Discontinuous (not-smooth) X/Y movement on Prusa i3

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Comments

  • Thanks. 
    I use a super simple object, a single wall triangle.
    The GCode created is super simeple.
    Example of a layer
    ---
    ; layer 9, Z = 1.8
    ; inner perimeter
    ; outer perimeter
    G1 X96.755 Y97.740 F4800
    G1 Z1.800 F1002
    G1 E0.1000 F1800
    G92 E0
    G1 X113.245 Y97.740 E0.6657 F1800
    G1 X105.000 Y112.020 E1.3314
    G1 X97.155 Y98.433 E1.9648
    G1 X96.755 Y97.740 F1800
    ; inner perimeter
    ; outer perimeter
    G1 X97.656 Y98.260 F4800
    G92 E0
    G1 X105.000 Y110.980 E0.5930 F1800
    G1 X112.344 Y98.260 E1.1860
    G1 X98.456 Y98.260 E1.7466
    G1 X97.656 Y98.260 F1800
    G92 E0
    G1 E-2.0000 F1800
    G1 Z2.500 F1002
    ---

    I created the log, but not sure what exactly to be looking for in it.
    Any hints?

    STL File:

    Log file:
  • The planner outputs
    "Buffer size" F "startSpeed" - "endSpeed" ("maxJunctionSpeed","joinflags" / next move

    It pretty much looks like maxJunctionSpeed is causing the speed changes, see in motion.cpp:

    inline void PrintLine::computeMaxJunctionSpeed(PrintLine *previous, PrintLine *current)

    the question is more which of these jerks is so low that it causes it to get the cause of slowdowns and which slowdowns are ok as you are in deed changing directions preventing full speed.
  • My settings are

    Max Jerk: 25 mm/s
    Max Z.Jerk: 0.300 mm/s
    Extruder1 Start Feedrate: 35mm/s (changed it before according to the previous posts)

    Accelerations are all at 1000 mm/s

    So the Jerk of 25mm/s is above the usual settings of 15 mm/s. It makes some nice clean sharp corners.
    I can increase the jerk even more and test but as the movement it itself is constant, the jerk should not come it play during it right?
    The gcode says to go from point A to B and then C, so it should only use the jerk when it reaches point B not all along the way from A to B.
  • Yes, it will slowdown in the corners depending on angle and jerk and then do the next move. But you have in your triangle always acceleration and deceleration at the end. Should still look smooth and give no ripples except for vibration and positioning inaccuracy.

    Since you have single walled print can you say if they come from extrusion fluctuations which means the width would vary with the pattern you see or is it offset from precise position.
  • just to chime in, I seem to have a related (?) issue here:
    I usually throttle down the print-speed for the first few layers (depending on the print, typically the first three) to 70% and then speed up to 85% for about a minute and then finally to 100% or higher.

    If X and Y are involved in a print-movement (infill, part rotated 45 degrees) AND the printer runs with <100% speed I see stalls during printing a straight line, about every ~5mm or so...
    _ = ~5mm
    . = stall for about 0.2-0.4 sec
    __._.__._.__. <- looks like my printer is trying to tell me something ("let me outta here" :-D)
    as soon as I ramp up to 100% the stalls are gone....*huh*

    Firmware: Repetier 0.92.9, printing via RepetierServer 0.80.2 on a rasPi3, RAMPS 1.4

    Print speed set in cura: 30/26/30 (Speed / outer / infill), the stalls left out the print comes out very smooth.

    #define MAX_ACCELERATION_UNITS_PER_SQ_SECOND_X 1000
    #define MAX_ACCELERATION_UNITS_PER_SQ_SECOND_Y 1000
    #define MAX_ACCELERATION_UNITS_PER_SQ_SECOND_Z 100
    ..
    #define MAX_TRAVEL_ACCELERATION_UNITS_PER_SQ_SECOND_X 1000
    #define MAX_TRAVEL_ACCELERATION_UNITS_PER_SQ_SECOND_Y 1000
    #define MAX_TRAVEL_ACCELERATION_UNITS_PER_SQ_SECOND_Z 100

    any idea?

  • Firmware does for cartesian lines not stop on straight lines. For deltas and with active distortion map these lines get split and could at least theoretically slow down. Especially on the limited AVR with 16kb ram and limited speed the ram usage and speed could get a problem specially if the resolutionis high (steps per mm). Does anything match for you?
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