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  1. #1
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    Oct 2018
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    Z axis loosing steps

    Hello again!

    We have not been able to increase reliable speed of our z axis above 1150 mm/m with 200 units acc. X and Y we got reliabale speed at 25 000 mm/m
    There is a weird "resonance" spot at 1200 where it makes weird noise and stalls and looses steps. If I push it over that point fast, we can get reliable speed up to 7000 mm/min.

    Have played for ever with different pulses, acc, speeds. This is the max we can get out

    We use UCCNC
    This is quite a limiting factor.
    Chinese driver and NEMA 34 motor, have tried changing them both, no change.
    Direct drive with ball screw.
    Tried "simulating" counter spring effect by taking most of the weight off by lifting it by hand during movement gently, but made no difference.
    Any ideas?

    There is a video here as well explaining and showing our setup more or less.

    https://www.youtube.com/watch?v=dGNY...&feature=share

  2. #2
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    Re: Z axis loosing steps

    Hi,
    that sounds like a mid-band resonance. Two phase steppers are very prone to a resonance at a moderate speed, if you can get them past the 'hump'
    then they will go a lot faster without losing steps.

    What microstepping regime have you in use? One of the real advantages of microstepping is the marked reduction in mid-band resonance. I would
    recommend either 8 or 10 microsteps per fullstep, that is 1600 or 2000 pulse per rev. You'll get most, if not quite all, the benefits of microstepping
    WITHOUT requiring really high pulse output rates from your controller.

    Craig

  3. #3
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    Re: Z axis loosing steps

    Quote Originally Posted by joeavaerage View Post
    Hi,
    that sounds like a mid-band resonance. Two phase steppers are very prone to a resonance at a moderate speed, if you can get them past the 'hump'
    then they will go a lot faster without losing steps.

    What microstepping regime have you in use? One of the real advantages of microstepping is the marked reduction in mid-band resonance. I would
    recommend either 8 or 10 microsteps per fullstep, that is 1600 or 2000 pulse per rev. You'll get most, if not quite all, the benefits of microstepping
    WITHOUT requiring really high pulse output rates from your controller.

    Craig

    Thank you so much for your input!

    I am at sea currently, and cannot check if we were using either 4 or 8 microsteps. (800/1600 pulse per rev)

    For testing purposes, we tested for 1.5 hours, with all the microsteps (2/4/8/16/32/64/128/256/5/10/20/25/40/50/100/200)

    The best speed and also the "sound"what we achieved was with 8microsteps.
    we did this testing to see how much affect did microstepping have on the situation.

    Although, we did not try to change current (A) But i think that should not be an issue?

  4. #4
    Community Moderator ger21's Avatar
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    34985

    Re: Z axis loosing steps

    What size is the motor? If it's one of those big 1600 oz motors, a smaller motor might run smoother.
    What exact drive is it? A better drive might run smoother?
    If it's a dual shaft motor, a damper will help
    I'd first try increasing microsteps, and perhaps decreasing current.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  5. #5
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    Re: Z axis loosing steps

    The driver is DM860A
    Motor is NEMA 34 1600oz single shaft
    Reducing current is something we can try of course.
    Ordering smaller oz motor is also something we can try. Recommendations? Although the spindle with the dust extraction and whole frame weighs nearly 30kg, thats why I opted for a quite big Stepper. It all came in a kit anyways

    A high quality drive is of course expensive and I would leave it as a last resort, but which one would you recommend?

  6. #6
    Community Moderator ger21's Avatar
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    34985

    Re: Z axis loosing steps

    I'd get rid of that motor first. Those 1600 oz motors are a terrible choice.

    If that's a 5mm pitch screw, a 450oz motor would probably be plenty. Get one with low inductance, and a 5-6 amp rating.

    I use AM882 drives from Ebay, which are about $80. They can be fine tuned via Leadshine's tuning software.
    The newer EM806's are slightly better, but a lot more money.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  7. #7
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    Re: Z axis loosing steps

    Quote Originally Posted by MikeTerasT View Post
    The driver is DM860A
    Motor is NEMA 34 1600oz single shaft
    Reducing current is something we can try of course.
    Ordering smaller oz motor is also something we can try. Recommendations? Although the spindle with the dust extraction and whole frame weighs nearly 30kg, thats why I opted for a quite big Stepper. It all came in a kit anyways

    A high quality drive is of course expensive and I would leave it as a last resort, but which one would you recommend?
    I had EXACTLY the same on my PM25.
    EXACT same resonance and EXACT maximum speed restriction.

    I've swapped to this below and it's all good
    https://www.ebay.co.uk/itm/1-PC-Nema...72.m2749.l2649
    (Wired it in parallel)

  8. #8
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    Re: Z axis loosing steps

    Hello guys!
    First of all, Thank you for giving my problem some attention, If you guys ever end up in Estonia, I will buy you a beer!!

    @ dazp1976, That is Effing nice to hear!! Since yesterday i ordered a new motor, and by chance i chose the exact same motor from same provider

    @Ger21, Thank you very much for the recommendations about drives, since I have some other problems as well and at one point I would probably need to change the drives for better ones, If it cannot be solved any other way, so I will keep it in mind.

    Until then, what do you think, is it possible that on the other axis-es I could have the same issues? Same motors, I chose such big motors, since the gantry and everything is quite huge in my opinion.
    Link to another topic where I have an even bigger issue, than just speed:
    https://www.cnczone.com/forums/uncat...99964-cnc.html
    If you post over there, maybe the subject will get some more attention, since currently all the parts need major finishing to look representable and it is really bumming me out, that a CNC under which I spent about 6000€ and Months of building time, is producing this sh*t.

  9. #9
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    Re: Z axis loosing steps

    UPDATE!
    FIXED!

    Changed motor to NEMA 34 1090oz and the boost what we got in speed is substantial. From 200 Acc and 1150 Speed to 500acc and 7500 Speed.
    SO I am happy

    Thanks alot guys!

  10. #10

    Re: Z axis loosing steps

    I had the same problem with my homemade CNC, but instead of changing the stepper motor I ended up changing the lead screw to one with 4 starts and 8mm lead; before I was using a one start 2mm pitch/lead lead screw. This way I could reach higher axis speed maintaining the same reliable limit speed/acceleration for the motor.

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