Two servos - one driver


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    Registered WoodSnarfer's Avatar
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    Default Two servos - one driver

    If I wanted to run two servos from a single driver, would that be okay? If so, how do you implement? Is it as simple as hooking all the power and encoder wires up in parallel?

    The goal would be to move a gantry with two parallel ball screws, driven by two identical (smaller) servos - having both servos stay in synch.

    Silly newbie question, or is this possible?

    Thanks,
    Chris

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    Registered braidmeister's Avatar
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    Chris,
    I don't believe that you can do that for a number of reasons. First of all, it is very possible that one encoder will fault before the other due to over driving the motor, dirt in the encoder and other causes. If run that way, BOTH motors would fault. All of the servo drives that I know of only interface with one encoder. There are not provisions for 2.

    You will also have issues with power to the motor because you will be pushing 2X the Amps compared to only that of 1 motor...

    The way to do would be to run 2 servos & 2 drivers for the X and then set it up in Mach2 to reverse the direction of the 2nd motor so that it spins backwards in relation to the 1st X motor.

    -Brady



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    @woodsnarfer: The most silly questions are the ones you don't ask. Because they don't make you smarter.

    No you can't do that because a servo motor feeds it's error back to the drive, that will then take corrective action. When you have 2 servos, they have different errors, and one drive cannot correct those as it will require different action.

    One solution is to use one motor driving both screws. The difference in error between them will be negligible if you make the coupling between them stiff and with as little backlash as you can.



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    If the shafts of the two motors were linked and only one encoder was used, this would work (to an extent), wouldn't it? Perhaps a timing belt synchronizing the two motors in this instance.

    Obviously not an ideal, but just a curiosity.



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    Thanks...yes, I now see that a better solution is to use one large servo, and tie the two separate ball screws together via common belt. With two servos running in parallel, I can also picture one motor failing, and the other one causing the gantry to rack (or worse).

    Thanks!
    -Chris



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    Community Moderator ger21's Avatar
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    Something like this.

    http://website.lineone.net/~rmtucker/

    3rd picture in the second row

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    This is what I am trying to do (two screws, one motor and belts) so it had better work



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    Quote Originally Posted by ger21
    Something like this.

    http://website.lineone.net/~rmtucker/

    3rd picture in the second row
    Ahh, yes...that would be the ticket

    Anyone know a source for the drive sprockets and idler bearings? I'm assuming that the motor mount was a custom-fabricated part...wonder if it has integrated tension adjustment (?)

    Thanks,
    Chris



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    The motor/mount can slide up and down for tension adjustment I think.

    You can get timing belts and pulleys from:

    http://www.sdp-si.com/

    They also have a lot of info on the site.



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Two servos - one driver

Two servos - one driver