Pinout for SED9421 - test-drb@ccmp.vtda.org

26 Nov 2005

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Subject: Re: Pinout for SED9421
   From: "Chuck Guzis" <cclist at sydex.com>
   Date: Fri, 25 Nov 2005 17:42:33 -0800
     To: cctalk at classiccmp.org

On 11/26/2005 at 12:48 AM ard at p850ug1.demon.co.uk wrote:

 Is the difference in inertia between the band and
the leadscrew really 
that significant?  I always thought the taught band was indroduced for 
cheapness... 
Micropolis drives were 30 ms. track-to-track.  I believe they used a 4-step
per track scheme.  The last Micropolis 5.25" drive (with buffered seek)  I
have has a closed-loop tach belt-drive spindle motor.   I've never verified
it, but I suspect that with longer seeks, the stepping rate is sped up
considerably.  I recall fooling with the step rate on a paper-feed motor on
a printer and discovering that once you've established direction, you can
crank the stepping rate pretty far up.  Try it before things really get
moving and you're likely to find yourself stepping backwards.

But you have a point about the speed.  I've got some Siemens 8" drives that
use leadscrew positioning and they do just fine at 8 msec.  track-to-track. 
The real problem is you can only step a stepper so fast.  Older and smaller
steppers tended to go async at relatively low speeds.

A band position needed one maybe two steps per track some of the leadscrews
were anywhere from 2(very fast ones) to 8.  At some point you hit the wall
for speed.  Between resonance and other oddities steppers are hard to use
for fast and precise at the same time.

Allison