M906 - Currents for three z motors with two of them in series?



  • Hi Forum, thanks to the excellent documentation I already got very far in setting up my Duet2 Wifi (24 V) for a CoreXY printer 👍

    But this is one of the issues I got stuck with: I have three motors for the bed height (i.e. z) and one extruder. As far as I understand[*], the only way to use them w/o using an expansion board would be to connect two of the z motors to Z2 and the third one to E1 (when using E0 for the extruder), i.e.:
    M584 X0 Y1 Z2:4 E3

    With this setup, do I need to worry about the currents of the z motors? The Duet2 Wifi is rated at 2.4 A max. motor current (per...?) and I have 2.5 A motors (ldo-42sth47-2504ac), so accoding to the guide to use motors at <=85% of their rated current, I should be fine to set
    M906 X2000 Y2000 ... E1000 I30 (extruder motor is 1.68 A)
    but what about z in this particular configuration?

    Thanks a lot for your help 🙂

    [*] Am I correct to assume that directly using the respective pins of the 50-pin-expansion for the third z motor is not possible? I would need the expansion board -- correct? (Also for the extruder? b/c otherwise E0 could be the third z and the extruder could be driven via the "expansion pins")


  • administrators

    Just use Z2000 or whatever value is appropriate. This will drive all 3 motors with the same current. Note, if you connected the 2 motors in parallel instead of in series, then the the two in parallel would only get half the current each.

    Depending on the motor, connecting all 3 in series to one driver may also work, although the maximum speed will be lower. See the motor EMF calculator at https://www.reprapfirmware.org/.



  • Hey, thanks a lot for the quick help! 👍

    Could anybody quickly check the "[*]-bit" of my question? Thanks again!


  • Moderator

    The expansion pins can be used to send step direction signals to an external driver, but they themselves do not have a driver to power a motor directly. If you want additional driver capacity you would need an expansion card like the Duex2 or Duex5.

    https://duet3d.dozuki.com/Wiki/Duex2_and_Duex5_Features

    https://duet3d.dozuki.com/Wiki/Using_external_stepper_motor_drivers



  • alright, great, thanks!
    (can I mark this as solved?)