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Onboard stepper drivers, vs external stepper drivers

Discussion in 'General Electronics' started by CraigF, Sep 29, 2019.

  1. CraigF

    CraigF New
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    trying to wrap my head around what the difference is between onboard, and external stepper drivers. all my google searching has come up in vain.

    I assume they have different capabilities.
    the external stepper drivers i see on ebay and various CNC builds, seem to be bigger in size, than what the Openbuids Blackbox has, or other boards like Duet.

    does bigger mean better?

    I know that external and onboard drivers both come in a variety, with different prices, and capabilities. Im just trying to get a sense of why someone would pick one, over the other, for a particular project. 3d prints, CNC mill, laser engraver, etc.
     

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  2. Gary Caruso

    Gary Caruso OpenBuilds Team
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    Hi Craig, It comes down to current and voltage.
    If you want to use higher torque - bigger motors, you need more current than something like a black box can do.
    Also voltage is limited to 24v on most all-in-one units, voltage is speed current is torque..
    Black box can do about 3.2A at 24V where as a 542 you showed can do about 4.2A and 48volts
    For the lightweight hobby size router machines we build here the Blackbox is fine.
    Also the Blackbox runs on GRBL for software which has its limits but is great for the hobby machines.
    Cheers
    Gary
     
    #2 Gary Caruso, Sep 29, 2019
    Last edited: Sep 29, 2019
  3. CraigF

    CraigF New
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    Thanks so much Gary, that helps a lot.
     
  4. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    BlackBox can do 3.2A comfortably and 4A at the max.
     
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  5. Gary Caruso

    Gary Caruso OpenBuilds Team
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    Right! I'll edit my response
    Gary
     
  6. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    BlackBox's onboard drivers are perfectly matched to our High Torque Motors. They can run 3.2A RMS max, with up to 4A peaks.
     
  7. Gary Caruso

    Gary Caruso OpenBuilds Team
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    Right, bigger motors than Openbuilds Big / little motors ;)
     
  8. phil from seattle

    phil from seattle Well-Known
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    No bigger doesn't mean better. You just need to size your drivers to your specific steppers and intended application (with a little extra headroom). Anything bigger is just wasted money.

    Something to consider for the general case, controllers with built-in stepper drivers suffer from one inherent weakness - driver failure (it happens) means replacing an entire board. With external, you only replace the failed driver. Of course with an onboard driver controller, you might be able to replace the failed onboard driver with an external one to avoid replacement of the entire board though that has issues as well.
     
  9. CraigF

    CraigF New
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    In terms of upgrading down the road.. say i wanted to put on a heavier spindle. if i upgraded my stepper motors to handle the extra weight, it'd be easier to upgrade the external stepper drivers? or perhaps its just as easy to replace the control board?

    its the control board that dictates whether its a GRBL machine or a Mach3 type machine with parallel ports. (as far as i understand)
    Are external stepper drivers built for one type of machine, or the other? Or are they agnostic.
     
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  10. Alex Chambers

    Alex Chambers Veteran
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    Bigger (heavier) doesn't necessarily mean better in terms of spindle either. You haven't said what machine you are thinking of but there are limits to the weight and forces that Openbuilds machines using aluminium extrusion can handle without flexing and causing accuracy problems. If you want advice on machine/controller/stepper drivers/motors the best starting point is the sort of jobs you want to do, maximum sizes etc.
    Alex.
     
  11. phil from seattle

    phil from seattle Well-Known
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    Replacing the control board may be easy though it may well be more expensive than just the drivers. Way too many degrees of freedom to answer your question even vaguely. Also, there is a lot of variation amongst control boards so you would probably spend a lot of time reconfiguring if nothing else. Wiring pinouts may be different. And it's quite possible your G-Code would have to be updated to deal with the differences. Keeping the control board will clearly avoid all those issues.

    Most stepper drivers have a generic and simple step/direction/enable interface. No such thing as a GRBL specific driver. Still, you have to look at the exact interface requirements like current draw and such to be sure. So, the definitive answer to your question is that any driver "probably will work".
     
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  12. Giarc

    Giarc Master
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    The Blackbox is a great all in one system for $149.99 with phenomenal support. I have one for a future build I am planning. I am currently running 4 (2 Y, 1 X , and 1 Z) DQ542MA drivers ($39.99) which I love. The Blackbox did not exist when I built mine and I did not want under-powered 3D printer drivers like the boards using DRV8825 drivers. I connected my drivers to an Arduino Uno. I purchased a genuine Arduino Uno for my CNC, not a clone. Too many people have had issues with cloned versions and to me an extra $10 is worth not having trouble shooting headaches. I added a screw shield similar to this one to make connections to the drivers, limit switches, probe, etc. eaiser. So essentially the drivers, screw shield, and arduino cost me about $188. If you want the ability to switch to mach 3 but want to start with using grbl, get the arduino/external driver combo. You can never go wrong with a spare arduino board if you switch to Mach 3. Someone out there will need an automated cat litterbox changer.
     
  13. CraigF

    CraigF New
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    In general im just trying to understand how it all works, but i do have a machine design in mind. Im going to start with a Lead 1010 machine, probably the biggest size, and put a dewalt router on it to start... id the like to add a second z-stepper motor (and assembly), and have 3 routers spaced out on a plate that goes from 1 z-assembly, to the other.
    put simply, 3 routers controlled by 1 machine.

    and maybe eventually, id like to replace all 3 routers with VFD spindles, which i know are heavier.
    i plan on using this contraption for production of parts, and products. the more routers i can fit on the machine, the faster i can produce them.
     
  14. CraigF

    CraigF New
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    :D
    very true lol
     
  15. Alex Chambers

    Alex Chambers Veteran
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    Lead 1010 and DeWalt or Makita - yes
    Lead 1010 and air-cooled spindle (not too big and heavy) - yes
    Three routers /spindles - no! - too heavy & too much force on C-beam X axis which would flex giving poor/inaccurate cuts.
    Better to think about what you could be doing while keeping an eye on the machine - once you have got the hang of things/ironed out any teething problems it will only need minimal attention if doing repetitive work.
    Alex. :cool:
     
  16. CraigF

    CraigF New
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    I could reinforce the gantry with a steel plate, or some extra aluminum extrusions, im sure i could find some solution to the flexing of the gantry.
    but the goal for me here with the 3 spindles/routers is to increase production, the cheapest way possible. so one machine with 3 routers, is cheaper than 3 whole machines. and while i do want a as much accuracy as i can.. im not working in machinists tolerances, maybe closer to carpenter tolerances. :)
     
  17. Giarc

    Giarc Master
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    How large are your parts? If you add two more spindles, you will loose a significant amount of cutting area. So, if all three gantry plates touched each other, you will loose 375mm of cutting area vs 125mm with one plate if you chose to cut one large part that you would have previously been able to cut. If you ave any space between the plates, your a overall area would shrink further. That does not include any subtractions for limit switches. But, if this setup is only to be used to mass produce smaller items, I do not see why it couldn't be attempted.

    Buy a 3 inch piece of 1/4" aluminum bar stock and cut it to length. Use your current configuration to drill 4 rows of many holes and buy drop in t-nuts and 12mm screws (or maybe 10mm). Bolt it to the front of the X axis C-beam, add another 1/4 inch spacer to the axles of the x axis gantry cart and you should have helped prevent sagging of the beam significantly. It should help a bit with flexing in the z axis as well. You could do the same with some steel, but then you add a lot of weight and the drilling becomes significantly harder. Or, since the lead x axis beams do not mount on a plate like the Ox or Workbee, bolt another 80x20 v-slot beam to it and add another row of wheels and spacers. I made my X axis by bolting together 2 pieces of 80x20mm v-slot using these as a guide.
     
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  18. CraigF

    CraigF New
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    The products i produce vary in size, at the smallest, they are smaller than a can of pop, at the largest, the size of a laptop. but id mostly be using this for smaller items, for mass production.
     

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