Re: Digest Number 28

From: john@... (John Stevenson)
Subject: Aha and Servos

On Sat, 29 May 1999 12:16:11 +0100, you wrote:



Andrew,
Contary to popular opinion the Ahha controllers can now control servo's.
As you already have a working controller you should be able to hook up to your
existing servo amps and save the cost of a servo card.
I went this way with my conversion as with all the help I received from the UK
agent for Ahha it made it quick and painless, especially for someone like
myself
who is not capable of working these thing out for himself.
Added to the fact that I needed this machine up and working to earn a living I
didn't have the time to experiment.
In fact from start to actually getting the machine under power took less than 5
hours.
I don't believe that Ahha web site has been updated for quite a while but the
servo work is actually being carried out by the Uk agents, Eagland Machine
Tools.
They have a web site at www.eagland.co.uk

Regards,
John Stevenson
Nottingham, England

[Thanks, John. I've been getting conflicting advice about this- is there a
model number for the Aha controllers that work with servos? Do they come
with opto-isolater relays, or do you get those separately? There was
somebody who was going to sell me an Aha controller, but he said I'd have
to switch to steppers, which I didn't want to do. I wonder if the ones he
had were an older style. Are you running EMC in Linux, or did you figure
out something else that works? Like you, I'd like to spend my time milling
instead of experimenting, if possible.]

Andrew Werby

From: Jon Elson <jmelson@...>
Subject: Re: Linux vs. DOS


Andrew Werby wrote:

> [Oh. I really don't know anything about Linux, but it seems intimidating.
> All the problems with "kernels", whatever they are, seem like they would
> take over my life.

Well, there is somewhat of a learning curve, and a fair amount of work to
set up the system for the first time. But when you get down to running
the machine, it really works quite reliably, with essentially no further
attention.

[Is there anybody that sells computers with the right flavor of Linux
preinstalled? Although this might be more expensive than doing it myself,
if it saves weeks of headache it might be worth it.]

The kernel is the basic center of the operating system. If
you don't like the way your Win-NT is configured, you are pretty well
out of luck. If you don't like the configuration of your linux kernel,
you can edit the configuration (graphically) and re-compile. It takes
less than 30 minutes on a Pentium. It would be a simple install, except
for the real-time patch. Apparently somebody is selling a CD with a
real-time patched RedHat Linux that will install directly, without you
having to install the patch.

[Anybody know who this might be?]

I should note there are people running
Linux that have had their machines up for YEARS without rebooting.
I'll also note that once I got the hardware all stable, I have had no
crashes with Linux. I have had earlier versions of the EMC program
that malfunctioned or hung up. The current version appears to be
ROCK SOLID!

[That sounds good, I'll admit. I know I'm going to have enough trouble
getting the hardware working- debugging an operating system I have no clue
about doesn't sound like much fun.]

> I read some previous discussion here on the fine points
> of running Linux , and I didn't understand thing one. Is there no
> alternative? Does NT run in real time?

NT is not a real time system. There are real-time extensions to NT, but
they didn't work as well as the people at NIST wanted, and had a $2000
per machine license, I think.

> Has anybody built a graphical user
> interface for Linux that makes it more user-friendly?

Of course! There are several, including a windows-like environment.
I'm using X windows, and it is fine for what I'm doing. This is all on the
CD.

[That would be the patched RedHat Linux CD you were referring to above?]

> Is there a Linux for
> Dummies?]

I've heard of such a thing. You certainly need to at least get a book on
using the Unix user environment, or specifically Linux. Probably any
Barnes&Noble or B. Dalton's has such books.

> [Would that be better than leaving the old relays in place?

The version of EMC I'm using sends all the auxilliary control signals
out the printer port. For the safety of your PC, if not yourself, it is
pretty wise to use opto isolators. They aren't too expensive. A
Grayhill card and 5 or 6 opto-relays will cost about $50. These are
compatible with the Opto-22 modules, just a lot cheaper. You will
likely cobble together some combination of opto-relays and the existing
relays to run things. The machine tools I've seen seem to run most
of the control stuff off 110 Volts. The opto-relays are for pretty
small loads, up to 5 Amps or so. So, you often use the opto-relays
to control the coils of the bigger relays, especially for the spindle
motor.

[That makes sense. Where do you get the Grayhill card and opto-relays?]

> Also, can you
> tell me why there's a strong smell of methyl mercaptans in the mill's
> control box? If I didn't know better, I'd swear it was leaking natural
> gas...]

Hmm, sounds like my fireplace. Whenever it gets humid, the fireplace
smells like natural gas. My wife was always worried the house was going
to blow up. (It wasn't that strong, just detectable.) Well, we finally
had the gas log disconnected, and the smell still shows up under humid
conditions. All I can figure is some rainwater gets inside the thing, and
seeps into crevices, breeding anaerobic bacteria. This is the same thing
that makes coolant sumps stink, especially on Monday morning, after
the plant has been shut down and sealed over the weekend.
Does the machine have a coolant sump? If so, the sump or anyplace
stray coolant may have settled could be causing the smell.

[That's probably it- the machine does have a sump full of antique water
soluble coolant. But it's strange that the smell is so strong in the
control box, while the sump itself doesn't smell so bad.]

Also, I';ll bet you're smelling H2S, not CH3SH (methyl mercaptan).
They smell somewhat alike (note the chemical similarity) and I think
the mercaptan is only produced under high temp, pressure or both,
like in an oil well.

[From my winemaking experience, I learned the difference between mercaptans
(the natural gas smell) and H2S (hydrogen sulfide, or rotten eggs) . This
is definitely the former. Left to itself, H2S will change to mercaptans
inside a wine bottle, so I don't think much heat or pressure is necessary.
Natural gas, by the way, is odorless when extracted- the mercaptans are
added so you can detect it.]

> [If you'd rather, we could take this off-list, but it seemed we were still
> discussing things of general interest, so I'm replying in "public". The 8
> axis Servo-to go card sounds interesting at $888 - it certainly beats
> paying $1500 per axis. They mention running NT in conjunction with their
> card, and something about how it (and DOS) can be induced not to interrupt-
> do you know anything about this? They also talk about writing your own
> algorithms, though- so I'm not sure how hard this would be. ]

Well, I don't think STG really has any software that does true real-time
control under NT or DOS. They do have some DOS demos, but they
are just loops, not real time.

Yes, initially, I didn't want to go through the learning curve of Linux,
but EMC showed REAL promise, even 18 months ago. I certainly
couldn't find any true servo package (from the ground up) that I could
afford. And, the idea of having servos controlled by step pulses from
a program that thinks it is driving steppers soulds almost worse than
just using steppers (which I hate, in this application). I couldn't be
more happy now with EMC. I did go through a LOT of hassle, but
I think the way has been cleared for those that follow.

Jon

[I salute you, brave pioneer! I also really appreciate the time you've
taken to explain all this- thanks again.]

Andrew Werby


Message: 19
Date: Sun, 30 May 1999 00:29:06 -0400
From: "Matt Shaver" <mshaver@...>
Subject: Re: Linux vs. DOS


1. If you have the brains to contemplate retrofitting a servo
controlled
cnc mill, do machine work as a hobby, and subscribe to this newsgroup, then
you have enough brains to deal with Linux.

[I was afraid you'd say that. With all the work I'm trying to accomplish,
the grey matter is getting stretched pretty thin...]

It looks really bad going into
it, but once you get over the initial hump in the learning curve it's not
bad at all. In fact Linux is becoming more and more popular all the time,
so unless you're already retired, there's more than a small chance you're
going to have some contact with it in the future if you work with or around
computers for a living. There's no time like the present to get up to
speed. By the way, DOS has a kernel too. It is found in two hidden files in
the root directory of the boot disk called MSDOS.SYS and IO.SYS. There
doesn't seem to be a /dos/src directory though... One difference between
the two systems is that support for accessory hardware devices is handled
in DOS by loading device drivers in the CONFIG.SYS file with a line
such as DEVICE=C:\MYDEVICE.SYS. In Linux this support is provided by
including the code in the kernel which means that the kernel is re-compiled
to add support for new hardware. In truth, Linux also has loadable modules
as well, but they are optional. Also, in Linux, there are directories full
of files that perform the function of DOS's AUTOEXEC.BAT and CONFIG.SYS.

[Are there any other big differences between how Linux works and other
operating systems? I suppose the biggest hump in the learning curve is to
figure out what new things I need to learn, and what are more or less the
same things but with different names. ]

2. Linux is a much more reliable OS (doesn't lock up, get weird, or
give
you the "blue screen of death") than Win95/98 or NT and the only
alternatives for a real time control application are systems like QNX and
LynxOS which are specifically meant for real time control. They are
expensive and there is a lot of debate (and I mean among guys with PhD
behind their names) on the RTLinux mailing list about whether there is any
real advantage to these systems over RTL.

[RTL stands for Real Time Linux?]

3. All the inexpensive control programs that folks talk about on
RCM and
this list such as DanCAM, MaxNC, Stepster, etc. are only for use with stepper
motor systems. This is to say that they output axis motion commands in the
form of step and direction signals. You would be much better off to keep
your existing servo motors, amps, and encoders due to their higher
performance.

[That was my feeling as well. ]

This leaves alternatives like Lighthouse Software (big $),
Delta-Tau (MEGA $), Bestsoft (no one can seem to get tech support), or a
commercial control such as Centroid or Fanuc, or ... This is the gap that
the EMC fills.

[And EMC is shareware? Sounds too good to be true...]

4. See my previous, very long post, for comments on NT and real time.

5. Caldera's latest version of OpenLinux has a graphical install
and comes
with a nice window manager called KDE (which I use on my Red Hat Linux
system as well). You can download KDE from http://www.kde.org .The only
problem is that the EMC doesn't run under the newer 2.2 version of the
kernel yet, so you'll need to stick with Red Hat 5.2 (which uses the 2.0.36
version of the kernel) for the moment. The installation isn't as bad as you
think, and you'll reduce your problems a lot if you pick hardware from the
compatibility list you can find at
http://www.redhat.com/corp/support/hardware/intel/52/rh52-hardware-intel.htm
l .

[It looks like I'm going to have to buy a new computer to run this beast,
so this list will be helpful, thanks. Is the compatibility different for
different kernels, or is it all basically the same?]

6. Yes, I think there is a Linux for Dummies book, but there is
also a lot
of documentation that comes with the boxed version of Red Hat Linux.

[Where do I get that? Does it have all the different versions of the kernel?]

There
is a printed installation manual and many helpful files in /usr/doc once
you get it up and running. In fact the online documentation on networking
goes into some information on how Microsoft's networking scheme works, and
this helped me solve some Win 95 problems I had been having! There is also
the Linux Documentation Project at http://metalab.unc.edu/mdw/ .

> [Would that be better than leaving the old relays in place? Also, can you
> tell me why there's a strong smell of methyl mercaptans in the mill's
> control box? If I didn't know better, I'd swear it was leaking natural
> gas...]

You'll need most, if not all of the existing electrical gear in your
control to run thing like the spindle, coolant pumps, etc. The solid state
relays that Jon refers to are simply an interface between the TTL level
world of the computer and the coils of the power relays you are talking
about which are probably actuated by 24 or 110 volt signals. You really
need to understand how you present system works before you attempt to
change it. Are their any schematics or other documentation like a
maintenance manual that came with the machine, or which you could get?
These will be INVALUABLE to you when you go to rewire things!

[Fortunately, this machine did come with a manual- I think I saw some
schematics in there someplace. Now all I have to do is figure out how to
read them...]

I'll venture
a guess that the smell is transformer varnish cooking.

[Wouldn't that be a burned sort of smell? This is like fresh gas- I wonder
if it's from fermenting PCBs.]

> [If you'd rather, we could take this off-list, but it seemed we were still
> discussing things of general interest, so I'm replying in "public". The 8
> axis Servo-to go card sounds interesting at $888 - it certainly beats
> paying $1500 per axis. They mention running NT in conjunction with their
> card, and something about how it (and DOS) can be induced not to interrupt-
> do you know anything about this? They also talk about writing your own
> algorithms, though- so I'm not sure how hard this would be. ]

What they are talking about are real time extensions to NT written by Venturcom
and other third party developers. I don't believe they have as good a level of
performance as RTLinux, probably because the developers didn't have access to
all the source code for the NT. In addition these extensions cost a lot of
money for the developers kit, plus a per machine runtime license, in addition
to the cost of NT itself. As for writing your own algorithms, if you can do
that, well, let's just say you don't need any of my advice.

[Yeah, I wish- no, that part was what made me think this was way out of my
range.]

I'm happy to see
this discussion stay on the list as I think there is a subset of subscribers
who is interested in this sort of thing. As I've said before, if you need any
help in getting the EMC up and running, don't hesitate to call or write.

Matt Shaver

(410) 521-3715
mshaver@...

[Thanks- you'll be hearing from me plenty, I'll bet...]

Andrew Werby



Andrew Werby - United Artworks
Sculpture, Jewelry, and Other Art Stuff
http://unitedartworks.com