ANy sucesseful xyz+spindle pic-based lpt drives? - Page 2

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Thread: ANy sucesseful xyz+spindle pic-based lpt drives?

  1. #13
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    Quote Originally Posted by A_Camera View Post
    That problem can easily be solved with proper buffering. Besides, if USB is suitable for video and other speed demanding applications, like digital oscilloscopes, logic analysers and other stuff, then driving a CNC is really a piece of cake. Parallel ports are a dinosaurs and really slow.
    The problem is that although usb is fast, the application needs to wait it's turn before it is allowed to send a packet. The amount of delay is enough to cause a motor to run rough or stall. I guess in theory, the lpt/usb converter could delay and buffer the pulse stream, but the common ones don't. They just wait their turn. I wonder how difficult it would be to write a cnc capable serializer for Windows.

    It's not about ARM vs. PIC and not really about oscillator clock speeds at all. Remember that what's important is the MIPS and for a PIC one clock cycle = one instruction cycle, for the ARM it is not (unless I am mistaken), so you can't really compare oscillator frequencies 1 to 1.
    Not counting the pic32, which is a MIPS processor, the fastest pic is the Dspic. It runs 16 bit code at up to 75 mips. The ARM is 32 bits and supposedly run 1.25 dmips per Mhz. The faster cortex M4 variants are close to 200 Mhz and has a floating point accelerator built in.
    I am pretty sure that the 12 MIPS of the 18F4550 is more than enough.
    It's probably enough to do a deserializer, but not a motion controller. Too many calculations are needed. At 50Khz, you only have 20 microseconds between steps.

    Also, it is not about how much a microcontroller costs, you need more than just a single ARM processor for $10 before you can make a working BOB, you need a whole development kit as well, and that is more than $10, not to mention programming experience, language, tools and debug platforms. To start a project like that with ARM costs a lot more than $10 if you already have everything set up for PIC. If you have nothing than you could say it really makes no difference, you must start from scratch anyway. For me this is a hobby, if I had commercial plans I may reevaluate my decisions, but even so, I would not jump to any conclusion before a deep analysis of the high end PICs first on paper and in a prototype.
    You can buy a ready to run 160Mhz evaluation board with the JTAG debugger for about $15. The C compiler is free for up to 32k of code. Don't get me wrong. The pic is a great chip. But there's no reason to limit yourself.

    It depends on what you prefer, but I don't think that PIC in general is a limiting factor. It depends of course on the PIC you chose and your own programing skills. For an application like this, I would not chose any other language than assembly because of the predictability of times and the possibility of measuring/calculating exact timings in every stage.
    Assembly is efficient for simple things, but I can complete a complex application much faster using C. For hobby projects, the chip cost is unimportant. This is largely true even in production. Time is more valuable to me.



  2. #14
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    [QUOTE=Larken;1275794]Tell that to the maker of the new AKZ 245 USB Mach3 interface that is driverless.
    The USB sends packets into a FIFO that sends out the step/direction.
    If your USB packets are big enough you can get the thru rate
    I did a search and did not find it. Do you have a link?

    A Pic32 costs about $5 and is as fast as your ARM.. They both run 1 clock cycle / instruction..
    PIC32 is a MIPS. It's not really a pic. It's a decent processor and I would use it if it was convenient, but learning to use the ARM opens up more doors.

    An 8 bit PIC 18F can run rapids at up to 100 khz if the code is written right.
    Your into overkill, you don't realize older machines ran fast on a Z80 processor.
    You don't need a ARM or CPLD logic array to make a good CNC controller. Just the write person programming it.
    I am capable of doing well optimized assembly code, but for regular applications, it's a waste of time. I recently did a DSPIC based stepper motor driver as a learning project. I could have done it with a much weaker 8 bitter, but why bother? The cost difference was neglible. Even if I was selling them, parts cost is not the main impediment to profitability.



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    Here is the USB controller that doesn't need a driver. It uses the FIFO technique, same as Mach does.
    3 Axis CNC USB Card Mach3 200KHz Breakout Board Automation Technology Inc

    H500, Your comparing a $10 ARM processor, but when i bring a $5 PIC32 which is as fast, you say its not really a PIC... Huh ??

    and
    We show you a number of CNC controllers running a 18F45xx processor and you say...

    "It's probably enough to do a deserializer, but not a motion controller. Too many calculations are needed. At 50Khz, you only have 20 microseconds between steps. "

    I guess you just aren't listening.

    Manufacturer of CNC routers and Viper Servo Drives
    www.LarkenCNC.com and www.Viperservo.com


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    H500, I am not interested in continuing this argument. I am convinced that a PIC easily can do the job of a BOB, and if I am wrong then so be it, I am willing to try. This is a PIC Programming / Design forum and your posts are not informative or helpful for anyone interested in PIC programming in relation to CNC. All you are saying is "use ARM", which is pretty pointless. Don't assume that just because you can't do something nobody else can.

    Last edited by A_Camera; 05-17-2013 at 04:03 AM.


  5. #17
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    Quote Originally Posted by Larken View Post
    Here is the USB controller that doesn't need a driver. It uses the FIFO technique, same as Mach does.
    3 Axis CNC USB Card Mach3 200KHz Breakout Board Automation Technology Inc
    That is clearly a full fledged motion controller that require a custom plugin for Mach. It's not the simple LPT serializer/deserializer that you make it out to be.

    H500, Your comparing a $10 ARM processor, but when i bring a $5 PIC32 which is as fast, you say its not really a PIC... Huh ??
    Do you understand the architectural difference between a PIC and a MIPS M4K processor? The PIC32 is no closer to a PIC than an ARM.

    and
    We show you a number of CNC controllers running a 18F45xx processor and you say...

    I guess you just aren't listening.
    You didn't show a single one that checked out. An 8 bit PIC is nowhere fast enough to do what that controller in your link does.



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    Quote Originally Posted by A_Camera View Post
    H500, I am not interested in continuing this argument. I am convinced that a PIC easily can do the job of a BOB, and if I am wrong then so be it, I am willing to try. This is a PIC Programming / Design forum and your posts are not informative or helpful for anyone interested in PIC programming in relation to CNC. All you are saying is "use ARM", which is pretty pointless. Don't assume that just because you can't do something nobody else can.
    This is a technical discussion forum, not a fan boy clubhouse. If you are offended because I said something that was not laudatory of your favorite brand, then you are free to ignore my posts. My perspective might not make you feel good, but thinking outside of the box is far from useless.



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ANy sucesseful xyz+spindle pic-based lpt drives?

ANy sucesseful xyz+spindle pic-based lpt drives?

ANy sucesseful xyz+spindle pic-based lpt drives?