Strange Stepper Behaviour Diagnosis

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  • February 12, 2020 at 3:47 pm #11783
    MonkeyManGuy
    Member

    My machine has begun stalling with an increasing fequency on the Xaxis at speed/workloads it could previously run. So I decided to remove the motor and found someting very strange making me think this motor could have gone bad. What do you all think of the symptoms?:

    It is a Nema 23 2.8amp motor. I set the amperage initially by sending a g0x10000 command while turning the potentiometer. It ran the quietest at the highest setting.

    Since then I have had a lot of machine crashes due to user error, so the motor has been stalled a lot. I removed it to test and found that now it has a very odd vibration when being freely spun at the highest amp setting. It now rus the quietest at about 1/3 of the potentiometer travel.

    When I reinstalled the motor into the machine it was stalling on the lightest workloads. I turned the amps back up and it was running normally. I sent a text file instructing the carriage to move back and forth on the Xaxis with g0 commands while adjusting the potentiometer and found it still runs best at the highest amp setting.

    But Im very confused where this vibration issue has come from indicating 1/3 of the potentiometer travel is its ideal. And I cannot determine why this motor has begun stalling sometime and working other times at speed/workloads that it could handle well when it was brand new.

    Is it possible that the crashes caused by me entering bad commands were damaging the motor?

    February 12, 2020 at 8:54 pm #11784
    cmcgrath5035
    Moderator

    I have no direct experience with your situation, so most of this is a bit of conjecture on my part.
    My read of the tinyG Tuning process (https://github.com/synthetos/TinyG/wiki/TinyG-Tuning)
    implies setting the current pot somewhat higher than a setting that produces minimal skipped steps. The problem is that the optimal setting this way is highly dependent on the load on the spindle – optimal for pine will not be the same as for aluminum or foam board.
    Setting the pot for ‘minimum noise’ is not likely optimal. I would expect perceived noise to always be minimum at max pot, but that does not necessarily translate to maximum energy transfer to the milling process.
    As the motor core heats up, less magnetic energy is generated by power pulses.
    Perceived ‘noise’ from the motors is a combination of the frequency with which pules of energy are sent and the duration of those pulses. The higher the pulse current setting, the shorter the pulse will be. But once a stepper has made it step movement, excess current during the hold position phase of the movement cycle will heat up the motor core.

    Damage a motor with bad commands?
    Maybe, but I find it difficult to say any stall could bend a motor shaft (that would be bad). Core heating could change ‘noise’. Repeatedly ramming a motor into a stop might tend to loosen a pulley? (belt machine)? check your Allen set screws.

    To really damage a motor the heat dissipated in the winding would have to be high enough to melt a winding wire and perhaps fuse it to an adjacent one.

    Not much help, probably

    February 13, 2020 at 12:37 am #11785
    MonkeyManGuy
    Member

    What is the maximum amount of amps the TinyG can put out?

    February 13, 2020 at 7:08 am #11786
    cmcgrath5035
    Moderator

    Spec says 2.5A

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