Head positioners (was: Orbis

[Fred Cisin]

> On Sat, 24 Sep 2005, Chuck Guzis wrote:
> > Portable Smith Corona word processors used a 2.8" drive that worked the
> > heads via a follower than ran in a spiral groove molded into a plastic
> > disk that was driven by the spindle motor through a clutch. Basically,
> > pulsing the clutch caused the head to move in a continuous spiral
> > pattern from the beginning of the diskette to the end. Sort of a
> > windshield-wiper auto-completion mechanism. You could read or write the
> > entire diskette (about 60K (MFM), if memory serves), but nothing less
> > than that. A gutless wonder if there ever was one. It was actually pretty
> > robust.

On Sat, 24 Sep 2005, Vintage Computer Festival wrote:
> Apple Disk ][ drives used a similar mechanism.

Yes, and no.

Shugart SA390 (used for Apple ][ disk drives), and the Shugart SA400
(used in TRS-80 and others) used a spiral groove on a disc for head
positioning.
(definitiely NOT a helical lead screw as Dick used to claim -
only helical lead screw that I saw on 5.25" was Micropolis).
It was a real joy when the MPI B51 came out with a split band
positioner, and later the Tandons.

The Shugart was with a separate stepper turning the cam.
I believe that Chuck is referring to a a similar mechanism connected
to the SPINDLE motor, resulting in a spiral track!  instead of the
usual series of concentric circles for tracks.


--
Grumpy Ol' Fred     		cisin at xenosoft.com