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    Default dbl y motor drive

    My mach has a single y axis motor with a belt to the other side. It's a nema 17 1.8A 30v. it has 33 in travel @ 110 in/min. 10mm @3mm pitch lead screws.
    I want to lengthen it to 1000mm to add room at the end for vertical milling and 4th axis.
    my axis drivers are A3979 set to 1.8A
    I think a nema 23 would perform better.
    I also like dual motor drive and lose the belt.

    If I purchase a high current driver, say 4-7A can I put 2 nema 23s in parallel on the driver, maybe add a 48v supply to the motors on that stand alone board. then drive that as the y axis with the connector for a 4th axis. That is an optional pwb but only uses the A3979. Then use the old y axis to drive the a axis. My mach uses uccnc + uc100

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    Community Moderator ger21's Avatar
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    Default Re: dbl y motor drive

    No, you need a separate drive for each motor.

    Gerry

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    Quote Originally Posted by ger21 View Post
    No, you need a separate drive for each motor.
    why is that, I heard two motors will run off one splitting the current depending on equal inductance.
    I suppose you could drive 2 separate driver pwb with the same signals for equal motor results if that's better?



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    Registered James Newton's Avatar
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    Default Re: dbl y motor drive

    Because when you wire the two motors together, you make a new motor (electrically) with half the resistance in the coil that real motors would have. Most drivers are not going to want to drive that unreal motor correctly. I /have/ seen people get away with it, but usually it doesn't work very well, resulting in drivers frying, overheating, or just moving poorly.

    The better solution, as ger says, is to use TWO drivers and, as you said, send them the same step and direction signals. The only time I've heard of issues with that, it was from:
    1. A poor signal source that couldn't drive two drivers with the step signal. Typically that happens with old laptop parallel ports. In your case, it shouldn't be an issue.
    2. One side losing steps, cocking the gantry sideways, and causing the entire thing to bind up. That probably won't happen, but I would leave the belt in place, just to keep the two motors working together mechanically.

    James hosts the single best wiki page about motors for CNC hobbyists on the net:
    http://techref.massmind.org/techref/io/motors.htm Disagree? Tell him what's missing! ,o)


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    Default Re: dbl y motor drive

    Quote Originally Posted by dobrodewed View Post
    why is that, I heard two motors will run off one splitting the current depending on equal inductance.
    I suppose you could drive 2 separate driver pwb with the same signals for equal motor results if that's better?
    It will work but only low rpm.



    This is a test with a drv8825 and two identical motors in parallel. Max rpm was only around 300rpm then the motors stall out. Changing supply voltage higher didn't make any difference. I also repeated the test using a high quality gecko stepper driver. Same results.

    Lots of 3d printers use parallel stepper motors for the z axis. It works fine for that application since z axis speed is very low.

    If you require higher speed, then individual drivers are required.



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    Quote Originally Posted by jfong View Post
    It will work but only low rpm.



    This is a test with a drv8825 and two identical motors in parallel. Max rpm was only around 300rpm then the motors stall out. Changing supply voltage higher didn't make any difference. I also repeated the test using a high quality gecko stepper driver. Same results.

    Lots of 3d printers use parallel stepper motors for the z axis. It works fine for that application since z axis speed is very low.

    If you require higher speed, then individual drivers are required.
    I just found a custom nema 23 that runs on 1.2A. That should solve any torque problems with the motors. http://store.quintessentialuniversalbuildingdevice.com/product.php?id_product=34. Anyone heard of these?



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    Default Re: dbl y motor drive

    Quote Originally Posted by dobrodewed View Post
    I just found a custom nema 23 that runs on 1.2A. That should solve any torque problems with the motors. NEMA 23 Stepper Motor 22kg*cm - Quintessential Universal Building Device - 3D Printers and Accessories Store. Anyone heard of these?
    300oz-in with 9mh inductance. The performance of the motor will be very poor unless you have a very good stepper driver with a high supply voltage. Ideally you want a stepper motor under 3mh inductance. I try to get ones closer to 2mh.

    You can google stepper motor inductance to explain why a high inductance motor doesn't perform as well.



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