Does pressure advance respect max speed/accel/jerk settings?



  • I am in the process of adding and tweaking pressure advance to my HEVO printer, and the main challenge is dealing with the 'jerkiness' that it brings.

    Does the pressure advance feature obey the max speed, acceleration and jerk settings of the printer? I have this test script which reduces the three to very low values but it doesn't affect the loud short chirp from the extruder when the 'purge on bed' extrusion below starts and ends. (that chirp sounds as high speed or acceleration of the extruder's motor).

    That noise is go away if I reduce the pressure advance constant to zero.

    Is it possible that the pressure advance algorithm ignores the E max settings of M201, M203 and M566?

    T0  ; select extruder
    M302 P1  ; allow cold extrusion
    
    
    M92 X200.00 Y200.00 Z400.00 E830.0   ; Set microsteps per mm
    M204 P1000 T3000                ; Set printing and travel accelerations
    
    ; Original values
    ;M566 X600 Y600 Z100 E3000       ; Set maximum instantaneous speed changes (mm/min) (Jerk)
    ;M201 X300 Y300 Z30  E8000       ; Set maximum accelerations (mm/s^2)
    ;M203 X15000 Y15000 Z3000 E15000 ; Set maximum speeds (mm/min)
    
    ; Ridiculously low values
    M566 X600 Y600 Z100 E30          ; Set maximum instantaneous speed changes (mm/min) (Jerk)
    M201 X300 Y300 Z30  E60          ; Set maximum accelerations (mm/s^2)
    M203 X15000 Y15000 Z3000 E180    ; Set maximum speeds (mm/min)
    
    M572 D0 S0.5                     ; Set pressure advance
    ;M572 D0 S0                      ; Set pressure advance
    
    G28      ; home all axes
    G29 S1   ; load mesh height map
    
    G1 X10 Y-5 Z10 F1000.0  ; go to starting point
    G92 E0.0                ; reset extruder
    
    ; Loud chirp from the extruder before and after this move.
    ; Chirp disappears if I set pressure advance to zero.
    G1 Y30.0 E20 F600       ; purge on bed
    
    G1 Y150.0 F2000         ; keep moving without extruding
    

  • Moderator

    @zapta said in Does pressure advance respect max speed/accel/jerk settings?:

    G1 Y30.0 E20 F600 ; purge on bed

    That is a rather large amount of filament to try and deposit in a 30mm track.



  • @phaedrux , yes, it's a small paddle of plastic to clean the nozzle before the print. The test case here is based on my before_print script which stated to have two short but loud extruder chirps since I added pressure advance.



  • Since pressure advance attempts to extrude even more plastic at the very start of a line, while the acceleration is happening, than usual, and since 20mm of filament is indeed a very large amount of filament to deposit in only three seconds (that's 6.67mm/s average) I'd guess you're seeing an instantaneous extrusion speed of higher-enough over 6.67mm/s at the very start of the line that the combination of your hotend and extruder simply can't keep up, and what you're hearing is the extruder motor complaining about being unable to advance as commanded, or else possibly your extruder hob's teeth grinding away at the filament.

    In my own experiments while setting non-linear advance, I found that at 265 C (that's pretty high for PETG) around the 5-6mm/s mark my hotend simply couldn't melt the plastic fast enough for my then-single-drive extruder to keep up and I got skipping. I've got a dual-drive extruder now, but the fundamental issue of simply not enough heat flux into the filament through the melt chamber would remain. So the question is, given a higher than 6.67mm/s instantaneous melt demand, why do you think it should actually succeed?

    You could test this in a few ways:
    Raise your hotend temp by 10-15 C and see if anything changes.
    Change your command to something like G1 Y30.0 E20 F300 and see if cutting in half the demanded flow rate completely mitigates this.

    Personally I think you're simply asking too much of your hotend and extruder. Phaedrux was too subtle in his comment.


  • administrators

    @zapta said in Does pressure advance respect max speed/accel/jerk settings?:

    Does the pressure advance feature obey the max speed, acceleration and jerk settings of the printer?

    Yes it does. This may cause the actual acceleration to be reduced, especially if the extruder jerk setting is low.



  • Thanks @dc42. I will play with it and see if I can find a counter example, if there is any.

    Meanwhile I solved the problem by mounting the bowden extruder on suspension so it doesn't resonate through the 3030 frame. I can barely hear it now.



  • @zapta said in Does pressure advance respect max speed/accel/jerk settings?:

    Thanks @dc42. I will play with it and see if I can find a counter example, if there is any.

    Meanwhile I solved the problem by mounting the bowden extruder on suspension so it doesn't resonate through the 3030 frame. I can barely hear it now.

    Have you some picture of the mounting ?


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