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  1. #1
    Hi, Iíve just started building my first attempt at a small CNC router based up an Arduino Uno running grbl and fitted with a V3 CNC Shield with four A4988 drivers (Y axis cloned) running NEMA 17 2A steppers. Iím then using UGCS to send the G-Code.

    I started by getting both the X and Y axis connected and running smoothly with no problems, my problems started when I fitted the Z. Jogging in X and Y gives me no problems with the Z motor unplugged and likewise running the Z up and down gives me no problems with the Y axis removed.

    However with all three connected I get an issue where jogging Y in either direction also causes my Z to move negative and moving my Z in either direction causes my Y to move negative.

    Click image for larger version. 

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    Iíve tried swapping my Chinese Arduino out for a genuine Italian R3 unit and although I thought it seemed better at first it is still present. Iíve also tried turning my vRef on my X and Z back down from 1.2v to 0.6v and this seemed to reduce the severity of the problem, but it is still there and this isnít running anywhere near the 2A limit of my motors or drivers as my A4988 are fitted with 0.1Ohm current sensing resistors. I've double checked all my connections and visually all looks okay.

    Any ideas what would cause this pattern of movement? Electronics like this are very new to me so just looking for some pointers in the right direction of things to check.


  2. #2
    My knowledge on the A4988 is limited to a couple of minutes googling, but you seem to have a standard Step/Direction signal from the controller (Uno). It sounds as though the Y and Z "Step" pins are acting together. In the first instance I'd check continuity between the Step input on both A4988s (Y/Z) - there shouldn't be any. I'm equally not familiar with a GRBL setup on the Uno, though I have a working knowledge generally of Arduino and similar SBC/microcontrollers. Somewhere you would have to bind the Uno discrete outputs for the X/Y/Z step/direction outputs to the output pins of the Uno, and ensure that these output pins drive the A4988s. Check all that.

    It could possibly be the software running on the Uno - though if this is a public-domain GRBL sketch then I would not expect this error to have propagated unnoticed.

  3. #3
    ...and if you have a rats nest build then a decent photo would help immensely with trying to figure out what wiring you may have.

  4. #4
    After having a look this morning it seems the problem is with the CNC Shield. When I put my multi-meter across it, it is showing a short between the Y.STEP and the Z.STEP outputs as marked in red here.

    Click image for larger version. 

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    That's with the shield removed from the Arduino and without any drivers connected. I can't see anything on either surface of the board that's causing it so guess it's a manufacturing defect and I just need to throw it in the bin and try again.

    Thanks for your replies btw. Although I'm new, after a quick look around it seems like a nice helpful forum here.

  5. #5
    Try gently prising the blue surround on the pin-headers EN/X,Y,Z,A-STEP/5V - it should (with a bit of persuasion) ride up on the pins - then you can see if there's anything salvageable under the surround. More likely an assembly issue (i.e. solder bridge) than a PCB manufacturing issue.

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  7. #6
    ...or... now I've woken up... rewire your Z-axis using the spare A-axis channel, assuming you're just looking to use 3-axis

  8. #7
    I'm currently using the A-axis channel as a clone of the Y-axis to drive twin leadscrews, but will try checking under the surrounds.

  9. #8
    Did what you said about lifting the surrounds and found the tiniest slither of solder linking them together. Scratched it away and all is now working. It just successfully drew it's first picture with a sharpie taped to the spindle. So thank you for the help. :)

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