Step Invert mask for GRBLShield?

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  • March 9, 2012 at 10:41 pm #1708
    toddkrein
    Member

    I’m trying to figure out why my X-axis is moving in the wrong direction. Nothing I do seems to invert the direction. Which lead me to some general questions about the configuration of GRBL for GRBLShield.

    If I read the TI data sheet correctly,

    $3 should be “2”, the number of uSec per step pulse.
    $7 should be 0bxxx111, since the step pulses for the TI 8811 are active high, while GRBL assumes that all signals are active low.

    Is that right?

    (BTW, I wasn’t able to find the GRBL forum to post questions. Do you have a link?)

    March 10, 2012 at 9:15 am #1709
    alden
    Member

    This sounds like a hardware problem to me. If the direction line for the X axis is not working correctly then the axis will only move in one direction. Do you have the ability to see if the dir signal is being set correctly? I know this is a bunch of work involving an oscilloscope and probes, and may be too much. Depends on your time, equipment and skills. Alternately we can send out another board if you will return yours.

    As for grbl SW support, the place to look is the grbl github. The Issues tab has a pretty active forum with Sonny Jeon (Chamnit) handling the lion’s share opf the requests. github.com/grbl/grbl

    – Alden

    March 10, 2012 at 4:53 pm #1710
    toddkrein
    Member

    Sorry, wasn’t clear: The X-axis will move in both directions, but the movement is reversed, i.e., g0x10 cuts to the left, g0x-10 cuts to the right. That’s what I need to change, and thus my questions about setting up grbl’s configuration variables.

    I can check it out on the scope, plenty of htem here in the lab. :-}

    March 10, 2012 at 5:06 pm #1711
    jmnoeth
    Member

    Have qyou tried reversing the connections on the motor? That should get the motor going in the opposite direction it does now.

    March 10, 2012 at 7:11 pm #1712
    toddkrein
    Member

    When you say “reverse”, do you mean swapping A & B, or A & A’?

    March 10, 2012 at 8:42 pm #1713
    alden
    Member

    Yes, this is the invert mask. It’s a bit confusing. You can use the invert mask to change the direction in software. I have to refer you to the grbl documentation on how to use this setting. https://github.com/grbl/grbl/wiki/Configuring-Grbl

    March 13, 2012 at 5:01 am #1715
    toddkrein
    Member

    Alden, not to be a pest, but I’m still looking for confirmation on my basic settings for $3 and $7.

    $3 can be anything larger than 2, correct?
    $7 can be anything matching 0bxxx111, correct?

    March 13, 2012 at 6:08 am #1716
    alden
    Member

    Todd,

    I do believe you are correct. I’ve never had to mess with the grbl default settings other than setting the motor steps, $0, $1, $2. Grblshield should be just plug and play.

    $3 is the step pulse width. The stepper drivers on grblshield can take as little as 1 microsecond, but I’m not sure what the lower range if grbl is. 2 should work.

    $7 is the invert mask. It should work with standard grbl settings – try $7=0. Note that bits 0 and 1 are not used, so the bitmask actually looks like: 0b Zdir Ydir Xdir Zstep Ystep Xstep 0 0

    Try this and see if it works. If the motors turn the wrong direction you have to add 32 to the number to invert the X direction, 64 to the number to invert Y and 128 to invert Z – i.e. $7=32 to invert X, $7=96 to invert both X and Y, etc.

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