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    Is it possible to slow a stepper using stall detection?

    Scheduled Pinned Locked Moved
    Using Duet Controllers
    stall detection compression molding
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    • MortarArtundefined
      MortarArt
      last edited by

      I've got an application where I'd like to use a stepper driven axis to compress melted plastic within a mold, and as I've already got some Duets, I thought I could drive the ram via a stepper and instead of stopping or rehoming as would be done on a printer, I could reduce speed to maintain a steady current draw.

      Is this out of the realm of possibility and achievable with current firmware?

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      • MortarArtundefined
        MortarArt
        last edited by

        @mortarart Side question; on the Wiki at; https://duet3d.dozuki.com/Wiki/Choosing_and_connecting_stepper_motors

        It notes that you should use 32v power for the Duet 3 and larger stepper motors like Nema23 and Nema34. Why is 24v insufficient?

        zaptaundefined 1 Reply Last reply Reply Quote 0
        • zaptaundefined
          zapta @MortarArt
          last edited by zapta

          Building current level in the motor coil takes time, and if you run a stepper at a higher current, the higher voltage compensate for that (assuming same inductance and same max steps/sec). If you don't care about high rotation speed, 24V should probably do.

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          • rjenkinsgbundefined
            rjenkinsgb
            last edited by

            I very much doubt it; by the time a stall is detected by the driver IC, it's probably already losing steps and the position would be lost. It's not intended for that type of use.

            However, if position tracking is not important, you could just set a reduced driver/motor current using M913 whilst in that mode to whatever percentage is needed so the motor provides the required torque and run it continuously.
            https://reprap.org/wiki/G-code#M913:_Set_motor_percentage_of_normal_current

            It would be slipping step-wise but providing a steady force to the axis.
            Then re-home it after the process is complete, if position is important, or start / stop it as needed, something like an extruder?

            Robert J.

            Printers: Overlord pro, Kossel XL+ with Duet 6HC and "Frankentron", TronXY X5SA Pro converted to E3D toolchange with Duet 6HC and 1LC toolboards.

            MortarArtundefined 1 Reply Last reply Reply Quote 0
            • MortarArtundefined
              MortarArt @rjenkinsgb
              last edited by

              @rjenkinsgb position shouldn't be important during the ramming procedure. Only for the start of and end of the ram, which can be set using end stops!

              So I think you've confirmed that this indeed useful to me. Thank you.

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              • rjenkinsgbundefined
                rjenkinsgb
                last edited by

                The only other thing to beware of is that the motor is kept below the speed it can start instantly from.

                If it stalls or "slips" at above that speed, it may never restart, as the acceleration ramps that allow higher speed only occur when the control system starts & stops the motor.

                Robert J.

                Printers: Overlord pro, Kossel XL+ with Duet 6HC and "Frankentron", TronXY X5SA Pro converted to E3D toolchange with Duet 6HC and 1LC toolboards.

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