Check my stepper math & stepper resonance


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Thread: Check my stepper math & stepper resonance

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    Registered mikemaat's Avatar
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    Default Check my stepper math & stepper resonance

    I have a garage built RF45 mill. I have a 2830 oz/in Nema42 on the z-axis. I bought such a big motor years ago because I didn't want to be undersized. I have found that I have severe resonance at 50 ipm that causes the axis to stall out. However anything below that number is fine, and anything above that number is fine (I have tried up to 135ipm).

    Tonight I swapped one of my 960oz/in Nema 34 motors on to the axis and it ran it fine, and the resonance "sweet spot" moved up to 70 ipm, I'm guessing due to the differing torque curves. I think a 640 oz/in motor would run the axis fine as well.

    My plan was to change the axis from direct drive to belt drive and keep the Nema 42. Then do a pulley setup that is 1:3 so that the actual speed of the axis at the resonance sweet spot would be 150 ipm and I can set my max speed below that and never worry about it.

    The only downside I could think of would be loss of resolution, so I'm hoping someone can confirm my math..

    Stepper motor is 1.8 degrees / step. I'm 10u micro stepping (Gecko g201) so that should be 0.18 degrees per micro step. Then multiply that by 3 for the gear increase and the ballscrew would be experiencing 0.54 degrees per micro step. 360 degrees / 0.54 would mean that it would take 667 micro steps per revolution. If the lead screw has a pitch of 5mm (0.197") that would mean that each micro step would be 0.197" / 667 = 0.0002".

    If that's all correct, 0.0002" hypothetical resolution would be more than fine by me. Did I calculate anything incorrectly? Am I overlooking anything?

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    Default Re: Check my stepper math & stepper resonance

    What size PSU are you using? Also, if I'm not mistaken, G201 has electronic mid band resonance damping. Might want to contact Marriss at GeckoDrive for an opinion.

    The math is actually easier than that. 200 steps X 10 microsteps = 2000 microsteps. Multiply by gear ratio 2000 X 1/3 = 666.6 microsteps/rev. Dividing your lead by that gives you .00029"/step



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    Registered jfong's Avatar
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    Default Re: Check my stepper math & stepper resonance

    The gecko201 has a nema42 jumper setting. It adjust the resonance for larger stepper motors. It also has a trim pot to adjust for smoother low speed motion. You can try those options if you haven't.



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    Default Re: Check my stepper math & stepper resonance

    Quote Originally Posted by jfong View Post
    The gecko201 has a nema42 jumper setting. It adjust the resonance for larger stepper motors. It also has a trim pot to adjust for smoother low speed motion. You can try those options if you haven't.
    I was just about to reply with a "already knew about those", and then figured id try WITHOUT the Nema 42 jumper installed. Turns out my resonance has disappeared. I ran a feed test from 0 - 135 ipm with increments of 5 ipm and no stalls anywhere. Im a happy guy now. Ill contact Mariss@Gecko just to make sure he knows about it.



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    Default Re: Check my stepper math & stepper resonance

    That's good. Saves you some $$ on upgrading.

    The biggest stepper I've used is a nema34 so I've never had the opportunity to try that jumper setting. I do know there is a jumper setting to turn off "anti-resonance". They are good drives. I have about a dozen geckos.



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    Default Re: Check my stepper math & stepper resonance

    G'day MikeMaat, are you still active? keen to find out about the ios pendant app, I have an RF30 mill which I am converting to CNC, and keen to use the ios pendant option please



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Check my stepper math & stepper resonance

Check my stepper math & stepper resonance