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Thread: Driving stepper motors

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    Default Driving stepper motors

    Hey again all!

    Just started to play with some stepper motors and was thinking about driving two stepper motors in one axis (i.e. running them in parallel)...

    So with two identical stepper motors, getting them to step the same would you use them so as each winding is fed in a serial fashion, parallel, or driving them separately??

    Cheers



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    Senior Member BCNZ's Avatar
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    I'm no stepper motor expert but at a guess I'd say you drive them separately and sync the drive pulses.

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    I would drive them seperately. If the motors are identical and they each have there own driver circuit, they'll rotate the same number of degrees for each pulse assuming the driver circuits share the same stepping pulse.

    Quote Originally Posted by Gitch View Post
    Hey again all!

    Just started to play with some stepper motors and was thinking about driving two stepper motors in one axis (i.e. running them in parallel)...

    So with two identical stepper motors, getting them to step the same would you use them so as each winding is fed in a serial fashion, parallel, or driving them separately??

    Cheers

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    Quote Originally Posted by Gitch View Post
    Hey again all!

    Just started to play with some stepper motors and was thinking about driving two stepper motors in one axis (i.e. running them in parallel)...
    Are they going to share load?

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    Quote Originally Posted by fromaron View Post
    Are they going to share load?

    Yep, same load...

    Sounds as though seperate drivers from the same control pulses is the way to go, I was more curious than anything for the moment

    Thanks all

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    Quote Originally Posted by Gitch View Post
    Yep, same load...
    Just a small note, not knowing all details of your project.
    Same load obviously demands pretty much syncronised movement, so the same control pulses (master pulses a must). Hopping that both motors have as much identical step size as possible to avoid them working against each other. If motors are powerfull enough this is a very important issue to consider. You might discover a flexible coupling link will be very usefull in your project as well.

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    thanks fromaron

    the future plan is for a fairly large cnc engraver (about 1.5m movement) and I was thinking along the lines of driving the X and Y axis from both sides... My thoughts are that it would be easier and more cost effective for a home built unit??

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    I am not sure which stepper motors you have in mind, depending on the machine targeted accuracy(repeatability) I would use AC servo motors with hi res encoders to provide feedback for position and velocity control loops.
    BTW, what benefit you expect to have by driving X and Y from both sides? Is it only to reduce motor size?

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    I am after something that has fairly accurate results - as i said it's all just thoughts at the moment...

    the main benefit i thought of was to reduce the sway (not the right term i'm sure) that i considered would be evident through either a center mounted slide or a single side driven or even center driven with slides on the outers??...

    any feedback would be much appreciated

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    Quote Originally Posted by Gitch View Post
    the main benefit i thought of was to reduce the sway
    Sorry Gitch, I don't quite understand this sway thing.
    Is it backlash are you talking about, having in mind each motor to travel one direction only, or something else?

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    I didn't think that would make sense..

    not back lash, but my thoughts at the moment are with using a gantry style so if the gantry is driven from one side only, using a screw type shaft... suppose I use (exaggerated example) a 20mm nut that is to slide up and down the screw shaft any error would result in an exaggerated error at the other end, correct?? Which then would result in substantial errors and binding...?

    and just to check - backlash is the steps backwards required before movement begins??

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    I don't think by driving the screw shaft from both ends will give you that error reduction you are after. At the end of the day the movement accuracy along the whole axis will be greately affected by the screw-nut assembly tollerances. So if you are to have the nut "Home" position at one end of the screw shaft, the accumulated position error will be there at the other end no matter where is your driving point is. Yes, you can half the error by assignung the nut "Home" position at the centre of the screw shaft. In the case even if you drive the shaft by one motor the accumulated error at both ends will be half of the overall shaft-nut assembly inaccuracy. This is if I understand your concept correctly.
    Usually two drive motors are used to share one load for an applications where a big constant torque is required from zero speed and if the load is that big that you have to use a huge size motor. By using two motors you can use smaller size, obviously.
    and just to check - backlash is the steps backwards required before movement begins??
    You can say that. The backlash is something that you have to leave with and fight against and is introduced by the gap in between two surfaces, one being the shaft and another of the nut. That means by spinning the shaft, the nut will start movement after certain degree shaft made. If you look at this from the electronics point of view it's simillar to hysteresis. Backlash is bad, we don't like it, we need to take measures to compensate it. By saying this I need to also say that without backlash you wouldn't be able to move as well. Your motor would stall. Heh, figure it out.

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    Quote Originally Posted by fromaron View Post
    I don't think by driving the screw shaft from both ends will give you that error reduction you are after.
    ok, there may some slight confusion here... what i meant was to drive two screw shafts on either side of the gantry

    but as I said, all just thoughts for the moment and thanks for the feedback guys

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