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Newbie needs advice (GRBL+Arduino+EggBot)

Discussion in 'DrawBot' started by Inzinjer, Feb 9, 2017.

  1. Inzinjer

    Inzinjer New

    Feb 9, 2017
    Likes Received:
    I have no idea where to post this, so I'm just gonna do it here and hope the mods move it where it belongs. :rolleyes:
    I made a construction of the EggBot for my school project (https://plus.google.com/collection/wL1hPE).
    I used the GRBL shield v3.0, Arduino UNO, Pololu A4988 Stepper Motor Driver.

    There is also a servo underneath the pencil arm, the images are a bit outdated. Okay, I finished the hardware part, everything is wired up and sorta responds to the GRBL Controller. I downloaded the 'robottini' modified firmware for GRBL that supports servo control. In the instructions it says I can control it via M03 Sxx (xx being the degrees I want to move it to), but in my case, it always tries to go to 255 degrees and whines because it can't go through all the wood in the way. :banghead:. I tried inverting the signal (again goes to the same direction, which I found weird, might be worth mentioning), playing with the SHORT and LONG duration, same thing always (the servo works fine through regular Arduino, I tested it).

    And that is why I'm looking for all the help I can get. If this is the wrong forum for this kind of stuff (I figure since there are some builds of the EggBot here people might offer some help), please point me in the right direction.

    I also have some other minor issues regarding G-Code, but I'm primarly looking for servo solutions. I'm will be happy to link all the components, dimensions, whatever you need if you help me out. Thanks in advance.
  2. David the swarfer

    David the swarfer OpenBuilds Team
    Staff Member Moderator Builder Resident Builder

    Aug 6, 2013
    Likes Received:
    Reading GitHub - robottini/grbl-servo: grbl 0.9i with Servo motor support
    it looks like they are trying for a very wide range of motion by giving pulses shorter than 1ms and longer than 2ms.
    The problem with this is that not all servos can handle it, since the standard is 1ms to 2ms.

    What happens if you output
    M3 S127

    This should make the servo move to the middle of its range, which is safe to do. From there you can work out how far in each direction it CAN go, safely, without hitting an end stop..

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