Hi Georg, welcome back! I have to admit, this is the first HDD motor I see that has only 3 winding ends (i.e. delta configuration) instead of 4 (wye configuration). All of mine are 4-leads ones and perhaps it's because the HDDs I've opened are all in the age bracket between very old and ancient
Anyway, there is a way to make the delta config motor spin really fast - you just need to be able to spin it up not faster than the rotor is able to catch up. As far as I recall, these motors are wound similarly to the CD-ROM ones i.e. 9 cogs/12 poles but it's absolutely possible that yours has more poles (or more cogs - same effect) and needs more winding commutation steps to achieve the same speed.
I have to admit, once I got involved with this laser scanning display project and got myself a 4-pin HDD motor, I stopped improving the schematics I've started from even though I don't plan on abandoning it completely.
Let me tell you where I'm at here (and perhaps I'll start a new thread about this later). I made an 8-mirror rotor for a 2.5" HDD out of a piece of a shiny metal sheet hoping that it will be reflective enough. It didn't work. Well, the metal is reflective all right, but the problem is: I cannot keep its surface flat enough for the laser dot to remain a dot. When the mirror surface warps, the dot becomes a line, a curve, anything but a dot.
Next I made myself a few small mirrors out of a split CD, like you said (this, BTW also needs its own thread - not at all straightforward
). It kinda worked but not really. I glued the CD pieces to the sides of the metal "flower" I made earlier and the dots were perfect in the beginning. But then I started to adjust the petals of that flower to reflect each at its own angle and the CD pieces had started to warp along with the metal - the CD is extremely flexible and bends too easy. The end result - I'm going to throw away the metal - based mirror because of the irregularities with the reflections.
Then I went as far as design a 3D part that will become the base for 8 pieces of split CD mirrors that I will glue to its 8 sides sloping at different angels. The part has been ordered at Shapeways and should come at some point next week, I think. See the attachments here for illustration.
As far as electronics, I picked a non-MCU based so-called "spin-up" circuit to drive the BLDC motor. There are problems with it, too: it's not auto-starting, i.e. you need to give it a light spin by hand for it to start working but it spins incredibly fast - at some point a CD mirror managed to break away from the base due to centrifugal force - I'd say easily 5,000 RPMs or even faster. This is where I got the circuit: http://forums.parallax.com/showthread.php/119874-Hard-Drive-Stepper-Motor-with-high-speed-spin-up-circuit?p=881285&viewfull=1#post881285
problem is: it requires
4-lead HDD motor, won't work with 3-lead one. Can you ask your IT guys for an older HDD? I'm using about 10 years old 16GB or 18GB laptop HDD for this.
I am yet to progress any further than the spin-up setup, for some reason cannot find an IR interrupt sensor which I know I have , and I need it for synchronization.
Anyway, just wanted to let you know that the project is well under way but includes some deviations from the original plan. I'll keep you posted.