Re: Apple 5.25 floppy drive

["Michael J. Mahon" <mjmahon@aol.com>]

Eric Rucker wrote:
> On Jan 4, 4:43 pm, applebite <l...@them.appls> wrote:
> > On Sun, 04 Jan 2009 21:15:12 GMT, lyricalnanoha
> >
> > <lyricalnan...@usotsuki.hoshinet.org> wrote:
> >
> > > On Sun, 4 Jan 2009, applebite wrote:
> > > > My 5.25 drive emits a rapid series of loud clicks when the computer
> > > > boots.  Is this normal?
> > > > Thanks!
> > > Yes - it's the head banging against the wall as it's the only way to
> > > ensure that it's at track 0.
> > > -uso.
> > I certainly hope you are serious :)
>
> He is. IIRC, when the drive controller is initialized, it basically
> sends commands to the drive to step down a track 40 times, because it
> has no idea what track it's on, meaning... if you're on track 35 (the
> highest track on a normally formatted floppy, although you can
> sometimes get more than 35 tracks on a floppy,) it will click 4 times.
> If you're already on track 0, it'll click 40 times.

But don't worry about it.  The design of the head positioner is such
that no extra force is applied to the head assembly.  The spiral cam
hub hits a bar that prevents the stepper motor from actually moving it.

Stepper motors have relatively low torque, so there is no undue stress
on anything.

That's why Woz found it a simple, reliable method for "calibrating"
the head position--no track 0 switch, no track 0 switch sensing.

-michael

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