3.5" floppy failure mode? Hub not attched to media.

Chuck Guzis cclist at sydex.com
Sat Feb 28 18:50:09 CST 2015

On 02/28/2015 04:00 PM, Mike Stein wrote:

> I knew they had two steppers but didn't know that they could actually
> step every sector if necessary.
> I'm convinced; pretty impressive, especially if it was implemented on a
> 3.5" drive.
> How much did these drives cost?

They were 5.25" drives.  Drivetek went bankrupt, but managed to get 
drives into the Kaypro Robie machines.  Kodak picked up the pieces and 
offered some of their own incarnations--there was a 6MB drive.

The killer was that media was fairly expensive (about $15 per disk) and 
was pre-formatted.  i.e., there was no low-level FORMAT utility.

The positioner mechanism was a little Rube-Goldberg-ish.  Think of a 
coarse leadscrew on a sprung slip fitting over a stepper shaft.  Moving 
the slip fitting was a fulcrum levering off a fixed pin at the end 
nearest the coarse stepper.  On the other end of the fulcrum was the 
fine stepper driving the fulcrum back and forth with a fine leadscrew.

Somewhat like driving a tapered shim into the works to provide a fine fit.

Both steppers have "flags" on the ends, so you can see what's going on.

FWIW, I did determine that the Robie disks could be read quite easily in 
two passes by using two 96 tpi drives, one being offset slightly from 
the other.


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