OK, now that I've swapped out the 10 ohm for a 680 ohm resistor the coil is running nice and cool. It might be better to advise using the 680 ohm first and fall back on the 10 ohm only as a last resort, since it seems to cause some serious coil heating. With the 680 ohm in place I do have to give it a pretty good spin to get it going, but that could be due to not enough turns on the coil, suboptimal bearings, unbalanced rotor, etc.

Now I'm getting some interesting results--before the 6V battery seemed to kick the 12V in the tail but now the 12V is doing amazing things! Here are some nominal measurements (these are crude BTW because my meter is kinda low end):

@ 6V: 70-80 mA, low RPM (guess-timate in the 100-300 range)
@12V: 150 mA, high RPM (guess-timate around double or so)

On one of those test runs with the 12V battery the rotor started spinning very fast (several times faster than the above measurement shows!) and I got a little nervous--I didn't want to have a magnet go flying into my chest at high velocity, tape or no tape. So I unhooked the battery and let it run down and decided to try again. This time it didn't spin up as fast and I couldn't get the coil as close to the rotor as before (definitely makes a difference in RPM!), so I shut it down again and found one side of one of the magnets had come loose. Apparently the glue I used doesn't bond well to ceramic magnets. So I got out the epoxy and glued it back down and tonight I gave a demonstration to my lovely wife (who doesn't know what to make of this stuff ) and it spun up to high RPM once more on the 12V battery. And, just my luck, another magnet came loose which put an end to tonights experimentation. I have a feeling I'm going to have reglue the entire rotor. Let this be a lesson to all of you experimenting with this thing: Make sure that you have some sturdy tape on the outside of your rotor--it will save you bacon!

At any rate, before the magnet came loose I was looking at the amp draw as the rotor spun up on the 12V battery. It started around 40 mA and then settled a bit around 100 mA. Then it took off; the draw was steadily climbing up to 190 mA as the RPM increased. Unfortunately, the noise from the bearings was making me nervous as it's a repurposed sliding glass door bearing meant for a vertical application and very low RPM--and here I have it horizontal and high RPM. I have a feeling it would have gone even faster and then the amps would probably settle back down. I'll have to get a box to put it into and just let it go as fast as it wants and see what happens.

After that, I'll just have to hang a diode between the coil and the collector and see what's there. I know there's definitely something there because one time as I was checking the transistor to see if it was heating up I accidentally shorted the collector and the base with my finger while it was running and received a pretty good bite--definitely more than 12 volts!

Ultimately I'd like to videotape the meter so I can make a nice graph of what's going on (basically amps vs. time, though I think amps vs. RPM would more interesting ). I guess before this is all over I'll have to find m'self a tachometer.