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nuisance hard limit alarms

Discussion in 'Controller Boards' started by Metalguru, Apr 29, 2016.

  1. Metalguru

    Metalguru Master
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    I recently put limit switches on my machine, and now I continuously get nuisance hard limit alarms. It's got an Arduino controller running GRBL .9. I used shielded wire for the switches, and ran the wires well away from all the power wiring. I first noticed it when an infrared motion light in my garage turned on, I got a hard limit error. So, I put in a good AC power filter on the laptop and control electronics supply. Seemed to correct the problem - for a while.

    Then, last night I was trying to cut some plates and the dang machine wouldn't run for more than 30 seconds without a hard limit alarm. Seems to be tied to the router being noisy, turning the router on and off will trigger it every time.

    I tried plugging the router into a different outlet, no luck. Rearrange the cords so they were nowhere near the system, no difference. I added low value (2k ohm) pullup resistors to +5v to the limit switch inputs on the Arduino board. I was thinking if the Arduino just used the internal programmable pullup resistors on the inputs, they may be just a suggestion of a pullup - 100k or so. No difference. I gave up for the day, but I need some ideas to try tomorrow.

    Should I try some caps to ground on the limit input pins? A tinfoil hat for the router? I notice the router does not have a ground wire, is this an issue? I have the frame of the machine grounded, but somebody once told me to run individual grounds to each axis motor. Is this a good idea?

    Help?
     
    #1 Metalguru, Apr 29, 2016
    Last edited: Apr 29, 2016
  2. Julius

    Julius Veteran
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    are they set to NO or Nc wiring? Might help to send $21=0 before any machining operations. Usually toggling it will work for me.
     
  3. Metalguru

    Metalguru Master
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    I believe they are NO. That's not a bad idea, if they were wired for NC, there is no way they could be triggered by noise, cuz they'd be shorted to ground all the time.

    Julius, you are a genius! Even if you do look creepy...:eek: Or at least your avatar does...

    BTW, what do you mean send $21=0? You mean in the GRBL settings?
     
  4. Julius

    Julius Veteran
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    yea, it disables the hard limit setting. Home the machine, then disable it.
     
  5. OldDogSleeping

    OldDogSleeping Well-Known
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    Adding some 1uf capacitors between the inputs and ground, solved the problem on mine.
     
  6. Metalguru

    Metalguru Master
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    Yeah, the 1uF caps worked fine. Who says an old dog can't teach new tricks?

    Next machine will have NC limit switches. Enabling and disabling the limit switches all the time would get old pretty fast.

    Thanks guys.
     
  7. RGUERI1

    RGUERI1 Well-Known
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    I have been going round-and-round, with the "Hard Limit" problem. I have built a hybrid of the OX-METAL, with XPRO V2. I ended up going for the NEMA23 HT motors. Long story short, I have tried all the mods/tricks to eliminate the "Hard Limit" error. I have come to the conclusion that it is not a true signal input but power issue with the XPRO controller. I somewhat verified this by disconnecting all limit switch wiring from the board and I still got the "Hard Limit" signal. Another proof was to monitor the verbose output and all the input/limit bits remained "000." I have found that adjusting the current potentiometers, on the XPRO V2, does help alleviate some of the false triggers but also limits the performance of the steppers. I would assume that this is due to the stepper current rating of 3.0A and the XPRO V2 peak current rating of 2.8A. I neglected to check this spec before building my machine. I have ordered replacement steppers and they should be in tomorrow. I actually ordered a set of 269 oz/2.8A and a set of 340 oz/1.8A steppers. I'll hopefully get them on this weekend and give a report on how they perform. I was skeptical of the 340 oz/1.8A, but wanted to see how they work. I'll keep y'all posted.
     

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