thu Dec 03, 2020 8:08 am

Re: One motor slowing down (stopping)

Post by felix » Mon Dec 14, 2020 9:55 am

Hi,
I haven't had time to do a long test, but during the short test I did everything seemed to be OK.
Thanks a lot.

Best regards
Felix

advaiths
Posts: 4
Joined: Fri Mar 19, 2021 9:04 pm

Re: One motor slowing down (stopping)

Post by advaiths » Wed Mar 31, 2021 10:24 pm

Is there a way to read more about the current blanking windows? I had the same problem with my motors, and changing from 5.4 to 10% fixed the problem. However, I would like to better understand this functionality.

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