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Tuning Jerk/Accel/Speed settings

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Tuning and tweaking
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  • undefined
    droftarts administrators @Phaedrux
    last edited by 5 Feb 2020, 21:22

    @Phaedrux Awesome post! Could you create a wiki page based on this, and the previous post on extruder calibration? I don’t think there’s one yet.

    Ian

    Bed-slinger - Mini5+ WiFi/1LC | RRP Fisher v1 - D2 WiFi | Polargraph - D2 WiFi | TronXY X5S - 6HC/Roto | CNC router - 6HC | Tractus3D T1250 - D2 Eth

    undefined 1 Reply Last reply 5 Feb 2020, 21:28 Reply Quote 1
    • undefined
      Phaedrux Moderator @droftarts
      last edited by 5 Feb 2020, 21:28

      @droftarts yes I have a rough draft document that goes into a full calibration with all this and more that's in the works. I should polish it up and push it out.

      Z-Bot CoreXY Build | Thingiverse Profile

      1 Reply Last reply Reply Quote 3
      • undefined
        wcj97 @Phaedrux
        last edited by 6 Feb 2020, 03:41

        @Phaedrux Amazing post! Thank you!

        I started right at the top and figured I'd get my extruder all figured out. My steps/mm were spot on at the theoretical value, so that step was quick and easy. Next I decided to find the max rate I could extrude filament through a given nozzle at a given temperature. I used that as an input to a little excel file I wrote similar to the one you posted an image of above. The issue is, the max theoretical print speed I'm getting seems crazy low. At 210C, I'm able to extrude filament through a 0.8mm nozzle at a max of around 8mm/s before my extruder begins to skip. That boiled down to a max print speed of around 26mm/s at a 0.2mm layer height, which seems crazy low. In the past, I've printed at 60mm/s with the same extruder, temperature, layer height, and nozzle without any missed steps or grinded filament. Any ideas why my theoretical max speed is almost half what I know to be possible?

        (I should note that I calculated the volumetric extrusion rate a bit differently than you noted in your other post. My math doesn't assume the shape of a printed line to be a perfect rectangle. However, the difference in values is not enough that it really changes the point of my above post).

        Original Prusa i3 MK2
        Hephaestus (Custom Duet based large format FFF)
        Aeon (Custom belt printer)
        Elegoo Mars

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        • undefined
          Phaedrux Moderator
          last edited by 6 Feb 2020, 03:52

          I'd have to see your math and compare it to mine.

          Here is my spreadsheet if you're interested. It has a lot more other things as well.

          https://www.dropbox.com/s/ihe3rl58z7sdyfu/Calculators.xlsx?dl=0

          Z-Bot CoreXY Build | Thingiverse Profile

          undefined 2 Replies Last reply 6 Feb 2020, 04:18 Reply Quote 0
          • undefined
            wcj97 @Phaedrux
            last edited by 6 Feb 2020, 04:18

            @Phaedrux Mind if I send you the excel sheet in this thread?

            Original Prusa i3 MK2
            Hephaestus (Custom Duet based large format FFF)
            Aeon (Custom belt printer)
            Elegoo Mars

            undefined 1 Reply Last reply 6 Feb 2020, 04:22 Reply Quote 0
            • undefined
              wcj97 @Phaedrux
              last edited by 6 Feb 2020, 04:21

              @Phaedrux Also, I should note that after looking a bit closer, it wasn't my extruder that was skipping, but rather the bondtech gears becoming unmeshed. I tried increasing the pressure on the gears, but then I went too far and the printer started grinding the filament real bad, so now I have to clean that up.

              Original Prusa i3 MK2
              Hephaestus (Custom Duet based large format FFF)
              Aeon (Custom belt printer)
              Elegoo Mars

              1 Reply Last reply Reply Quote 0
              • undefined
                Phaedrux Moderator @wcj97
                last edited by 6 Feb 2020, 04:22

                @wcj97 said in Tuning Jerk/Accel/Speed settings:

                @Phaedrux Mind if I send you the excel sheet in this thread?

                It's your thread. Do as you wish. 👍

                Z-Bot CoreXY Build | Thingiverse Profile

                undefined 2 Replies Last reply 6 Feb 2020, 04:29 Reply Quote 1
                • undefined
                  wcj97 @Phaedrux
                  last edited by 6 Feb 2020, 04:29

                  @Phaedrux Extrusion_Speed_Calculator.xlsx

                  Original Prusa i3 MK2
                  Hephaestus (Custom Duet based large format FFF)
                  Aeon (Custom belt printer)
                  Elegoo Mars

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                  • undefined
                    wcj97 @Phaedrux
                    last edited by 6 Feb 2020, 04:33

                    @Phaedrux Ha! I realized where I messed up immediately after posting that file. I determined my max volumetric flow rate to be the max speed I could move my extruder for a given temp/nozzle size, multiplied by the area of the nozzle orifice. That would be incorrect. I fixed that calculation so that now it's the max extruder speed multiplied by the cross-sectional area of the filament and my numbers look much more appealing now. Something more like 110mm/s print feedrate. This is why it's important to always double-check your math, I guess.

                    Original Prusa i3 MK2
                    Hephaestus (Custom Duet based large format FFF)
                    Aeon (Custom belt printer)
                    Elegoo Mars

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                    • undefined
                      wcj97
                      last edited by 6 Feb 2020, 04:37

                      Here's the updated spreadsheet, just in case anyone else would like to take a gander and maybe make use.Extrusion_Speed_Calculator.xlsx

                      Original Prusa i3 MK2
                      Hephaestus (Custom Duet based large format FFF)
                      Aeon (Custom belt printer)
                      Elegoo Mars

                      undefined 1 Reply Last reply 6 Feb 2020, 17:25 Reply Quote 0
                      • undefined
                        jens55
                        last edited by 6 Feb 2020, 05:04

                        This post is deleted!
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                        • undefined
                          Phaedrux Moderator @wcj97
                          last edited by 6 Feb 2020, 17:25

                          @wcj97 said in Tuning Jerk/Accel/Speed settings:

                          Here's the updated spreadsheet, just in case anyone else would like to take a gander and maybe make use.Extrusion_Speed_Calculator.xlsx

                          Yeah that looks reasonable. The exact shape of the extrudate isn't super critical. It's just a ballpark limit to work within. I usually suggest a 10% safety margin to allow for instances where the amount of plastic being pushed is heavy enough and continuous enough to cool the hotend significantly enough to temporarily drop your volumetric throughput. Such as may occur in large areas of solid infill.

                          We're just measuring a brief instance of volumetric throughput. What we really should be measuring and modeling is the melt rate of the plastic in relation to the thermal system of the hotend, including pressure feedback, elasticity, drag/friction, expansion, etc, etc, but that's way beyond complex and a bit superfluous for our needs. We just need to know how much plastic we can reliably extrude in a time frame long enough to capture 99% of all printing moves.

                          Z-Bot CoreXY Build | Thingiverse Profile

                          undefined 1 Reply Last reply 19 Feb 2020, 23:19 Reply Quote 1
                          • undefined
                            wcj97 @Phaedrux
                            last edited by 19 Feb 2020, 23:19

                            @Phaedrux Coming back to this thread for a quick question regarding jerk (instantaneous speed change).

                            The instantaneous speed setting is the speed the motor can jump to before acceleration is taken into account, correct? So if my max speed for my extruder is 6mm/s, and I set my instantaneous speed settings to 360mm/min (6mm/s), acceleration isn't being taken into account at all, right? The controller is assuming that it can instantaneously accelerate from 0 to 6mm/s?

                            Currently, performance is good at my current jerk values, which are set well above my max speed. I guess what I'm asking is: at this point, increasing jerk or acceleration settings doesn't really make any difference right? I've already told my printer that it can instantaneously jump to extrusion speeds well beyond my max speed, so does increasing my jerk values from here (or making any change to my accel values for that matter) have any affect at this point?

                            Original Prusa i3 MK2
                            Hephaestus (Custom Duet based large format FFF)
                            Aeon (Custom belt printer)
                            Elegoo Mars

                            undefined deckingmanundefined 2 Replies Last reply 19 Feb 2020, 23:43 Reply Quote 0
                            • undefined
                              Phaedrux Moderator @wcj97
                              last edited by Phaedrux 19 Feb 2020, 23:43

                              @wcj97 said in Tuning Jerk/Accel/Speed settings:

                              if my max speed for my extruder is 6mm/s

                              That may be the max for extrusion, but not the max for retraction. So don't set your extruder M203 that low.

                              You'll want to set your extruder jerk higher than that as well so that your retractions can be faster and so that pressure advance can quickly change direction.

                              The extrusion speed is so low that it doesn't really matter, but retraction and pressure advance can be much quicker.

                              The extruder doesn't have a lot of mass to throw around like the other axis do, it's just rotation, so your jerk/accel can be quite high without issue (without skipping of course). Basically you can set the max speed and jerk/accel high enough that they ever really come into play. That allows pressure advance and retraction and the acceleration and jerk of the XY axis to dictate.

                              Z-Bot CoreXY Build | Thingiverse Profile

                              1 Reply Last reply Reply Quote 1
                              • deckingmanundefined
                                deckingman @wcj97
                                last edited by deckingman 20 Feb 2020, 07:54

                                @wcj97 No. "Jerk" doesn't work like that in RRF firmware. Jerk is never applied at the start of a move. (True instantaneous speed change is actually impossible in any case). Think of it as a speed change threshold which gets applied when a the object is in motion and there is a change of direction. So instead of one move slowing down to a complete standstill before the next move starts, the move will slow down to the instantaneous speed change threshold (jerk) instead, and the next move commences at that speed. Given that any print move will be a combination of XY and E, and the speed will be the lowest of any of those axes at any point in time, then the only time that extruder jerk would be applied to a print move is if it is set to give a lower speed than X or Y, in which case it would slow down the entire print move. There are only two (I think) instances where extruder jerk is applied. One is when using pressure advance, and I can't remember the other. But in both cases, setting extruder high rather than low is the way to go.

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

                                arhiundefined dc42undefined 2 Replies Last reply 20 Feb 2020, 11:50 Reply Quote 1
                                • arhiundefined
                                  arhi @deckingman
                                  last edited by 20 Feb 2020, 11:50

                                  @deckingman said in Tuning Jerk/Accel/Speed settings:

                                  Jerk is never applied at the start of a move.

                                  How does the start of the move look like? I had an assumption that start of the move, since going from 0, will always use acceleration from 0 but I had issues with new Orion sensor triggering falsely and the guy's from precise piezo asked me to set the Z jerk to 0 as Z move would "jump to jerk speed" and that triggers the Orion. I made the change and solved the problem so looks like that jerk value do affect the start of the move.

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                                  • dc42undefined
                                    dc42 administrators @deckingman
                                    last edited by 20 Feb 2020, 11:52

                                    @deckingman said in Tuning Jerk/Accel/Speed settings:

                                    "Jerk" doesn't work like that in RRF firmware. Jerk is never applied at the start of a move.

                                    It does in recent versions of RRF if you set the jerk policy to 1 in M566.

                                    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

                                    arhiundefined deckingmanundefined 2 Replies Last reply 20 Feb 2020, 12:18 Reply Quote 0
                                    • arhiundefined
                                      arhi @dc42
                                      last edited by 20 Feb 2020, 12:18

                                      @dc42 this is interesting. why would

                                      M566 X500.00 Y500.00 Z0.00 E6.00

                                      not trigger my piezo on G30 while

                                      M566 X1500.00 Y1500.00 Z50.00 E6.00

                                      will trigger G30 when the bed starts to rise?

                                      that's the only M566 in all the files, I never set P to 1 ?

                                      It is confusing me. I kept the M566Z0 as I didn't notice any difference in print behavior between Z0 and Z50 and with Z0 piezo sensor works ok. Why I would like to know how it actually behaves is I was thinking about adding support of RRF to the gcodestat so that I can calculate precise print time from a g-code, but I'm waiting for the few more 3.x versions as I see you are still changing things 🙂

                                      botundefined undefined 2 Replies Last reply 20 Feb 2020, 17:47 Reply Quote 1
                                      • deckingmanundefined
                                        deckingman @dc42
                                        last edited by 20 Feb 2020, 12:49

                                        @dc42 said in Tuning Jerk/Accel/Speed settings:

                                        @deckingman said in Tuning Jerk/Accel/Speed settings:

                                        "Jerk" doesn't work like that in RRF firmware. Jerk is never applied at the start of a move.

                                        It does in recent versions of RRF if you set the jerk policy to 1 in M566.

                                        I missed that - thanks (and thank goodness its optional)

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

                                        undefined 1 Reply Last reply 20 Feb 2020, 18:22 Reply Quote 0
                                        • botundefined
                                          bot @arhi
                                          last edited by 20 Feb 2020, 17:47

                                          I seem to recall having similar behavior displayed on my machine when commissioning the Z axis. It wasn't related to a piezo probe, but merely the fact that jerk was "being applied" from a stand still. I'm not certain of this, but it rang a bell for sure. I even remember making a thread about my Z axis making noises at one point.

                                          *not actually a robot

                                          arhiundefined 1 Reply Last reply 20 Feb 2020, 19:38 Reply Quote 0
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