z axis random reverse homing

  • hi all and sorry for my bad english.
    That's the problem:sometimes , randomly, my z axis homing in reverse direction.
    I have core xy and my home for z is on the top

    config.g :
    ; Drives
    M569 P0 S0 ; Drive 0 goes forwards
    M569 P1 S0 ; Drive 1 goes forwards
    M569 P2 S1 ; Drive 2 goes forwards
    M569 P3 S1 ; Drive 3 goes forwards
    G91 ; relative positioning
    G1 Z5 F6000 S2 ; lift Z relative to current position
    G1 S1 X-360 Y-340 F1800 ; move quickly to X or Y endstop and stop there (first pass)
    G1 S1 X-360 ; home X axis
    G1 S1 Y-340 ; home Y axis
    G1 X5 Y5 F6000 ; go back a few mm
    G1 S1 X-360 F360 ; move slowly to X axis endstop once more (second pass)
    G1 S1 Y-340 ; then move slowly to Y axis endstop
    G1 S1 Z-400 F1800 S1 ; move Z down stopping at the endstop
    G90 ; absolute positioning
    G92 Z0 ; set new Z position
    ;G1 Z5 F100 S2 ; uncomment this line to lift the nozzle after homing
    G91 ; relative positioning
    G1 Z5 F6000 S2 ; lift Z relative to current position
    G1 S1 Z-400 F1800 ; move Z down until the switch triggers
    G92 Z0 ; set Z position to trigger height

    ; Uncomment the following lines to lift Z after probing
    ;G91 ; relative positioning
    ;G1 Z5 F100 S2 ; lift Z relative to current position
    ;G90 ; absolute positioning

    any idea?
    thx for suggestion

  • administrators

    If the Z axis sometimes goes down when it should go up, this can be a sign of insufficient motor current and/or voltage, or trying to move the Z motor(s) too fast. How many Z motors do you have, and if you have more than one, how have you connected them to the Duet? What is the specification of each motor, what motor current have you set in M906, and what VIN voltage are you using? What is your Z steps/mm, and what Z acceleration have you set in your M201 command?

  • Hi and thx
    -2 z motors connected using double slot of duet wifi EDIT---(parallel i think)

    • 800mA M906
      -400 steps/mm EDIT--- 16 microstep interpolated
      -100 acceleration in M201
      -12,2 V EDIT---PSU
      i'have used your excel.
      i'll change to 24v but for now 12,2V

    The SL42STH40-1684A motor specs are:

    Step Angle: 1.8°
    Step Angle Accuracy: ±5% (full step, no load)
    Voltage: 2.8V
    Current per phase: 1.68A
    Resistance per phase: 1.65Ω
    Resistance accuracy: ±10%
    Inductance per phase: 3.2mH
    Inductance accuracy: ±20%
    Holding torque: 3.6 Kg·cm (0.4 N·m)
    Moment of inertia: 54 g/cm^2
    Weight: 0.28 kg
    Orientation torque: 150 g/cm
    Length: 40 mm
    Temperature rise: 80°C max (rated current, 2 phases on)
    Ambient temperature: -20°C ~ +50°C
    Insulation resistance: 100MΩ min, 500VDC
    Shaft radial play: 0.02 mm max (450g load)
    Shaft axial play: 0.08 mm max (450g load)
    Max. radial force: 28N (20mm from the flange)
    Max. axial force: 10N

  • administrators

    Try increasing the Z motor current to 1200mA in M906, and/or reduce the Z homing speed from F1800 to F1000. 12V power should be sufficient.

  • done...but i think z drivers no longer work.
    z motors vibrates and z axis don't move 😨

    M906 X800 Y800 Z1000 E1000 I30 config.g
    G1 S1 Z-400 F900 ; move Z down until the switch triggers homez.g


  • M120
    G1 Z10 F6000

    Error: G0/G1: insufficient axes homed
    Error: Pop(): stack underflow!

  • i'have changed using y motor in to z plug...home z no movement

  • administrators

    The most likely cause is a bad motor cable. So test the motors and their cables by powering down the Duet then plugging a motor into a known good output (for example, X or Y). Power up the Duet, send M564 H0 (if you don't already have it in config.g) to enable movement before homing, and try jogging the axis whose driver you have the motor connected to. Check that it moves in both directions and has enough torque.

    When testing the Z motor output with just one motor, remember to put 2 jumpers in the unused Z connector, because Za and Zb are connected in series.

  • @dc42 said in z axis random reverse homing:
    I don't understand...
    -wires checked ok
    -switched z motors to x and y connectors they work
    -plugged x motor in to z plug plus jumpers in the unused z connector it work ( switched between z1 and z2 connectors +jumpers ---all ok)
    -plugged x and y motors in to both z connectors ----just one work when i home Z (no sense!!)
    -plugged both z motors in to both z connectors homing z -----1 motor go fast 1 motor go slow (O.o)
    i have reduced M203 in config.g for Z to 900
    i have reduced in homez.g and in homeall.g F to 250 for z


    thanks for the help if other strange things happen I will let you know

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