Not sure if this should go here, but It's electronic.
So before attempting active stability in all 3 axes, I figured I would start with just roll. On hand, I had an arduino chip, supporting hardware, a cheap servo, and a 2-axis magnemometer (compass, essentially).
And here's a test of the magnemometer controlling the position of my servo. It's a bit jumpy, but as far as I see, jumpy is better than slow-to-react. Plus, this is stabilizing roll, so if it goes totally nuts, not much bad will come of it.
This will all be housed in a hunk of 2.6" BT on top of my Aerotech Initiator. This rocket is quite stable, and thus the decrease in stability from a single fin sticking out the side *shouldn't* cause giant problems. Not to mention I'm shoving a ton of weight up front and launching on an F.
Still to do is putting the whole thing in a rocket... Aka the hard part