Peter Todd <pete <at> petertodd.ca> writes:

> In playing with the voice coil actuators I've noticed that the movement
> of the heads seems to be a velocity linearly perportional to the current
> through the coil. The drive obviously uses feedback from the encoded
> data on the platters to position the heads accurately. I'd like to be
> able to have a PIC chip do some sort of PWM to position the heads and
> make pretty patterns. So this means I'll need to just have my PIC
> blindly guess and run the heads to the limits every so often to
> "recalibrate" the location right?

With spinning platters the heads are pushed outwards by the air blown off by the
platters (Tesla compressor like). There is usually a point where they stabilize
before trying to fall off, when the air impinges also on the coil/counterweight
assembly. At low speed the friction with the platters also causes the heads to
travel to the mid-platter zone.

So you can rely on this effect to try to move the heads using a small current
into the voice coil. The movement will not be accurate but it should work for
art. The restoring force of the air and friction should cause the heads to
return to the mid-platter position when you turn the current off.

Peter

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