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IndustryArena Forum > CNC Electronics > Servo Motors / Drives > What else do you need to run AC servo motors?
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  1. #21
    Join Date
    Jan 2005
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    15362

    Re: What else do you need to run AC servo motors?

    [QUOTE=Goemon;2190838]Are the SGDA drives the only ones that would work? Should I assume that others like the SGDS will not work?

    How much would you pay for a used SGDA max?

    can you use a 750w drive with a 400w servo or does it have to be a 400w drive for a 400w servo?[/QUOTE

    As you thought SGDS will not run a Sigma series Motor

    How much to pay can be if they are new or used from $60 to $150 would be a normal range

    Yes you can use a larger Servo Drive but there is a max to this also, usually a max of 2 drive sizes above the motor you are using, so 750W would be the max

    The important part is the P for position control, SGDA-04AP are the Drives you want for Step / Dir

    I have some new Drives in stock, but they are SGDA-04AS, these are for +/- 10v control
    Mactec54

  2. #22
    Join Date
    Mar 2017
    Posts
    926

    Re: What else do you need to run AC servo motors?

    I found (and bought) 2 new 400w SGDA drives for $80 a piece. The others I saw were all a lot more expensive (and used).

    I'll keep an eye out for a deal on a third drive but I'm going to use 3.5a Nema 34 steppers with my Gecko G540 in the meantime so I don't delay my build any further while I figure out the servo thing. The Nema 34's have a longer shaft so it can reach the coupling once I mod the actuator housing.

    I am assuming that there is no info out there on my servos because they were a custom order from NSK for their actuators. I feel like I have a lot of reading to do before I can use them.

  3. #23
    Join Date
    Jan 2005
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    15362

    Re: What else do you need to run AC servo motors?

    Quote Originally Posted by Goemon View Post
    I found (and bought) 2 new 400w SGDA drives for $80 a piece. The others I saw were all a lot more expensive (and used).

    I'll keep an eye out for a deal on a third drive but I'm going to use 3.5a Nema 34 steppers with my Gecko G540 in the meantime so I don't delay my build any further while I figure out the servo thing. The Nema 34's have a longer shaft so it can reach the coupling once I mod the actuator housing.

    I am assuming that there is no info out there on my servos because they were a custom order from NSK for their actuators. I feel like I have a lot of reading to do before I can use them.
    That was a good price for new, the other tip for drive selection is if you see one that is SGDA-04A with no other letter after it, they do both Step /Dir and analog +/-10v for controlling them, so either a P or nothing at all

    It will only be the encoder PPR that will be different, so not much to worry about, the only thing that is important is they are wired correctly, and the manuals are very good at showing wire connections, for these Yaskawa servos
    Mactec54

  4. #24
    Join Date
    Jun 2011
    Posts
    692

    Re: What else do you need to run AC servo motors?

    I think someone said earlier you can't mix servos and steppers. This isn't really true, if you're using step/dir, a servo and a stepper don't look any different to the controller.

  5. #25
    Join Date
    Mar 2017
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    926

    Re: What else do you need to run AC servo motors?

    Quote Originally Posted by skrubol View Post
    I think someone said earlier you can't mix servos and steppers. This isn't really true, if you're using step/dir, a servo and a stepper don't look any different to the controller.
    I was planning to try it to see for myself anyway. I don't really know how programs like Linux CNC deal with feedback from a servo motor. The way they receive steps should be the same. I just don't know what happens if you miss a step on one of the servos but have no data fed back from the stepper. I don't know if you can use a servo in open loop mode

    I am also interested to see what happens if you mix different brands of servo motors. E.g. If you used two Yaskawa with one Mitsubishi as it is easier to find bargains if you can mix and match.

  6. #26
    Join Date
    Mar 2003
    Posts
    35538

    Re: What else do you need to run AC servo motors?

    With a step/dir control, you can mix and combination of steppers and servos.

    Most if not all step/dir servos close the loop in the drive, so the control is always running open loop.
    You can close the loop in LinuxCNC, but you'll have to feed the encoder signals from the drive back into LinuxCNC.
    Gerry

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

  7. #27
    Join Date
    Jun 2011
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    692

    Re: What else do you need to run AC servo motors?

    There are 2 different basic ways to communicate with a servo, step/dir (control isn't in the loop, behaves just like stepper,) and encoder/pwm (servo drive tells the control where it is and the control tells the servo drive how fast to go or how much torque to generate.)
    Servos still won't 'miss steps', even in step/dir mode. They may fall behind a bit where more torque than they can generate is needed, but they will either catch up when the load lightens or fault and stop completely. You will definitely want the fault line properly wired back to your control.

    I'm not sure what it takes to mix step/dir and closed loop in LinuxCNC. I'd guess it's possible, but maybe difficult? (I'm still in the research phase on my LinuxCNC projet as well.)

  8. #28
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    Jan 2005
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    15362

    Re: What else do you need to run AC servo motors?

    Quote Originally Posted by skrubol View Post
    I think someone said earlier you can't mix servos and steppers. This isn't really true, if you're using step/dir, a servo and a stepper don't look any different to the controller.
    I don't think anyone said that, you can mix any combination you want, and can even mix control method's if you want, there are no real constraints, on how you can use either Step/Dir or analog
    Mactec54

  9. #29
    Join Date
    Jan 2005
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    15362

    Re: What else do you need to run AC servo motors?

    Quote Originally Posted by skrubol View Post
    There are 2 different basic ways to communicate with a servo, step/dir (control isn't in the loop, behaves just like stepper,) and encoder/pwm (servo drive tells the control where it is and the control tells the servo drive how fast to go or how much torque to generate.)
    Servos still won't 'miss steps', even in step/dir mode. They may fall behind a bit where more torque than they can generate is needed, but they will either catch up when the load lightens or fault and stop completely. You will definitely want the fault line properly wired back to your control.

    I'm not sure what it takes to mix step/dir and closed loop in LinuxCNC. I'd guess it's possible, but maybe difficult? (I'm still in the research phase on my LinuxCNC projet as well.)
    That sure is not correct, a servo will never behave just like a stepper, the loop is closed in the servo drive, and is just as affective as closed in the control
    Mactec54

  10. #30
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    Jun 2011
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    692

    Re: What else do you need to run AC servo motors?

    Quote Originally Posted by mactec54 View Post
    That sure is not correct, a servo will never behave just like a stepper, the loop is closed in the servo drive, and is just as affective as closed in the control
    I misspoke, I should have said is controlled just like a stepper (in step/dir mode.)

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