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Running 2 stepper motors on one connection

Discussion in 'CNC Mills/Routers' started by pappydan, Oct 2, 2016.

  1. pappydan

    pappydan Well-Known
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    I have watched a couple of build videos where 2 stepper motors are hooked up to one set of outputs. Will the Xpro v2 controller handle the power requirements of 2 motors. I am already running the Z axis using the slave setup. This is for another mod I wanna do a little down the to road. Basically, I need to control 5 steppers. 1 onY, 2 on Z, and 2 on X.
     
  2. snokid

    snokid Veteran
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    yes it will work, just remember the motors will be splitting the current...
     
  3. Metalguru

    Metalguru Master
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    pappydan:

    You can't really hook up 2 * 2.8A motors like the OB part store motors onto one driver. The XPro cannot put out that much current.

    Having said that, the XPro has 4 stepper drivers, one of which can be slaved to the Y axis, allowing you to drive 2 motors off one set of signals. But, the signals are paralleled on the digital input side, not the motor side. You can parallel as many stepper drivers as you want off the same digital step/direction signals using the inputs tied together. (well, within the drive limitations of an Arduino or whatever).

    I would never recommend running 2 motors off the same stepper driver even if it was rated to handle the current. There are too many other variables involved, like motor inductance, differences in motor winding resistance, back EMF, etc.

    Nothing personally against XPro, but I am opposed to running this type of "all in one" board. If you blow 1 stepper channel, you've just blown a $200.00 board. Separate stepper driver modules make much more sense, IMHO, and are easier and much cheaper to repair and upgrade. Also, XPro recommends using an ATX PC power supply, but that's only 12V, you can get much better stepper performance off 24V or even 36V.

    But that's just my opinion.:cool:

    MG

    PS: I just realized after rereading your post that you are already using the slave channel for something else. There was some discussion on the Forum somewhere that the XPro was not capable of driving external stepper drivers, so I think you are SOL.
     
    #3 Metalguru, Oct 7, 2016
    Last edited: Oct 7, 2016
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  4. pappydan

    pappydan Well-Known
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  5. Metalguru

    Metalguru Master
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    pappydan, was there a reply in there somewhere?
     
  6. pappydan

    pappydan Well-Known
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    Thanx for the reply. I had really thought that was the case but in a video somewhere I saw someone hooking up 2 motors. When I ordered the C Beam machine I just ordered everything from OB that I thought I would need to get it off the ground. Before the parts were delivered I had already decided that a stock C Beam wouldn't do what I wanted to do so I made another order, and, on and on . Anyway down the road a little I am going to need a 5 motor system 2 sets of slaves. And , before I figured out what I really wanted I ordered a 5 axis Planet CNC controller. Not going to worry abbout it for now. I have machine one finished and am down to getting it to home correctly. Actually reading some of your threads from a couple years ago on that topic
     
  7. Metalguru

    Metalguru Master
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    Cool! Glad to help. Just because someone puts up a video of something doesn't necessarily mean its a good idea...

    Yeah, CNC machines are like boats, they are a giant black hole into which you throw money...:D It's an addictive hobby...

    There was some stuff recently in Has anyone tried the Arduino Nano for control? about some homing problems I had. .1uF caps on the homing input pins to ground fixed it.

    MG
     
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  8. snokid

    snokid Veteran
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    looks like you solved your problem.
    Stepper drivers will only deliver the current up to what that they are rated for.
    So you can have a stepper that draws 10A and a driver that will deliver 2A and the board will be happy to provide up to 2A of current to the stepper motor...
    The motor might not be happy to run at 1/5 the current it wants...

    Kind of like driving a sports car with 600HP but having granny driving it!!!

    Just like granny should get a better fitted car for her, the best option is to get a board that will do what you are looking to do.

    But in the end if you hook 2 steppers to 1 driver it will work....
    Bob
     
  9. Giarc

    Giarc Master
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    I had to hook two motors to one DQ542MA Stepper Motor Driver to finish a project this weekend due to an unexpected incident involving a glass of beer (now broken), a shiny object that distracted me (causing me to set my beer down), a moving gantry, and the electronics enclosure temporarily being on a stand down below the beer. Let's just say that a drunk driver will not work properly on my CNC. After hearing a glass break, noticing a gantry not moving, and smelling a burnt up chip, I realized that I partially consumed a very expensive Three Creeks - Five Pine Chocolate Porter.

    Lessons learned: Probably none. This is the third time I have had one spill somewhere on the machine. Although the previous two were minor. That is the problem with building an extra large one. There is too much space to set stuff on it "for just a second." :banghead:

    Positive notes: The OB Part Store now sells that driver so it is on its way much faster than when I ordered the first set. Since I was ordering from the OB Part Store, I figured I may as well tack on those parts needed for building an Eggbot. The 3D Parts are printing at work as I write this post. :thumbsup:
     
  10. Metalguru

    Metalguru Master
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    There is an obvious solution to your problem - You need to add a Cupholder to your machine!

    MG
     
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  11. Metalguru

    Metalguru Master
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    I probably shouldn't have said that you can't hook up 2 stepper motors to one driver, because you can. It's just such a bad idea on so many levels:
    • Each motor has only half (approximately) of the current. This means the power to each motor is cut by a factor of 4, since power is derived from I^2.
    • You are doubling the reactance or inductance applied to the driver. This will likely cause instability and loss of torque of the motors at higher drive frequencies resulting in lost steps. This is a nonlinear function, meaning torque drops more rapidly with increasing drive frequency. This will severely limit the maximum speed of your machine.
    • Each motor will almost certainly have a different winding resistance, thus one motor will hog more current than the other, meaning one will tend to lose steps more than the other. If you have both motors on the same axis, which is likely the case, it will mean your axis keeps getting out of square, not to mention losing position.
    • As snokid pointed out, the driver will likely survive having two motors attached to it for a while, because it limits it's own current internally. But, the back EMF from two motors under certain operating conditions may add up to the point where it exceeds the voltage rating of the driver, causing it to self destruct.
    Again, just because you are able to do something, doesn't mean its a good idea. Giarc, was justified in his decision because it was necessary to test his machine. He had the good sense to not leave it that way.

    MG
     
  12. Giarc

    Giarc Master
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    Yup. I was able to finish what needed to be done, but I noticed strange sounds and vibrations that were not there before. I was just cutting foam so there wasn't a lot of stress, but I did not like what I was hearing, or feeling. So, I will not use it again until my Obenbuilds Part Store order arrives with it included tomorrow. Thanks for the quick shipping.

    As for the cup holder, I think I will be printing out a clip that fits in the v-slot at the front of the machine now that I have access to a 3D printer. Metalguru, you are brilliant. I should probably add a lid to keep the chips out. :)
     
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  13. Metalguru

    Metalguru Master
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    Why, thank you Giarc. I try. Definitely yes to the lid. Or get a nice stein with one built in...

    Yeah, the store has been on a hot streak lately. Even larger orders are hitting the road in just a couple of days. They've really stepped up the efficiency of the OB store.

    And, they are consummate packers. It takes me a while to get at my parts, through all the bubble wrap and tape, but they are guaranteed to arrive in one piece!

    Kudos to Trish and the rest of the store staff. She definitely goes above and beyond, I've caught her replying to emails at 9:00PM more than once...

    MG
     
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  14. GrayUK

    GrayUK Master
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    I seem to remember it was common practice to connect the two Y Axis motors to one driver on the early Ox models.
    Of course, one motor was wired oppositely to the other to drive the gantry in the same direction. :)
    We never heard many complaints at that time of driver overload, or an imbalance of power. However, Stepper motors have increased with Torque
    and size considerably since those days. (Yea yea, sound like an old fart don't I?) :D So this may cause the lack of power in today's drivers. :rolleyes:

    Gray
     
  15. OldDogSleeping

    OldDogSleeping Well-Known
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    You can wire two motors to one driver without halving the current, or loosing any torque. If you wire them in series rather than parallel, they will see the same current. The trade-off is the effective voltage to each motor will be halved instead, and this limits how fast you can run motors.

    I have my Y-axis wired this way; two Nema23's wired to one DRV8711 driver set to 2A with a 24v motor supply. My testing show that the reduced max speed of the steppers at an effective 12v each was still faster than my GRBL controller could provide steps.
     
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  16. JAPartridge

    JAPartridge Well-Known
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    LOL, that was truly one expensive beer! I'm in the process of gathering parts for a sphinx. Thought about going XXL on it and realized that (at least in my mind right now) I don't have anything that I need that much space for... and don't have the space to put an XXL version; and I'd end up doing the same as you, I'm sure! :rolleyes:
     

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