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Resolved Replacement motor struggling in a direction, SMC3 Crashing

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by TheYellowBatman, Mar 22, 2021.

  1. TheYellowBatman

    TheYellowBatman New Member Gold Contributor

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    My Motion Simulator:
    2DOF, DC motor, Arduino
    Hi All

    So after my motomonster died it was replaced with a Pololu Dual VNH5019. PSU was upgrades to a single 70A 12V, all wires were upgraded to the correct size for the amperage (10mm2 for the PSU to the Pololu) and fuses have been added in all the right places as per my other thread.

    The sim was working fine, but the left motor was getting hot and smelt funny. A teardown showed it had burnt out/shorted in the windings and the smell was some melted coatings. I figured fair enough, with all the issues I previously with a dodgy MM, melted wires etc it may have compromised the motor.

    Its been a few weeks, got around to ordering the new motor, it is the exact same model. Tested it with a battery, smooth as butter both directions. Installed it onto the sim, (unloaded) and it goes fine one direction but struggles in reverse.

    Symptoms/Notes
    • Struggles a bit then stops (see video), SMC3 crashes
    • Powering off motor driver and trying to restart SMC3 does not work, it freezes
    • Only way to get SMC3 going again is unplug usb then plug back in
    • Right motor operates fine, rotate halls sensor either direction and motor will spin smoothly
    • Left motor only operates smoothly in one direction, other direction crashes SMC3 and sounds like its struggling. Definitely notice left motor is getting hot again.
    • When new motor is connected to battery runs smoothly in both direction (see video)
    • Confirmed 12V being supplied from motor driver to new motor
    I'm not starting to wonder is it possible that the motor driver is somehow killing the left motor? But the old motor ran still, just smelt bad and heated up. The new motor i can't even seem to get it to function. No fuses have blown. I've replaced the majority of the electronics on the sim since I purchased it, can't seem to get a break :(

    Any suggestions on where to go from here?



  2. Ads Master

    Ads Master

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  3. Zed

    Zed VR Simming w/Reverb Gold Contributor

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    Is there any way you could have a ground fault in your circuit? With DC motors getting polarity reversals, it ends up being all too easy for shorts that do what you describe. One bout with high current can melt insulation and set you up for more shorts. Especially with the motor working properly off the sim, but not working correct on the sim flags a ground fault for me.

    But issues can also come and go with applied polarity on one or both motors, too. With the motor off the sim, you can energize it in both directions and test the voltage between the motor frame and the power source terminals. There should be no voltage difference to either terminal with the motor powered in both directions. Many wiper motors have one terminal grounded to the motor frame internally and those motors work great until you bolt them to a metal frame.

    Sure sounds like a fault/short to me, though. Good luck!
  4. TheYellowBatman

    TheYellowBatman New Member Gold Contributor

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    Hi Zed

    Thank you for the prompt reply. I have done more testing switching connections between motors so it is powering the opposite motor etc. With both hall sensors not connected to the motor shafts I have been able to get both motors to run forward and back by adjusting the hall sensors. They move smoothly now. I did realise that the cutting out of the motor as i rotated the hall sensor is when the hall sensor is rotated too far that it goes outside the limits (clip limits, orange line on SMC3?). I also checked the temperature of the motor and it was icy cold which is great.

    These wormdrive motors from motion dynamics did not require additional modifications to the wiring, i pulled it apart to confirm it wasn't grounded to the body to be safe.

    At times it was only running one motor as indicated by LEDs on the motor driver output however when i switched the system off and on again or reset the arduino this seemed to sort it out. I don't think this is normal behaviour but I'll need to investigate further to see why it sometimes needs a reset.

    What is concerning is I haven't really found a clear problem.... I removed some connections, reconnected them in the same spots, removed some of the male heads and put them back in the same female heads. Perhaps i have a loose connection somewhere or I need to rewire from the driver to the left motor?
  5. Zed

    Zed VR Simming w/Reverb Gold Contributor

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    It’s really hard to know the issue from this side. But you can spot motors that are grounded internally just by testing continuity from both terminals to motor frame/ground. No need to open them. It actually wouldn’t surprise me that the motor itself is cold even with a short to ground - if there is a short to ground (don’t know - just saying). Depending on the duty cycle in the bridges, it might not be heating much even though the motor isn’t working correctly. It will heat where you have the most resistance and voltage drop. You want no continuity. Similarly, you can check for voltage on your frame but that would be during the time the system is trying to damage itself if it’s there. Keep currents limited and at low duty cycle and you can be ok.

    Other than that, I don’t know what else to tell you. All I have mentioned may not be your issue. I would get the motors working off the sim at first, and when the feedback is all working right and the motors are too, then put them on the sim frame. That makes testing simpler and removes the chance for other damage or even injury if a feedback has the wrong polarity or such. If it all goes south then, I would check for voltages on the frame. But it also could be any number of other things tripping you up.
  6. TheYellowBatman

    TheYellowBatman New Member Gold Contributor

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    Thanks Zed - you hit the nail on the head. Upon further investigation it turned out the motor was not grounded correctly. This explained working correctly off the frame and via direct battery supply but not when connected to the motor driver.

    For those that purchase wormdrive motors from motion dynamics in Australia, please be aware that this model ZD1631 (both R and L) require grounding: https://www.motiondynamics.com.au/zd1631l-12v-70w-45-65-rpm-6-35nm-torque-right-angle.html

    SMC3 crashing is a result of the hall sensors being rotated past their clip limits. This causes SMC3 to automatically turn the motor off.
    • Informative Informative x 1