Re: Stepper motor specifications

Pete,

What can you deduce? Inductance for one. The low volts, high amps
example you cite is a low inductance motor; probably newer, and will
work best with a bipolar chopper style drive. The eight wires are
also a clue. Most motors sold with 8 wires are relatively hi-torque.

As Jon Johnson mentioned case size can give you addtl. clues. Also
case SHAPE. Older motors were round, many newer hi-torque models are
some version on square-ish...

Hi inductance motors have a short fat winding; low inductance motors
have a long thin winding. (No you cna't see this from the outside,
but it will be reflected in the nameplate values.) By the way, it's
the WIRE that is short and fat, or long and thin, NOT the winding...

After you read the Gecko site JJ recommended, be sure to read the
linistepper site(by Roman Black and James Newton) for the "other
side" of the story.

As a ROUGH guide, the older round models were usually pretty close to
this:

23SS-the typical 5V,1A surplus motor found EVERYwhere- ~50oz.in.
23DS ~100 oz.in.
23TS ~150 oz.in.

34SS-like the IBM printer 4.5V,1.4A surplus- 110-150 oz.in.
34DS ~250-300 oz. in.
34TS ~350-500 0z.in.

The newer square motors use better magnets, and closer tolerances
(some use magnetic "focusing") and so have a higher output.

A 23SS is easily 100-125 oz.in. The other sizes are also typically
shifted "one higher" in the list above.

I don't agree with JJ that you are always wanting the lowest
inductance, though that is a popular notion which is becoming
a "mantra" here on CCED. It IS true for modern bipolar chopper
drives, but many CNC'ers are having a lot of fun(and good results)
with less expensive older style drives like unipolar, and even L/R
types.

One thing to understand is that unipolar and bipolar are two
different ways to DRIVE a motor. The motor itself may be optomised
for one or the other, and the number of leads will make some motors
only capable of one of these two types of DRIVE.

Next, Chopper, L/R, Linear, and Bi-level, are ways to control the
CURRENT in a motor winding. All these types of current control can be
used with EITHER unipolar OR bipolar methods of driving the motor
coils.

Finally, microstepping can be done in a unipolar OR a bipolar drive.
And the current control FOR the microstepping can be Chopper, linear.
I've not ever seen an L/R or bi-level microstepper.

Point is, many would have you believe that only a chopper bipolar
microstepping drive is worth having/using. Often these folks will say
it's the microstepping, or the bipolar, or the chopper, that makes it
so, as if the only way to get ANY of these features is to get ALL of
them. But as you now know, it aint so. Unipolar chopper microstepping
drives also exist, and work well. Bi-level drives have their place as
well.(less emi than choppers.)

Bipolar microstepping chopper drive of steppers is a very good way,
but not the only way. Some other pretty good ways are also pretty
inexpensive...

So, If you find high inductance surplus motors, you may want to
pursue another direction for your drive. And in ALL things CNC, there
is a balance which can (and should!) be achieved in many different
ways...

Hope this helps,

Ballendo

P.S. Anything short of mfr. ratings is a guess (and some of those by
the MFRS. are too<G>). There are many variables for the motor
designer to play with, and any surplus motor may have been designed
for a "strange" use. I've found BIG motors with wimpy output on more
than one occasion. And sometimes, fortunately, the other way as
well...











--- In CAD_CAM_EDM_DRO@yahoogroups.com, Peter Harrison
<peter_harrison@n...> wrote:

> Hi
>
> I am looking for surplus steppers for my little mill conversion. As

I am

> sure you have noticed, surplus stepper motors frequently show a

voltage

> and current rating on them but nothing else. if you are lucky, you

can

> look up the part and discover the torque and such. Frequently that

is

> not the case.
>
> The question then is: given just the voltage and current rating,

what

> can I deduce? In particular what can I infer about the motor

torque?

> Also, do the manufacturers generally mean these are the maximum

ratings

> for just one coil?
>
> As an example, I came across a motor rated 1.4V, 3.8A, it has eight
> wires. I would guess this to have relatively low torque and that

the

> rating refers to a single coil.
>
> Any thoughts?
>
> Pete