Driving 8 wire stepper with 2 outputs?

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  • January 28, 2014 at 11:11 pm #5306
    flightfollowing
    Member

    Is it possible or recommended to drive a single 8 wire stepper from two of the tinyg drivers in order to get beyond the 2.5amp output limit? Setting the two drivers to mirror one another?

    January 29, 2014 at 6:43 pm #5309
    alden
    Member

    Interesting thought but probably not a good idea. Each stepper driver regulates current in it’s own clock, so the power transfer would not be uniform. By using an 8 wire, though I assume you will electrically isolate the phases, so it might actually work.

    I’ll make you a deal – if you try it and blow up the board (which should not happen – but you never know) we’ll replace it if you provide a full report of how it did or did not work. Be aware that we are out of stock for about the next 2 weeks, so I’d hold off on the experiment for just a little.

    If you attempt this let’s sketch it out and discuss things before you try anything. I’m pretty sure doing this w/o driver isolation will have bad results.

    January 29, 2014 at 7:46 pm #5311
    flightfollowing
    Member

    Alden,

    Thanks for the interesting reply. I bought the tinyg for a shapeoko sized cnc router I am building. However, I have a g0704 3 axis mill that I am considering using the tinyg on, with 3 of the 428oz 2.8amp nema-23 8 wire motors on each axis leaving an extra driver spare, running at 27V with an existing power supply. Converting the mill to cnc is pretty quick, but the tinyg sounds marginal to drive it (please offer any advice here, I am new to cnc) according to:
    http://www.g0704.com/G0704_electronics.html#hoss

    My tentative plan will be to try out the tinyg for this mill with these motors and see how it works, with fan cooling on the tinyg. If it has problems, I have a few options: adding the 4th tinyg driver to the extra coils on the Z axis as per this thread, or getting something like:
    http://www.automationtechnologiesinc.com/products-page/kl-stepper-drivers/microstepping-driver-kl6852
    to the Z axis connected to the tinyg, or else removing the tinyg completely (using it for the router) and getting something like:

    3 Axis DSP Based Digital Stepper Driver Max 60 VDC/6.0A, MX3660

    I would welcome any advice as I do not know what I am doing. If you think the dual output on the 8 wire stepper might be feasible, it will be at least a few weeks before getting to that point and I would definitely get your advice on wiring it up and testing it.

    January 30, 2014 at 7:34 am #5315
    alden
    Member

    I have been using TinyG to drive the X and Y of a Probotix v90 using these motors:
    http://www.automationtechnologiesinc.com/products-page/nema-23/nema-23-bipolar-stepper-motor-425-oz-in-14%E2%80%9D-shaft-with-a-flat

    Perhaps these are the one’s you are referring to? These are 8 wire motors I have wired in parallel per phase. I don’t quite get full power out of them as they take 2.8 amps and TinyG delivers a bit less than that – the actual current is of course set by the current pots, which are up pretty high.

    You could start there and see if you get acceptable results. If not, go to the KL or Gecko drivers. The step, direction and enable are available from the v7 and the v8 boards. There are a few things you should know.

    – Be aware that the step, direction and enable signals are 3v outputs, and the enable is active low.

    – I have not personally tested either of these drivers with TinyG so I have no guidance to know how well this works or if it works at all. I’m tempted to buy one of the KLs and try it out.

    – The code currently in the edge branch (build 412.xx) has some pulse stretching in it. The master branch (380.08) does not. This might not matter. The pulse widths from the master are slightly less than 1 microsecond. Pulse widths from edge are 3 to 6 uSec. Might be friendlier for some outboard drivers.

    February 4, 2014 at 12:52 pm #5344
    flightfollowing
    Member

    Those are the same motors I am using. I did receive my tinyg yesterday and hooked it up to the mill and got things up and running pretty easily in a draft mode, only two axis as I am waiting for one more part for Z. Turned up the pots pretty much all the way, but I can still get stalling when running at full speed even without a load (but the mill needs to be lubed and tuned). When running slower it seems to do fine when simple resistance is applied by hand.
    I don’t have very heavy milling requirements so not achieving top speed may not be a problem and it would work fine as is, but I can tell I will be limited with the tinyg at 28V and the 2.8amp motors, so I might be interested in more output with either the dual output 8 wire from the tinyg or else the KL driver.
    However, you mention some issues I should be aware of, specifically the 3v output formats, the pulse stretching and the untested KL’s.
    If you have any more insight into using the KL, or if you have a wiring and configuration plan for dual outputs from the tinyg to an 8 wire motor, feel free to let me know and I could give it a try (unless you try it yourself as a test 🙂

    Couple of other questions: If I were to use a KL driver, where physically would it get its step-dir-enable outputs from, the J17, J18, j19, or J20 headers on the board? Or are these matched to the existing motor drivers 1-4? This is confusing and does not appear documented in the schematic.
    Also, are their any settings or tricks to deal with backlash using the tinyg? Or if not in the config files, maybe in creating the gcode?
    Thanks

    February 7, 2014 at 5:10 am #5374
    alden
    Member

    Interesting.

    “Stalling at full speed” might indicate that full speed is too high for the setup / tuning. Every machine needs to have the max velocity tuned for each axis – it’s just a question of how much you can get out of it. With a more powerful driver you might be able to get a higher max velocity. Perhaps this is what you are saying and I just wasn’t listening correctly.

    I have started a page on using TInyG with external drivers.
    https://github.com/synthetos/TinyG/wiki/TinyG-Using-External-Drivers
    It’s pretty sketchy right now (as of this morning), but we should collect all facts, voodoo, folklore and wisdom there as this topic evolves. You are welcome to contribute if you want – the entire wiki is open to anyone with a github login.

    I will start the page by answering your questions above.

    • This reply was modified 10 years, 9 months ago by alden.
    February 7, 2014 at 5:56 am #5376
    alden
    Member

    One other thing – there are no settings to control backlash in tinyg. This is something we are considering.

    February 7, 2014 at 9:00 am #5379
    flightfollowing
    Member

    Thanks very much for the feedback. My questions might have been premature as I am pretty happy with the tinyg driving the G0704 directly without any external driver or dual outputs to a single motor. After slowing down the fastest transit rates a bit, switching from 1/8 steps to 1/2 steps, and tuning/lubing the mill it works great. Now you just need some more tinyg’s in stock for ordering for another machine, (and getting tgFX out of beta!). Thanks.

    February 7, 2014 at 5:52 pm #5390
    Riley
    Keymaster

    Ha! We should be getting more boards in, in the next few weeks. As far as tgFX goes I have a bunch of changes that I am working on fixing bugs and getting a stable release.

    I am very interested in seeing your mill in action! Would you post some videos of tinyg tgfx and the mill doing something? That is some serious awesome!

    ril3y

    February 15, 2014 at 12:51 pm #5413
    flightfollowing
    Member

    Riley,
    I posted a little something in the projects threads, as you will see I am not a videographer.

    CNC mill conversion G0704 Grizzly – cheap

    I am working through some issues with tinyg and tgfx, using cambam for gcode and linixCNC format (?) machine code. Seems like I am having a Z axis issue at the beginning of runs, and the machine does not return home when finished?

    Cliff

    February 18, 2014 at 11:03 pm #5427
    Riley
    Keymaster

    Cliff,

    The Synthetos team is aware of this bug. We are not 100% sure where its at but I think we are close to finding it. Can you post your gcode file you are having issues with? Also the steps on how to reproduce this?

    Like so,

    1. I jog to some position.
    2. I load this file (pasted)
    3. I click run.

    Then,
    You will notice that some behavior occurs at the start of the job. Etc?

    I will help me reproduce this bug.

    Thanks Cliff!

    Riley

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