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IndustryArena Forum > CNC Electronics > CNC Machine Related Electronics > Interfacing homemade servos with NC Software (LinuxCNC or grbl?)
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  1. #1
    Join Date
    Dec 2016
    Posts
    2

    Interfacing homemade servos with NC Software (LinuxCNC or grbl?)

    Hi all,
    Over the past couple months I've managed to make some little brushless servo drives, with the intent of putting them on a little mill I made last year. I've currently got them closed-loop tracking a hardcoded position, in this case sine(time):



    In the video the stack of things from left to right is optical encoder, bellows coupling, NTM propdrive motor, and a magnetic encoder I will probably be using in the future. While you can see there is a fair amount of work to go in terms of packaging everything, the software does at least work (mostly) and I am beginning to wonder what is next on the heirarchy. The big question I can't figure out is how to interface my low-level board with any NC program. Ideally i would like to send PVT commands over USB or something like that, but I have no idea.

    The easiest option is to simply go with step/direction outputs, using grbl. LinuxCNC also offers this option out of the parallel port. However, this is just really not a good option for many reasons. Ideally I would like to use some more sophisticated method such as sending position and velocity data over USB or something like that. I've heard that writing a USB driver for linuxCNC is extremely hard, and deciphering the GRBL code to add in PVT output didn't look very easy either. Any thoughts on how to solve this problem? All I need is PVT out of something!

    Thanks.

    The controller:


    The mill, made from the backing of a granite AFM. Read more here: minimill – Austin Brown


  2. #2
    Join Date
    Mar 2005
    Posts
    303

    Re: Interfacing homemade servos with NC Software (LinuxCNC or grbl?)

    with linuxcnc, you can use mesa card with smart serial
    SSERIAL

    stmbl have smart serial
    https://github.com/rene-dev/stmbl

    b.r

  3. #3
    Join Date
    May 2015
    Posts
    684

    Re: Interfacing homemade servos with NC Software (LinuxCNC or grbl?)

    the problem with USB and LinuxCNC is that LinuxCNC requires a real time operating system. The USB specs allow for latency so its not suited for use in a real time environment. Some of the Mesa interface cards might solve your problem either with a PCI/PCIe or ethernet interface to the board but there are other hardware options from General Mechatronics and Pico Systems that interface with LinuxCNC. You could take it one step further an build an ethercat slave on your servos and get LInuxCNC to talk to that! Plenty of options but best to ask questions on the Linuxcnc forum.
    Rod Webster
    www.vehiclemods.net.au

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