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SOLO spontaneously drives DC motor when PWM controller powers off

Forum 1
(@alexandertmills)
New Member

Hello,

I'm using an ESP32 to drive a brushed DC motor with a SOLO mini in closed-loop, analog torque-control mode (FN pin floating) via PWM. Control itself is working swell! However, whenever SOLO is powered on and the microcontroller is not (common ground, but different power supplies), SOLO puts the motor into *ghost mode*. About 0.5-1.0s after the ESP32 loses power, SOLO begins driving the motor "forward" (always the same direction) at roughly half of max speed. This occurs regardless of whether I disconnect power from the ESP32, or if I power up SOLO without also powering the ESP32.

I'm guessing that there's some noise on either the ST or PF pins, but I don't have an oscilloscope to confirm this. Any suggestions on how I might prevent this undesired behavior?

Thanks,

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Topic starter Posted : 10/11/2021 4:12 pm
SOLO Team
(@milad)
Chief Member Moderator

Hi @alexandertmills

Yes, that is most probably some sort of noise or an elevated voltage over the "S/T" pin forcing SOLO to apply torque on the Motor.

To prevent this behaviour you have some options like:

  1. Use shielded cables for S/T, and make sure the shield is connected to the GND ( Grounded)
  2. You can use a relay so that whenever EPS32 is Off, that relay goes in Open mode ( a Normally Open relay will be good), so in that case, you make sure there is no noise from EPS32 going to SOLO once it's OFF and S/T is floating.

Let me know if you need other information or you have some questions in this regard

Regards
Milad

If you found the answers helpful and you could solve your problems, please kindly verify here to help others in the future.

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Posted : 10/11/2021 5:41 pm
Forum 1
(@alexandertmills)
New Member

Thanks @milad. Alternatively, would it work to throw a pull-down resistor on the ST line?

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Topic starter Posted : 11/11/2021 6:45 am
SOLO Team
(@milad)
Chief Member Moderator
Posted by: @alexandertmills

Alternatively, would it work to throw a pull-down resistor on the ST line?

It might be also possible to use this option (Not my personal favorite one), however, you need to consider using a pull-down resistance with high values ( between 50k - 200k ) to avoid draining excessive current from EPS once it's actually driving the line with PWM pulses.

Milad

If you found the answers helpful and you could solve your problems, please kindly verify here to help others in the future.

ReplyQuote
Posted : 11/11/2021 11:54 am
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