Re: EMC compatible computers

[Ray Henry <rehenry-at-up.net>]

Erie

Great idea for a big machine.  Could you make a list of the bugs.  I've 
found a couple but a good listing of them should make it possible to fix 
them.

Ray


On Wednesday 15 January 2003 09:32 am, you wrote:
> I've had good success running tkemc on a remote machine, with
> EMC running on a salvaged (<$50) PIII-450. The remote has a few bugs
> but my machine is huge and allows me several consoles around it.
>
> erie
>
> -----Original Message-----
> From: emc-at-nist.gov [emc-at-nist.gov]On Behalf Of
> jmkasunich-at-ra.rockwell.com
> Sent: Wednesday, January 15, 2003 9:09 AM
> To: Multiple recipients of list
> Subject: Re: EMC compatible computers
>
> John Sheahan wrote:
> > My picture is a small, dedicated  box near the machine.
> > If its a standard motherboard - with a parallel port,
> > thats ok.
>
> Do you mean a dedicated box near the machine, connected
> to a PC that is running EMC?  Or a dedicated box near the
> machine that _IS_ the PC running EMC?
>
> I think the latter is much simpler.  Just because RTLinux
> lets you surf the web while running the machine doesn't
> mean it's a good thing to do.  I for one intend to have
> a PC dedicated to running the machine, with display and
> keyboard set up to be used while standing in front of
> the machine.  Not a nice setup for CAD or web browsing.
> I'll have another PC for "normal" PC work, at a nice
> comfortable desk.  I will use ethernet or floppynet to
> connect the two machines.
>
> > If its a dedicated chunk of hardware - say a fpga,
> > electrically its a lot like a parallel port.
> > Either way its essentially co-located with the  motor driver.
>
> As above, I'd like to co-locate both the PC and any
> "helper" hardware next to the drivers.  That way, none
> of the cables will be very long.
>
> > > "other related costs"?
> >
> > I was including the motor driver and perhaps the machine..
>
> Understood.
>
> > > > And the parallel port (electrical) performance sucks
> > > > compared to any ethernet - particularly optical ones.
> > >
> > > Do you mean isolation?
> >
> > isolation/noise/esd in general.
> > GbE over fibre still works better in a particularly
> > noisy environment.
> >
> > parallel ports can't drive long wires, have lousy
> > edge rates, die from ESD, and very occasionally
> > miss transfers.
>
> Agreed about long wires.  Again I was assuming PC near
> drivers, and short wires.  Noise issues don't worry me
> so much - my day job involves IGBTs switching 1000A at
> 800V in 100nS, near digital and analog electronics.
> I'm confident I can lay out, ground, and shield my
> system to make it work.  For the average machinist
> with limited electronic experience it would be a much
> more inportant factor.
>
> > I just dislike parallel ports! :)
>
> Everyone is entitled to their opinion...  ;)
>
> > > The real burden is step pulse generation and
> > > encoder counting.  That is best handled by
> > > dedicated hardware, not software of any kind.
> >
> > agree, although modern PC's are quick enough to blur
> > the difference.
>
> They are getting there.  It still takes quite a PC if you are
> using high count encoders or microstepping.  I would prefer
> that the fastest PC in my house be on my desk.  I'd like to
> use older, slower, cheap PC(s) to run machinery.
>
> > I still prefer designs that hang in there over time..
> > PC hardware is just so ephemeral compared to the stuff
> > its controlling, particularly now.
>
> You hit the nail right on the head.
>
> My approach (right or wrong) is to freeze the technology at
> some point, and try to be able to maintain that point, rather
> than always going for the latest and greatest.
>
> Maintainence is the trick - if the motherboard I use today
> breaks 4 years from now, I won't be able to find a replacement
> that works the same.
>
> Since I am an incurable dumpster diver, my approach is to use
> cheap or free stuff and keep spares on the shelf.
>
> For example, my CNC project.  I will use one of the following
> two options - both came from dumpsters.
>
> 1)  Allen Bradley 6180 industrial PC.  Picture at:
>     http://www.ab.com/opinter/eoi/icb/rac6180.html
>     200 MHz Pentium, 128MB, in industrial enclosure.
>     Has 14" flat screen, full alphanumeric membrane keypad,
>     all sealed, you can splash it with coolant and metal
>     chips and it doesn't care.  Has connectors for external
>     keyboard and mouse.  I have a spare power supply,
>     motherboard, display, backlight, video card, and
>     membrane switch interface card.  The motherboard is
>     ATX form factor, but the BIOS may be semi-proprietary.
>     Disks, CD-ROM, etc, are standard PC components.
>     By the time I add stepper power supply and drivers,
>     it will be a big heavy box that has to be mounted
>     where I can see the display.  Maybe I'll remote
>     mount the stepper stuff and use a 6' parallel port
>     cable.
>
> 2)  Cubix BC5200-TS "server blade" single board PC.
>     http://64.173.211.2/support/techinfo/bc/ts/intro.htm
>     200 Mhz Pentium, 64 or 128 MB, SCSI & IDE interfaces,
>     floppy, video, LPT & COM, keyboard, ethernet.
>     Everything you'd find on a motherboard.  Plugs into
>     a 16 bit ISA slot, but the only thing it needs from
>     the slot is power.  I have eleven of these.  If I use
>     these, one box about the size of a tower case will
>     contain stepper and PC power supplies, Gecko drivers,
>     Jon Elson's universal stepper board or my homemade
>     version, the "blade" PC, and disk drive(s).  Connect
>     monitor, keyboard, and motors and away I go.  Box
>     mounts anywhere, monitor and keyboard where easily
>     seen and reached.
>
> > used motherboards suitable for emc are generally
> > in the free category now.
> > fpga based proto boards are not unfortunately.
>
> Used 200MHz motherboards are free, but if you want to
> microstep, you might want something faster.  I like
> the idea of spending $200 for Jon's board, and being
> able to use a $0 motherboard.  Others might prefer to
> put the $200 into the computer, so they have enough
> speed to generate step pulses in software with no
> external "helper" hardware.
>
> One perspective - there are two kinds of maintainable
> hardware in the long term.
>
> A)  Simple boards built with commodity parts, with
>     complete documentation.  That's what I would have
>     if I build my own version of Jon's board.
>     Jon's own version of the board isn't too bad,
>     but the long term availability of the FPGA is
>     unknown, and I don't think he supplies schematics.
>     These boards can be repaired at the component
>     level.
>
> B)  Complex mass market boards that are cheap enough
>     that you can stock up on spares.  That way when
>     (not if) the vendor discontinues the board, you
>     still have the spares.  Dumpster boards qualify
>     here, as long as you can get multiple identical
>     ones.
>
> C)  Mass market parts that adhere to a standard interface
>     and can be replaced with work-alike units later,
>     even if the original unit is no longer made.
>     IDE disk drives, for example.  This is chancy though,
>     since even "standard" interfaces change and go
>     obsolete.  Try finding a MFM disk drive today...
>
>
> This has been an interesting discussion, made me think
> about things I have ignored.  Thanks for listening to
> my wordiness...
>
>
> John Kasunich