Re: Steppers

> I hate to ask the same questions, but I still don't know which way is the

most economical way to go.

No problem at all!

> I have a piece of iron which has 840 oz.in. steppers and encoders already

mounted on all 3 axis.

>
> I would like to use what I have because of the cost of replacement.
>
> I am not an electronics man. I can follow instructions. I can not design

any electronic circuits.

>
> Is there a place I can get instructions for any of the ideas which get

batted around in this group?

> Not design instructions, but instructions on what is needed and where to

get it.

If you could let us know the Make/model of the motors, that would help as
we'd need to know the current drive requirements in order to recommend
suitable driver circuitry. As to how to hook it up, steppers are fairly
simple to hook up and many commercial drivers come packaged with enough
instructions to get you going.

> If I offend anyone by wanting to use steppers instead of servos, just

remember I already have the steppers and they are mounted.

I don't think anyone will be offended by a person's choice of motors! I've
got some experience with both types now, and they both have their pros and
cons. In your situation I think I'd be inclined to go along with the motors
you already have to save some money, providing your machine is mill/drill
sized or smaller. The maximum traverse rate of stepper systems is generally
lower than servo systems, but for the cost difference between the two
(especially since you've already got stepper motors) this may be a limitation
that you'll be willing to live with. Let us know more details and I'm sure
you'll get lots of opinions on what to do (!).

Matt

P.S. After I wrote all that I looked back in my mail and found that you had
sent me mail on this before and I never answered! I'm sorry about that and
I'll try to answer it now:

>I have RTLinux working and have EMC loaded in a P166 machine.

OK!

>I saved a previously converted MOOG from the scrap yard.

This answers the size question.

>It has SLO-SYN 1.75 volt 12.7 amp steppers mounted complete with ball

screws. 840 oz.in. with 200 steps per rev.

>I have the old power supplies, but have been told I should replace the

monsters.

Ok, I'd like to know if the power supplies are just power supplies or are
they stepper motor drivers. One way to tell would be that all the motor leads
will be connected directly to them. If this is the case, I'd recommend trying
to salvage (keep) them if they work, or can be repaired. First, these drivers
will probably have been designed to work optimally with your particular
motors, and second, replacement drivers capable of that current level will be
expensive (about $350-$400/axis). What sort of control is on it now? I ask
because it was "previously converted". If the control is gone, see if there's
any clue as to how the stepper motor drivers (if that's what they are)
operate. By this I mean to check if any of the connections are labeled.
Possible labels might be AC, STEP, DIR, A+, A-, B+, B-, ENABLE, FAULT, etc.
Did it come with any documentation?

>I have been using a standard Bridgeport which I converted using the Ah-ha

system and 650 oz.in. motors.

>It runs dependably at 65 inches per min. Ok speed, but more would be nice!
>I want to get all I can from this new ( to me ) machine.

Well, this is the core of the problem. At the moment the top speed you'll be
able to achieve using the EMC will be limited by the number of steps/inch,
the speed of your computer, and the characteristics of your
motors/drivers/machine. I can all but guarantee that you'll be able to go
faster with Ahha than with the EMC because Ahha uses external circuitry (that
board you plug into your PC) to help them generate the step pulses that
control the motors, while the EMC does this entirely with software. The
actual issues are a little more complicated than that, but I won't go any
farther than that here as it doesn't change the conclusion that Ahha is going
to be faster, at least marginally (for now). I've ordered some hardware* that
I expect will be able to be supported by the EMC software to enable us to
control the step frequency at least as well as Ahha and also support encoder
feedback if desired. The cost of this hardware is less than $200, so it's
affordable. The drawback to this is that the software isn't available today
(Fred Proctor has to write it yet, and he's been a busy guy lately). On the
other hand buying another Ahha setup is a fair amount of money, but it also
means that your two machines would be "code compatible" and have identical
user interfaces. Another thing to think about is that after you eliminate any
limitations on speed imposed by the control software, there will still be an
upper limit on how fast your motors will work reliably.

>I am a good mechanical person, but lack any good electronics experience.

Don't worry about this, you're about to get some experience...

* That hardware consists of one of Tom Kulaga's 4 axis DRO (quadrature
interface) boards available from Dan Mauch for about $100 ($80 as a kit),
some wire, connectors, and one of these:

http://www.web-tronics.com/webtronics/ar-b9221.html

Sorry I failed to respond before, but I've been slow as far as paying work is
concerned and have had to scramble around a lot lately to make ends meet.

Matt (again)