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

[Mike Stein]

----- Original Message ----- 
From: "Eric Smith" <spacewar at gmail.com>
To: "General Discussion: On-Topic and Off-Topic 
Posts" <cctalk at classiccmp.org>
Sent: Saturday, February 28, 2015 5:56 PM
Subject: Re: 3.5" floppy failure mode? Hub not 
attched to media.


> On Sat, Feb 28, 2015 at 11:14 AM, Mike Stein 
> <mhs.stein at gmail.com> wrote:
>> Are you saying that it actually stepped in and 
>> out
>> during a rotation to follow the eccentricity?
>
> Yes, it did fully closed-loop servo positioning, 
> with embedded servo
> bursts in all inter-sector gaps. That's why they 
> have not one, but TWO
> stepper motors for positioning, with a 
> mechanical adder mechanism.
> The coarse positioning stepper doesn't have the 
> resolution needed for
> track following.
>
> This can also be seen in their US patent 
> 4,630,145:
>
...

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?

Thanks!

m