🚀 go-pugleaf

tsunami@pnc.com.au (Graham Dinning) writes:

>The motor assembly in the disk drive would probably make a reasonable SUB
>SUB woofer motor but in the actual disk drive it is probably servo
>controlled by feedback from the actual platter(s) it is reading. In the

I still repair these washing-machine drives (well, somebody has to :-)), 
and in most cases there are several feedback loops - the DEC RK07 had 3 (The
position loop from the servo track, the velocity feedback from a 
coil/magnet on the positioner, and a optical position/velocity feedback 
transducer used for load/unload). The second of these, the velocity feedback
would work without the rest of the drive being operation, and would probably
be useful for this application.

A basic position feedback system is going to be essential as well - 
otherwise any offset in the electronics is going to move the coil to one 
end stop and stick there. The optical load/unload transducer (if present) 
could be used here, or maybe you could design something to do this.


>case of old CDC drives the coil is driven hard forward and the tracks are

The CDC drives I've worked on have a velocity feeback coil inserted in 
the centre of the magnet assembly - it's the 3-4 wires coming out the 
back of the positioner.

>counted as it moves. When the heads are in the right posy the motor is
>given a huge reverse (Braking) pulse to stop about the right spot. Its

It's a little more complex than that, at least in the drives I've worked 
on. The positioner current is controller by a DAC that is driven by an 
encoded difference between the wanted cylinder and the actual cylinder. 
This is then combinded using analogue circuitry with the velocity signal 
(to provide damping), and a few other things. In some drives, 
particularly winchesters, the velocity information is provided by the 
positioner coil current.

>Grajam Dinning 
>TSUNAMI@Halibut.pnc.com.au

-tony