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Debugging Limit Switches

Discussion in 'CNC Mills/Routers' started by DarkPenguin, Jul 30, 2020.

  1. DarkPenguin

    DarkPenguin Well-Known
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    Hi,

    So my Openbuilds limit switches have been peachy since I installed them and figured out how they work.

    Suddenly they are tripping in the middle of a job. Randomly. I've changed nothing on the setup. The only thing wrong with the machine are two wheels that need adjustment. Not a limit switch thing.

    I've moved wires around. Added ferrite beads to just about everything. No joy. And no change.

    How do I debug this? Why does this start out of nowhere? Can my router (makita) be screwing me? Do these things start making more noise out of nowhere? I have two wall warts connected to my PC. Can they start to noise things up?

    I have not power cycled the BlackBox. Is this worth doing? I've reset it a number of times. But not the power.

    I'm trying to figure out how to tell which one is tripping. I homed the machine and pulled the y axis plug.

    Thank you for your help.

    Tom
     
  2. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
    Staff Member Moderator Project Maker Builder Resident Builder

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    Grbl uses port-group interrupts to speed up detection (important to stop in time, polling is too slow) but that does mean even grbl does not know which input it was. The group as a whole reports a limit hit.

    Apart from emi, a switch itself can get damaged mechanically (vibration makes it close) which wiggling it while running an aircut can help diagnose

    Power cycle probably wont make a difference.
     
  3. Corey Corbin

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    I had a EMI problem when I got my XYZ probe. Now its not the probes fault it was mine. When I first built the machine I was aware of the emi of limit switches so bought opticouplers to isolate them. I had not had one problem with interference. When I first got the probe after I was done zero'in my part I would place the probe on the table next to the machine. Well I started having trips here and there. I would have job here and there not finish. Then the machine would finish a job. Then on one job it couldn't even travel a inch and then it would say it had to re home for safety. Then I looked over and realized I had thrown the probe on the table and the little magnet had attached its self the PSU of my 500w spindle. Ahhh! So now I place it far away from any power supply. I put it goes in a drawer on the workbench. I have not had a emi trip since. Just thought I would share, something small like a habit of where I placed a piece of equipment was causing the trip. And I do believe it was tripping through the probe cause I still have the opicouplers on the limit switches.
     
    Peter Van Der Walt likes this.
  4. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
    Staff Member Moderator Project Maker Builder Resident Builder

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    That's one to remember for sure!

    And yeah, it happens
    The other day I couldn't understand why all of a sudden my plasma was killing the USB ports on the PC all at once all of a sudden. Turns out i was just shooting some video, unplugged the camera but left the USB cable plugged into a front-usb port on PC. That hanging cable acted like an antenna
     
  5. DarkPenguin

    DarkPenguin Well-Known
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    Neato. I just leave the xyz probe hanging off the back of the machine. Guess I'll disconnect it.

    But I haven't had it trip since I power cycled it. Still running tests.
     
  6. DarkPenguin

    DarkPenguin Well-Known
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    It ran for hours today. All I did was kill the power and pull the usb cable. Re-homed and ran what was failing for hours and hours.
     
  7. Corey Corbin

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    Good catch. And a note to self to remember to remove all USB cords not in use.

    @DarkPenguin nice glad you found something that worked.
     

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