Re: [CAD_CAM_EDM_DRO] EMC2 Servo Loop

Your approach makes a lot of sense. I guess it really depends upon one's
priorities. A lot of people are intimidated by the prospect of setting up
and maintaining a Linux system. I know that Ubuntu and most of the other
mainstream distros have done a lot to make Linux look and feel like Windows,
and in fact Ubuntu is actually easier to install. Unfortunately it still
requires quite a lot more knowledge of computer science if you need to debug
or configure anything that is not handled automatically by some kind of
wizard, and the wizards are not as extensive or complete.

Also, ironically, Linux (at least the graphical versions) seems less
efficient. I say ironic because Linux as a web server was alwats touted as
being so much more efficient than Windows. I suspect because it generally
ran in mode 3, no GUI. Everything with a GUI seems to run on top of X11, and
the Linux community seems to have a policy never to rework anything that
works, but only to extend or add layers. As far as I know, nothing has ever
been done to make use of the vector processing instructions added with the
PII and newer processors from Intel.

I have an old Pentium 166MHz 64MB machine I'm thinking of using for a CNC
controller, and I'm concerned it might not be fast enough or have enough
memory for EMC2. I know the answer is to just try it, and I will unless
someone can tell me, "don't bother, that definitely won't suffice." I know
the EMC2 kernel is optimized for speed, but I presume the GUI still relies
on X11, which I'm fairly sure is bloatware.

--Phil M.

----- Original Message -----
From: "Jon Elson" <elson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Friday, December 17, 2010 8:53 PM
Subject: Re: [CAD_CAM_EDM_DRO] EMC2 Servo Loop


> Phil@Yahoo wrote:
>> Yes, I get the idea. I just wonder what the main advantage is of having
>> the
>> servo loop run through the PC if not to reduce the external hardware. If
>> you
>> have to add external encoder counters it doesn't seem the cost would be
>> much
>> different from having a self-contained servo controller that simply takes
>> step-direction commands and reports errors, etc. Cheap microcontrollers
>> can
>> easily handle that computing load.
>>
> If you already have a fully-debugged N-axis motion controller that does
> everything you
> want, then the EMC way doesn't buy you much. But, what if Joe in Idaho
> wants to
> change something, add a feature, whatever. With EMC2, everything is
> available to him,
> and can be easily debugged directly on the PC.
> With some external box, then there is a second kind of machine code, and
> cross-compiling
> and cross-debugging tools, etc.
>
> In great volume, little micros are really cheap, so it is quite
> reasonable to use them.
> But, look at what happened with Gecko Drives' G100 (GREX) product. It
> was all of that, but they
> NEVER got the firmware working to everybody's satisfaction. A good part
> of that was related
> to the cross-development tools that kept a wider range of parties from
> helping.
>
> Taking step commands from the PC is very limiting. With my hardware,
> you can run the encoders
> at well over 300,000 counts/second, and only send velocity commands to
> the board. So, the
> computer is reading position at some specific rate, and sending new
> velocity commands out
> at that rate, typically 1000 times a second.
>
>
> Jon
>
>
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