Auto Bed compensation torque problems.



  • Hello,

    First of all, my printer is custom built, and for some reasons I had to change my buildplate from 10mm aluminium to a 15mm steel sheet. Now its about 35 kgs, give or take some, as the plate size is 760x700, and the printer itself 800x800x2200 outer sizes with 550x500x~800 buildsize. I have DuetWifi and Duex5(Z's only), 1x, 1y 2E and 4 independent Z motors(Nema 17, 0.5 Nm, 1,8°) and TR 12x3 threaded rods directly driven, with linear rails.

    And now the problem itself:
    Motors can move good, but when I give G32, the probing finishes, then the compensation move seems to happen too fast or with less torque, so its move some but lost some steeps(about 0,1-0,3 mm off each). And its obviously not really good.

    The solutions I tried: I slowed down my acceleration to 2 mm/s^2 (from 40), and crank my amp from 1800 to 2800(its the max since the motors overheating if i crank it up more). (With this I also lowered the max Z speed form 200 to 50)
    The change microstepping from 16 I1 to 8 or 4, its getting loud, the gap lowered a bit, but not much(from the 0,4-0,5 range to 0,1-0,3)
    I also lowered the probing fed from 20 to 10, but this doesn't made any change.
    Firware version: 1.19.2, with 1.19.3 WebInterface version.

    I know stronger motors or if I gear them, probably solves the issue, but I would be happy if I can solve it with a software change, and not with a hardware one, since I should printing at the weekend.
    Regards.


  • administrators

    @sastas said in Auto Bed compensation torque problems.:

    And now the problem itself:
    Motors can move good, but when I give G32, the probing finishes, then the compensation move seems to happen too fast or with less torque, so its move some but lost some steeps(about 0,1-0,3 mm off each). And its obviously not really good.

    Do you mean that the Z motors are missing steps when the you do XY moves and the firmware attempts bed compensation? If so then you may need to do one or more of the following:

    • Reduce Z jerk
    • Reduce Z acceleration
    • Reduce Z max speed
    • Increase Z motor current, if you have any headroom
    • Use stronger/geared motors

    If normal Z moves work without losing steps then it's probably the Z jerk that you need to reduce.

    HTH David



  • Not when XY moves.
    The bed compensation goes as probe the 4 points, the bed moves away a bit, then the bed compensation happens, and then the printer moves the desired point. When the probing moves happens, there is no hearable step loss, but when the compensation move happens, there is hearable loss.


  • administrators

    @sastas, please explain what you mean by "when the compensation move happens".



  • The compensation move is(for me at least), when the 4 leadscrews align the bed. It do the 4 probe point, then it goes down, then it does the compensations, then it goes to the point I configured.


 

Looks like your connection to Duet3D was lost, please wait while we try to reconnect.