Lets say I have 16 1" diameter magnets (per disk) placed so there is a 1/2" gap between them. (Using a Japanese brake disk 8 1/2" dia)
How many coils and what size inside between legs?
If you want a single-phase alternator I'd say eight coils, positioned so they wrap every other magnet at some rotor position.
If you want three-phase you've got a couple ways to go:
If you don't mind bending the part that doesn't go between the magnets on some or all of the coils, you can use 24 coils. (This is the good way since you can get more power, though it's a bitch to construct.)
If you DO mind bending them, use 12 coils.
Phase counts other than three take more copper for a given amount of power (which is why three has been popular since Tesla came up with polyphase and sold it to Westinghouse.) On the other hand, if you're limited by magnet spacing and want to get every bit of power you can go to as many coils as you can put between the magnets and rectify whatever number of phases that comes out to - provided you don't mind stringing a lot of wires.
Regardless of the number of coils, the "inward" and "outward" parts of each coil should be spaced to sit in the dead spots between two magnets simultaneously, and magnets of opposite direction should be over the two halves of a coil simultaneously. (This is most easily accomplished by winding them so the diameter, measured between the midpoints of the bundle of turns on oppoiste sides, is the magnet spacing.)
You can hook the coils that generate the same phase in series, parallel, or series strings of parallel groups to get the voltage/current tradeoff you want, and hook the result in Y or Delta to play in the cracks (though Delta dissipates much of the harmonic energy by heating the coils so it's good to avoid).
