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  1. #1
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    May 2005
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    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
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    Jul 2003
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    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
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    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
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    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
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    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
    Junior Member
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    Sep 2005
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    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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