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Grbl hard limits and homing

Discussion in 'Control Software' started by John Meikrantz, Sep 5, 2015.

  1. John Meikrantz

    John Meikrantz Veteran
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    I have been using my Ox (Cebu) for a while now with minimal problems. Today for some reason, I started having noise issues that kept setting off my limit switches. Most annoying, and no source for .47uf capacitors anywhere locally. I only have limit switches set up for homing, with soft limits defined for the "far" end.

    So, to get a job done today, I disabled hard limits ($21). That works for the time being.

    My question is - can I still use a homing cycle with hard limits disabled?

    Thanks,

    John
     
  2. John Meikrantz

    John Meikrantz Veteran
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    Follow up question - is there any debounce on hard limits? Or is the homing debounce value $26 used by both homing and hard limits?

    -- John
     
  3. John Meikrantz

    John Meikrantz Veteran
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    Okay, I answered this question by myself! Yes, homing still works with hard limits disabled. Still not sure on the debounce question.

    -- John
     
  4. Sonny Jeon

    Sonny Jeon Veteran
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    Yes, the homing cycle still works with hard limits disabled. Although, if you have severe limit switch line noise, you may run into a problem with homing not working correctly.

    As for helping eliminate line noise, I've heard that shielded cables work well. Also, you can place any small value capacitor in parallel with your limit pin and ground. Larger values will simply take a little longer to change, but will be more resistant to noise. (Basically will increase the low-pass filter cutoff frequency). You can also try using NC switches instead and changing the Grbl limit invert setting. I've been told that NC switches can behave better.

    As for debounce, the Grbl homing debounce setting is a simple delay after a homing switch is hit. Nothing else. If you have a lot of line noise, debounce won't help you much anyway. That said, Grbl does have a compile-option in config.h that enables hardware debouncing, but I haven't checked if it still works in ages, as it's not a feature that anyone uses. It's just there for reference.
     
  5. John Meikrantz

    John Meikrantz Veteran
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    Thanks for the response. I should be able to get some capacitors wired in this evening. I have shielded cables, and things had been working well. Just recently had the issue start - seems to be router related.
     
  6. Joe Santarsiero

    Joe Santarsiero OB addict
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    They grounded at one end or both? They should be grounded at supply end only. :) Just checking.
     
  7. John Meikrantz

    John Meikrantz Veteran
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    One end. Haven't had a chance to add the caps yet, but I've turned off hard limits which "fixes" the problem for now. I only have limit switches wired for homing anyway with soft limits configured, not at all machine extents.

    -- John
     
  8. Sonny Jeon

    Sonny Jeon Veteran
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    If it's router-related, the problem is usually caused by an improper grounding or even the house circuit you're using. I've seen users have problems like yours get solved by moving their router to a different circuit than their electronics. Or altering their grounding scheme to a star-ground.
     

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