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IndustryArena Forum > CNC Electronics > Stepper Motors / Drives > Steppers stall/oscillate at low feed rate. High feed is OK.
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  1. #1
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    Oct 2017
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    Steppers stall/oscillate at low feed rate. High feed is OK.

    Hi all,


    I have a problem with my steppers.


    When running at a low feed range (~100), then the steppers look to start stalling/oscillating (stepping back and forth irregularly).
    I have no problem at higher speeds (e.g. 1000) - at least that's how it looks like.
    Single steps are also ok.
    I reduced the max acceleration significantly, made a long move, and during this rather long acceleration period the problem occurs for a moment when in this low feed range.


    I have DRV8825 drivers, use GRBL as controller and NEMA17 motors.
    Anyone a clue where to search for.


    Thanks in advance for any tips,
    Grt, Patrick

  2. #2
    Join Date
    Aug 2005
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    1091

    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    You are experiencing resonance in the stepper motor. This is normal and occurs at low speeds as you are observing.
    To solve this you could use a stepper driver with an anti-resonance function built in such as the Geckodrive stepper motor controllers. If you’re current stepper driver hah anti-resonance, then it may need to be adjusted.

    Another solution is to use a resonance damper on the back shaft of the motor. If you do a search you should be able to find a lot of information on the damper me.

    Cheers

    Peter.


    Sent from my iPhone using Tapatalk Pro
    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com/store

  3. #3
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    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    Thanks. A damper at the motor is not easy. Needs mechanical redesign.
    I cannot find anything about anti-resonance for my DRV8825 drivers.

    Though I found following statement on another forum:
    "The value of micro-stepping is lower mechanical noise and resonance problems (steps skipping) can be more easily avoided."
    Hence I will try micro-stepping and see if that helps.

    Grt, Patrick

  4. #4
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    Jun 2012
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    153

    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    Quote Originally Posted by pfpmeijers View Post
    Thanks. A damper at the motor is not easy. Needs mechanical redesign.
    I cannot find anything about anti-resonance for my DRV8825 drivers.

    Though I found following statement on another forum:
    "The value of micro-stepping is lower mechanical noise and resonance problems (steps skipping) can be more easily avoided."
    Hence I will try micro-stepping and see if that helps.

    Grt, Patrick
    This is called mid-band resonance. Since stepper motors latch from one magnetic pole to another they oscillate and settle. When that matches the step period it will resonate and skip or stall.

    Micro-stepping will cost a lot of lost torque. Half-step is not too bad and resonates a less easily. Adding extra inertia ( some fly wheel effect ) can help. Also a frictional damper will impede resonance but again available torque takes a hit. Avoid hanging around near resonance, accelerate through if possible. Depends upon your needs.

    Without detailed mathematical modelling of the mechanical system it's a case of trial and error to find what works for what you need to do.

    If you can not get the speed ranges you need to be stable, you may need to use a different motor, with difference properties.

    You could try monitoring the current going into the driver chip, it will generally be a minimum at resonance. Torque varies hugely with speed in steppers and it is not a simple function of speed as one may expect with conventional motors.

  5. #5
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    Feb 2008
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    644

    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    Quote Originally Posted by reg.miller View Post

    Micro-stepping will cost a lot of lost torque..
    This is frequently repeated but absolutely false.

    The microstep ratio does not significantly affect _stall _ torque.

    In fact because higher microstep ratios reduce resonance issues
    high microstep ratios actually improve low speed torque

  6. #6
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    Oct 2017
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    3

    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    I switched to 1/4 micro-stepping and could no longer see the resonance effect. So this worked.
    I have enough torque for my application I think.

    (Now ran into a next issue - when enabling the spindle my dual motors for single axis get out of sync. Looks like lost/extra steps due to EMI - which is widely discussed on the internet. So don't want to go off-topic with this.)

    Thanks again for the help! Grt, Patrick

  7. #7
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    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    Quote Originally Posted by PCW_MESA View Post
    This is frequently repeated but absolutely false.

    The microstep ratio does not significantly affect _stall _ torque.

    In fact because higher microstep ratios reduce resonance issues
    high microstep ratios actually improve low speed torque
    Yes, microstepping does not significantly affect stall torque, but it does affect the top end speed. That's why Geckodrives morph from microstepping to full-stepping once the stepper speed reaches around 3 revs/Sec.
    Microstepping was designed primarily for smoothing out the movement at low speed by removing the cogging of full stepping the motor. The side affect of this is that it reduces the affect of mid band resonance. To eliminate this resonance the drive needs to implement an anti-resonance function.

    cheers,

    Peter
    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com/store

  8. #8
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    Jun 2012
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    153

    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    I have an unreferenced "Application Note" pdf wtih ST Micro written all over it:

    users.ece.utexas.edu/~valvano/Datasheets/Stepper_ST.pdf
    in the half-step position the motor has only
    about half of the torque of the full-step.
    If this "myth " is being spread by majors like ST , maybe there is some truth to it. From the graphics , it does look rather old but fundamentals like this should not change over time.

    it does affect the top end speed
    Steppers move at the programmed speed or they stall ( or miss steps ). If something 'affects' top end speed that means the stall speed.

    phomann, what other than reduced torque is the cause of high speed stalling? That would seem to corroborate, not refute the idea mirco-stepping reduces torque.

  9. #9
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    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    Quote Originally Posted by reg.miller View Post
    I have an unreferenced "Application Note" pdf wtih ST Micro written all over it:

    users.ece.utexas.edu/~valvano/Datasheets/Stepper_ST.pdf


    If this "myth " is being spread by majors like ST , maybe there is some truth to it. From the graphics , it does look rather old but fundamentals like this should not change over time.


    Steppers move at the programmed speed or they stall ( or miss steps ). If something 'affects' top end speed that means the stall speed.

    phomann, what other than reduced torque is the cause of high speed stalling? That would seem to corroborate, not refute the idea mirco-stepping reduces torque.

    Sure, full stepping has double torque every other step relative to 1/2 stepping but resonance issues ( full stepping is nearly unusable on most systems )
    make low speed torque of full stepping and half stepping lower than systems using higher microstep ratios.

    The " higher microstep ratios result in lower torque" nonsense is just a myth.
    In fact studies have shown that usable low speed torque increases with microstep ratios up to about 64

  10. #10
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    Apr 2004
    Posts
    733

    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    Microstep vs. Full Step Torque | GeckoDrive

    Most people care about torque when the motor actually turns. This is why I use gecko drives on my larger machines. The anti-resonance and full step morphing really does work well. I have several dozen different stepper drivers collected in the past 25 years. Only a few work as good as geckos.

  11. #11
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    Apr 2004
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    733

    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    For the OP this may not be your problem but.....

    The DRV8825 has a small issue with poor microstepping accuracy/stalling. Mostly why I use A4988 on my smaller belt driven machine. It can be partially fixed by adding some diodes. This is a hack but it seems to work for some people. I haven’t tested the diode “fix” yet. It was easier to replace with a4988. These diode fix boards are sold on eBay for a couple dollars.

    https://webcache.googleusercontent.c...&ct=clnk&gl=uk


    I did my own testing and you can see this issue with this not so nice looking sine wave from a DRV8825 spinning a motor on my oscilloscope.

    https://uploads.tapatalk-cdn.com/201...c1740a12a5.jpg

  12. #12
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    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    Quote Originally Posted by reg.miller View Post
    Steppers move at the programmed speed or they stall ( or miss steps ). If something 'affects' top end speed that means the stall speed.

    phomann, what other than reduced torque is the cause of high speed stalling? That would seem to corroborate, not refute the idea mirco-stepping reduces torque.
    Steppers stall because the rotor cannot keep up with the commanded speed. After a few hundred RPM (depends on the motor) the torque drops off with speed. Increasing the supply voltage delays this drop-off. A lot of your questions can be answered by reading Geckodrives's "Step Motor Basics Guide"
    Support | GeckoDrive

    Cheers,

    Peter
    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com/store

  13. #13
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    Aug 2005
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    1091

    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    Quote Originally Posted by PCW_MESA View Post
    Sure, full stepping has double torque every other step relative to 1/2 stepping but resonance issues ( full stepping is nearly unusable on most systems )
    make low speed torque of full stepping and half stepping lower than systems using higher microstep ratios.

    The " higher microstep ratios result in lower torque" nonsense is just a myth.
    In fact studies have shown that usable low speed torque increases with microstep ratios up to about 64

    Higher microstep ratios DOES reduce torque at all speeds except at very low speeds. Have a look at this.

    How Morphing Works - Step Drives - Application Notes - Support | GeckoDrive

    Cheers,

    Peter
    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com/store

  14. #14
    Join Date
    Mar 2005
    Posts
    303

    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    Quote Originally Posted by pfpmeijers View Post
    Hi all,


    I have a problem with my steppers.


    When running at a low feed range (~100), then the steppers look to start stalling/oscillating (stepping back and forth irregularly).
    I have no problem at higher speeds (e.g. 1000) - at least that's how it looks like.
    Single steps are also ok.
    I reduced the max acceleration significantly, made a long move, and during this rather long acceleration period the problem occurs for a moment when in this low feed range.


    I have DRV8825 drivers, use GRBL as controller and NEMA17 motors.
    Anyone a clue where to search for.


    Thanks in advance for any tips,
    Grt, Patrick
    check decay mode

  15. #15
    Join Date
    Mar 2005
    Posts
    303

    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    Quote Originally Posted by PCW_MESA View Post
    This is frequently repeated but absolutely false.

    The microstep ratio does not significantly affect _stall _ torque.

    In fact because higher microstep ratios reduce resonance issues
    high microstep ratios actually improve low speed torque
    high microstep give smooth moving when motor run very very slow, about lower 5rpm
    microstep can't give smooth moving at mid low speed about 25 75rpm

  16. #16
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    Jun 2012
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    153

    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    The microstep ratio does not significantly affect _stall _ torque.
    Yes, microstepping does not significantly affect stall torque, but it does affect the top end speed
    After a few hundred RPM (depends on the motor) the torque drops off with speed
    So motors stall because torque reduces with rpm. Microstepping reducing torque is a "myth". So why do advanced drivers switch to single step at higher speeds?

    It seems that the difference in current in each winding is very small between mircostep 63 and microstep 64 in a 128 step scheme. This means that there can be very little torque differentiating the two positions and very little resistance or resonance is needed to fail or overshoot.


    Once you get into higher speeds the driver is unable to get the winding current to change fast enough to assert a strong enough current in either direction in a bipolar motor. This is because of inductance. Reduced current amplitude leads to reduced torque and eventually to stalling. I would have thought that the fastest change in current would come from abrupt change in driver state, though things like cross-conduction and dead time will complicate this.

    In my experience, actual behaviour of inductive circuits under fast switching are rarely adequately explained by mental thought experiments.

    The Gecko doc is very interesting but is nothing more than handwaving thought experiments on this subject.

    If someone has a study : ie actually observational measurements rather than handwaving generalities of what happens in complex mechanical electro-inductive systems like stepper motors that would be more convincing than forum assertions.

  17. #17
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    733

    Steppers stall/oscillate at low feed rate. High feed is OK.

    Reg.miller,

    Like most thing designed and made in the world, not all will perform equally and that holds true for stepper drivers. I can use the same power supply, motor, current settings. One driver will stall at 600rpm while another will spin the motor at 2000+rpm.

    You can keep asking questions and get many different answers. My advice is to buy a bunch of different stepper motors, drivers and do some empirical testing yourself. All drivers will spin a motor, just some do it better than others.

    If you haven’t yet, try contacting ST, Allegro, Trinamic etc application engineers. That will usually help explain how their driver chips work or point to a application note that will help.

  18. #18
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    153

    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    Like most thing designed and made in the world, not all will perform equally
    A truism, thanks.

    So I should ignore all existing science and engineering knowledge and invest significant amounts of my time and money investigating this myself.

    I seem to recall some time toward the end of the last millennium that google claimed to have about a billion pages indexed. I assume that this figure has increased by several orders of magnitude since. Somewhere in that mess there must be some solid information about the effect of microsteps on stepper motor torque.

    Sadly Google now seems to rate sites on how many Google ads they carry , rather than content. several of the first page results are CNCZone and Gecko.

    https://softsolder.com/2011/09/11/st...ode-vs-torque/
    One reasonably careful measurement trumps a kilo-opinion, so here’s a chart
    https://softsolder.files.wordpress.c...-17pm-j034.png

    So this empirical evidence shows that mircostepping is an advantage at low rpm but somewhere around 500 rpm becomes a liability. That is presumably the reason that more advanced controllers swap to full step at higher rpm. because microstepping reduces torque and by implication leads to stalling at lower speeds.

    It is not a "myth" but neither is it a black / white situation.

  19. #19
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    644

    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    Quote Originally Posted by reg.miller View Post
    So motors stall because torque reduces with rpm. Microstepping reducing torque is a "myth". So why do advanced drivers switch to single step at higher speeds?

    It seems that the difference in current in each winding is very small between mircostep 63 and microstep 64 in a 128 step scheme. This means that there can be very little torque differentiating the two positions and very little resistance or resonance is needed to fail or overshoot.


    Once you get into higher speeds the driver is unable to get the winding current to change fast enough to assert a strong enough current in either direction in a bipolar motor. This is because of inductance. Reduced current amplitude leads to reduced torque and eventually to stalling. I would have thought that the fastest change in current would come from abrupt change in driver state, though things like cross-conduction and dead time will complicate this.

    In my experience, actual behaviour of inductive circuits under fast switching are rarely adequately explained by mental thought experiments.

    The Gecko doc is very interesting but is nothing more than handwaving thought experiments on this subject.
    So motors stall because torque reduces with rpm. Microstepping reducing torque is a "myth". So why do advanced drivers switch to single step at higher speeds?
    If someone has a study : ie actually observational measurements rather than handwaving generalities of what happens in complex mechanical electro-inductive systems like stepper motors that would be more convincing than forum assertions.

    Nope, same myth repeated again, at low speeds microstepping improves stall torque because it reduces resonance
    You are doing what many people do and confuse stall torque with incremental torque per microstep
    which is not relevant to stalling/oscillation

    Note the OP posted about _LOW_ speed _STALLING_

    Also note that the OPs problem was SOLVED by going to a higher microstep ratio
    If he had listened to the advice about not increasing the microstep ratio he might still be struggling

    Note that the Gecko drive only starts morphing to quadrature mode at 267 RPM (not a low speed for a step motor)

  20. #20
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    Re: Steppers stall/oscillate at low feed rate. High feed is OK.

    Nope, same myth repeated again,
    if you are going to accuse something of being a "myth" quote EXACTLY what you are contesting, not a whole post making several different points.

    The way Gecko works is consistent with the graph I liked above. It is not black and white issue. uStepping is helpful at low rpm and detrimental at high rpm.
    Attachment 387100

    Simplistic statements in either direction are inaccurate and only partially true.

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