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Stepper moves twice as far/fast at it did before.

Discussion in 'CNC Mills/Routers' started by Rendermandan, Sep 28, 2016.

  1. Rendermandan

    Rendermandan Journeyman
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    Hey guys. I have a C-beam machine with an arduino grbl controller. I'm using stepstick DRV8825 stepper drivers and up until last night, they have been working just fine for almost 5 months. Last night I had a problem with my X axis. About 2 minutes into a cut in wood, there was a slight pause in movement, then all of a sudden my x axis moved twice as fast and twice as far as it should. I stopped the cut and did some testing. Y and z axis move fine, but x. Moves twice as fast and twice as far. I turned it off, restarted and still have the same problem. I checked the grbl settings and all axis steps were at 200. I also have two fans blowing across the heat sinks. So I don't think heat would have been the issue.

    Any ideas what happens?
     
  2. Paul Stoller

    Paul Stoller Veteran
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    Do you have the possibility of switching the drivers between X and Z or X and Y, if you can it might help to pinpoint where the failure could be happening. If the problem moves from axis to axis with the driver switch there is likely something going on with the driver hardware. if the problem persists on the same axis I would think it would have to be an issue with the stepper or software.

    All that being said I'm just taking my best guess from a general troubleshooting perspective.
     
    Mark Carew and GrayUK like this.
  3. David the swarfer

    David the swarfer OpenBuilds Team
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    seems to me the microstepping setting has changed, check the jumpers for proper contact. (turn everything off first)
     
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  4. dddman

    dddman Master
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    twice as fast or 2.54x faster? ;) Might have switched to imperial by itself?
     
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  5. Rendermandan

    Rendermandan Journeyman
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    Thanks guys for the suggestions, I will check them out tonight. As for being 2.54x faster. I'm not sure. It only seems to effect the X axis, If it were a units issue, I don't think it can be changed for a single axis.

    Thanks again.
     
  6. Rendermandan

    Rendermandan Journeyman
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    So I did some debugging tonight, I pulled the driver off the board, and checked the jumpers. Reinstalled the driver and had the same issue. I then swapped the driver with the z axis and the problem moved over to that axis, so its something with the driver chip. Luckily I had a spare since it came with 5 and I only needed 4. I replaced the bad driver and now all is fine. So here is my next question, what would have made the driver go bad? I'd hate to have this happen again, especially on a long cut, or expensive piece of material.....

    Thanks.
     
  7. joe li

    joe li New
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    Hi Rendermandan, I am working on build using the same hardware as you are. Do you mind sharing your grbl settings. And what step is your 8825 set to? I am having issues with travel distance being off. Thanks for the help.
     
  8. Rendermandan

    Rendermandan Journeyman
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    Joe, I know the are set to 1/8 step. I'm not at my machine, next time I get to it, I will copy my grbl settings for you.

    Unfortunately the new driver didn't last long. It did it again this morning ( edit: on the same x axis), So something is up... I was able to slow it back down by changing the steps from 200 to 100. But i want to figure out what is causing it to fail in the first place.
     
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  9. GrayUK

    GrayUK Master
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    Giving it some thought, the original fault would appear to be further down the line, i.e. wiring? If there were a wiring fault, say an intermittent short to earth, it could cause the failure in the driver, which you then moved to another axis and proved the driver to be faulty. However, you replace the driver, and the same fault knocks out the new driver! :banghead:
    You say it functioned well for 5 months, then I would seriously check all your wiring for wear and tare. :rolleyes:
    Gray
     
  10. Rendermandan

    Rendermandan Journeyman
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    Thanks Gray, I will have to tear into my controller box and look around for some loose wires or connections.

    Joe, here is a couple screen shots showing my grbl settings. You will note that my X axis steps are set to 100 at the moment instead of the normal 200.

    upload_2016-10-1_11-53-40.png

    upload_2016-10-1_11-53-58.png
     
  11. joe li

    joe li New
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    Thank you Rendermandan. Those settings were very helpful. The steppers are running much smoother.
     
  12. Rendermandan

    Rendermandan Journeyman
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    No problem, Joe, glad it helped.

    I went through my machine and checked all the wiring, solder connections, etc. everything seemed fine. My driver board is located on the back of the machine with quick connectors. It has two 50mm fans that blow air through the box. So it has great airflow.

    I opened it up to check things out, I also replaced the step jumpers just in case one was faulty. I loaded up some code and ran a dummy cut with the router turned off. After a few minutes I felt the heat sinks on the drivers and they were much warmer than I had anticipated, The x axis was quite hot actually. I turned the potentiometer down or up slightly and that did not seem to make a difference in heat. I also checked that I could rotate the x axis by hand freely. There was no binding. Any thoughts?

    I blew it out with the air hose, and buttoned it back up with a new driver and returned the steps back to 200. Lets see how how long this one lasts. I don't want to do any real work on it because I'm afraid of ruining a piece...
     

    Attached Files:

  13. snokid

    snokid Veteran
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    First I like your controller box, Great idea!!!

    using those 4 pin connectors how did you do the end of the cables where they enter the plug? If you look at microphones that those plugs were designed for they usually slide a small bit of tubing over the cable before they tighten down the screws. Might want to check or redo the x axis wires (cut the plug off and rewire it)

    I would run a facing code or better yet a large circle pocketing path that would work the motors pretty hard. till you get it figured out I don't think I would walk away from the machine anytime soon...
    good luck!
     
    GrayUK likes this.

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