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Thread: step motors

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  1. #1
    Member
    Join Date
    Oct 2020
    Posts
    1

    step motors

    hi
    i am new here.
    i build a cnc machine.
    i have 2 step motors for y axis open loop name 34 4.5 n.m 2 phases.
    can i connect two step motors to one drive (st-5045) ?
    i have to buy another step motor is it critical not to buy an open loop (price)?
    i have 3 open loop motors.
    thanks for your help
    dudi

  2. #2
    Registered
    Join Date
    Nov 2013
    Posts
    944

    Re: step motors

    Hi,
    it is possible to run two steppers off one drive but you need to add balancing resistors so that they share the current equally.

    The consequence is that the steppers see a little less than 1/2 the drive output. This is a poor use of your steppers, you should get another
    drive.

    Open loop steppers miss steps and stall IF OVERLOADED......guess what, closed loop steppers miss steps and stall IF OVERLOADED.
    The manufacturers of closed loop steppers would have you believe that their steppers 'catch up' because of the closed loop.......BS,
    the extra steps inserted by the drive get missed just like the ordinary steps because the stepper IS OVERLOADED.

    The bottom line is that if you overload a stepper of any description it will miss steps, conversely if your stepper is adequately sized
    (and not commanded to move faster than its capability) then it will never lose steps.

    I use open loop Vexta 5-phase steppers on my mini-mill and have not lost a step in six years.

    An often overlooked specification when buying steppers is inductance. All steppers lose torque the faster they go, thats just plain physics.
    Inductance determines how badly the torque will degrade as speed increases, the lower the inductance the better the torque will hold up.

    Manufacturers make what look to be great steppers with heaps of torque but a commensurately high inductance. Many first-time buyers
    get these things only to find that they miss steps at very low speeds. Don't be duped, you want as high a torque as you can but at the
    LOWEST POSSIBLE inductance.

    If buying 23 size steppers look for 1-2mH, 1mH preferred and reject anything over 2mH.
    If buying 34 size steppers look for 2-4mH, 2mh preferred and reject anything over 4mH.

    The next thing is the voltage of the drives. In order to go as fast as you can WITHOUT losing steps you need as high as possible voltage driver
    and matching high voltage supply. At the current time the effective maximum voltage of stepper drivers from the leading manufacturers is 80V,
    I would suggest you get them and an 80VDC supply.

    If you buy right....you'll buy once and then use the steppers/drives/supply for years without complaint. If you try to save dollars you'll almost
    certainly end up with under performing components which you will have to upgrade later, so you didn't save any dollars but rather cost yourself
    in the longer term.

    Craig

    - - - Updated - - -

    Hi,
    it is possible to run two steppers off one drive but you need to add balancing resistors so that they share the current equally.

    The consequence is that the steppers see a little less than 1/2 the drive output. This is a poor use of your steppers, you should get another
    drive.

    Open loop steppers miss steps and stall IF OVERLOADED......guess what, closed loop steppers miss steps and stall IF OVERLOADED.
    The manufacturers of closed loop steppers would have you believe that their steppers 'catch up' because of the closed loop.......BS,
    the extra steps inserted by the drive get missed just like the ordinary steps because the stepper IS OVERLOADED.

    The bottom line is that if you overload a stepper of any description it will miss steps, conversely if your stepper is adequately sized
    (and not commanded to move faster than its capability) then it will never lose steps.

    I use open loop Vexta 5-phase steppers on my mini-mill and have not lost a step in six years.

    An often overlooked specification when buying steppers is inductance. All steppers lose torque the faster they go, thats just plain physics.
    Inductance determines how badly the torque will degrade as speed increases, the lower the inductance the better the torque will hold up.

    Manufacturers make what look to be great steppers with heaps of torque but a commensurately high inductance. Many first-time buyers
    get these things only to find that they miss steps at very low speeds. Don't be duped, you want as high a torque as you can but at the
    LOWEST POSSIBLE inductance.

    If buying 23 size steppers look for 1-2mH, 1mH preferred and reject anything over 2mH.
    If buying 34 size steppers look for 2-4mH, 2mh preferred and reject anything over 4mH.

    The next thing is the voltage of the drives. In order to go as fast as you can WITHOUT losing steps you need as high as possible voltage driver
    and matching high voltage supply. At the current time the effective maximum voltage of stepper drivers from the leading manufacturers is 80V,
    I would suggest you get them and an 80VDC supply.

    If you buy right....you'll buy once and then use the steppers/drives/supply for years without complaint. If you try to save dollars you'll almost
    certainly end up with under performing components which you will have to upgrade later, so you didn't save any dollars but rather cost yourself
    in the longer term.

    Craig

  3. #3
    Member
    Join Date
    Jul 2018
    Posts
    2011

    Re: step motors

    Hi - Can you run two drives from one BOB output? So they would be in parallel? Peter

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