Broken current sensor?

General discussion of using Roboclaw motor controllers
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felix
Posts: 14
Joined: Thu Dec 03, 2020 8:08 am

Broken current sensor?

Post by felix » Mon Feb 22, 2021 9:05 am

Hi,
we just mounted 2 2x60A roboclaws on a new robot (the hardware and configuration is exactly the same as before, where everything worked fine).
One of the roboclaws work fine. For the second one, channel 1 works fine, but on channel 2 we have the following problem (all tests done through motionStudio):
- when setting a negative duty cycle, the motors turns perfectly fine (in reverse direction).
- when setting a small positive duty cycle, the motor turns normally, in motion studio the current is 0A (probably normal, I think it's less than 0.5A)
- when increasing the (positive) duty cycle, the motor starts making a strong noise, and motion studio displays a current about 170A!!! The speed remains slow.

We tried to swap the 2 motors : it is always the motor on channel 2 that has the strange behavior.

Do you have any idea what may be wrong?
My guess would be some hardware issue on the current sensing circuit of the channel 2, resulting in entering over-current protection which might result in switching the current on and of with an audible frequency (not sure if it is implemented like that on a roboclaw, but I have seen current chopping working like that on other H bridges).

Is there anything that we can try?
Or should we return the roboclaw for an exchange? If so, how to proceed?

Thanks a lot in advance
Best Regards
Felix

EDIT : we changed the roboclaw (putting the same config), and it works well. So it seems to point even more to a hardware problem of the roboclaw

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Basicmicro Support
Posts: 1506
Joined: Thu Feb 26, 2015 9:45 pm

Re: Broken current sensor?

Post by Basicmicro Support » Wed Feb 24, 2021 11:50 am

It most likely is not. Current is measured through a shunt resistor and an A/D pin on the main processor. There is little to nothing that can break.

You symptom indicates a false overcurrent at low duty cycles. This can be caused by too low a current blanking percentage. The default is 5.4% which can be too low on some motors. Setting between 8 and 10 usually fixes the problem on motors with issues and the value can be set as high as 20.

felix
Posts: 14
Joined: Thu Dec 03, 2020 8:08 am

Re: Broken current sensor?

Post by felix » Thu Feb 25, 2021 1:33 am

Thanks,
It is already quite high (at 14), but we will try at 20 to make sure

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