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  1. #1
    Join Date
    May 2005
    Posts
    925

    Question Identifying a servo motor

    Hello folks, Im posting looking for help identifying these motors, they are hooked to a small CNC mill, I have absolutely no reference about them, just my educated intuition. I think these are servos because they have a 4:1 reduction and have encoders on their back.

    Here are photos of the units:

    Both are NEMA34 mount

    One is square, 8 wires coming out of it, 2 sets of the same color

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    the wires go to a connector:

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    4 of the wires are hooked together, if this where a stepper, doing this would prevent the unit from turning, or am I wrong?

    The other is round, same US Digital Encoder on the back:

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    This also has 8 wires all different colors, but the connector is connected in the same fashion:


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    These are connected to a small board that looks like some sort of protection (has 4 diodes) since its not wired like a rectifier

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    also attached to this little board is this power resistor that looks like an energy dump:

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    The driver is homemade and its made out of a set of 8 darlingtons BU941ZP and three 74HC00 logic gates.

    So my conclusion is these are brushless DC servos (but I may be wrong of course)

    I would like to know how to determine the wires and if possible determine their voltage, so I know if I can use them with any known servo drive.

    Thanks a lot in advance!


    Pablo
    Attached Thumbnails Attached Thumbnails XsiZUrb.jpg  
    ● Distribuidor Syil en Argentina ● "www.syil.com.ar" ●

  2. #2
    Join Date
    Jul 2003
    Posts
    1753
    My guess is a 8 wire stepper hooked up like the first example here

    Stepper Motor Connections - Motion Control Information

    Notice 4 wires are hooked together to V+

    and that would make sense why there are 8 darlingtons as that would give you bipolar switching..

    sam

  3. #3
    Join Date
    May 2005
    Posts
    925
    maybe, but if these are steppers indeed, I wonder why they use a 4:1 reduction, that would be counter productive.

    Also, on the square motor, there are two sets of cable of the same color, one set, all the 4 wires are hooked together, wouldn't this prevent the motor of turning due to the induced current?
    ● Distribuidor Syil en Argentina ● "www.syil.com.ar" ●

  4. #4
    Join Date
    May 2005
    Posts
    925
    upon further reading, maybe these are steppers wired unipolar as you told me, unipolar has less initial torque but the torque curve is flatter, maybe this explains the 4:1 reduction
    ● Distribuidor Syil en Argentina ● "www.syil.com.ar" ●

  5. #5
    Join Date
    May 2005
    Posts
    925
    Sam, today I was able to remove the motors from the machine and you were right, these are steppers. The obvious confirmation came when I turned the shaft and felt the steps

    Already deduced the wiring but I could use some help regarding how to determine their inductance.


    Pablo
    ● Distribuidor Syil en Argentina ● "www.syil.com.ar" ●

  6. #6
    Join Date
    Sep 2005
    Posts
    322
    To be pedantically correct, they are steppers being used as servos (since they have feedback). Sounds like someone did an interesting sort of roll your own CNC...

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