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dual gantry lag

Discussion in 'CNC Mills/Routers' started by Michael Warchut, Nov 1, 2015.

  1. Michael Warchut

    Michael Warchut Well-Known
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    So I was doing some testing today on engraving on AL plate. Overall it was coming out ok but I noticed while watching it that one side of the dual gantry seems to lag behind the other when the Y axis is moving. Any recommendations on what to look at here or to adjust? Or could it be a bad motor or a misadjustment on the motor driver not completely matching the other one? If the latter is there a good way to sync both steppers so they get driven the same or is it pretty much trial and error?

    Thanks

    Michael
     
  2. Joe Santarsiero

    Joe Santarsiero OB addict
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    Hi Mike,
    What drivers and software are you using?
    Double check your motor couplings or belt pulleys to make sure they're not slipping.
     
  3. Michael Warchut

    Michael Warchut Well-Known
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    Sorry.. I should have included that rather important info. I have a TinyG V8 board and was using chilipeppr to run some gcode generated by f-engrave. I've already looked at the most obvious (to me that is) stuff. I'm hoping there is something I didn't consider. It would seem to me that if one driver is pushing one stepper a little harder than the other that something like this might happen as well. Or am I reaching here.
     
  4. Joe Santarsiero

    Joe Santarsiero OB addict
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    Swap the wiring to the two motor drivers and see if the lag occurs at the other motor.

    The driver pots do have to be tuned to within each other. I think one needs an oscope to do this objectively, but most members here seem to get things running by eyes and ears without a problem.
     
  5. Michael Warchut

    Michael Warchut Well-Known
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    Ill try that.. Luckily I have a scope if I need it. Thanks.
     
  6. Hamdi Hirzallah

    Hamdi Hirzallah Well-Known
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    guys, when you say scope, do you mean Oscilloscopes? how would those be useful for stepper calibration?
    would one of those $18 oscilloscopes on aliexpress do the trick?

    just for reference, I can get this one for about $18

    and this one for about $60
     
    #6 Hamdi Hirzallah, Nov 2, 2015
    Last edited: Nov 2, 2015
  7. Joe Santarsiero

    Joe Santarsiero OB addict
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    Yes. Oscilloscope. I'm not that electrically savvy unlike some of the other members, but I believe you would check the coils of each motor for matching current while energized and adjust the pots accordingly. In writing this, I think you might be able to just check and go by the resistance back at the pot with a regular multimeter to get fairly close with both motors. Then again I could be way off base here. I don't have my tinyG anymore either.
     
  8. Michael Warchut

    Michael Warchut Well-Known
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    I haven't looked at using the scope yet so I can't input much about accuracy but I'd be wary of those scopes and their value. When you say scope I think of this one here that I have.. http://goo.gl/A5px2L
     
  9. Ronald van Arkel

    Staff Member Resident Builder Builder

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    Micheal,

    Make sure both wires are the same length to the left and right motor, and for sure have the same diameter (I think Joe also says this but with other words :D). Also, make sure the potmeters are set the same. Looks like one motor is loosing steps. No scope needed as you might need to spend more time on how to use a scope than you need to do the easy steps ;).

    -Ronald
     
  10. Michael Warchut

    Michael Warchut Well-Known
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    So I did several things and something along the way seems to have fixed my issue. Without even pulling out the scope. I changed the motor connections but while doing that I tinned the wires as they felt sloppy in the terminal without it. I made sure the wires were the same length even though I am doubtful it matters that much due to the speed electrical current travels I shouldn't have been able to notice an electrical lag. I also made sure the pots were in a similar setting. Today I did several cuts and they came out spot on and no apparent lag. Cool beans..
     
    Joe Santarsiero likes this.
  11. Jonny Norris

    Jonny Norris Veteran
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    If it occurs again it could well be a pinion slipping, they seem to do it intermittently where they graunch enough metal burrs to hold for a while then let loose again. Though it sounds as though you have fixed it its worth keeping in mind. If it does happen dont bother trying to tighten you will likely round out the grub screw, instead remove the grub screw completely and remove pinion and re drill and tap a larger m3 grub screw in there.

    The original m2 grubscrew is a poor design.
     
  12. Flash22

    Flash22 Veteran
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    How do you have you wired them ? in parallel or serial ? driven from the same channel or run from the Y and 4th channel ? how have you got grbl setup re the axis(s)

    nema 17 or 23 ? 12v or 24V ?
     

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