Dual Z Synchronization

  • Hi

    I have a cartesian printer with a box gantry that holds my heated bed. This is my Z for vertical motion. I have open build VSlot Nema23 lead screw based linear actuators each each side of the frame which I need to synchronize. Y is front / back and carries the X axis. It is also a VSlot Nema23 screw based linear actuator. X is left / right and carries the hot end. The hot end is a 2 in 1 out bowden Cyclone with a single heater. The bed is heated.

    My power supply is a 30A 12V Meanwell.

    While installing the Cyclone, my Z movement was correct and both motors were working. I have a single end stop at the top of the Z axis and homeall pulls the gantry up to the top. The two motors for Z are connected to the ZA and ZB ports on the DuetWifi. The X and Y motors are on their designated ports. E0 and E1 connect to the bowden extruder motors. X, E0 and E1 are Nema17 motors.

    Since adding the 2nd extruder, only 1 Z motor is stepping. The other remains idle. If I use the Web interface, the motor on the right side (connected to the top Z port on the board works fine. The motor on the left side does not move. I swapped the motor cables between the upper and lower connectors on the board and the movement is the same. Right motor steps, left does not.

    If I use the PanelDue to move the Z axis, the left motor steps and the right motor does not.

    I have read a number of different approaches on the forum and it looks like I should define an alternate axis which I should combine with Z to home and split to drive. I can read up on the gcode changes required, but before I do that, I was wondering if I should change my physical configuration. I have the impression from the forum that I should switch to a 24v power supply. I have the list of which parts I should change (bed / hot end heater). I need a new bed since I have increased the available print area and the hot end heater is not a problem to change.

    Should I add a Duet2/5 to make remapping the steppers easier or is the existing DuetWifi board ok with the 6 stepper motors in this configuration?

    I 'd appreciate input in changing to 24v and whether I should add an expansion card.


  • administrators

    As you have your two Z motors connected in series and one of them works fine (I assume you can move it both up and down), I think there are only a few possibilities:

    1. There is a short across one of the phases of the motor that is not moving. I think we can discount this because it is not always the same motor that doesn't move.

    2. You have a mechanical issue, perhaps binding because the leadscrews are out of sync, so there is too much friction on the side that is not moving. Using more motor current (if it isn't already close to the limit of either the motors or the Duet) or lubricating the leadscrews may help.

    3. You are trying to move the motor too fast, bearing in mind that they are in series so they will need more drive voltage at high speeds. Try reducing the Z max speed in the M203 command and the Z acceleration in M201.

    Changing to 24V power will only help if there is insufficient driver voltage to achieve the speed you want. Use the calculator at reprapfirmware.org to check. The other advantage of 24V power is lower bed heater current. If your printer bed is significantly larger than 200x200mm then changing to 24V power is advisable IMO.

    Using a DueX2 would allow you to use a separate output for each motor, so double the drive voltage would be available for the Z motors. It would also allow you to do automatic side-to-side bed levelling if you have a Z probe, see https://duet3d.dozuki.com/Wiki/Bed_levelling_using_multiple_independent_Z_motors.

  • Thank you for the detailed, reasoned response. The background information is appreciated.

    Yes, the one motor at a time will move in both directions.
    1. I agree since both motors fired although from different controls.
    2. Prior to switching to this configuration, each of these linear drives worked without obvious issues in a horizontal position (1 as X and the other as Y) and they were both working in the current Z configuration for a time. Moving them manually does not show overwhelming friction.
    3. This would seem most likely. I will reduce both the max speed and acceleration for Z and see if that makes a difference. I believe that I also have room to increase the current, so that is another check I can do.

    I like the idea of reducing the current to the heaters. The new configuration allows for a 300 x 300mm heat bed, so that an additional consideration to sway toward 24V

    I do have a Z probe and getting double the drive voltage via the DueX2 along with automatic side to side bed leveling is an attractive incentive. I'll order the board.

    Thanks for your input and suggestions. I will read the material that you linked above.

    Best regards,


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