Pinout for SED9421

[Allison]

>
>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