Quality of a G1 move



  • So I was trying to speed up my head parking and unparking to reduce my IDEX ooze, and when I yanked the speed of the heads up to 42000mm/min, the motion of the movement is just horrible.

    I made a video:

    https://www.youtube.com/watch?v=Ku4A4F1NcgI

    Here I am sending G1 X0 F42000 and G1 X250 F42000 to test how fast I can go.

    I never comes close to 42000mm/min, but what worse is, the linearity of the movement is really bad.

    I have seen something like this before - on a delta with far too many steps/mm running marlin. Here the problem was that too many interrupts were generated at one time, and it would overflow. (https://www.youtube.com/watch?v=bjIAw8gmyWM)

    But with the Duet, we should have near unlimited resources, so what is happening here?


  • administrators

    The resources of the Duet are not unlimited. The maximum rate at which step pulses can be generated on the Duet WiFi and Duet Ethernet is about 380kHz with just one motor moving, and 180kHz each to 3 motors moving simultaneously. You can hit these limits if you use a combination of high movement speed and high microstepping,



  • So you think that with 16 microsteps I am not able to move at F42000?

    I was just now testing a bit, and it turns out the ugly movement disappears if I disable bed compensation. Any idea why?

    Thanks.



  • Tested a bit more - it was caused by my Z-jerk being too low, and this would cause a deceleration and acceleration at every knot of my heightmap. Changing my Z-jerk to 1000 resolved the problem.



  • Glad you got it fixed but 700mm/s? That's fast!



  • Yeah, I guess. It works though:

    https://www.youtube.com/watch?v=wiQwGDisMR0

    Question is, how can I make it go equally fast back? - I tried using R1 in my post.g but that seems not to be set. Is there a way to set it? Other ideas?


  • administrators

    I'm glad you solved it. I'll add a note about jerk setting to the wiki page on mesh bed levelling.

    G1 R2 is intended to move the head to the position just before a tool change, but I don't think it's working for IDEX machines yet.

    700mm/sec using x16 microstepping should be no problem for the Duet, assuming you have a typical steps/mm of around 80, because the step rate for that speed is only 56kHz.



  • It would be nice to have a "Set R1 point to here" or something like that - then you could just "save" the current position in the start of your scripts, and not worry about where you move the head.


  • administrators

    That too is on the wish list. Buy first I need to get R2 working so that you can use it when switching between the X and U carriages.


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