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controllers - which one (for wood carving on workbee)

Discussion in 'CNC Mills/Routers' started by halfshavedyaks, Apr 13, 2018.

  1. halfshavedyaks

    halfshavedyaks Journeyman
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    I'm about to buy a workbee and I am wondering about alternative controller boards instead of the Xpro that ooznest bundle as standard. I have nothing against the Xpro per se - just doing my research.

    I'm familiar with 3D printers, but new to CNC so I may be worried about the wrong things, or missing important things- that's why I'm asking here!

    my concerns are:

    * would a 32 bit board give me better /smoother results? if so which one? smoothie board is limited to 2A - will it matter? other 32 bit boards? external stepper drivers for flexibility and more current? if so which ones?

    * I've seen at least one report that the Xpro steppers result in noisy movement compared to other stepper drivers, can anyone confirm or deny this?

    * Making the machine as quiet as possible is important to me partly because my workshop is in the house and noise will be an issue for when and how long I can run it, and partly because noise tends to indicate inefficient machinery and more wear and tear.

    * which boards have the best support and are most straightforward to configure?

    * which boards have advanced software features that will help with quietness and smoothness and precision. I'm thinking of things like modulating travel and cutter speeds for curves and corners. (rather like acceleration and lin_advance settings in printers.)
     
  2. Techvette

    Techvette Journeyman
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    I have two xPros and love them. With the bluetooth module, rather than a really long USB cable, they're wonderful, very well-made devices, and they perform very, very well.

    If you want to use Mach3, rather than any GRBL board, you'll need a parallel port (and an old computer and OS) and a breakout board. This approach sucks.

    On to your questions:

    * 32-bit: You're not going to be cutting anything fast enough to exceed what even an 8-bit micro can do. Funny story: at my first embedded system job, I was trying to get some LEDs to blink on an 8051-based, 11.0592MHz board. They lights refused to turn on. Turns out that they were turning on and off so fast that it was invisible. Unless you're running a 10-axis machine, I doubt you're going to see a difference based on the type of processor used here. (Others may have different experience - mine is limited to a 1000x1500 DIY router and a Minimill.)

    *Amperage I was initially concerned about the driver output amps on the xPro, but they're inline with just about every other controller board. Your current requirement is a function of what motors you're using, what material you want to cut, and how fast you need to go. The material will probably be the limiting factor. If you want to be really informed, figure out what you want to cut, recommended feeds and speeds for that material, and use that to determine what motor you'll need, configuration (bipolar, unipolar, parallel or series coil configuration), and you can get an accurate number. In my case, I had dial the current on the xPro down to keep the motors happy. Note that the xPro, and some other boards, support connecting external drivers. If the onboard drivers aren't up to the task, you can always use some external ones. I haven't had an issue cutting AL plate using the onboard drivers.

    *Noise If the motors are making noise at idle - typically an annoying buzzing - you're probably pushing too much current for the motor.

    *Support Again, I know you're looking at other options than the xPro, but I've received amazing support from Spark Concepts (xPro creators). I can't speak to the responsiveness of other vendors.

    *Advanced Features This will be a function of the firmware on the board. Most of the boards you'll see run GRBL. There are other options - EstlCAM reflashes the board with it's own firmware, and adds support for things like trochoidal milling. Given that many (if not most) of these are Arduino-based, you can probably tweak and reflash without much trouble. Every board I've used supports smooth interpolation for curves, which is implemented by GRBL. (In reality, your CAM app will rasterize the curve based on your tool size.) Modulating cutter RPM is a different topic. That's typically a function of your workpiece material (AL, MDF, etc.). Your CAM app will make sure that the cutter doesn't dwell too long at any one point.

    Hopefully this is helpful. I'm relatively new to this area.
     
  3. halfshavedyaks

    halfshavedyaks Journeyman
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    thanks!

    I know very little about it but from what I've seen I have no desire to use mach3.

    I have seen some hints that Xpro may be noiser than other drivers - but there's lots of variables there and nothing conclusive.

    is there an advantage of getting Xpro vs an arduino with 4x DQ542MA?

    I already have an arduino uno R3 and the cost of 4x DQ542MA is similar to the cost of an Xpro - and modularity in the setup appeals.
     
  4. Techvette

    Techvette Journeyman
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    Maybe a silly question, but when you say noise - do you mean electrical, or audio?
     
  5. halfshavedyaks

    halfshavedyaks Journeyman
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    I meant audible noise. Electrical noise may also be an issue but it isn't want i meant in this case.

    Seems like the loudest noise is the mill in the wood although that will vary a lot depending on what is being cut and how fast - then there's spindle/router noise and the noise of the motors turning the screws and any/all of those being transmitted and radiated through the Vslot extrusions.

    So although I imagine direct motor noise is never that loud the motor turning smoothly will have an impact on how much vibration is transmitted into the screw and into the Vslots.

    Driver performance could have an impact on how smoothly the motors turn, so the drivers used could have an impact on audible noise.

    3 axes of drivers moving at different rates will create interference patterns from the combination of 3 different vibrations at different frequencies, these can add up in unpredictable ways. (at least that's what seems to happen on my 3d printer)

    Since I expect a finishing pass on one of my 3D carved part designs might well take 6-8 hours or more and my workshop is in the house, and the mill will be cutting minimal depth in that case, so mill cutting noise will be as low as it can get, then it might be relevant to keep other sources of noise such as motors and spindle vibration as low as possible. Plus lower vibration through the structure of the machine has got to be good for accuracy and longevity.

    No doubt it will become clearer once I actually have a machine, but that's rather too late for the main purchasing decisions.

    It seems that an Xpro is just an arduino uno with 4 DRV8825 drivers combined on one board. Since I already have an arduino, and value modularity I like the idea of just buying drivers separately. Cheaper too. Though the DQ542MA 4A drivers I mentioned may well be overkill!
     
  6. halfshavedyaks

    halfshavedyaks Journeyman
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    It's a bit OT for what I'm asking here, but I'm also thinking of filling the V slot extrusions with mortar, or maybe resin/sand mix, to reduce vibration. I don't know if it is necessary or even helpful yet though.
     
  7. halfshavedyaks

    halfshavedyaks Journeyman
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  8. GrayUK

    GrayUK Openbuilds Team Elder
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    You should consider a sound deadening booth if noise is a great concern.
    There is a thread already running with regard to sound proofing. :thumbsup:
    Take a look at it.
     
  9. halfshavedyaks

    halfshavedyaks Journeyman
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    yep I'll build a box for it if I need to. Would need to get dust extraction in the box too though to really benefit.

    I'm not that enthusiastic about a box as it takes up space and reduces access to the machine, but I'll do it if my other optimisations are not enough.

    A lot depends on job times and I'm just not really sure how long they will take yet. An hour or two of noise is OK, but long periods and it will become a big problem. I regularly do 30hr prints on my 3D printer, But i'm hoping it won't come that with the CNC.
     
    #9 halfshavedyaks, Apr 15, 2018
    Last edited: Apr 15, 2018
  10. halfshavedyaks

    halfshavedyaks Journeyman
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  11. halfshavedyaks

    halfshavedyaks Journeyman
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    about this - I would think that the issue is not the cutting speed, but the complexity of the gcode - a complex object with lots of continuously varying curves in all 3 dimensions is going to take a lot more cpu than cutting simple lines and arcs , especially only in 2D.

    That said It may still be fine - at the moment I'm intending to start with 8bit GRBL and see how it goes. Maybe when GRBL gets going on ARM i'll upgrade - another reason to keep the system modular.

    Something I really don't get is the need for a computer sending gcode and a separate arduino controller controlling the machine. Is it not possible to combine them in one device? ie running stepper drivers directly from a raspberry pi or something like that? I haven't found anything like that - and I'm accepting that it is how it is for now - but it seems odd that no-one has made one device to manage the whole thing.
     
  12. GrayUK

    GrayUK Openbuilds Team Elder
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