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Using stepper currrent to detect a tool is loaded

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  • undefined
    GeneRisi
    last edited by 29 Apr 2021, 15:37

    Is there any way to ask the stepper controller on the Duet2 how much current was last used to move the stepper? I am wondering whether I can use it as a way to compare free rotation (no tool loaded on the e3d tool changer) vs rotation with friction (tool loaded)?
    Thanks!

    undefined 1 Reply Last reply 29 Apr 2021, 23:53 Reply Quote 0
    • undefined
      zapta @GeneRisi
      last edited by 29 Apr 2021, 23:53

      @generisi, I believe that the current is the same regardless of the mechanical load.

      undefined 1 Reply Last reply 30 Apr 2021, 08:13 Reply Quote 0
      • undefined
        dc42 administrators @zapta
        last edited by 30 Apr 2021, 08:13

        @zapta said in Using stepper currrent to detect a tool is loaded:

        @generisi, I believe that the current is the same regardless of the mechanical load.

        Correct, the drivers are constant current. However, the drivers do contain a means to measure load. The M122 report includes the load measurement, it's the SG values in the driver reports. The SG values get reset each time M122 is run.

        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

        undefined 1 Reply Last reply 1 May 2021, 02:29 Reply Quote 0
        • undefined
          GeneRisi @dc42
          last edited by 1 May 2021, 02:29

          @dc42 Are the SG values available in the object model ( if that's the right terminology )? I am running RRF 3.3b3 right now.

          undefined 1 Reply Last reply 1 May 2021, 13:15 Reply Quote 0
          • undefined
            dc42 administrators @GeneRisi
            last edited by 1 May 2021, 13:15

            @generisi said in Using stepper currrent to detect a tool is loaded:

            @dc42 Are the SG values available in the object model ( if that's the right terminology )? I am running RRF 3.3b3 right now.

            No they are not.

            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

            undefined 1 Reply Last reply 1 May 2021, 13:34 Reply Quote 0
            • undefined
              rzi @dc42
              last edited by 1 May 2021, 13:34

              @dc42 CNC user here. Is it possible to add. I'm using two free drivers for a motorised vise. Would be super to have a mean of applying same force on each part I'm machining.

              undefined undefined 2 Replies Last reply 1 May 2021, 13:44 Reply Quote 0
              • undefined
                dc42 administrators @rzi
                last edited by dc42 5 Jan 2021, 13:44 1 May 2021, 13:44

                @rzi I suggest you check whether the stallGuard values (as reported by M122) are useful first. I doubt that the instantaneous values would be useful. The values reported by M122 are the min and max values since M122 was last run. If we did add them to the OM then we would need to decide what period of time to sample them over, and whether to report an average or the min/max values over that period.

                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

                undefined 1 Reply Last reply 2 May 2021, 18:55 Reply Quote 1
                • undefined
                  fma @rzi
                  last edited by 2 May 2021, 06:33

                  @rzi said in Using stepper currrent to detect a tool is loaded:

                  @dc42 CNC user here. Is it possible to add. I'm using two free drivers for a motorised vise. Would be super to have a mean of applying same force on each part I'm machining.

                  You could set the current of the vise motor to set the wanted force (torque). Then, just turn the motor until it stalls (using stallGuard feature, through a homing procedure, for example), and you should get roughly the same force each time.

                  Frédéric

                  undefined 1 Reply Last reply 3 May 2021, 06:29 Reply Quote 0
                  • undefined
                    GeneRisi @dc42
                    last edited by GeneRisi 5 Jun 2021, 12:32 2 May 2021, 18:55

                    @dc42 In my case the SG values are useful (for the E3D tool changer coupler stepper). If I had a gcode command that would clear any min and max values in the object model and begin sampling and another gcode command would set the min and max values in the object model, then I could do whatever I want to measure between the two gcode commands. This behavior is almost identical to the M122 behavior. It might also be useful to include a "start sampling" time stamp and an "end sampling" time stamp.

                    What do you think ?

                    1 Reply Last reply Reply Quote 0
                    • undefined
                      rzi @fma
                      last edited by 3 May 2021, 06:29

                      @fma said in Using stepper currrent to detect a tool is loaded:

                      @rzi said in Using stepper currrent to detect a tool is loaded:

                      @dc42 CNC user here. Is it possible to add. I'm using two free drivers for a motorised vise. Would be super to have a mean of applying same force on each part I'm machining.

                      You could set the current of the vise motor to set the wanted force (torque). Then, just turn the motor until it stalls (using stallGuard feature, through a homing procedure, for example), and you should get roughly the same force each time.

                      Ah yes, going to test that. A much more straight forward approach. Thanx

                      1 Reply Last reply Reply Quote 0
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