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Unanswered Where to set Marlin offset from -X limit for proper "home" position

Discussion in 'Troubleshooting' started by joea, Mar 18, 2023.

  1. joea

    joea Active Member

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    What is the label for where to set the distance to move X while homing, after hitting the -X limit switch? Marlin seems to say that is "fixed" and can be set with M206, but, frankly, their descriptions of things are not always crystal clear.
     
  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    It is defined by the size of the print bed and the dimensions of each axis which is then used with the configuration of the home position and some math to sort out where the bed center is.

    These are all parameters in the CONFIGURATION.H

    If you tell it the bed (or the printable area) is 200x100 (ignoring the Z for now) and that the HOME position is 0 x 0 it determines that the center is 100 x 50 :)

    It will stop once the HOME switches are tripped (same for endstops if those are installed and configured). In fact HOME is the one position that is mechanically "known" on the Robo. It is the one with sensors... (everything else is math)
     
  3. joea

    joea Active Member

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    OK. My issue is that when I do an X home, (this is NOT a ROBO, but support elsewhere is scant), it hits the limit and goes _X a small distance. Where it stops the left extruder nozzle is not at X:0 but at X:-20 or so. Far too much to adjust with the X limit switch .

    I want to believe there is a value somewhere in configuration.h or elsewhere that can fix that.

    FWIW, I have confusion over where "home" is. To me "home" is where the start is (ahem), that is X0,Y0. And when homing X or Y (or both) that is where, more or less, the carriage ends up. However, if homing Z, it meanders out to "bed center" and probes for the bed. I get the last part, but, "I" ( as in master of the universe (small "U")) fee; it should them meander back to 0,0, for . . . well . . because.
    Granted, from the LCD display of X, Y and Z, it appears to know where it is, but . . . sigh.
     
  4. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Is it running Marlin? If so do you know which version?

    The endstop behavior is controlled in the firmware and the default for HOME endstops in the recent versions of Marlin is to FULL STOP the axis when an axis endstop is hit.

    However... depending on the version there actually were a few bugs on this:

    https://github.com/MarlinFirmware/Marlin/issues/21559

    https://3dprinting.stackexchange.com/questions/2996/endstops-will-not-trigger-using-marlin-firmware

    If it is not Marlin then -- not clear although it would almost have to be a firmware setting.
     
  5. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    All of the R1 series came with version 1.0.x, the R2/C2 initially had 1.1.x -- there are folks who have figured out how to run later versions on the Robo (2.x) but I left mine stock versions (because they work and nothing new I needed).

    I do have some other brands that use later versions of Marlin and even one that uses Repetier firmware. :) On all of them the home endstops work.

    I think I would sanity check that the endstop switch is actually reporting open/close correctly. If there is an even slight delay it will continue to drive the extruder until it see the switch toggle. A faulty/flakey switch would not help things.
     
  6. joea

    joea Active Member

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    The end stop seems to work properly. The problem is moves slightly off the stop, just as Y does, and holds there. Y is right on the Y0 mark but neither extruder is correctly on X0. And, after homing Z and it stops near bed center, shows it moved 1/2 the bed width (150mm), as indicated on the LCD, but the nozzle(s) do not line up on 150mm, being off by the same amount as at "0,0".

    I'll probably call it a day now.
     
  7. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Hmm, check the drive. A loose belt (for example) or anything that can make the drive for an axis (X or Y) slip can cause that effect. It thinks it move 100mm but really only moved 90% of that -- the reverse can be true as well where it moves further than it calculated. Start simple can check that a 100mm move on an X or Y is actually 100mm
     
  8. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    This does sound like the X or Y origin (home) is not acting correctly and an involuntary offset is getting introduced
     

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