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    Motor stall detection as Z probe

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    • Shenundefined
      Shen
      last edited by

      I've successfully tuned my motor stall detection to work reliably on the z axis. The precision and repeatability is more than enough. Is it possible to configure motor stall detection as Z probe?

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      • dc42undefined
        dc42 administrators
        last edited by

        The resolution of stall detection is +/- 1 full step at best. If you had a high steps/mm then you might get sufficient resolution, for example 2000 steps/mm @ x16 microstepping would give you (16/2000)mm = 8um resolution. But then at a high steps/mm the force with which the motor drives the nozzle into the bed would be high even with reduced motor current. So I doubt that it is possible. But I haven't tried it.

        Duet WiFi hardware designer and firmware engineer
        Please do not ask me for Duet support via PM or email, use the forum
        http://www.escher3d.com, https://miscsolutions.wordpress.com

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        • Shenundefined
          Shen
          last edited by

          Each full step of the motor translate to 0.05mm z movement in my case. I've lowered the z acceleration to 100 and used the most sensitive stall detection threshold value and lowest motor current possible. The nozzle does not leave any mark on my PEI sheet. and it only left a small mark on the surface of an ABS print, so I'm not too concerned by the force.
          I'd love to be able to config it as a Z probe. Since even though my ir sensor is extreamly precise under the same condition, the trigger distance varies for different bed material(I'm using buildtak flexplate), for different temperatures, and even for different spot on the PEI sheet I coated with ABS juice using a brush. The difference could be as high as 0.3mm in some cases.

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          • dc42undefined
            dc42 administrators
            last edited by

            Are you saying that you have motor stall working as a Z endstop, assuming of course that you position the nozzle over the bed when homing Z? If so then I'll look at adding a another Z probe type that monitors the Z motor stall. You would still need to reduce the motor current during probing and restore it again afterwards, but I guess that could be done in the deploy and retract files.

            Duet WiFi hardware designer and firmware engineer
            Please do not ask me for Duet support via PM or email, use the forum
            http://www.escher3d.com, https://miscsolutions.wordpress.com

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            • Shenundefined
              Shen
              last edited by

              Yes that's correct. I'm using motor stall as Z endstop.
              https://youtu.be/asz7eWImvFY

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              • dc42undefined
                dc42 administrators
                last edited by

                Ok, I'll add this in 2.0alpha as an experimental feature. It will be Z probe type 10.

                Duet WiFi hardware designer and firmware engineer
                Please do not ask me for Duet support via PM or email, use the forum
                http://www.escher3d.com, https://miscsolutions.wordpress.com

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                • dragonnundefined
                  dragonn
                  last edited by

                  Does stall detection works when using two motors connected to one driver? Z probing with stall detection is just a brilliant idea!

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                  • dc42undefined
                    dc42 administrators
                    last edited by

                    It probably won't work as well that way because the drop in back emf of the motor that stalls will be attenuated by the other one. But worth trying. If your E1 driver is free then you can connect the second motor to that instead. Stall detection monitors all drivers for an axis.

                    Duet WiFi hardware designer and firmware engineer
                    Please do not ask me for Duet support via PM or email, use the forum
                    http://www.escher3d.com, https://miscsolutions.wordpress.com

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                    • Phaedruxundefined
                      Phaedrux Moderator
                      last edited by

                      This is interesting. I have very high steps on my Z axis. 3200, giving 0.005mm for a single step. That's better than the repeatability I'm getting from the BLTouch.

                      @Shen Would you mind sharing how you have it configured?

                      Z-Bot CoreXY Build | Thingiverse Profile

                      DjDemonDundefined 1 Reply Last reply Reply Quote 0
                      • Shenundefined
                        Shen
                        last edited by

                        [[language]]
                        M913  Z30:30 ; Reduce current
                        M201 Z100; Reduce acceleration
                        M915 P1:2 S1 F0; Set stall detection threshold (you don't need this if you have it in config.g file)
                        
                        G91
                        G1 S1 Z-210 F600 ; probe
                        G90
                        
                        M201 Z1250 ; Restore acceleration
                        M913 Z50:50; Restore current
                        
                        G92 Z0
                        G1 Z0.4 F3600; Stall triggers at -0.4mm, raise nozzle by 0,4mm.
                        G92 Z0
                        
                        ```Here is my code for z probe. The exact configuration would probably be different between each setup. You'll need to look for a setup that trigger the stall detection with the lowest impact force between the bed and the nozzle. Here is how I figured out mine:
                        First you need to lower your Z acceleration so stall detection won't trigger due to the force of z acceleration.
                        Then you need to figure out the lowest current that stall detection works reliably(M913). I found my motor moves reliably at 20% current, but stall detection works reliably at 30% current.
                        Then find the lowest stall detection thresh hold(M915). Mine is 1\. To avoid damage your printer always start with low values that would trigger the stall detection immediately, and increase the value until you can move the z axis.
                        You might also want to find the lowest speed as well to further reduce the impact force, but I just used F600.
                        Change any of the current, stall detection thresh hold and speed will probably effect the other 2\. You need to find a combination that works reliably and has the lowest impact force. To determine the impact force, I put a piece of print between the nozzle and the bed, and check the mark left by the nozzle after impact.
                        I don't have a spring under my bed, this might now work for you if you have a soft sprint under the bed.
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                        • DjDemonDundefined
                          DjDemonD @Phaedrux
                          last edited by

                          @phaedrux said in Motor stall detection as Z probe:

                          This is interesting. I have very high steps on my Z axis. 3200, giving 0.005mm for a single step. That's better than the repeatability I'm getting from the BLTouch.

                          @Shen Would you mind sharing how you have it configured?

                          This is what I wondered about. It's not, according to what I read about it here when the stall detect and sensorless homing was first included microsteps, it's full motor steps.

                          This is why I am wondering how this can work well. My delta (0.9deg steppers and 16t pulleys) is 200 (micro)steps/mm, but this is at 1/16th so its 12.5 full steps/mm which is 80 microns per step! That's quite a big chunk given we are getting (upto) 5 micron accuracy using the Orion Z-probe.

                          However I might try it.

                          Simon. Precision Piezo Z-Probe Technology
                          www.precisionpiezo.co.uk
                          PT1000 cartridge sensors NOW IN, just attach to your Duet board directly!

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                          • Mystaundefined
                            Mysta
                            last edited by

                            I'm going to try on my 1.5m delta as well, I will probably probe each print since so far most of my prints take forever anyway so why not.

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                            • dc42undefined
                              dc42 administrators
                              last edited by

                              I have implemented this as Z probe type 10 in the latest build of firmware 2.0alpha. I've a few more things to test and at least one thing to fix before I do another 2.0alpha release.

                              Duet WiFi hardware designer and firmware engineer
                              Please do not ask me for Duet support via PM or email, use the forum
                              http://www.escher3d.com, https://miscsolutions.wordpress.com

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                              • Shenundefined
                                Shen
                                last edited by

                                This would probably not work very well on deltas. If you use 5mm pitch screw with 0.9 degree stepper on Z axis, each full step is only 0.0125mm.

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                                • dc42undefined
                                  dc42 administrators @Shen
                                  last edited by

                                  @shen said in Motor stall detection as Z probe:

                                  This would probably not work very well on deltas. If you use 5mm pitch screw with 0.9 degree stepper on Z axis, each full step is only 0.0125mm.

                                  That's right, it will only work when the Z steps/mm is high enough so that one full step provides sufficient resolution, but low enough that the motor stall can be detected before too much force is applied between the nozzle and the bed.

                                  Duet WiFi hardware designer and firmware engineer
                                  Please do not ask me for Duet support via PM or email, use the forum
                                  http://www.escher3d.com, https://miscsolutions.wordpress.com

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                                  • Mystaundefined
                                    Mysta
                                    last edited by

                                    Oops must have followed a link and forgot, was referring to endstop not probe. Have smart Effector for probing.

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                                    • DjDemonDundefined
                                      DjDemonD
                                      last edited by

                                      It works fine for endstops, but because it is not very accurate, and I can confirm this having an endstop-less delta running, you need to auto-calibrate after each homing or you will not have an accurate enough calibration to print. Not a particularly big problem, but it highlights that it won't work for most deltas as a z-probe. My cylinder delta is 400steps/mm as it is leadscrew driven on XYZ but this is still only a 40-microns-accuracy z probe which is a good factor of 4-8 out on a smart effector or piezo probe.

                                      Simon. Precision Piezo Z-Probe Technology
                                      www.precisionpiezo.co.uk
                                      PT1000 cartridge sensors NOW IN, just attach to your Duet board directly!

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                                      • Mystaundefined
                                        Mysta @DjDemonD
                                        last edited by

                                        @djdemond said in Motor stall detection as Z probe:

                                        It works fine for endstops, but because it is not very accurate, and I can confirm this having an endstop-less delta running, you need to auto-calibrate after each homing or you will not have an accurate enough calibration to print. Not a particularly big problem, but it highlights that it won't work for most deltas as a z-probe. My cylinder delta is 400steps/mm as it is leadscrew driven on XYZ but this is still only a 40-microns-accuracy z probe which is a good factor of 4-8 out on a smart effector or piezo probe.

                                        Yeah I'm excited to try out the smart effector, my arms finally arriving today. 500mm from Haydn. Do you have your calibrate script for endstop less? I definitely don't mind probing each print.

                                        dc42undefined 1 Reply Last reply Reply Quote 0
                                        • dc42undefined
                                          dc42 administrators @Mysta
                                          last edited by dc42

                                          @mysta said in Motor stall detection as Z probe:

                                          Yeah I'm excited to try out the smart effector, my arms finally arriving today. 500mm from Haydn. Do you have your calibrate script for endstop less? I definitely don't mind probing each print.

                                          For a script to home a delta without endstops, see the example macro file towards the end of https://duet3d.dozuki.com/Wiki/Stall_detection_and_sensorless_homing#Section_Configuring_sensorless_homing. This file is for testing homing without endstops. For actual use as a homing file you could simplify it. For example, you don't need the M574 commands to change the endstop type because you can just set stall detect endstops in config.g if that's the only type of endstop you ever use.

                                          Duet WiFi hardware designer and firmware engineer
                                          Please do not ask me for Duet support via PM or email, use the forum
                                          http://www.escher3d.com, https://miscsolutions.wordpress.com

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                                          • Mystaundefined
                                            Mysta
                                            last edited by

                                            Thanks, I'll start from there. I left the endstops on my frame just in case but I'm really interested in using some of the new functionality of the 2660

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