Apparent cross-motor stepper feedback in CNC axes.


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Thread: Apparent cross-motor stepper feedback in CNC axes.

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    Member salukikev's Avatar
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    Default Apparent cross-motor stepper feedback in CNC axes.

    I've been reminding myself for at least a year now to try and sort out this quirk of my machine and I finally remembered:

    So I have an old Tripower bridgemill that 99% of the time I use manually, but it's also wired for CNC which is great when I need it. Still in the process of converting to ballscrews instead of acme thread. A thing I noticed more pronounced recently is that if I rotate my X axis crank fast enough, I feel occasional pulses relaying through the Y axis handle. Usually it's not a huge problem and I can generally eliminate it by slowing down my rotations but I've always thought there was probably just a setting or strategic diode I could put in there somewhere and that this would be a good place to ask. I haven't yet found a post describing exactly this problem- I guess I was expecting it to be a bit more common.

    Anyway, thanks for any help!
    -kevin

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    Default Re: Apparent cross-motor stepper feedback in CNC axes.

    Quote Originally Posted by salukikev View Post
    I've been reminding myself for at least a year now to try and sort out this quirk of my machine and I finally remembered:

    So I have an old Tripower bridgemill that 99% of the time I use manually, but it's also wired for CNC which is great when I need it. Still in the process of converting to ballscrews instead of acme thread. A thing I noticed more pronounced recently is that if I rotate my X axis crank fast enough, I feel occasional pulses relaying through the Y axis handle. Usually it's not a huge problem and I can generally eliminate it by slowing down my rotations but I've always thought there was probably just a setting or strategic diode I could put in there somewhere and that this would be a good place to ask. I haven't yet found a post describing exactly this problem- I guess I was expecting it to be a bit more common.

    Anyway, thanks for any help!
    -kevin
    What types of drives/motors do you have?

    Cranking servo Axis faster than they can move under machine control could overvoltage the drives



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    Member salukikev's Avatar
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    Default Re: Apparent cross-motor stepper feedback in CNC axes.

    Keling 640 oz in steppers- like these. I use gecko drives in this system too- I think one or two are the 'V' model.
    Your overvoltage theory seems very plausible- can you suggest a way to remedy that?

    Also- I'm sorry, this will be my 3rd attempt today at posting this response. For some reason the forum does not seem to be posting it.



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    Default Re: Apparent cross-motor stepper feedback in CNC axes.

    try to power on the drivers and have them disable the outputs. but leave the power on which keeps them in a controlled state.
    This looks like you generate power which gets uncontrolled to the other motor.



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    Member john-100's Avatar
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    Default Re: Apparent cross-motor stepper feedback in CNC axes.

    when you hand crank an axis the stepper motor will act as a generator

    The AC currents produced will be rectified by the diodes in the two "H" bridges in the stepper driver
    the resulting DC voltage can power and other stepper driver connected to the same power supply

    Once the voltage generated is high enough for the driver to function
    the other axis stepper drivers will start to pass a holding current through the other stepper motors

    John

    PS
    part of stepper driver showing
    one motor coil connected to one stepper driver H bridge
    ( the 2 points marked VM are the positive bridge rectifier output and AISEN the negative )
    Apparent cross-motor stepper feedback in CNC axes.-one-h-bridge-inside-stepper-driver-jpg


    looks very like a transformer secondary connected to a bridge rectifier made of 4 diodes

    Apparent cross-motor stepper feedback in CNC axes.-bridge-rectifier-circuit-diagram-jpg

    Last edited by john-100; 08-15-2019 at 04:53 PM. Reason: add PS


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Apparent cross-motor stepper feedback in CNC axes.

Apparent cross-motor stepper feedback in CNC axes.