Random Y axis question.

Discussion in 'General' started by Miasmictruth, Oct 25, 2016.

  1. Miasmictruth

    Miasmictruth Well-Known Member

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    I have been thinking about how to rebuild the big box frame to be more ridged but this could apply to any printer.

    If one were to make modification to minimize flex in the rods I see that a lot more inertia exspecially effecting the Y.

    To combat this I am sure a larger stepper could be used, but what about splitting the Y between two seperate steppers like the Z.

    Is this not done becuse it's easier for the steppers to loose sync when powered off or is there something else?

    What would be the best why to increase the power of the Y axis to compensate for the extra weight?

    Can a second stepper be added to the opposite side and tie it in to the existing Y axis drive system or would the two steppers just be battling each other? I was thinking if Y axis was powered before tightening the set screws on the second pully that they would be locked in phase with eachother.
     
  2. dc42

    dc42 Well-Known Member

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    There are certainly printers using dual Y stepper motors, because I have been asked how to configure them on a Duet WiFi.

    As you suspected, the issue is that dual motors on any axis are prone to losing sync. When the motors power up, they will jump in the shortest/easiest direction to a position that matches the way the phases are energized. Such positions occur every 4 full steps. The risk is that If you power the motors down at a position mid way between those positions, then when you power up again the two motors may jump in opposite directions.

    I have some firmware work scheduled for the Duet WiFi to use the power monitor to detect impending loss of power and jog the motors so that they will be in the correct positions at power up.

    There remains the possibility that if the head snags on a blob or curl-up, the two motors might skip different multiples of 4 full steps.
     
  3. Miasmictruth

    Miasmictruth Well-Known Member

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    Gottcha, so that's why you wouldn't want to tie them together, if they jump in opposite direction could cause issues?

    If they are on the same driver would they not jump in the same direction?
     
  4. dc42

    dc42 Well-Known Member

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    It doesn't make any difference whether they are on the same or different drivers, because the types of driver that I am familiar with always power up with the phases energised in the same way. To avoid the problem, at power down you need to leave the motors in a position that matches this state at least approximately, to avoid the situation in which the motor positions are about equidistant from two suitable positions and can't decide which way to jump.
     

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