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Using an encoded DC motor as a stepper equavalent. CNC. - Page 3 — Parallax Forums

Using an encoded DC motor as a stepper equavalent. CNC.

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  • That's right, my encoder is not a high resolution type, just having a look online to see what's there.
    It can however do smaller step sizes at a faster rate with what's there currently, I selected a bigger step and slow pulse rate for the sake of clarity in the video :)

    As for 'longer, higher speed moves'
    That is in fact what I want to learn about now .. in the past, when I've done this with steppers, my code worked on a pulse-by-pulse principle, so if i had a vector 3x by 2y, that's what my code would do, X X Y X Y ... or similar.
    My code never looks further ahead than what the next step will be.

    I bought a GRBL board online and waiting for it to arrive, which looks like it drives stepper motors directly, I'm hoping to have a PIC monitor those pins, and just work out which way the drive sequence is going, and drive the DC motor accordingly...

    but more on that when it arrives.
    in the meantime I'll educate myself reading that product manual Mickster sent me a link for, now that i can put this aside for a while and read at leasure :)
  • ok... been reading up a bit and finally it's making more sense to me now specially about the longer and faster pulse durations.. so i should be able to give it a command such as G01 X50 F20 ..
    As you can probably tell my CNC and g-code knowledge are close to nill but thanks to this thread it's slowly coming together.
    so my step-by-step idea probably wont cut it, but that is the output of my GRBL board, so that would mean I'd also have to write my own g-code interpreter (or find code online) if i want to use DC motors (?)
  • Once you have good stable point to point motion perfected, the G-codes simply command what the target positions are. What is your loop update rate and did you implement the motion trajectory generator?
  • You forget G2 and G3 which describe circular arcs, not straight lines, so point-to-point motion is not enough. Actually they can describe helices in 3D too, but I don't think GRBL handles that.

    Just write a motor driver that takes step and direction pulses as input, most of the CNC servo offerings
    these days do exactly that. They just hit an ISR that updates the desired-position variable thats input
    to the motion loop.
  • MicksterMickster Posts: 2,691
    edited 2016-04-10 14:50
    I think he's only worried about the one axis, ATM (G01).
    Step and direction, if you mean as in stepper motor commands is pretty crude and limited and not what the big boys of motion control do.
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