14 Jan
2011
14 Jan
'11
11:52 a.m.
On 13/01/11 21:33, Tony Duell wrote:
Not really. I am talking about a spiral, not a helix. The Shugart
mechanism I am thinking of (it was used in the Apple Disk II for example)
has a flat plastic disk with a coarse spiral groove in it. The disk is
mounted on the stepper mtoro spindle, and is parallel to the floppy disk
itself. The head carriage has a follower (looks like a ball bearing on a
leaf sprign) that runs in the groove. As the plastic disk rotates, the
follower runs in the goove and moves the head.
And you can imaging, it was not a prcise mechanism when new. And after a
bit of wear it's next-to-hopeless..
Some floppy drives, certain;y 8" ones, had a helical leadscrew on the
stepper motro shaft that moved the head cariage via an anti-backleash
nut. This mechanism seems to have no major problems.
I don;t think they're any worse than other
disk drives. And a lot better
than that darn Shugart thing with the spirally-gooved plastic disk to
move the hean. ARGH!
Sounds a bit like the helicoid in a camera lens... Not all 3" drives are belt driven, altough I
think the Amstrad ones we're
discussing are.
Indeed they are. Cheap cassette motor tied to an even cheaper thin
plastic "flywheel" by means of a shoddy little drive belt. On the plus side it's a fairly standard cassette drive belt so
fairly easy to replace...
The worst part about them is that damn flywheel. Most 3.5in drives I've
seen use a honking great slab of heavy metal as a combined flywheel /
rotor (the ring magnets for the brushless motor are inside). There's
Sure. Driect-drive 5.25" drives have that too.
The belt-driven 5.25" and 8" drives that I've worked on have quite
massive metall spindle pulleys that act as flywheels.
enough weight on one of those to smooth out any
reasonable level of
speed variation...
I think if I was rebuilding this drive as you are, I'd be tempted to make
a metal spindle pulley, which should have some flywheel effect.
-tony