Martin
Ok, old is 23 years the and motors sound like they are round so they
are probably not rare earth magnetic material so they will have lower
performance than newer designs of the same size. 6.8 ohms with only a
40 volt supply sounds relatively low power since usually the inductance
goes up with the resistance which limits how fast you can step the
motor. (power = torque * speed). Size sounds like Nema 34 class, but
Modern Nema 23 could probably give similar performance. A chopper
drive is a common drive for stepping motors as you get higher efficiency
by switching the full voltage on until rated current is reached then off
and on modulating the current until the step is completed. Step and
direction are signals given to control the drive circuit but are not
necessarily integral to the drive card on older cards. You may just
have the two phases or pulses of the proper duration(one for each
winding) being supplied. The relationship of these two pulses is
determined by an earlier stage that uses the step and direction signals
to determine that relationship. While 40 volts can produce more than 3
amps across 6.8 ohms, modern drive circuits usually use a voltage 10 to
25 times the static votage (IR drop) rating. Somebody on the list may
be familiar with older bipolar transistor circuits but I am starting to
think that we may want to start at the machine end. What is the size of
the machine. What is the hardware drive components. IE. what is the
pitch of the leadscrews, are they direct drive or are they timing belt
driven or gear driven. If so what is the ratio. These we can use to
determine what size motors are needed and how to drive them. However,
if you have an oscilloscope and a pulse generator we may be able to
determine what is functioning and where and what is required to
interface a Pentium class computer to your hardware. The age of the
hardware says you have a bipolar transistor design but it also means
that most of the circuit is discrete so you probably can reverse
engineer it. Only two sided circuit boards and not many IC's and
probably no custom ICs. I still have my old Data books around. So it
sounds like time vs money tradeoff. You could replace everything for
about $200 per Axis maybe less depending on desired performance, or you
can dig out some test equipment and determine what you have and what it
takes to/repair or replace it.
Hubert
Martin Pinkston wrote:
> O.k. guys, Now I really feel like an idiot.....lol
> You guys are freaking serious about this....
> I "assumed" I would get a little encouragement, but I guess I
> "under-assumed" the levels of commitment to success that is apparent and
> really kind-a awesome.
> So, from here out I will try to be more open with the sharing of my road
> blocks and the likes.
> Here goes:
>
> The old (1987) Centroid contoller I have is called a CNC-3. Model number
> CNC-3-B24-MS3
>
> The control box (approx 2 cubic feet in size) is only half of the system,
> the other half is a computer program running on DOS. (True DOS)
>
> There are 6 IC Cards within the box.
> One is a communication card with the RS232. It has 3 header plugs, 4 EProms
> and a battery backup which has long since given up the ghost. The only
> writting on this board is" CPU3 REV870830, Copyright 1987, Centroid Corp,
> State College PA" I would consider this the mother board of the system.
>
> Another card is an I/O card and is basically used to control external relays
> which would turn on things like coolant, air, spindle, clamps and the likes.
> It has 2 header plugs. The only writting on this card is "Centroid InputG,
> REV 880111"
>
> Then there are the three axis cards and the only writting on these cards is
> "Chop2 Rev 880615, copyright Centroid, State College, PA" I have the header
> pin out for each of the 2 header on this card.
>
> The last card is a power supply card. It is fed from the 40V power supply
> and puts out 40V for the bipolar stepper motors, 12V for I/O card and other
> front panel buttons and 5V for the system. The back panel of the box
> indicates that the power supply is 800W
>
> The stepper motors are thought to be MAE motors. I have gone to MAE web site
> and I can't find the motors. No surprise there, they are over 20 years old.
> But I think they are either 2 or 3 amp motors. The MS3 in the model number
> makes me think 3 amp motors. These motors have 4 wires feeding them red,
> green, black and white. They are 6.5 ohm across the two fields. The physical
> size of the motors are 3.5" in diameter and 4" long with an output shaft out
> the face and back.
>
> If you give me about a half hour, (it's now 10pm est) I will post pictures
> of each card front and back on my blog. I have 3 or so PDF files which
> describe the pin out config. I can not post pdf files on my blog, but I will
> be happy to send them to you in a .zip file if you wish or one at a time,
> what ever works.
>
> Stepper motors use step, direction and enable. Chop drives use pulse, pulse,
> pulse, pulse. That 4 pulse signal is fed into the drive cards.
>
> For me, this is a pretty intense learning experience. I know I am in over my
> head, although some things I do understand. And if this can get converted
> over, that's great, but I want to learn how and why, in the process.
> So, Thanks in advance for your help and patients.
> Thanks guys.
> Martin
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