M566 has no effect



  • Hi guys,

    I try to find the absolut maximum jerk for my ne Printer. But M566 seems to have no effect?

    First I have set my acceleration an jerk very low by sending:
    M201 X1 Y1 Z1 E1
    and
    M566 X1 Y1 Z1 E1

    As expected, every move has a very slow ramp now.
    Then I increased the XY jerk:
    M566 X1200 Y1200

    Now I was expecting no ramp as long as I do not travel faster than F = 1200 mm/min. But still I have the very slow ramp. The Jerk seems to be ignored. Only the acceleration can increase the ramp. Might the Jerk be overwritten or limited somehow?



  • I guess its acceleration (M201) what slows you down, cos its almost nonexisting with value 1.

    Use https://blog.prusaprinters.org/calculator/#acceleration to see yourself.



  • But my understanding was, that the jerk sets an initial speed.
    In the posted link it is not considered.
    So if I set the jerk to 20 mm/s and I want to travel at 20 mm/s, there should be no ramp, because the travel already begins at 20 mm/s. Or am I wrong?



  • @jorge The extruder works like an axis so every print move will be the slowest of either X Y or E. So changing X and Y without also changing "E" will have no effect on a print move because the move needs to slow down to the "E" value before the next move commences.



  • But the extruder jerk/acceleration/speed should not affect travel moves, right?
    I just increased the extruder acceleration and jerk.
    XY acceleration is still very low.
    But XY jerk ist very high. But still the jerk seems to be ignored and the ramp starts from 0 mm/s.



  • @jorge As i underrstand, your meaning of jerk is right when it comes to speed with what changing direction is allowed. But if your accelerarion is very slow and you start from 0 speed, your final speed never reaches that 20 mm/s, so it doesnt matter how high your jerk is, if your speed is much under it.
    I may be wrong of course....



  • @aidar That is my understanding also. I'm fairly sure that in the past, David (DC42) has said that in RepRap firmware, "jerk" is not applied when moves start from a speed of zero - only when there is a change in direction at the boundary between successive moves.



  • Ah OK. I will write a little gcode file to test this.

    I am pretty sure, that marlin behaves different. For my marlin printers I was able to drive single extrusion moves while increasing jerk by hand until I could hear the extruder loosing steps.



  • I could verify it. changing extruding speed from 0 allows no jerk. But when changing the speed from one direction to another, the jerk works fine.


 

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