Axes Real Position Feedback

edited July 28 in Motor Control
I need to know the real position of the axes in a kind of feedback from the firmware. I've tried M114 but, the answer is given with the ending position of the current movement, not the real positions of the axes. I know these is an open loop motion control, but I thought M114 could give the position updated after each step or something like that. There is an alternative to get the real position as feedback?

Comments

  • Real position actually is in general unknown. We have motor positions in steps (speaking about V1 firmware) but even these are not in all cases updated per step as they are not needed and would slow down especially on 8 bit hardware. Also for deltas or corexy the motor position need more or less complex reverse transformation to get a real position especially if motor steps include autolevel und bump corrections. 

    So no, you only can get position at the end of the moves. Logic is to always add changes to these which is all we need to know. Exception is z leveling where we use z count to see where we are.
  • Thank you very much, I understand perfectly.
  • Last weekend I found out that V2 firmware has nearly perfect motor position in steps if that helps. They are updated a few hundred times per second. But include also rotation correction and bump correction and there is no reverse calculation to make them real positions again.
  • That assure the control but not UI tracking of moves. I'm considering others options like fork a GRBL Firmware and adapt it to my requirements. I know that Repetier is very precise, but I really need this features of feedback for UI. Thanks any way.
  • M114 S1
    would return steps counter, but such responses are always with delay due to move buffering and command locking. Only when no moves are being send or command queue is empty it will be quite timely.
  • Repetier said:
    M114 S1
    would return steps counter, but such responses are always with delay due to move buffering and command locking. Only when no moves are being send or command queue is empty it will be quite timely.

    Yeap, I also try that. It's the same result, while moving, gives back the last calculated position, but in steps
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