Jon Elson's comments:

Hi Jon,

I quote your comments:

1. )

Because you want the machine to be at the right position at all
times, not
just the start and end of the move. I built a similar voltage
amplifier circuit
to quickly drive my machine while I worked on the PWM servo amp.
The performance was AWFUL! The following error was at least .002"
per IPM of the move. That means that the machine had an error of
1/8th
of an inch at 63 IPM! You can't make any parts with that! The
following
error was about .020" even with the machine motionless!

Clearly, a simple voltage amplifier won't cut it!

2. )


Sure, just leave those parts out! But, then, when you go to tune it
up,
you'll really want the info display, or else you'll have a DVM
hooked up
all the time.

3. )

It COULD be done, but it has not. The STG card's ADC could be
used to read the armature current, and the encoder counter could be
used to compute the velocity (although it needs to be filtered or
de-glitched, as we now know the LS7166 encoder counter chips
occasionally read glitched data into the CPU).

------------------------------------------------------

Jon, I hope that I am speaking for a lot of us guys out here. (
That is what I hope for, anyway )

What we lack is education ! We don't know too much about these
things, and not all of us will be able or willing to invest in
the kind of servo drives you have - just like that. Right now I
just have to have something that can drive a small DC motor for
research into a machine design - that I don't know would work. I
need several axis, so it adds up. I have used some step motors,
and know something about them, - but to switch from steppers to
servos is a major turn. I am not into machining at all, so I don't
know
much what to expect.

Take a look at this site: http://www.4qd.co.uk/ccts/pwm.html

Take a trip around their site - it is so good !

Ok, they sell controllers, - but give schematics and explain what
is good, what is bad. This is the kind of stuff I would like to see
in the FAQ and as an example of how I would like this mail list to
participate in. Why not post the design you had in your #1 comment,
and tell more what is wrong with it. The site above make me very
confident in their products - because of the way they have done
this. I understand what a good controller is, how it should work, -
and what it is about.

As you probably can understand, - I have picked up some of my
knowledge - thanks to these guys. I am also very eager and glad to
share such sites to my friends. Sure, I could build some of their
early designs, - but it is working more like - I rather have their
most sophisticated controller. But if I should test a design of a
small motor vehicle, I might build one of their design - just to
test my mechanical system before I upgrade. If I should buy one of
your controllers - I need 5 or 6 of them + large motors + power
supply + encoders ++++ I have to save money for some time to do a
thing like that. But, doing is believing - so starting out small,
get things to run, - then I would start saving money for a project
like this. See ?
I think you may gain, and the rest of us will gain education into
this field. Check it out - all of you - and tell what you think.

2: ) Your second comment:

I did not think of that ! But do you often have to tune them ?
Remember what I said about the self calibration system I proposed
could be put into the EMC code. What do you think ?

3: ) This you have to explain ! "we now know the LS7166 encoder
counter chips
occasionally read glitched data into the CPU " - I have never
heard of this problem, is it serious ?


In closing:

What I would like - was I informative design guide put together from
this group. How to select motor sizes, stuff like that. Visit the
URL above and think about it. It would be so helpful to us all. I
have never seen a bridgeport - or other machines. If it could be
cut down to some thumb rules of what your size of components should
be, - then we would surely dig into with more determination and
enthusiasm.

Here is another link: http://www.theriver.com/apexmicrotech/ ,
The only thing is - they are expensive and I don't think it is for
the HMS. I was in contact with them, - and you really need to know
a lot of things to use them. They are expensive to toast !!!


//ARNE