Mark Willis wrote:

> <G>) - You know me, though, I want to know MORE, MORE, MORE <G>  I
> have a LOT of old steppers around here & will be using them for other
> uses (some of which will have to be PIC driven, and are no-where near
> as simple as his needs.

  I just feel that someone's done virtually *all* the design work to
make those things and I doubt they would have failed to optimize the
design, at least to any significant extent.  IOW, you should have a 12V
motor with the appropriate driver (chip) driven in the optimal manner.

  Now, you might begrudge the current drawn by the other parts of the
disk drive electronics but of course you will have split off the capstan
motor anyway, and any components obviously unnecessary can be removed
(or disabled) and I doubt you can make any other efficiencies.

>  I want to automate feeding the cats, some day, for one thing.

  Hmmm.  That'll be interesting.

>  He wants an absolute minimal cost solution,

  Using the drive electronics is certainly that.

> I also was already talking to him about half-stepping the motor, which
> I'd probably do here - but I doubt he'll do, for finer smoother
> rotation of the motor.

  Is it *really* necessary?

>  (I've wondered - Does half-stepping give you more effective torque
> out of the same stepper?  Or no effect there?)

  Mmm, various "scraps" on similar topics on this list.  It seems to me
you *may* get marginally more torque by half-stepping (having adjacent
coils simultaneously energized for alternate steps) but really, the half
step from two-coils-driven to one-coil-driven must by definition be cor-
respondingly weaker than its converse.

  Assuming each step is met with limiting friction, if the one-to-two
coil transition is only just sufficient to overcome the friction, the
next half-step would be too weak to overcome that friction and the rotor
would tend to jam.  A subsequent two-coil activation involves the
opposite drive on one of these coils and would have some net torque away
from the previous position, but you'd have lost resolution.  I don't see
that the analysis would be much better in continuous motion with
"flywheel" effect.

> I might scavenge driver parts off floppy boards, but want to be able
> to be independent (on some designs) of a PC power supply <G>

  Well...  The 5¹" drives use 12V motors, so you need a 12V supply for
that.  If you use logic (PICs) to drive them, you need 5V.  The (tiny)
steppers in many 3¸" drives use 5V of course.  You can be independent of
a PC power supply, but you'll end up supplying the same voltages.  And
I'm sure you have *plenty* of spare plugs on the end of RD-BK-BK-YL
leads!
-- 
  Cheers,
        Paul B.