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stepper motors pulsing each other

Discussion in 'DrawBot' started by hantercans, Apr 11, 2019.

  1. hantercans

    hantercans Well-Known
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    Hi
    I've built a simple pen plotter using 3 stepper motors X/Y/pen control.
    They are driven by an Arduino Uno with Ver3 CNC shield and three drivers.

    Everything works very well using GRBL 1.1

    Only thing that niggles me is that when I jog any of the three motors, the motor moves
    as expected but there is aso a pulse (clunk) from the other two..

    Is this normal?

    PSU is more than adequate for the job..


    Thanks for any pointers

    Phil
     
  2. Alex Chambers

    Alex Chambers Openbuilds Team
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    A stepper motor is a powerful electromagnet - a large inductance. When it is switched off the collapsing magnetic field generates an electric current - often of reverse polarity and high voltage. Check your cable routing to see if you can minimise the chances of interference being transmitted back to your electronics.
    Alex.
     
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  3. hantercans

    hantercans Well-Known
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    Hi Alex
    Thanks for the response.
    I moved the cables around but to no avail.
    This "niggle" doesn't cause a problem to the working of the plotter but I could do without the clunk noise.

    Hmmmmmm... very odd

    Phil
     
  4. Alex Chambers

    Alex Chambers Openbuilds Team
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    If the "other" stepper is not moving (I realise you may not detect a single step) it sounds as though the power is switching off and back on again. An oscilloscope would be needed to confirm that - not usually standard workshop equipment. If your power supply has a display look for any flicker - again probably too brief to show up. Are your stepper cables screened? Most aren't. If so make sure screen is only grounded at one end.
    Alex.
     
  5. hantercans

    hantercans Well-Known
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    This is my DIY plotter....
     

    Attached Files:

  6. hantercans

    hantercans Well-Known
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    Alex, my cables aren't screened...worth trying I guess
    No ground loops as everything is mounted on plywood

    Your comment about the power switching on/off is interesting as it's the same
    clunk as when the plotter is first switched on and connected to my laptop...


    Phil
     
  7. Alex Chambers

    Alex Chambers Openbuilds Team
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    Apart from at the controller (where you haven't got much choice) your cables seem well separated. Screening might work. Have you done any calibration checks - I would expect interference between steppers to have an unpredictable effect when two motors were running (diagonal moves)
    Alex.
     
  8. hantercans

    hantercans Well-Known
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    Yes, I checked calibration and it's spot on with no bad effects during a plotter run.
    It just seems to happen when I press the jog control in Universal Gcode Sender (tried other gui's but same effect)

    Also tried a different CNC shield and a different Arduino Uno to no effect.
    And, tried using a 12 volt lead acid battery.... no effect on the clunk.

    Could be that this is normal with the shield and the large plywood base is acting as a sounding board for the clunk...


    Phil
     
  9. hantercans

    hantercans Well-Known
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    Alex
    I think you have set me on the right path to explaining the clunk with your comment about
    the power going on/off.

    I noticed that there was no holding current running through the steppers at rest.
    I altered a setting in GRBL to allow a holding current and yes, the clunk has gone but replaced
    by a "hissing/singing" noise in the steppers.
    So, you were right.....the power was indeed going off to the steppers between jogs ...

    Thanks to you I can now go and research in the right area

    Phil :thumbsup:
     
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