Running 2 stepper motors off a single drive


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    Default Running 2 stepper motors off a single drive

    Hi Guys, I am building my second CNC machine. My first was a small format gantry mill which works superbly with a G540 running under Mach3.
    I now wish to build a large format router. The Y axis will run 2 nema 34 motors slaved together electronically via the A axis. As this is a belt drive design I also wanted to run 2 nema 24 (60 frame size, 570 Oz in) on the actual gantry X axis. One at each end of the gantry moving the spindle assembly also via belt drive.

    My question is that since I have already used the slaving axis of mach3 on the Y axis. Is my only choice to wire the 2, "X" axis nema 24 motors (3 Amp) on the gantry to a single drive. So question is will a single drive such as the Gecko G210x (7Amp) run the 2 steppers on the gantry simultaneously?


    Thanks in advance for any advice

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    Member arizonavideo's Avatar
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    Many say you can't but it will work if the steppers are the same and if the load is about equal. The current will be double to the driver so you will only be able to run around a 4A stepper.

    You can also use a single step pules output and connect two drivers if the lead is the same.

    Let us know how it goes.



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    1) Gecko says it will work ok at slower speeds, but not at higher speeds.

    2) You can have up to 3 slaved axis in Mach3, so you can use a drive for each motor.

    3) Using two motors to move a single belt may not be a good idea, as the two will always be fighting each other a small amount, so you may not actually see twice the power.

    I don't know what your building, but from the sound of it, one 570oz motor should be more than enough. Rack and pinion users are getting 600-1000ipm with a single 380oz stepper on 4 foot gantry's.

    Gerry

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    I have 2 x-steppers connected with a timing belt on the same controller output. However, each stepper has its own Gecko drive with the step and direction inputs in parallel. Advantage is it never racks or gets out of sync and homing is not needed.

    That works absolutely fine but as Gerry mentioned, the 2 motors must be set to the same zero-step angle or you may lose torque instead of gaining. This is however very simple: loosen the belt pulley set screws, turn power for both steppers on so that they hold in the same idle position, set proper belt tension, make sure the gantry is perpendicular, then tighten the pulley set screws.

    It assumes that the Gecko drives always power up in the same microstep position (intuitive but Gecko never confirmed that to me). But as mentioned it works on my machine.

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    Thanks for the replies guys, The design is for a 4'x3' Gantry style router. Was intending to use a 570 Oz in motor for the X axis , but was worried that might be marginal, hence the second motor question.

    Also what do you think about the Y axis. This is the 4' dimension. This motor will have to move a 40 pound gantry. At the moment I have designed it using twin 1" wide belts. (one running either side connected with a 3/4" round rail. (The round CNC type). Would you recomend a nema 23, 570 Oz, (Geared 3:1) or would you go up to a nema 34 1200Oz in? Maybe geared 2:1. I was going to make the final drive pulleys that the main belt wraps around a 20T with a 5mm pitch.


    Thanks again for all your help


    Thanks again for your help



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    For a machine that size, A Gecko G540 driving 380oz steppers is the ideal setup, and should be quite a bit less expensive than the 570's and more expensive drives they require.

    570oz motors are overkill for your application.
    And generally, 1200oz steppers have no place at all on any size CNC Router. In almost all cases, they are easily outperformed by 400oz motors. The reason is that they have very high inductance, which limits there power range to very low rpm. Sure, you can reduce the reduction to gain speed. But then your giving away resolution, it'll still be slower, and you'll have paid more money.

    A 40lb gantry is very light, and I'd suspect that you might have some rigidity issues with it. Many people try to build there machines as light as possible. This is the wrong approach. The goal should be to build the most rigid machine possible. Weight really shouldn't be a concern. Even at 100lbs, weight wouldn't be an issue.
    Unless.
    You intend to use belt drives. On a machine that size, belts aren't really rigid enough. You'll likely find that the cut quality won't be a good as a screw or rack and pinion driven machine. Look through the hundreds of build logs here, and you won't find many belt drive machines that are this size.
    If I was building a machine that size, I'd look into using Chinese ballscrews.

    As for driving the gantry with two motors, just slave them together in Mach3. No mechanical connection is needed, and it's very simple to set up.

    Gerry

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    Default Re: Running 2 stepper motors off a single drive

    Just found this thread-
    I have a machine running the Gecko 540 and Mach 3. Currently I am running a 400 OZ/IN motor on the Z axis, but I need a more powerful motor so I can change the drive pulley ratio for more speed. Can I wire an 800 OZ/IN motor with a dual plug to connect to the Z and A outputs and then slave the A to the Z and in effect get sufficient output to run the larger motor?

    Thanks in advance for any help



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    Default Re: Running 2 stepper motors off a single drive

    I'd recommend against it. Very high risk of burning out the drive.



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    Default Re: Running 2 stepper motors off a single drive

    Well i asked this same question and all people just told: no, not got idea... Actually, the major qty of all 3dPrinter run 1 driver for 2 stepper and that work quite perfectly and it's an uber precision. Only difference is 17 to 23 and the load to move around. So i will soon post a real working test with a 6amp driver , driver 2x stepper of 3amp max, from 48v. Same motor, both very low inductance, running a rack pignon on belt gear. So it will probably work directly I will comment on missing step and so on if any.



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    Default Re: Running 2 stepper motors off a single drive

    Quote Originally Posted by Docop View Post
    Well i asked this same question and all people just told: no, not got idea... Actually, the major qty of all 3dPrinter run 1 driver for 2 stepper and that work quite perfectly and it's an uber precision. Only difference is 17 to 23 and the load to move around. So i will soon post a real working test with a 6amp driver , driver 2x stepper of 3amp max, from 48v. Same motor, both very low inductance, running a rack pignon on belt gear. So it will probably work directly I will comment on missing step and so on if any.
    Actually, when you say "the major qty of all 3dPrinter run 1 driver for 2 stepper and that work quite perfectly" your conclusions are wrong. Yes, true that many (I don't know if really the most) 3D printers use one single driver to run 2 steppers on the Z, but that does NOT mean that it is a good idea or they work perfectly at all. First you have to remember that there isn't the same forces involved in 3D printer applications, as in CNC. Also consider the reason why they are made like that, it is because of costs saving. The cheap 3D printers are so cheap that every penny counts, so they save on this, and compromise on quality. It is a very bad idea to do it, but many people don't care. I cared, so I modified my cheapo 3D printer, and run only one stepper with one driver. This increased the speed, as well as the precision, and reduced the constant need for levelling the printer. In my next printer, which I am working on now, I will use two steppers on the Z, but also two drivers, one for each, which is the way it should be done if you have two steppers. I would never design a CNC with two motors driven by a single driver. It is a bad idea, but of course, if you don't believe anyone, just do it. Be prepared for a LOT of struggle with squaring, and you will need to square at least once a day, after every power up.

    Here is how I modified my 3D-printer, and the results are larger precision, more power and less need for levelling.



    A major part of the work was changing the way the Z was made, removing one motor, adding ball bearings and moving the single Z stepper to the top BECAUSE it is better to have one driver for each stepper.

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    Default Re: Running 2 stepper motors off a single drive

    Awhile back I did some testing running dual stepper motors with single drive. I used various different drives from cheap a4988 to expensive geckodrive. They all ran the dual motors just fine however the most I could get the motors to spin was around 300-400rpm before stalling. Increasing power supply voltage didn’t increase rpm either. All the drivers had no problem spinning a single motor at much higher rpm speeds.

    300rpm would suffice for a 3d printer z axis but that is a limitation for a leadscrew/ballscrew type machine. 300rpm for a belt or rack/pinion would be pretty fast depending on pulley/gear size.

    The price of decent stepper drivers are so low now that trying to save a few dollars is kinda silly.



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