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Is Stall detection a reliable safety feature w/ MB6HC

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  • undefined
    3DPMicro
    last edited by 3DPMicro 3 Apr 2021, 03:42 4 Mar 2021, 03:40

    Working through a new printer design which if the Z axis were to run away for some reason or a dumb thumb ocurred could cause serious damage. Probably will implement some type of break away or pin shearing feature incase but redundancy would also be nice too so would stall guard be an option. To give perspective the Z will be actuated by 2 mema 23's - 2.5v, 2.8a, 4.5mh, 1.26nm .9deg driving 2mm lead ball screws up to possibly 500 rpm....so lots of force multiplication and potential carnage.

    Duet controlled Lathe, micro mill, 3d printer and 1992 Haas VF2 VMC

    undefined 1 Reply Last reply 8 Mar 2021, 05:27 Reply Quote 0
    • undefined
      Phaedrux Moderator
      last edited by 4 Mar 2021, 04:15

      Is Stall detection a reliable safety feature

      safety? 😕 I would say no.

      The force multiplication would be a downside making the back emf tricky, but on the plus side, the high rotational speed might help. Really only one way to know for sure is to try and configure it and see what happens.

      I've actually been using stall guard for probing my Z axis lately. Originally because the bltouch pin broke, but I've left it in place because it works pretty reliably and consistently. 2mm lead screw, 2:1 reduction, and high steps per mm, high rpm. Just nema17 though and I don't use it during a print, just homing.

      It is a bit tricky to tune, and you do have to let it crash into something, so not for the weak willed or those with good judgement.

      Z-Bot CoreXY Build | Thingiverse Profile

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      • undefined
        3DPMicro
        last edited by 5 Mar 2021, 04:37

        Thanks for the input and good point on the torque multiplication reducing sensitivity. That reminded me, I think I asked a similar question regarding stall guard a couple years ago. Forgot until now.
        I may experiment with a cheap 2mm lead screw and bang on that to see if it can be tuned. Regardless its probably best to have some form of mechanical fail safe.
        Probably not a bad idea for folks to check out this little calculator that quickly gives you force using a ball or lead screw for any axis. It can get nutz with low lead numbers
        https://www.lintechmotion.com/sizing/Thrust-Force/thrust-inputs.php

        Duet controlled Lathe, micro mill, 3d printer and 1992 Haas VF2 VMC

        undefined 1 Reply Last reply 5 Mar 2021, 08:13 Reply Quote 0
        • undefined
          deckingman @3DPMicro
          last edited by 5 Mar 2021, 08:13

          @3DPMicro Another problem with stall guard is that it can be affected by motor temperature, which can make it unreliable. Dropping the motor current when homing can also be a useful safety feature to implement (and it's free and easy to do).

          Ian
          https://somei3deas.wordpress.com/
          https://www.youtube.com/@deckingman

          undefined 1 Reply Last reply 7 Mar 2021, 20:47 Reply Quote 0
          • undefined
            3DPMicro
            last edited by 6 Mar 2021, 15:43

            @deckingman said in [Is Stall detection a reliable safety feature Dropping the motor current when homing can also be a useful safety feature to implement (and it's free and easy to do).

            I use that technique on my Duet 2 micro mill. I'll make a note to implement that in 3.

            Duet controlled Lathe, micro mill, 3d printer and 1992 Haas VF2 VMC

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            • undefined
              Phaedrux Moderator
              last edited by 6 Mar 2021, 16:30

              One problem I had in tuning stall detection for homing is that I had to lower the current LESS than I was because it would stall too easily. It's a balancing act.

              Plus if you intend to use stall detection during an actual job operation you're tuning for a different current entirely.

              Z-Bot CoreXY Build | Thingiverse Profile

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              • undefined
                hackinistrator
                last edited by 6 Mar 2021, 17:56

                i'm in the same boat . my current (not yet implemented) solution is to use 3 optical switches . 2 switches close to the edge of the axis on each side (around 10mm before dead stop) , another switch for homing which will be approx 30mm of the edge , before the "edge switch".

                2 edge switches should never be triggered , and will be connected to EMO / power disconnect of some sort .

                undefined 1 Reply Last reply 7 Mar 2021, 21:18 Reply Quote 0
                • undefined
                  3DPMicro @deckingman
                  last edited by 3DPMicro 3 Jul 2021, 21:07 7 Mar 2021, 20:47

                  double post

                  Duet controlled Lathe, micro mill, 3d printer and 1992 Haas VF2 VMC

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                  • undefined
                    3DPMicro
                    last edited by 3DPMicro 3 Jul 2021, 21:11 7 Mar 2021, 21:03

                    My main concern is the 2 motors getting out of sync (Z axis) or 1 running and 1 not. I recently had that happen on another machine and it tore stuff up big time before I could stop it and that's what got me thinking. This new build has way more power but that's an unwanted byproduct of trying to have an insanely accurate and repeatable Z

                    Duet controlled Lathe, micro mill, 3d printer and 1992 Haas VF2 VMC

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                    • undefined
                      Phaedrux Moderator
                      last edited by 7 Mar 2021, 21:04

                      stacked optical switches seems like a viable option?

                      Z-Bot CoreXY Build | Thingiverse Profile

                      undefined 1 Reply Last reply 7 Mar 2021, 21:21 Reply Quote 0
                      • undefined
                        3DPMicro @hackinistrator
                        last edited by 7 Mar 2021, 21:18

                        @hackinistrator said in Is Stall detection a reliable safety feature w/ MB6HC:

                        i'm in the same boat . my current (not yet implemented) solution is to use 3 optical switches . 2 switches close to the edge of the axis on each side (around 10mm before dead stop) , another switch for homing which will be approx 30mm of the edge , before the "edge switch".

                        2 edge switches should never be triggered , and will be connected to EMO / power disconnect of some sort .

                        That would only work close to "home" though. Correct?

                        Duet controlled Lathe, micro mill, 3d printer and 1992 Haas VF2 VMC

                        undefined 1 Reply Last reply 8 Mar 2021, 20:41 Reply Quote 0
                        • undefined
                          3DPMicro @Phaedrux
                          last edited by 7 Mar 2021, 21:21

                          @Phaedrux said in Is Stall detection a reliable safety feature w/ MB6HC:

                          stacked optical switches seems like a viable option?

                          Only close to "Home"?

                          Duet controlled Lathe, micro mill, 3d printer and 1992 Haas VF2 VMC

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                          • undefined
                            jrockland @3DPMicro
                            last edited by 8 Mar 2021, 05:27

                            @3DPMicro NOPE.
                            Not safe. At all.
                            put some safety switches on your bed.

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                            • undefined
                              hackinistrator @3DPMicro
                              last edited by 8 Mar 2021, 20:41

                              @3DPMicro close to axis limits .
                              i don't have anything else that can crash , except axis limits ( for each axis) . well maybe the printed part in case of warping , but that's nothing serious .

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                              • undefined
                                3DPMicro
                                last edited by 9 Mar 2021, 00:11

                                Thanks. I may implement the dual switches . Looks like there are solutions except for if 1 motor moves and the other doesn't say if it was at the bottom of travel going towards home. I think I have an idea that can take care of that mechanically/electrically. If it gets too far out of wack it will open/close a circuit that kills power or activates an emergency stop

                                Duet controlled Lathe, micro mill, 3d printer and 1992 Haas VF2 VMC

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