Extrusion inconsistencies when using external servo drive.



  • Hi,

    I'm currently experiencing two very strange problems while trying to extrude using an external servo drive plugged into a "Duet Expansion Stepper Breakout Board".

    First Problem
    When I input "G1 E10 F10" I expect it to feed 10mm of material in one minute, however it does it in 20 seconds, 3 x faster than expected.

    When I input "G1 E10 F100 I expect it to feed 10mm of material in 6 seconds, and it does it in 6 seconds.

    This prompted me to do a test to see where the extrusion starts correcting inself and this is what I found:

    G1 E10 F10 - 20 seconds
    G1 E10 F20 - 20 seconds
    G1 E10 F30 - 20 seconds
    G1 E10 F40 - 15 seconds
    G1 E10 F50 - 12 seconds
    G1 E10 F60 - 10 seconds

    and so forth. I guess what I'm asking is, is there a minimum extrusion speed when using a external drive?

    Second Problem
    When I send a command via the gcode console the servo reacts exactly as I want it. For instance if I send G1 E100 F500 I expect the servo to be running at 1500rpm.

    Now when I use a gcode file prepared by slicer asking for the same speed the servo runs 3 times faster.

    Does this somehow tie into my first problem where for some reason the servo was rotating 3 times slower than the requested speed?

    If anybody could shed some light on this I would really appreciate it.

    Regards,

    Andre



  • -what servo are you using?
    -what M569 (T) Parameters are you using?
    From the wiki:

    Taa:bb:cc:dd (firmware 1.21 and later) Minimum driver step pulse width, step pulse interval, direction setup time and direction hold time, in microseconds

    If those are set too high (or low) they might cause issues. Depending on your servo of course



  • I'm not using a name brand servo unfortunately.

    My M569 parameters are T2.5:2.5:0:0

    As mentioned earlier though I'm just suspect that the low F value I'm requesting is not supported, it seems that only from F40 onwards it works as predicted.

    I can also send it a command through the console and it executes it perfectly, however when I run a gcode file it runs 3 times faster than predicted.



  • Still, what servo are you using? Link?
    Can‘t help you when you don‘t say what you‘re using


  • administrators

    The default minimum total movement speed is 0.5mm/sec so 30mm/min. Recent firmware versions allow you to change it using an extra parameter in the M203 command.



  • @dc42 is that applicable to the extruder axis in a linear sense? Or does that apply only to toolpath feederate?



  • @dc42 can you clarify the minimum speed setting/behaviour? The documentation says minimum "overall" speed. Does that mean a global minimum for each axis independently (inlcuding the extruder axis) or is it only applicable to the toolpath feedrate?

    IE, with default settings, is the E axis limited to a minimum speed of 0.5 mm/s whie extruding? Would the motion planning system coordinate the other axes to move faster to accomodate if that limit was exceeded (IE less than 0.5 mm/s)?


  • administrators

    @bot said in Extrusion inconsistencies when using external servo drive.:

    @dc42 can you clarify the minimum speed setting/behaviour? The documentation says minimum "overall" speed. Does that mean a global minimum for each axis independently (inlcuding the extruder axis) or is it only applicable to the toolpath feedrate?

    For moves that include axis movement, it is the movement speed of the combined movement of the axes. For extruder-only moves, it is the extrusion speed.


 

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