Dual stepper resonance



  • My Duet WiFi drives two Z-stepper in parallel. I switched to some 0.9° steppers and have hit a strong resonance when moving the bed significantly. Would rewiring the steppers to be in series (as Duet documentation recommends) be expected to change the resonant frequency? If so would it move up or down?


  • administrators

    I wouldn't like to express an opinion on that. Try it and see.



  • How is the z axis built up ? 1st i would start to check if your z axes does really move smoothly, without any stiction. If in some area (z-height) one of you e.g. rails starts to "stick/block" a little bit and your bed is "twisted/rotated" it is game over with the "weak" steppers used in 3D printing.

    Did you try to increase or reduce the amps ? This will change the torque stiffness and should also change the resonance frequency.

    I assume that you don´t operate your steppers in a speed range where they come into resonance, but with 0.9 this will happen much earlier as with 1.8 steppers.



  • Motion is pretty smooth with the leadscrews removed and me moving the platform along the four guide rods. I did try moving the current up to near the rated limit and it seemed to move the resonance up. I tested various things by commanding long moves up and down at different speeds.

    It's not critical since the only time Z moves quickly is during homing after a tall print is removed. It's just the first time I'd bumped into a stepper resonance in a printer. Next time I'm in the mood, I'll toss some larger (48mm vs 40mm) steppers from the same series to see what that does.


  • administrators

    Have you tried changing the Z homing speed to avoid the resonance?



  • I used M203 to reduce the maximum Z-speed to stay below the resonance. So long as it's still able to make the mesh leveling adjustments fast enough I'm not seeing much downside.



  • I have stumbled across the same problem with my CoreXY machine. The operation is mostly quiet but there are certain speed where the whole printer emits loud noises.

    The only way to fix it is either slowing down way below what the printer is capable of (which defeats the purpose of having a nice printer) or dial up the voltage all the way, which causes my steppers and drivers to almost burn up.

    Is there anything that can be done from the software side?

    I can provide video if necessary, the resonances occur mostly on moves where both motors have to contribute inequal amounts of speed.


 

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