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  1. #81
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    Default Re: What effect does microstepping have on torque?

    Quote Originally Posted by PCW_MESA View Post

    The motor lag vs load does _NOT_ change with the amount of microstepping so increasing
    microstepping will not decrease your accuracy. The torque vs displacement curve depends on the
    number of poles, the motor current, and the motor construction, none of which vary appreciably
    with the microstep ratio.
    Do you have any evidence to support that accuracy is not effected? Plenty of companies out there that say it does and have proven it. just like to see some factual evidence to say that it does not.

    Its a simple enough test, it requires a reasonable size machine to test the motors better , ive done this, found problems by doing the same test myself. simply set up a dti step back and forth into it by 1mm beginning with full step all the way up through your microstep settings, calculating backlash error and correcting and testing for correction accuracy between changing microsteps. If you are right the dial on every setting will be within the mechanical accuracy of the machine every time.

    It wont It will drift out of accuracy as you go higher up the settings i promise you that.

    And if you were correct, when i say my machine was struggling at 10x, by which i mean it was running unsmoothly and it would not stop correctly, Then tell me if this problem doesnt exist, Why at half step does it run perfectly?



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    Default Re: What effect does microstepping have on torque?

    Quote Originally Posted by PCW_MESA View Post
    Nope, you are still missing it.

    What the MICROMO paper means by incremental torque is that if you have 64 microsteps per full step the
    torque required to displace the shaft 1/64 of a full step is much less than the torque required to displace the shaft
    1/2 or 1/4 of a full step, which is not terrible surprising.

    The holding torque is _not_ affected by the microstep ratio (well 1/2 stepping is a special case and may have more static torque but you lose on resonance)
    **** now you mention it, well excuse my language, i stand corrected about torque, so that paper is on all about accuracy then. and none of this explains why my machine acts the way it does over 10x.

    sorry guys i had convinced myself that was the cause it seems.. now who knows.

    That paper explains why accuracy is lost between changing directions which makes sense but nothing on the scale my machine plays up. Its around a 1/4 ton gantry running 2 x 20:1 plantary gearboxes (45nm ea) with 3nm nema 23's geared back up with a 40 tooth pinion on mod 1. So it a case that low speed torque may not be an issue usually but im seeing a drop in torque between half and 10 because my motors are at thier limit? or they are lower resistance motors, is it that they simply cannot store enough current between full steps? because thats whats happening right? and these motors, are they 100% efficient at it, i.e between full steps there is no current loss? They would have to be to not loose torque wouldn't they?

    Really Im not loosing anything as i get mechanical accuracy with no noticeable resonance at 2x so it will likely remain a mystery.

    However wrong i was about the torque, accuracy error still is an issue so some of what i said still makes sense :S

    i had read that paper a few years back and understood it the way you explained it then i think then in practice my machine alters my understanding of things and in this case got the two mixed up. my appologize and thanks for re-enlightening me.



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    Last edited by Jon.N.CNC; 10-22-2015 at 05:19 PM.


  3. #83
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    Default Re: What effect does microstepping have on torque?

    Yes we have instrumented step motors with high resolution encoders for just this purpose.
    high microstep ratios do not reduce accuracy at all, nor do they reduce holding torque
    They increase resolution (but not accuracy typically because the torque vs displacement curve is unchanged)

    You may get more repeatable steps with a very raspy 1/2 stepping simply because the motor rings at every step
    so may settle closer to the actual 1/2 step positions, dont know

    But the basic idea that you lose torque when increasing the microstep ratio is just plain nonsense.

    ( And I think largely results from people misinterpreting the MICROMO paper )

    Last edited by PCW_MESA; 10-22-2015 at 05:28 PM.


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    Default Re: What effect does microstepping have on torque?

    Quote Originally Posted by Jon.N.CNC View Post
    Are you possitive about this? can you back it up with any evidence? because a simple search on googles image search for microstepping torque graph brings up a hell of a lot of graphs that seem to disagree. Here is a company for example with a nice explanation of it and a nice graph: Microstepping: Myths and Realities | MICROMO

    quote: "The real compromise is that as you increase the number of microsteps per full step the INCREMENTAL torque per microstep drops off drastically. Resolution increases but accuracy will actually suffer."

    I agree completely and i know this first hand.. my planetary gearbox motors struggle for torque at anything over 10x microstepping. I run them at half step. they run great, they match my R&P accuracy. And that is all that is required. if torque drop wasnt happening at just 10x then how would you explain this?

    Even on my direct drive screws i see accuracy starts to drop at over 32x, there's another very true quote that explains this on that link:

    "taking an infinite number of microsteps per full step results in two-phase synchronous permanent magnet ac motor operation, with speed a function of the frequency of the ac power supply. The rotor will lag behind the rotating magnetic field until sufficient torque is generated to accommodate the load."



    If you increasing steps to reduce resonance, just need to be aware of torque drop and lag affecting accuracy. when it comes to electronics you never get anything for free, amps - volts, torque - smoothness, everything has its cost so its always a compromise.


    so going by that graph and the many others floating around the net exactly the same, it looks as though at 64x steps its not just 64x less torque, its a massive 97x decrease.





    No point in telling someone go for 64 microsteps and you will get a resolution of 0.005 for example if their screw or r&p is 0.05. Just wasting torque. And the same goes for encoders. That was my point.
    Your paper was compelling, I would have gathered the same facts from it had PCW_Mesa not come in and give his input.

    In industry I use Schneider M-drive stepper motors. We run them at 52000+ steps/rev or ~256 microstepping. The torque curves are not derated for higher microstepping values, but there are electrical limitations where the DSP capabilities fall off - I imagine greater than 256microstepping for most controllers is an issue in that sense. We load these motors to 70% of their rated load (over the ideal 50% or 2x safety factor) and they have never stalled out due to running torque. We are super repeatable; I took a 10um resultion (8um accuracy) linear encoder provided by balluff and did a series of studies, we were extremely repeatable on a C10 ballscrew actuator over 1000mm. I will have to pull that data out if I can find it.

    Ultimately, if your system is behaving the way you want it to at the settings that you have it at, then you've met your requirements (I just kind of repackaged what you said in this sentence here).

    I'm always up for a good discussion, good information here.



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    Default Re: What effect does microstepping have on torque?

    Quote Originally Posted by UA_Iron View Post
    Your paper was compelling, I would have gathered the same facts from it had PCW_Mesa not come in and give his input.

    In industry I use Schneider M-drive stepper motors. We run them at 52000+ steps/rev or ~256 microstepping. The torque curves are not derated for higher microstepping values, but there are electrical limitations where the DSP capabilities fall off - I imagine greater than 256microstepping for most controllers is an issue in that sense. We load these motors to 70% of their rated load (over the ideal 50% or 2x safety factor) and they have never stalled out due to running torque. We are super repeatable; I took a 10um resultion (8um accuracy) linear encoder provided by balluff and did a series of studies, we were extremely repeatable on a C10 ballscrew actuator over 1000mm. I will have to pull that data out if I can find it.

    Ultimately, if your system is behaving the way you want it to at the settings that you have it at, then you've met your requirements (I just kind of repackaged what you said in this sentence here).

    I'm always up for a good discussion, good information here.
    Its funny you mentioned dsp. this is the first machine ive run with dsp drivers, It is two slaved drivers running my y and both do the same thing at 10x and above, Sorry you got me thinking that might have something to do with it. The fact they both do it the same and i have other axis same drivers running higher settings, i dont think it could be that.

    voltages all very stable, with surplus watts available with just the two 5a drivers set at 3.7a per 48v 800w psu so not there.

    Like i say they are on 20:1 reduction boxes, geared back up on the pinion but still a reduction good reduction and the errors im seeing are far too large to be magnetic backlash, at worst around 0.15mm.

    I have no other explanation than due to heavy load, the motors are at the top of there rated load range and are more susceptible to drops in torque, and that i am getting a drop. but then again motors stall at 8m/min, seeing issues at 5.5m/min. suppose this comes back to this holding vs stall torque and the drop is therefore just with holding torque?

    Going to have to stop thinking about this otherwise its going to drive me nuts

    Anyone got a torque wrench and and un unused motor they don't mind welding together?

    Last edited by Jon.N.CNC; 10-22-2015 at 05:55 PM.


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    Default Re: What effect does microstepping have on torque?

    Can anyone explain how motors/drivers compensate for inefficiency? I.e the heat the motors generate during Holding?

    Doesn't seem to be factored in to any of the papers I've read on torque and microstepping.

    Or is that because it's irrelevant?



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    Default Re: What effect does microstepping have on torque?

    Quote Originally Posted by Jon.N.CNC View Post
    Can anyone explain how motors/drivers compensate for inefficiency? I.e the heat the motors generate during Holding?

    Doesn't seem to be factored in to any of the papers I've read on torque and microstepping.

    Or is that because it's irrelevant?
    It's because they are operated exactly like a servo-mechanism and require the encoder as position feedback. When a position deviation is detected, then the compensator function applies current to the motor to go back to the intended position.

    Documentation, literature and theory of operation is kind of weak on the internet to be honest. This is because the use is typically commercial but is spreading into the consumer world. In the commercial and industrial applications these drivers are sold through distributors who are application experts.

    I had a copley controls stepnet driver setup with a stepper and encoder feedback. It requires software to tune your stepper motor, set some gains, set other parameters. It's cool to have a stepper powered up, and grab the shaft to rotate it and feel the driver compensate nearly on the fly to prevent that movement.

    I can never guarantee the operation of anything on ebay, but if you're interested in messing around with one of these drivers for a low price:
    Copley Controls Stepnet Digital Stepper Digital Drive Model STP 075 07 | eBay

    Then there's the chinese leadshine
    2PH 57mm Nema23 2 2nm 5A 1000LINE Encoder Closed Loop Stepper Motor Drive Kit | eBay
    DSP Closed Loop Step Motor Drive Kit 20 50VDC 3PH 4A 3nm Nema23 57mm Engraving | eBay

    not sure how tunable the above are, and I have no experience with them - the effort spending in making the above listings work might negate any benefit you get from them when all is said and done.



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    Quote Originally Posted by UA_Iron View Post
    It's because they are operated exactly like a servo-mechanism and require the encoder as position feedback. When a position deviation is detected, then the compensator function applies current to the motor to go back to the intended position.

    Documentation, literature and theory of operation is kind of weak on the internet to be honest. This is because the use is typically commercial but is spreading into the consumer world. In the commercial and industrial applications these drivers are sold through distributors who are application experts.

    I had a copley controls stepnet driver setup with a stepper and encoder feedback. It requires software to tune your stepper motor, set some gains, set other parameters. It's cool to have a stepper powered up, and grab the shaft to rotate it and feel the driver compensate nearly on the fly to prevent that movement.

    I can never guarantee the operation of anything on ebay, but if you're interested in messing around with one of these drivers for a low price:
    Copley Controls Stepnet Digital Stepper Digital Drive Model STP 075 07 | eBay

    Then there's the chinese leadshine
    2PH 57mm Nema23 2 2nm 5A 1000LINE Encoder Closed Loop Stepper Motor Drive Kit | eBay
    DSP Closed Loop Step Motor Drive Kit 20 50VDC 3PH 4A 3nm Nema23 57mm Engraving | eBay

    not sure how tunable the above are, and I have no experience with them - the effort spending in making the above listings work might negate any benefit you get from them when all is said and done.
    Thanks UA Iron, yes with a closed loop system it's almost an irelevant factor. It's more open loop systems where there is little feedback, In fact after writing that post I remembered how drivers, with dsp drivers doing this more often, measure motor inductance and trim output current acordingly to improve repeatability. I suppose this is how.



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    Default Re: What effect does microstepping have on torque?

    Microsteps per full-step Incremental holding torque per microstep
    1 100%
    2 70.71%
    4 38.27%
    8 19.51%
    16 9.80%
    32 4.91%
    64 2.45%
    128 1.23%
    256 0.61%



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What effect does microstepping have on torque?

What effect does microstepping have on torque?