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Z-Axis Erratic Behaviour

kptjrnkptjrn
in Motor Control
Hi,
I have built a relatively large CoreXY pen plotter with a stepper controlled pen lift, very similar to the setup on a CNC-router.
The Z-axis has a single end-stop situated at the top of the stroke, so homing should lift the pen up to maximum height.
X and Y-axes work flawlessly and homes to the end-stops, retracts a bit and all is ok.

My problem is that I seam to have some erratic behaviour on the Z-axis, that I can't figure out. It might be, that I have got some settings wrong, but homing does not work as I would expect. I made the configuration file on the website and downloaded that. I might have missed something there. The issues are:
  • When homing all axes the pen lifts, homes XY and drops the pen down again. It never goes to the switch and stays there, as I would expect
  • Flipping the Z-Axis motor cable does not help and changing z-axis minimum to a negative number makes it worse, as it goes up, hits the switch and ignores it, and keeps going, losing steps
  • When hitting HomeZ button it just does a strange bounce around 10mm up and down again (it is set to move quite quickly), but it also never goes to the switch, retracts a bit and stops, as expected.
  • The end-stop seems to be working fine when using manual control. If It is hit while moving (up) it stops as expected, and will not let me move further up, but will let me move down again
I don't really care if I have to move the Z-axis in positive numbers to go down (away from the end-stop) or not. I would just like it to work like the X and Y-axes.

Any help would be greatly appreciated :)

Comments

  • RepetierRepetier
    Could be that you have cross talk to z end stop causing early trigger. Use a host software with console and send
    M111 S71
    to enable endstop debugging. Note that this can crash firmware so use that flag only for testing if it is z endstop.
    Then home Z and see if it reports endstop hit. If this is not the case check your z height. homing is 1.5 * printer height so if height is not high enough it will not move until endstop as well.
  • kptjrnkptjrn
    Ok, thank you, that might be the cause, but I still couldn't get it to work. I'll try to wire up some other switches tomorrow, and see if I can home it manually with those.
    I've tried running through the firmware configuration tool again, and messed about with the stepsticks on the RAMPS-board, and think I might have fried some of them, because now it doesn't even run the right direction anymore, it does run though, which is strange... Oh well, guess I have to pick up some new ones tomorrow as well and try again from scratch...
  • RepetierRepetier
    Config can not fry them only if your current is too high I'd say. 
    Maybe make sure ALWAYS_CHECK_ENDSTOPS is disabled. In this case cross talk can only make problems during homing. Also check with
    M119
    if an endstop is high. Moves in endstop direction are prevented if endstop is triggered or if you leave move area after homing.
  • kptjrnkptjrn
    Hi again,
    No, sorry I didn't mean it like that. I think I fried one or two of the stepper drivers, because I inserted it the wrong way round. I got a little confused because I have several different sets of drivers, and some have a pot pointing one way, the other kind is the opposite.
    I went through the configurator very meticulously this time, trying to understand everything that is going on and now I finally seem to have it homing properly on all axes.
    I think I must have had something mixed up with the homing direction and endstop placement, so sorry about that.
    Thank you for all your work and fast response, it is very much appreciated! Donation upcoming soon :-D
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