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    Calibrating a large delta

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    Tuning and tweaking
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    • pabomanundefined
      paboman
      last edited by

      Hi,
      I am trying to calibrate a large delta printer with a printable radius of 500mm and a height of 1500mm
      doing the autocalibration at factor 6 I get : Calibrated 6 factors using 16 points, deviation before 0.016 after 0.013 which i think is good enough but when I run Mesh Grid compensation I get a very deformed mesh
      0_1527170584105_cal-results.jpg

      The bed.g file was created with the Escher wizard the I added the H value for each probe point, as you can see the deviation in H is quite large, I think this is due to tilted bed.

      ; bed.g
      ; called to perform automatic delta calibration via G32
      
      M561 ; clear any bed transform
      ; bed.g file for RepRapFirmware, generated by Escher3D calculator
      ; 16 points, 6 factors, probing radius: 500, probe offset (0, 0)
      ;The value of each H parameter should be (probe trigger height at that XY position) - (probe trigger height at centre of bed).
      
      G28
      G30 P0 X0.00 Y500.00 Z-99999 H3.298
      G30 P1 X321.39 Y383.02 Z-99999 H2.815
      G30 P2 X492.40 Y86.82 Z-99999 H2.305
      G30 P3 X433.01 Y-250.00 Z-99999 H1.957
      G30 P4 X171.01 Y-469.85 Z-99999 H0.956
      G30 P5 X-171.01 Y-469.85 Z-99999 H0.997
      G30 P6 X-433.01 Y-250.00 Z-99999 H2.687
      G30 P7 X-492.40 Y86.82 Z-99999 H3.444
      G30 P8 X-321.39 Y383.02 Z-99999 H3.585
      G30 P9 X0.00 Y250.00 Z-99999 H1.266
      G30 P10 X216.51 Y125.00 Z-99999 H0.899
      G30 P11 X216.51 Y-125.00 Z-99999 H0.254
      G30 P12 X0.00 Y-250.00 Z-99999 H-0.204
      G30 P13 X-216.51 Y-125.00 Z-99999 H0.565
      G30 P14 X-216.51 Y125.00 Z-99999 H1.423
      G30 P15 X0 Y0 Z-99999 S6
      

      The build plate is quite planar as I have checked it with a calibrated 1m steel straight edge tool and a filler gauge
      For sure the bed is tilted in some direction because my zprobe triggering height is not the same across the build plate while the repeatability is something like this :

      Stopped at height 12.008 mm
      Stopped at height 12.005 mm
      Stopped at height 12.009 mm
      Stopped at height 12.008 mm
      Stopped at height 12.007 mm
      Stopped at height 12.018 mm
      Stopped at height 12.011 mm
      Stopped at height 12.028 mm
      

      Bed rest on 6 points which can be regulated, I have tuned them to get it coplanar with the straight edge tool in 3 directions each parallel to X, Y and Z towers.

      The probe I am using is a very simple design, when triggered it close the signal to ground as the nozzle touch a metal piece under it of a know height ( 12mm = trigger height )

      0_1527172152476_probe.jpg

      Why my probed mesh is so deformed ? Am I missing something?

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      • denkeundefined
        denke
        last edited by denke

        From the looks of your bed mesh I'd say that you need to decrease the "delta radius".
        You should also check the steps/mm and diagonal rod length.

        The delta radius is the horizontal span of the delta rod from joint center to joint center when the carridge is centered.

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

          With the probe at the same XY coordinates as the nozzle, the trigger height should be the same all over the bed, so you should not need any H parameters.

          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

          pabomanundefined 1 Reply Last reply Reply Quote 0
          • pabomanundefined
            paboman @dc42
            last edited by

            @dc42
            I understand, do you agree that my in probing height difference is due to tilted bed ?

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

              @paboman said in Calibrating a large delta:

              @dc42
              I understand, do you agree that my in probing height difference is due to tilted bed ?

              Not necessarily, it could also be due to the endstop adjustments being out. The trigger height of the probe arrangement in your photo should not be sensitive to effector tilt.

              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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              • pabomanundefined
                paboman
                last edited by

                endstop are fixed on the top, optical type, but yes they can be triggered not at equal height

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

                  @paboman said in Calibrating a large delta:

                  endstop are fixed on the top, optical type, but yes they can be triggered not at equal height

                  That doesn't matter, calibration will correct the offsets. The main issue with the height map that you published is that one or more of the M665 rod length, the M665 delta radius and the M92 tower steps/mm is out by a large amount.

                  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

                  1 Reply Last reply Reply Quote 0
                  • pabomanundefined
                    paboman
                    last edited by

                    I will be able to measure steps/mm with a dial gauge but getting the rods length is quite problematic as they are theoretically long 1155mm, I measured them with a steel ruler...but I was unable to find a caliper that big

                    Do you think changing the calibration factor to 7 can get the rod length correct ?

                    1 Reply Last reply Reply Quote 0
                    • pabomanundefined
                      paboman
                      last edited by

                      I have corrected the R Radius manually to get the nozzle at the same height from the bed in the center as on the circumference of the printable area, then I run the Mesh Grid and get better result then my previous:

                      0_1527179534493_cal-results.jpg

                      Why the probed mesh is lower than the reference plane ?

                      Now I will measure if steps/mm are dialed in precisely

                      thanks again

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

                        That looks a lot better!

                        The probed mesh may be lower than the reference plane if your H parameter is not correct in the M665 command, or if you home the printer when mesh bed compensation is already applied (this is fixed in firmware 2.0RC5).

                        You should run delta calibration and mesh bed compensation at the same bed and hot end temperatures, in case thermal expansion has an effect.

                        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

                        pabomanundefined 1 Reply Last reply Reply Quote 0
                        • BenDieselundefined
                          BenDiesel
                          last edited by

                          If like to see bigger pic of the whole thing

                          1 Reply Last reply Reply Quote 0
                          • pabomanundefined
                            paboman @dc42
                            last edited by

                            @dc42

                            I have upgraded to the last RC5
                            Corrected my 640 step/mm as I was getting a real Z travel shorter by 3%
                            Done the automatic delta calibration and copied the values in the config.g, then run the Grid Mesh and now I am getting this mesh....something is wrong i will try to calibrate the radius by hand because before the result was more comfortable.
                            what do you think?

                            0_1527187708245_cal-results.jpg

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                            • dc42undefined
                              dc42 administrators
                              last edited by

                              Are you sure that you have the correct rod length, measured between bearing centres, in the M665 L parameter?

                              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

                              pabomanundefined 1 Reply Last reply Reply Quote 0
                              • pabomanundefined
                                paboman @dc42
                                last edited by

                                @dc42 I am pretty sure is right within half a millimeter
                                I am using magnetic rods articulated on 10mm steel spheres.

                                From one end of the sphere to the other end of the sphere is 1155mm - 10mm = 1145 (I am subtracting 5mm from each sphere as the centre of rotation is given by the radius of the 10mm sphere which is 5)

                                I am getting better result, or maybe its just an illusion, with the Radius manually adjusted instead of using the R values proposed by the automatic probing, why ?

                                0_1527192206703_cal-results.jpg

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

                                  Automatic calibration minimises the sums of the squares of the height errors. So for good results the probe points should cover all areas of the bed. How many probe points did you use, and how were they distributed?

                                  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

                                  1 Reply Last reply Reply Quote 0
                                  • pabomanundefined
                                    paboman
                                    last edited by

                                    the probing points are generated by the wizard using radius 500mm as input (for 1000mm printable area)

                                    0_1527193755489_probe-points.jpg

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                                    • Danalundefined
                                      Danal @paboman
                                      last edited by

                                      @paboman said in Calibrating a large delta:

                                      I am using magnetic rods articulated on 10mm steel spheres.

                                      From one end of the sphere to the other end of the sphere is 1155mm - 10mm = 1145 (I am subtracting 5mm from each sphere as the centre of rotation is given by the radius of the 10mm sphere which is 5)

                                      1145 sounds correct if YOU MEASURED 1155 to the "outer" part of the spheres.

                                      If you obtained a measurement from the manufacturer of your rods, they are NORMALLY labeled "joint center to joint center" and the subtraction would be incorrect.

                                      Delta / Kossel printer fanatic

                                      pabomanundefined 1 Reply Last reply Reply Quote 0
                                      • pabomanundefined
                                        paboman @Danal
                                        last edited by

                                        @danal they are manufactured by myself and yes 1155 mm is the distance between the outer part of the spheres 🙂

                                        Danalundefined 1 Reply Last reply Reply Quote 0
                                        • Danalundefined
                                          Danal @paboman
                                          last edited by

                                          @paboman said in Calibrating a large delta:

                                          @danal they are manufactured by myself and yes 1155 mm is the distance between the outer part of the spheres 🙂

                                          Excellent!!

                                          When it is convenient, it would be really cool to see some pictures. There's a few pics of my 600 Dia x 600 Z Delta if you scroll down on this blog:

                                          http://danalspub.com/

                                          Delta / Kossel printer fanatic

                                          1 Reply Last reply Reply Quote 0
                                          • pabomanundefined
                                            paboman
                                            last edited by paboman

                                            @dc42 To use the saved mesh grid I understand that I need to add G92 S1 in the config.g, is that right ?

                                            dc42undefined 1 Reply Last reply Reply Quote 0
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