C Axis Homing / Moving

Discussion in 'Tool heads & ToolChanger' started by phoenix, Nov 9, 2019.

  1. phoenix

    phoenix Member

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    Hello, I have finally completed my build and gotten the first print :)

    However as I try to get the actual toolchanging going I am hitting a problem with the C Axis (the locking mechanism). Homing seems to work well for all axis, but this is the behavior I am encountering on the C Axis:
    - Homing works, but seems to take longer than expected: when going to 0, the C axis stays about 6-7 seconds at 0, before returning to the 123 position (horizontal).
    - The 123 position does not correspond to horizontal: that would be 130.
    - The first locking of a tool works (toolhead aligns and grabs the tool, with C Axis turning to 33 and locking the head).
    - Upon returning the tool I often see that when unlocking, the C axis 123 position has slightly shifted (it is then more aligned to horizontal)
    - When grabbing another tool, I very often have that after aligning and grabbing the tool, the C axis shows "33"(ie locked) but the locking mechanism has not moved. Meaning the tool is then not locked (and obviously falls out).

    I suspect there is a challenge with the homing and Driver Amps, but not sure how to fix this.
    Any ideas?

    Thanks!
     
  2. Greg Holloway

    Greg Holloway Administrator
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    Hi,

    We, I, havent been able to tune stall detection for the C axis, so it's homeing cycle is to basically crash the endstop. the power is dropped so there is no damage to the motor.

    There are very small difference with all the machines and you may find the horizontal is different for your machine, and it may be different on others too. The refernce configuration is exactly that, a reference point on which you can start with and then fine tune to your own machine.

    If you find that the 123 position isn't good, but 130 is, feel free to change it :)

    The same goes for all the other configured options.
     
  3. phoenix

    phoenix Member

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    Thanks Greg, I have tuned the 123 position to 130. But why does the tool not lock: when doing a Tx, it grabs the tool, the motor position shows 33 (locked) but the axis hasn't turned. Do I risk anything turning up the Amps - what is your experience?
     
  4. Greg Holloway

    Greg Holloway Administrator
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    what's the actual error?

    Is it that the head isnt going into the correct position to pickup the tool, or is the bar not rotating?

    Move the head to the front and drop the bed down ~50mm. Take the tool off it's dock and hold it against the toolhead tool coupler, then click the Coupler - Lock Macro.

    If the toolhead is working ok it will grab the tool, if not then the issue is with the toolhead. if it picks it up fine I would suggest the tool pick up positions are not quite aligned correctly.
     
  5. phoenix

    phoenix Member

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    The actual error is that the bar is attempting to turn but not doing so (or minimally).

    This happens at all tool docks (T0 to T3), and when I do it manually (as you describe, with the macro) it works just fine...
     
  6. Greg Holloway

    Greg Holloway Administrator
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  7. phoenix

    phoenix Member

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    Yes, the toolhead looks fine and I had the same idea that the bar is not going far enough. I have been going through the Step 10, and have just done so again (adjusting the docks as close to Y243 as possible). It looks a bit better, but it is still not reliable (about 50% of the tool pickups are jamming the bar).

    Could it be that there is an issue with positioning: during rapids (G0 moves), the toolhead seems to stall (although it looks like the electronics are detecting and compensating as I was not seeing large positioning errors, but I have only tested simple one toolhead prints).

    Really appreciating the support - is there anything else I can try?
     
  8. Greg Holloway

    Greg Holloway Administrator
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    can you check the grubscrews holding the pulleys onto the motors are tight.

    the stop-start movement is caused by bed mesh compensation.
     
  9. phoenix

    phoenix Member

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    Thanks Greg, I ensured the motor pulleys are properly tightened. I could tighten a bit more, but I don't think they were loose.

    In any case after tightening I am seeing the same behavior: running the toolchange_test.gcode works fine for the first 3-4 toolchanges, but then invariably fails (it doesn't lock).

    Another datapoint is that I tried to print the toolchange cover stl. I was surprised to see the outside quite rough (walls are not flat) and dimensionally not accurate (as if there are lost steps in both directions). Is there a simple way to slow down the rapids and see if that could be the case? I've checked for binding / difficult movement but all I can sense is that the axis is stiff, but not difficult to move (as it is supposed to be).

    Thanks for any pointers!
     
  10. Greg Holloway

    Greg Holloway Administrator
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    you can adjust the speed of the machine in the web interface. you could also edit the config.g file and lower the acceleration and top speed settings.

    Can you post photos of the prints you are getting?

    Go over everything and check nothing has come lose.
     
  11. phoenix

    phoenix Member

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    This is what I am getting... Stock settings using Simplify3D. While the Benchy came out ok, so really puzzled.

    I'll check tightness and slow down machine to see if I can find something.


     

    Attached Files:

  12. Greg Holloway

    Greg Holloway Administrator
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    What material is that?
     
  13. phoenix

    phoenix Member

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    Colorfabb PLA, printed at 200deg.
     
  14. Greg Holloway

    Greg Holloway Administrator
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    What print settings are you using?
     
  15. phoenix

    phoenix Member

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  16. Greg Holloway

    Greg Holloway Administrator
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  17. phoenix

    phoenix Member

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    Closing - I think I have found the culprit: as usual kicking myself for overlooking the simplest cause... After going through all mechanical parts I found that the hotend on T1 was wobbling and the plastic nut was not tight anymore...

    After 20 successful toolchanges without intervention I need to conclude that toolchanger now seems to change tools without trouble :)

    Thanks Greg for your help!
     
    Greg Holloway likes this.

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