26 Jun
2014
26 Jun
'14
6:49 p.m.
On Jun 26, 2014, at 18:21 , Eric Smith <spacewar at gmail.com> wrote:
I think you'd need to do a good job of degaussing
the entire surface before
writing the servo patterns. I don't think using any normal degaussing coil
will be sufficiently effective, but doing it with a normal head and
stepping in increments less than the track width might be viable.
As I understand it, the actuator in the RL02 is a DC motor with a band-and-track mechanism
much like floppy drives often have, and no positional feedback independent other than the
error signal derived from the servo bursts on the media. It seems to me that by adding a
positional transducer to the head and a suitable servo system, it should thus be possible
to position the head arbitrarily, with resolution limited by the transducer. I don't
know whether an off-the-shelf rotary optical encoder attached to the DC motor shaft would
be adequate, or if something like the diffraction plates used in drives like my Data
General 6045 (*) would be needed.
If the normal servo bursts are written with a head that has a wider track width than
normal, then maybe usable bursts could still be written with a narrower track width? And
if they're normally narrower, then it'd be a matter of being able to position the
heads enough off-track to write the bursts, but not so far as to trash adjacent tracks.
Without knowing the track and head geometries, I can only speculate, based on my minimal
knowledge of hard drive innards based on starting my career around 1992 at a company that
made chips for the hard drive industry.
(*) It uses a pack that appears to be mechanically the same as the RL02's pack, other
than a different sector pulse pattern on the hub. I believe that it positions the heads
based on feedback from a glass diffraction grating mounted to the positioner, rather than
on feedback read from the media. So in effect, it acts much like an open-loop stepper
motor drive despite using a linear voice coil motor. In contrast, the RL02 acts much like
a modernish drive with closed-loop servo derived from the media, even though its mechanism
looks a lot like a floppy-drive's positioner at first glance. I spend way too much
time geeking out over this stuff!
--
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/