Step 1: The Slipring
This particular project uses a "Rotating Electrical Connector" a.k.a "slipring" so the fan can fly indefinitely.
Mine came from Mcmaster-Carr http:www.mcmaster.com it is part# 7631K51 it costs $27.54 plus some extra for couple of connectors. The one I'm looking at right now has the markings "Mercotac 205 T95". It contains two little puddles of mercury with the contact wires dipped into them. When you order one it comes with a little container to ship it back to the manufacturer for disposal. I've built a couple of flying fans containing these gadgets, one of which has flown for more than a decade. Of course I now have no idea where the return mailer is, but it sure was a nice gesture.
I used to make my own sliprings which were either unreliable or too much work.
There are other cheaper sources of sliprings. Some types of electric motors have them built in. Some vcrs have them for making contact with the rotary head assembly. You can even use a "telephone line untangler" if you find one that will carry enough juice for your fan.