Z Probe Trigger Height G30 S-1 height changing every probe



  • I have an Ender 3, every time I run G30 S-1 I get a different height. I thought this would be a mechanical or mounting issue with the BLTouch so, I have gone through to make sure everything is tight. Here are the results from 5 probes

    8:24:50 PMG30 S-1
    Stopped at height 0.595 mm
    8:24:45 PMM120

    G91
    G1 Z5 F6000
    M121

    8:24:39 PMG30 S-1
    Stopped at height 0.582 mm
    8:24:34 PMM120
    G91
    G1 Z5 F6000
    M121

    8:24:32 PMG30 S-1
    Stopped at height 0.570 mm

    8:24:27 PMM120
    G91
    G1 Z5 F6000
    M121

    8:23:49 PMG30 S-1
    Stopped at height 0.553 mm

    8:23:44 PMM120
    G91
    G1 Z5 F6000
    M121

    8:23:40 PMG30 S-1
    Stopped at height 0.540 mm

    Any ideas on what the cause could be? I saw an older post with the same issue but no resolution. The forum prompted me to open a new discussion.


  • Moderator

    @apex2011 Please post your config.g, and a picture of your printer (so we can see how Z axis is set up). My first guess would be, as the probe result is moving in one direction rather than randomly, that you're somehow losing steps or something is slipping on your Z axis, so checking Z motor settings is important, and the speed you are doing the probing at. It may be as simple as slowing down the probing speed. What probe are you using? When you are doing the probing, is the bed hot, cold or warming up? If the bed is warming up, this may also effect probing results.

    A longer set of probing results, like 20, might also help narrow down the problem, to see if it stabilises, or keeps increasing.

    Ian



  • @droftarts Thank you,
    I am using a BLTouch for a probe, I have been probing with the bed cold
    here is my config.g and below that is a picture of my setup

    ; Configuration file for Duet Maestro (firmware version 2.03)
    ; executed by the firmware on start-up
    ;
    ; generated by RepRapFirmware Configuration Tool v2.1.4 on Thu Jan 02 2020 08:26:36 GMT-0500 (Eastern Standard Time)

    ; General preferences
    G90 ; send absolute coordinates...
    M83 ; ...but relative extruder moves
    M550 P"Ender3 Duet 2 Maestro" ; set printer name
    M918 P1 E4 F2000000 ; configure direct-connect display

    ; Drives
    M569 P0 S0 ; physical drive 0 goes backwards
    M569 P1 S0 ; physical drive 1 goes backwards
    M569 P2 S1 ; physical drive 2 goes forwards
    M569 P3 S0 ; physical drive 3 goes backwards
    M584 X0 Y1 Z2 E3 ; set drive mapping
    M350 X16 Y16 Z16 E16 I1 ; configure microstepping with interpolation
    M92 X80.00 Y80.00 Z400.00 E741.00 ; set steps per mm
    M566 X600.00 Y600.00 Z60.00 E120.00 ; set maximum instantaneous speed changes (mm/min)
    M203 X9000.00 Y9000.00 Z600.00 E300.00 ; set maximum speeds (mm/min)
    M201 X500.00 Y500.00 Z120.00 E100.00 ; set accelerations (mm/s^2)
    M906 X800 Y800 Z800 E800 I30 ; set motor currents (mA) and motor idle factor in per cent
    M84 S30 ; Set idle timeout

    ; Axis Limits
    M208 X0 Y0 Z0 S1 ; set axis minima
    M208 X235 Y235 Z260 S0 ; set axis maxima

    ; Endstops
    M574 X1 Y1 S1 ; set active high endstops
    M574 Z1 S2 ; set endstops controlled by probe

    ; Z-Probe
    M558 P9 H3 F100 T6000 A10 S0.03 B1 R0.5 ; set Z probe type to bltouch and the dive height + speeds
    G31 P25 X-47 Y-10 Z1.018 ; set Z probe trigger value, offset and trigger height
    M557 X5:190 Y10:215 S60 ; define mesh grid

    ; Heaters
    M307 H0 B0 S1.00 ; disable bang-bang mode for the bed heater and set PWM limit
    M305 P0 T98801 B4185 R2200 ; set thermistor + ADC parameters for heater 0
    M143 H0 S80 ; set temperature limit for heater 0 to 80C
    M305 P1 T98801 B4185 R2200 ; set thermistor + ADC parameters for heater 1
    M143 H1 S280 ; set temperature limit for heater 1 to 280C

    ; Fans
    M106 P0 S0 I0 F20 H-1 ; set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned off
    M106 P1 S0 I0 F20 H1 T45 ; set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned on
    M106 P2 S1 I0 F20 H1:0 T45 ; set fan 2 value, PWM signal inversion and frequency. Thermostatic control is turned on

    ; Tools
    M563 P0 S"Hotend" D0 H1 F0 ; define tool 0
    G10 P0 X0 Y0 Z0 ; set tool 0 axis offsets
    G10 P0 R0 S0 ; set initial tool 0 active and standby temperatures to 0C

    ; Custom settings are not defined

    ; Miscellaneous
    M501 ; load saved parameters from non-volatile memory
    M911 S21 R23 P"M913 X0 Y0 G91 M83 G1 Z3 E-5 F1000" ; set voltage thresholds and actions to run on power loss
    T0 ; select first tool

    f071455d-86d3-4855-9550-d98c2b763b93-image.png



  • @apex2011 said in Z Probe Trigger Height G30 S-1 height changing every probe:

    I am using a BLTouch for a probe,

    is it a genuine bltouch? clones are known to be inaccurate.



  • @apex2011 said in Z Probe Trigger Height G30 S-1 height changing every probe:

    M558 P9 H3 F100 T6000 A10 S0.03 B1 R0.5 ; set Z probe type to bltouch and the dive height + speeds

    Just a quick guess but change the above line to:

    M558 P9 H6 F100 T6000 A10 S0.03 B1 R0.5 ; set Z probe type to bltouch and the dive height + speeds

    If that works, try upping the feed rate (the F100) to something like F200.. But making this too fast can quickly break things 😉



  • @Veti Yes, It is a genuine BLTouch



  • @jrsphoto I tried making this adjustment, unfortunately I am still having the same issue


  • administrators

    It looks like the trigger height is decreasing with every probe. The most likely cause of this is that when the probe triggers and Z movement is stopped abruptly, the Z motors are unable to stop immediately. So they overshoot, leaving the print head lower than the firmware thinks it is.

    To test this theory, try reducing the probing speed, which is the F parameter in M558. You currently have F100, so try F50.

    Another possibility is that you have the Z acceleration too high or the motor current too low, so that when you command Z to move back up 5mm, steps are lost during the initial acceleration. To test this, try reducing the Z acceleration in the M201 command. You currently have Z120, so try Z60.


  • Moderator

    @dc42 said in Z Probe Trigger Height G30 S-1 height changing every probe:

    It looks like the trigger height is decreasing with every probe.

    Isn't the trigger height increasing with each probe? Newest is first, oldest last. That's what had me stumped.

    8:24:50 PM Stopped at height 0.595 mm
    8:24:39 PM Stopped at height 0.582 mm
    8:24:32 PM Stopped at height 0.570 mm
    8:23:49 PM Stopped at height 0.553 mm
    8:23:40 PM Stopped at height 0.540 mm

    Ian



  • @dc42 I tried both of these suggestions one at a time. I am still receiving the same result.

    6:19:38 PMG30 S-1
    Stopped at height 0.452 mm

    6:19:29 PMG30 S-1
    Stopped at height 0.438 mm

    6:19:01 PMG30 S-1
    Stopped at height 0.423 mm
    6:18:54 PMM120

    6:18:50 PMG30 S-1
    Stopped at height 0.410 mm

    6:18:29 PMG30 S-1
    Stopped at height 0.382 mm

    6:18:17 PMG30 S-1
    Stopped at height 0.368 mm

    6:18:08 PMG30 S-1
    Stopped at height 0.357 mm

    6:17:57 PMG30 S-1
    Stopped at height 0.340 mm

    6:12:57 PMG30 S-1
    Stopped at height 0.315 mm

    6:12:42 PMG30 S-1
    Stopped at height 0.298 mm



  • Thank you everyone that has given me input, I am very confused with this. I've been messing with the M558 Line. It now reads every 2 stop heights the same.

    Here is what I changed it to M558 P9 H6 F80 T6000 A10 S0.005 B1 R0.5

    8:33:00 PMG30 S-1
    Stopped at height 0.510 mm

    8:32:51 PMG30 S-1
    Stopped at height 0.510 mm

    8:32:42 PMG30 S-1
    Stopped at height 0.507 mm

    8:32:33 PMG30 S-1
    Stopped at height 0.507 mm

    8:32:24 PMG30 S-1
    Stopped at height 0.507 mm

    8:32:13 PMG30 S-1
    Stopped at height 0.505 mm

    8:32:00 PMG30 S-1
    Stopped at height 0.505 mm

    8:31:47 PMG30 S-1
    Stopped at height 0.498 mm

    8:31:37 PMG30 S-1
    Stopped at height 0.498 mm



  • As a temporary measure I've backed up my config and reverted back to manual leveling. I have yet to successfully print since switching to the Duet board. Hopefully this gets me going.


  • administrators

    Let us know how you get on. I notice that you are currently losing about 0.0025mm every other probe attempt, which at the 400 microsteps/mm you are using is 1 microstep. This gives me an idea about what may be happening.


  • administrators

    @apex2011, how do you have the Z motors connected to the Duet?



  • I followed this document (Step 10) https://duet3d.dozuki.com/Guide/Ender+3+Pro+and+Duet+Maestro+Guide+Part+1:+Wiring/37

    Modified the plug so it would connect directly to the Duet without re-terminating.



  • @dc42 I decided to take everything back to step one and go through the entire process again in case I missed something. I am still getting the same issue where the probe reads a different value every time



  • @apex2011 What's your current on the z motors? it definitely sounds like you're losing a step.



  • @Turbo Sorry if this is a dumb question but how do I confirm this?



  • @apex2011 in your config.g file, you'll have a line that looks like this:

    M906 X1000 Y1000 Z1000 E850:850 I50 ; Set motor currents (mA) and motor idle factor in per cent
    

    the z value is what you're after, and should be around 800 or so.



  • @Turbo ah OK, that is
    M906 X800 Y800 Z800 E900 I30 ; set motor currents (mA) and motor idle factor in per cent



  • okay so current looks fine. you could try bumping up by a factor of 50 to 100 and see if you get any changes, but I'm not sure about that one.
    you could also adjust the electromagnet on the bltouch by tightening/loosening the allen screw on top, again, not sure, but im throwing things out there that might help.



  • @Turbo thanks! I'll give those a try


  • Moderator

    Also might help to check the tension on your V wheels on the Z carriage. Check the lead screw nut as well to see if it's loose in its mount or something. Check the lead screw coupler too. And Z motor mount.

    It was asked earlier, but are you testng with the bed warmed up? Have you PID tuned the bed heater? Running the bed heater in bang-bang mode can cause the heating plate to flex slightly as it cycles current through it. Hard to probe a moving target.



  • @Phaedrux I just checked the tension on the V wheels, it looks good, there's no play on the rail. I have done PID tuning. I have been testing with the bed cold


  • Moderator

    Firmware version?


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