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Stepper precision +-5%

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  • undefined
    arhi @A Former User
    last edited by 4 Jan 2021, 10:34

    @LB said in Stepper precision +-5%:

    @arhi
    I could send it to you

    I'd love to test it out but the problem is I fear sending it to me would be too expensive, our customs officers are not known for their kindness ๐Ÿ˜ž .. Where are you, maybe we can arrange something (I'm in Belgrade, Serbia)

    Providing step/dir is not a big deal, I have to do that for all the motors I will be testing too :), major problem I have is that none of my printers are operational as I could not get them up and running due to some injury (lasting more than a year ๐Ÿ˜ž ) so I got STL's to omni to print for me ..

    ? 1 Reply Last reply 4 Jan 2021, 15:17 Reply Quote 0
    • undefined
      JoergS5 @A Former User
      last edited by JoergS5 1 Apr 2021, 13:16 4 Jan 2021, 12:09

      @LB said in Stepper precision +-5%:

      the most with 2-phase openloop steppers!

      for 3D printers I agree with you, but I am also planning to build a CNC, and there servos are preferred.

      I would like to have information about how to best design the stepper - gear - belt/ball screw chain. E.g. when using full steps to avoid microstepping (microstepping only for noise reduction), then a big gear ratio => is this a good idea? And how big are the errors of the belts and pulleys in respect to the stepper and gear errors?

      Example:
      a) stepper with +-5%, no gear, 20 teeth pulley, GT2, turning 1.8 degree: stepper rotates between 1.71 and 1.89 degree, distance of belt between 0.19 and 0.21 mm => error 20 micrometer
      b) stepper with +-5%, 1:200 gear, 20 teeth pulley, GT2, turning 360 degree: the stepper rotates between 359.91 and 360.09 degree, which results in belt distance between 0.19995 and 0.20005 => error 0.1 micrometer
      Now the question, is the gear error bigger or smaller than the stepper's?

      ? undefined 2 Replies Last reply 4 Jan 2021, 15:15 Reply Quote 0
      • ?
        A Former User @JoergS5
        last edited by A Former User 1 Apr 2021, 15:41 4 Jan 2021, 15:15

        @JoergS5

        exactly what I am currently exploring! Letยดs crack this "nut"! (the biggest benefit of gearing is the torque you can gain beside the resolution IF accuracy of the belt can be guaranteed... -> Also the inertia lever is more beneficial because it increases/decreases ^2 if I remember correctly -> That is why most cncยดs use a 1:1,5 up to 1:5 belt for ohmp ๐Ÿ™‚ )
        -> But it might be wise to use also half-steps since those seem to be also quite accurate and pick a lower gearing to gain some end speed ๐Ÿ˜‰ otherwise you might need a higher voltage (external) stepper to gain end speed

        undefined 2 Replies Last reply 4 Jan 2021, 22:07 Reply Quote 0
        • ?
          A Former User @arhi
          last edited by A Former User 1 Apr 2021, 15:19 4 Jan 2021, 15:17

          @arhi said in Stepper precision +-5%:

          @LB said in Stepper precision +-5%:

          @arhi
          I could send it to you

          I'd love to test it out but the problem is I fear sending it to me would be too expensive, our customs officers are not known for their kindness ๐Ÿ˜ž .. Where are you, maybe we can arrange something (I'm in Belgrade, Serbia)

          Providing step/dir is not a big deal, I have to do that for all the motors I will be testing too :), major problem I have is that none of my printers are operational as I could not get them up and running due to some injury (lasting more than a year ๐Ÿ˜ž ) so I got STL's to omni to print for me ..

          Sorry to hear about your injury - all the best!
          Would ship from germany -> is there any reliable parcel service like UPS or DPD that would work?

          undefined 1 Reply Last reply 5 Jan 2021, 02:51 Reply Quote 0
          • undefined
            mendenmh @JoergS5
            last edited by mendenmh 1 Apr 2021, 22:01 4 Jan 2021, 21:57

            @JoergS5 One of the magical properties of belts such as the gt2/gt3 designs is that they are almost completely free of backlash. They are easy to make perform much better than gears. A HUGE amount of money was put into making these belts work for ink-jet printers and the like. I suspect that a belt-driven system will be much easier to make work with high precision than a gear-driven system. It only takes a tiny bit of backlash to drive a servo-system crazy, if you are planning on reversing direction very often.

            You still get to plan the reduction factors to work around microstepping defects, or at least make them easy to solve with a servo.

            Another advantage of belts is that you can pick any ratio you want, instead of always having to find relatively prime tooth combinations to even wear. You can also set the shaft spacing independently (nearly) of the reduction ratio, since you can get belts in a wide variety of lengths.

            Belts also engage much more of the circumference of the gear than you get in direct-geared systems. Thus, although one's first reaction is that belts aren't going to be as strong, it's no where near as big a factor as one might think. And belts with steel or glass backbones don't stretch very much as all.

            undefined 1 Reply Last reply 4 Jan 2021, 22:05 Reply Quote 0
            • undefined
              JoergS5 @mendenmh
              last edited by 4 Jan 2021, 22:05

              @mendenmh a belt driven gear is what I currently use:

              https://forum.duet3d.com/topic/20209/robot-type-1-45-cm-belt-gear-direct-drive-r0
              and especially
              https://forum.duet3d.com/topic/20209/robot-type-1-45-cm-belt-gear-direct-drive-r0/8

              The reason is exactly the low backlash. Only Harmonic and cycloidal drives is also very good in that respect, but difficult to DIY.

              1 Reply Last reply Reply Quote 0
              • undefined
                JoergS5 @A Former User
                last edited by 4 Jan 2021, 22:07

                @LB said in Stepper precision +-5%:

                might be wise to use also half-steps si

                I read somewhere that half steps are even more precise than the full steps. Torque is a different matter. I don't find the source of the information.

                undefined ? 2 Replies Last reply 5 Jan 2021, 02:57 Reply Quote 0
                • undefined
                  JoergS5 @A Former User
                  last edited by 4 Jan 2021, 22:19

                  @LB said in Stepper precision +-5%:

                  That is why most cncยดs use a 1:1,5 up to 1:5

                  I am a big fan of Mr. Mรถderl in the CNC area, who used belt gears with big pulleys 48/60. Big pulleys have more teeth connected with the pulley and can transfer more force. https://www.ems-moederl.de/ws201.html with the image https://www.ems-moederl.de/bau3/IMG_1141.jpg is nice.

                  1 Reply Last reply Reply Quote 0
                  • undefined
                    arhi @A Former User
                    last edited by 5 Jan 2021, 02:51

                    @LB said in Stepper precision +-5%:

                    Would ship from germany -> is there any reliable parcel service like UPS or DPD that would work?

                    dhl, dhl-express, fedex, ups ... they all work but can be rather expensive, I have best experiences with fedex so far ... we are "so close but so far away" ... EU all around us and we are the hole in the middle ๐Ÿ˜ž .. would be rather easy to organize the shipment in "normal times" as ton of ppl normally go from de to rs every day but due to the known issues we face now that transfer of ppl is not there any more... I'll ask around if I can find someone arriving soon but since holidays are "in progress" I think most who planned to arrive are already here, if I knew few weeks ago...

                    anyhow I have often access to these (and similar) encoders so we can do it in second batch if not now

                    ? 1 Reply Last reply 5 Jan 2021, 17:38 Reply Quote 0
                    • undefined
                      arhi @JoergS5
                      last edited by 5 Jan 2021, 02:57

                      @JoergS5 said in Stepper precision +-5%:

                      I read somewhere that half steps are even more precise than the full steps.

                      not sure how half step can be "more precise" than full step, but "same" might work... def way more precise than microsteppings. I was doing some halfstep+gearing on one mill platform (nema23 motors) and I didn't like it too much, while precision is much better than with microstepping (especially on those 3Nm motors where microstepping was heavily grouping around half and full step) the sound was terrible (imno 3-4times more loud than with microstepping) and there was a lot of vibrations during acceleration, took me a looooooooong time to configure the accel curve to get rid of vibrations... I had no backlash that I could measure on that machine (double ballnut for bot x and y and 30mm wide 5mm pitch belt between motor and ballscrew)

                      undefined 1 Reply Last reply 5 Jan 2021, 03:58 Reply Quote 0
                      • undefined
                        JoergS5 @arhi
                        last edited by JoergS5 1 May 2021, 04:16 5 Jan 2021, 03:58

                        @arhi said in Stepper precision +-5%:

                        not sure how half step can be "more precise" than full step,

                        the mode was half step and the positions alternate full step and half step. The half step positions were said to be better. If I remember right, the magnetic forces were higher for them. (only slightly)

                        Maybe http://users.ece.utexas.edu/~valvano/Datasheets/StepperHalfstep.pdf page two torque variations and higher current at the half step positions.

                        undefined 1 Reply Last reply 5 Jan 2021, 11:16 Reply Quote 0
                        • ?
                          A Former User @JoergS5
                          last edited by A Former User 1 May 2021, 17:37 5 Jan 2021, 10:13

                          @JoergS5 said in Stepper precision +-5%:

                          @LB said in Stepper precision +-5%:

                          might be wise to use also half-steps si

                          I read somewhere that half steps are even more precise than the full steps. Torque is a different matter. I don't find the source of the information.

                          I guess what you are referring to might be (please look up here https://www.zaber.com/w/Microstepping_Tutorial) :

                          old wave-stepping for full-stepping with only 1 phase on of course is torque-wise inferior to full-stepping with 2 phase on. So regarding the springiness of a position you would of course use 2-phase-on-fullstepping nowadays

                          BUT

                          If you use that with microstepping interpolation you get a "torque-square" on 1 full ยฐ electric rotation (4 full steps for a 2phase stepper) -> Most modern drivers DO NOT use that any more but rather have a "circular-torque" distribution for 1 electrical rotation (4 full steps for a 2phase stepper). People rather tend to go "torque-true" instead of an uneven torque-max, which makes sense in terms of vibrations/jitter or whatever you wanna call it.

                          The benefit of having an even torque will be the smoother run and that is part of the accuracy discussion here.

                          If the application needs higher torque I would rather go for a bigger motor then having an uneven torque distribution ๐Ÿ˜‰

                          Edit: Typed this when you already replied, but the BUT section might be of interest for you

                          1 Reply Last reply Reply Quote 0
                          • undefined
                            mendenmh @JoergS5
                            last edited by mendenmh 1 May 2021, 11:17 5 Jan 2021, 11:16

                            @JoergS5 Old stepper drivers that only did full and half step operations ran both coils at full current on the half steps. That might have resulted in better positioning, but the motors got hot as hades if you left them parked there. Modern sine/cosine microstepping drivers would have slightly higher (sqrt(2)) total current, split between the two windings, at the half step, but I would be surprised if this would be enough to really compensate for being away from the poles.

                            1 Reply Last reply Reply Quote 0
                            • undefined
                              JoergS5
                              last edited by JoergS5 1 May 2021, 17:27 5 Jan 2021, 17:26

                              You are probably both right, modern steppers and drivers will have changed all. The document I found seems to be very old.

                              Maybe the best approach is to build a test station, measure and compare different solutions, then select the best for the requirement. I wished there were better books about measuring. I have problems finding good sources how to use dial gauges etc.

                              1 Reply Last reply Reply Quote 0
                              • ?
                                A Former User @arhi
                                last edited by 5 Jan 2021, 17:38

                                @arhi said in Stepper precision +-5%:

                                anyhow I have often access to these (and similar) encoders so we can do it in second batch if not now

                                Sounds good - letยดs wait for a time to do this when almost nobody speaks any more about coron...

                                1 Reply Last reply Reply Quote 1
                                • undefined
                                  arhi @JoergS5
                                  last edited by 11 Jan 2021, 14:37

                                  @JoergS5 said in Stepper precision +-5%:

                                  BTW think of me at 11th, this is my birthday.

                                  happy birthday ๐Ÿ˜„

                                  Unfortunately, I did not do anything with this yet. I managed to find some code that simulates profibus slave but I'm having issues making code that simulates master in order to talk with this encoder. My profibus adapter is missing, ordered a new one but I doubt it will arrive quickly ๐Ÿ˜ž (not yet sent by the seller)... Still working on getting the master code to work but I have to slow down since today as ... work ๐Ÿ˜ž

                                  undefined undefined 2 Replies Last reply 11 Jan 2021, 21:50 Reply Quote 0
                                  • undefined
                                    JoergS5 @arhi
                                    last edited by 11 Jan 2021, 21:50

                                    @arhi thank you!

                                    Improving precision is a continuous process, so take your time. Unfortunately, I don't know Profibus yet, I cannot help you.

                                    undefined 1 Reply Last reply 12 Jan 2021, 10:56 Reply Quote 0
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                                      mendenmh @arhi
                                      last edited by 12 Jan 2021, 01:54

                                      @arhi There seems to be a python package which can be a profibus master:

                                      https://pypi.org/project/pyprofibus/

                                      undefined 2 Replies Last reply 12 Jan 2021, 10:54 Reply Quote 0
                                      • undefined
                                        arhi @mendenmh
                                        last edited by 12 Jan 2021, 10:54

                                        @mendenmh thanks that's awesome, testing immediately ๐Ÿ˜„

                                        1 Reply Last reply Reply Quote 0
                                        • undefined
                                          arhi @JoergS5
                                          last edited by 12 Jan 2021, 10:56

                                          @JoergS5 said in Stepper precision +-5%:

                                          Improving precision is a continuous process, so take your time.

                                          yeah but I can't keep the encoder indefinitely ๐Ÿ˜ž .. this one will have to go back in a week or two ... I'll get another one next time they get a new order for few weeks again but it's not something I have on a shelf forever ๐Ÿ˜ž (these things go into some nasty military equipment made to do some ugly military stuff)

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