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Partially Solved X-Axis Shifting Arbitrarily

Discussion in 'Troubleshooting' started by GooBazooka, Aug 30, 2016.

  1. GooBazooka

    GooBazooka New Member

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    X-axis seems to shift arbitrarily during prints. Example picture attached. The shift seems to be always to the right at different times in a print. I've attempted to print the same object a few times and the shift has occurred in different spots every time.

    What I HAVE tried:
    • Lubricating linear bearings. Lithium grease
    • Inspected chrome rods for damage None that I can see or feel
    • Tightening the set screws on the toothed pulley. No change in print shift
    • Changing the linear bearings. LMUU8 bearings from Amazon. Lubed with lithium grease
    • Replacing the X-axis belt. Toothed belt from Amazon
    • Replacing the X-axis stepper motor. Compatible NEMA 17 from Amazon. No flat on motor shaft for set screw but I don't see that contributing to the issue.
    What I HAVE NOT tried:
    • Updating drivers. Reason: I don't really want to mess with anything that complex. I would imagine all drivers would be handled by software/firmware updates. In any case, if it were firmware, all the axes would be misbehaving, which isn't the case.
    • Replacing any boards I don't want to mess with them if I don't have to
    Any and all suggestions are welcome.
     

    Attached Files:

    #1 GooBazooka, Aug 30, 2016
  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Belt tight enough?
    Getting it right is not a thing I can describe in detail, but it needs to be tighter than I would have imagined.

    Assuming it is not the belt skipping (you already eliminated the drive cog) ...the only other thing that could be an issue is the RAMPS itself or (more likely) the X axis stepper driver. You can tune them (the stepper driver) if you want to try, it is easier in my opinion to just replace them. These are far more likely to fail than the actual stepper motor.

    Of course, under warranty you should be having this conversation with Robo support and get some parts out to you :)
    Out of warranty the driver cards are cheap: https://www.amazon.com/Hobbypower-StepStick-Stepper-Driver-Printer/dp/B00MQR93QC
    (merely an example)
     
    #2 mark tomlinson, Aug 30, 2016
  3. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Oh and obviously you have checked this :) but the other than that can cause an axis shift suddenly is something blocking the travel. Like a wire getting caught or in the way, etc. Just including that for completeness.
     
    #3 mark tomlinson, Aug 30, 2016
  4. GooBazooka

    GooBazooka New Member

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    The belt seems to be tight. Enough to give a hum when plucked. I have it pulled together with zip ties at the moment. And there are no wires in the vicinity or even tight enough to cause any kind of shift.

    I just thought of another way to diagnose the problem. I might switch the X and Y stepper outputs to see if the problem is located on the board. If the problem moves to the Y-axis, at least I've located the a potential problem source.
     
    #4 GooBazooka, Aug 30, 2016
  5. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Bingo. Excellent idea.
    Swapping the stepper driver card itself would be even better, but more work :)
     
    #5 mark tomlinson, Aug 30, 2016
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  6. GooBazooka

    GooBazooka New Member

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    Has there been an issue like this before? Could it be voltage/current related?
     
    #6 GooBazooka, Aug 30, 2016
  7. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Absolutely. If the stepper driver card is malfunctioning then you can be certain this would happen. Stepper dying could cause it as well, but that is less likely and you already swapped them so your steppers are likely fine.
     
    #7 mark tomlinson, Aug 30, 2016
  8. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    The most common cause is loose belt or belt drive cog, but you checked those.
     
    #8 mark tomlinson, Aug 30, 2016
  9. GooBazooka

    GooBazooka New Member

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    Something I forgot to mention is the heat generated by the original stepper. It wasn't too hot to touch but it seemed hotter than it should be. I estimate it topped out at ~120 F
     
    #9 GooBazooka, Aug 30, 2016
  10. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    The heat generated is controlled by the amount of current the stepper driver is pushing. Too little and your stepper will drop steps, too much and it will run hot. Hard to say how hot is too hot... they do run warm.
     
    #10 mark tomlinson, Aug 30, 2016
  11. GooBazooka

    GooBazooka New Member

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    Weird thing happened: I switched the X and Y stepper drivers and the print is going smoothly....too smoothly... Only an hour into the print so there's time to screw up.
     

    Attached Files:

    #11 GooBazooka, Aug 30, 2016
  12. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    So the stepper driver was not tuned correctly for that stepper motor (and is working better with the other).
    They are cheap -- I'd suggest some spares :)
     
    #12 mark tomlinson, Aug 31, 2016
  13. GooBazooka

    GooBazooka New Member

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    The print turned out great but as good as that is for me in the short term, it's the long term implications that I have a problem with. Why did this manifest itself like this? That is, why did it choose to become "out of tune" with my stepper motor after several hundred hours of printing? And why did it work so well when I swapped the X and Y stepper drivers? If they were interchangeable, that should have exhibited the same modes of failure but on the other axis. WHY?!?

    I guess I need to do some research. How does one go about tuning a stepper motor to a driver anyway?
     
    #13 GooBazooka, Aug 31, 2016
  14. Ryan TeGantvoort

    Ryan TeGantvoort Active Member

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    #14 Ryan TeGantvoort, Aug 31, 2016
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  15. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Yea, the stepper drivers are current divers and they want to be fine-tuned for the specific stepper. But (always a but) in most cases they will work fine out of the box. Sometimes a slight tweak up or down helps. I would suggest having a spare on-hand in case that one completely fails. They are a couple of dollars (US) each max. Eventually they will need replacement :)
     
    #15 mark tomlinson, Aug 31, 2016
  16. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    P.S. Welcome to the State Of Technology in the majority of the 3D printing world :)
    A lot like personal computing back in the 80's
     
    #16 mark tomlinson, Aug 31, 2016
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  17. Ryan TeGantvoort

    Ryan TeGantvoort Active Member

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    Also if you have an R1+, they have separate Z drivers for the motors. Which I could see causing problems if they are not calibrated the same, but might not ever be noticeable. So I calibrated mine to match, or at least really close.
     
    #17 Ryan TeGantvoort, Aug 31, 2016
  18. danzca6

    danzca6 Well-Known Member

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    Totally agreed. I was pondering that the other day as to why Robo thought that was a good idea. Definitely best to have them dialed in the same.
     
    #18 danzca6, Aug 31, 2016
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