Issue #2. Randomly reversing and not working Z steppers.



  • So another issue has popped up.

    I have two Nema23’s (2.8A) with 20:1 planetary gearboxes doing the heavy work of lifting my build platform on my printer through a 1605 ballscrew with 16mm supportee linear rails and bearing blocks at the corner (build platform is about 15lbs with the glass plate which is currently no installed). One stepper is wired into ZA the other into ZB.

    Occassionally when i go to home the Z axis, only one of these motors will turn. Once i tap the Z probe (precision piezo orion) and go to move the Z into the +50 direction, both motors will then turn.
    Then while moving the Z axis (in either direction) i can press +10mm multiple times and it’ll start going the correct direction, then it’ll go the opposite direction, back the correct way, then back the opposite, over and over randomly.

    Currently i have max speed and direction change at 1000 w/ acceleration at 150. Motor current is set to 2000mah (i tried 2800 and it made no difference). Steps/mm are at 1003.2, but i havent even been able to verify if this is correct.

    The Z axis is a 1605 ballscrew with bearing support blocks at either end and turn freely by hand.

    The Z axis also makes a horrible vibration harmonic through the 8020 structure (sounds like grinding without the metallic sound) when the X and Y axis is initially homed and after they hit the endstop switches.

    I have tried reducing steps/mm and max speed (down to 5mm/min) to see if that made any change and it has not.

    The only thing i havent tried is remapping one of the Z steppers to the open extruder driver to see if the Z driver just cant keep up with two large motors on it (if this is even possible). Its also likely that i’ll end up having to add 2 additional steppers in order to keep the bed from racking.

    Any help wouls be greatly appreciated.



  • We had this issue, basically is one of these...
    Don't forget to power everything off while plugging and unplugging!

    1. Its the motor itself. - take the load off and see if the behavior continues, swap another motor to see if its the motor.

    2. Its a break in the wire, probably direction. Use a continuity checker to confirm no breaks in the wires

    3. its the driver, Hook the same motor wire to another axis and test. -- don't forget to change all the power and speed settings for the test axis.

    In our case, we had one motor that was just plain bad, hard to imagine, but i guess occasionally it happens. We also had one case of a broken/loose wire.



  • #1 it is. I removed one of the Z steppers and it would almost in an alternative sequence reverse direction even as your telling it to go in the same direction each time..



  • Now after figuring out all of that, my Y axis is now all screwey. It worked fine before, now it just vibrates trying to turn but doesnt.

    I checked the driver using the X axis motor and it worked fine. The Y axis motor did the same vibrating thing on the X driver.

    This is becoming frustrating.



  • Also I forgot to mention be sure your motors are correctly wired, incorrect wiring will have the same symptoms as broken wires.


  • administrators

    Are you using 12V or 24V power? With two high-power Z motors connected in series, 12V power may be insufficient depending on the speed you are commanding. See the motor back EMF calculator at http://reprapfirmware.org/ to calculate the maximum speed you should command with the supply voltage you are using.


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