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.
Step 2: Typical Installation
I butchered a harddrive that had a hollow shaft through one of the bearings. I installed the Mercotac slipring atop the hollow shaft just as the directions said to do.
I ran thin insulated copper wires wires through the shaft. I hoseclamped the whole unit to a pipe.
Underneath I clamped a split bar to the shaft and tied a piece of spectra string to it to suspend the fan.
I twisted the power wires around the spectra string.
The harddrive guts look too complicated. A bicycle hub with a hollow axle is just as good and looks better.
The tail of this fan is two interlocking rectangles cut from a 3-ring binder cover. The tail is attached to the fan by a couple of car antennas and some zipties. The fan is a giant muffin fan from a 19" rack. It used to cool a pdp or somesuch "mini" computer. If you have any fans like this you could give me I'd sure appreciate them.
Step 3: Speed Control
Some other light dimmer type thingy would probably work as well. There are rules that various dimmers don't work for resistive, inductive, or capacitive loads. You can test the limits of those rules for small motors as long as you keep them away from flammable things like houses.
To get the fan flying you'll need to throw it. That will take some practice. The fan will only fly in one direction due to coriolis/vortex voodoo reasons.