BLTouch Always reports -3.00mm

  • Hello All,

    I have the following hardware:

    • Genuine BLTouch v3.1
    • Duet3 6HC
    • Duet3 ex 3HC
    • Z Axis with 3 steppers

    When executing the steps written in Test and calibrate the Z probe, I always get the message back "Probe stopped at -3.00mm" whatever I do.
    Homing however, is no problem.

    • I increased / decreased the distance of the BLTouch with washers
      (Between 10 to 6 mm from bottom of BLTouch to end of printhead)
    • I tried playing around with the Z trigger height
    • Checked the wiring of course

    What am I doing wrong? I'm lost...

    The following is my config.g:
    (The {1}'s seem to be added by this site, I don't know where they are coming from...)

    ; Configuration file for Duet 3 (firmware version 3)
    ; executed by the firmware on start-up
    ; generated by RepRapFirmware Configuration Tool v3.1.4 on Wed Jul 29 2020 22:00:06 GMT+0200 (Midden-Europese zomertijd)
    ; General preferences
    G90                                                ; send absolute coordinates...
    M83                                               ; ...but relative extruder moves
    M550 P"Monstro"                       ; set printer name
    ; Network
    M551 P"******"
    M552 P0.0.0.0 S1
    M586 P0 S1
    M586 P1 S0
    M586 P2 S0
    ; Drives
    M569 P0.0 S1
    M569 P0.1 S0
    M569 P0.2 S0
    M569 P0.3 S1
    M569 P0.4 S1
    M569 P0.5 S1
    M569 P1.0 S0
    M569 P1.1 S0
    M569 P1.2 S0
    ; set drive mapping
    M584 X0.0:0.1 Y0.2:0.3 Z1.0:1.1:1.2 E0.4:0.5
    ; configure microstepping with interpolation
    M350 X16:16 Y16:16 Z16:16:16 E16:16 I1
    ; set steps per mm
    M92 X160.00 Y160.00 Z1600.00 E420.00:420.00
    ; set maximum instantaneous speed changes (mm/min)
    M566 X900.00 Y900.00 Z200.00 E120.00
    ; set maximum speeds (mm/min)
    M203 X6000.00 Y6000.00 Z800.00 E1200.00
    ; set accelerations (mm/s^2)
    M201 X500.00 Y500.00 Z20.00 E250.00
    ; set motor currents (mA) and motor idle factor in per cent
    M906 X1200 Y1200 Z1600 E1200 I30
    ; Set idle timeout
    M84 S30
    ; Axis Limits
    M208 X0 Y0 Z0 S1
    M208 X550 Y500 Z740 S0
    ; Endstops
    M574 X1 S1 P"!"
    M574 Y1 S1 P"!"
    M574 Z1 S2
    ; Z-Probe
    M950 S0 C"io7.out"
    M558 P9 C"^" H4 F120 T6000 R0.5
    G31 P500 X-40 Y-10 Z1
    M557 X15:545 Y5:495 P4
    ; Heaters
    M308 S0 P"temp0" Y"thermistor" T100000 B4138
    M950 H0 C"out1" T0
    M307 H0 B0 S1.00
    M308 S1 P"temp1" Y"thermistor" T100000 B4138
    M950 H1 C"out2" T1
    M307 H1 B0 S1.00
    ; Fans
    M950 F0 C"out4" Q500
    M106 P0 S1 H1 T45
    M950 F1 C"out5" Q500
    M106 P1 S1 H1 T45
    ; Tools
    M563 P0 S"ext1" D0 H0 F0
    G10 P0 X0 Y0 Z0
    G10 P0 R0 S0
    M563 P1 S"ext2" D1 H1 F0
    G10 P1 X0 Y31.3 Z0
    G10 P1 R0 S0
    ; NeoPixels
    M150 X1
    ; Miscellaneous
    M911 S10 R11 P"M913 X0 Y0 G91 M83 G1 Z3 E-5 F1000"

  • Moderator

    @Kiomatri said in BLTouch Always reports -3.00mm:

    M558 P9 C"^" H4 F120 T6000 R0.5

    The pin shouldn’t need to be inverted pulled up. Your probe is probably reading 1000, ie already triggered. Remove the ‘^’. See

    1. The Z probe input pin will be on a Duet 2, or one of, or on a Duet 3. If using, you need to enable the pullup resistor using the ^ character in front of the pin name.


  • @droftarts Hey Ian, Thanks for your reply.
    Sadly, that doesn't seem to fix the -3.00mm I get from performing the G30 S-1 command 😞

    (Also, I'm not constantly seeing 1000, that seems to do what it should)

  • in your home (either homeall or homez) macro, do you have a g92? I had that for Z for some reason and it reset its position and I could not figure it out.

  • @Kiomatri said in BLTouch Always reports -3.00mm:

    (Also, I'm not constantly seeing 1000, that seems to do what it should)

    that is correct for the bltouch, it only triggers for a split second, you might never see it triggered in the web ui.

  • Moderator

    @Kiomatri said in BLTouch Always reports -3.00mm:

    Probe stopped at -3.00mm"

    A negative number here sounds very wrong and also very weird that it's exactly 3. How exactly are you doing the steps described to test the trigger height?

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