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    Z-Probe granularity

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    • kraegarundefined
      kraegar
      last edited by

      I've noticed my z-probe results tend to land only on full step values, is this typical?

      If I run a series of probes, the increments between any two results is also 0.012mm (My step size is 0.0125).

      Just want to be sure that's expected behavior, and if not, what settings I should investigate to change it? I'm using 16i microstepping, but increasing that doesn't change the results I get. This is when doing repeated G30 S-1 on a delta, to check accuracy and repeatability of my piezo probe.

      Thanks!

      Co-Creator of the RailcoreII CoreXY printer
      https://www.thingiverse.com/thing:2407174

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      • dc42undefined
        dc42 administrators
        last edited by

        The firmware only knows the head position to the nearest microstep. I'm guessing that you have a delta printer with 1.8deg motors and 20 tooth pulleys.

        If you increase microstepping then you may possibly see the resolution improve - it all depends on how friction-free your mechanics is. Doubling the microstepping to 32x reduces the torque per microstep by almost 50%, so you may need 2 microsteps to overcome the friction. Higher motor current may help. The other ways of getting better resolution are to use smaller pulleys (e.g. 16 tooth will improve it to 0.01mm) or 0.9deg motors (which will halve 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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        • kraegarundefined
          kraegar
          last edited by

          Thanks David - sounds like I'm seeing the expected behavior, which is what I was really after.

          I may convert over to 0.9 steppers at some point (and 24v at the same time) but I just wanted to confirm what I was seeing is what I should be seeing. I haven't seen an improvement from increasing the microstepping, it still gives results in the same increments in my tests. That's all fine, as long as it's what it's supposed to do.

          There's only one step worth of variation in my tests currently, at any rate. Here's my last round of testing, which seems pretty reasonable.

          12:28:25 PMStopped at height 0.002 mm
          12:28:22 PMStopped at height 0.002 mm
          12:28:18 PMStopped at height 0.002 mm
          12:28:15 PMStopped at height 0.002 mm
          12:28:11 PMStopped at height 0.002 mm
          12:28:07 PMStopped at height 0.002 mm
          12:28:04 PMStopped at height 0.002 mm
          12:28:00 PMStopped at height 0.002 mm
          12:27:56 PMStopped at height 0.002 mm
          12:27:53 PMStopped at height 0.002 mm
          12:27:49 PMStopped at height 0.002 mm
          12:27:45 PMStopped at height 0.002 mm
          12:27:42 PMStopped at height 0.002 mm
          12:27:38 PMStopped at height 0.002 mm
          12:27:35 PMStopped at height 0.002 mm
          12:27:31 PMStopped at height 0.002 mm
          12:27:28 PMStopped at height 0.002 mm
          12:27:24 PMStopped at height 0.002 mm
          12:27:20 PMStopped at height 0.014 mm
          12:27:16 PMStopped at height 0.014 mm
          12:27:13 PMStopped at height 0.014 mm
          12:27:09 PMStopped at height 0.014 mm
          12:27:06 PMStopped at height 0.014 mm
          12:27:02 PMStopped at height 0.014 mm
          12:26:58 PMStopped at height 0.014 mm
          12:26:55 PMStopped at height 0.002 mm
          12:26:51 PMStopped at height 0.002 mm
          12:26:47 PMStopped at height 0.002 mm
          12:26:44 PMStopped at height 0.002 mm
          12:26:40 PMStopped at height 0.002 mm
          12:26:36 PMStopped at height 0.002 mm
          12:26:33 PMStopped at height 0.002 mm
          12:26:29 PMStopped at height 0.014 mm
          12:26:26 PMStopped at height 0.002 mm
          12:26:22 PMStopped at height 0.002 mm
          12:26:18 PMStopped at height 0.002 mm
          12:26:15 PMStopped at height 0.002 mm
          12:26:11 PMStopped at height 0.002 mm
          12:26:07 PMStopped at height 0.002 mm
          12:26:04 PMStopped at height 0.002 mm
          12:26:00 PMStopped at height 0.002 mm
          12:25:57 PMStopped at height 0.014 mm
          12:25:53 PMStopped at height 0.014 mm
          12:25:49 PMStopped at height 0.014 mm
          12:25:46 PMStopped at height 0.014 mm
          12:25:42 PMStopped at height 0.014 mm
          12:25:38 PMStopped at height 0.014 mm
          12:25:35 PMStopped at height 0.014 mm
          12:25:31 PMStopped at height 0.014 mm
          12:25:28 PMStopped at height 0.014 mm

          Co-Creator of the RailcoreII CoreXY printer
          https://www.thingiverse.com/thing:2407174

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          • dc42undefined
            dc42 administrators
            last edited by

            I am somewhat surprised that you never see the values from intermediate microsteps. Please confirm that you are using a Duet WiFi or Duet Ethernet, not the older Duet 0.6 or 0.8.5. Also, after setting microstepping to something higher than x16, please run M350 with no parameters to check that the microstepping really has been changed.

            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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            • kraegarundefined
              kraegar
              last edited by

              This is a duet wifi, running 1.18

              I'll test that now and report back.

              Co-Creator of the RailcoreII CoreXY printer
              https://www.thingiverse.com/thing:2407174

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              • kraegarundefined
                kraegar
                last edited by

                Ok, I set it to 32 steps for x/y/z, homed, and then re-ran my test. I am seeing results smaller than a full step now. Perhaps I'd done something wrong in my past tests, it's been a while since I tried that.

                5:24:18 PMStopped at height 0.012 mm
                5:24:15 PMStopped at height 0.005 mm
                5:24:11 PMStopped at height 0.005 mm
                5:24:07 PMStopped at height 0.005 mm
                5:24:04 PMStopped at height 0.012 mm
                5:24:00 PMStopped at height 0.012 mm
                5:23:56 PMStopped at height 0.012 mm
                5:23:53 PMStopped at height 0.012 mm
                5:23:49 PMStopped at height 0.005 mm
                5:23:45 PMStopped at height 0.005 mm
                5:23:42 PMStopped at height 0.005 mm
                5:23:38 PMStopped at height 0.012 mm
                5:23:35 PMStopped at height 0.012 mm
                5:23:31 PMStopped at height 0.012 mm
                5:23:27 PMStopped at height 0.012 mm
                5:23:24 PMStopped at height 0.012 mm
                5:23:20 PMStopped at height 0.012 mm
                5:23:17 PMStopped at height 0.012 mm
                5:23:13 PMStopped at height 0.012 mm
                5:23:09 PMStopped at height 0.005 mm
                5:23:06 PMStopped at height 0.012 mm
                5:23:02 PMStopped at height 0.012 mm
                5:22:59 PMStopped at height 0.012 mm
                5:22:55 PMStopped at height 0.012 mm
                5:22:51 PMStopped at height 0.012 mm
                5:22:48 PMStopped at height 0.018 mm
                5:22:44 PMStopped at height 0.018 mm
                5:22:40 PMStopped at height 0.018 mm
                5:22:37 PMStopped at height 0.012 mm
                5:22:33 PMStopped at height 0.012 mm
                5:22:29 PMStopped at height 0.012 mm
                5:22:26 PMStopped at height 0.012 mm

                Co-Creator of the RailcoreII CoreXY printer
                https://www.thingiverse.com/thing:2407174

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