Hi Tanz,
I'm not going into equations of magnetic force etc.,for my assembling the alternator for the VAWT. I have 16 magnets ( 8 magnet pairs) One set comes on top and the other set at the bottom and the non magnetic carrying the coils in between. I have followed Piggot's design by having six coils (air core) quasi rectangular placed at 60 deg intervals on an aluminium composite disk . The steel disks (1mm) carrying the magnets ( placed symmetrically at 45 deg intervals) and the disk carrying the coils are on the same vertical axis. The gap between the two faces of the magnet would be around 20 mm including the coil thickness. I'm still in the assembling stage. I'll msg you when I get some result first with manually rotating the alternator shaft at different speeds. Ultimately it is to be friction driven by a bicycle wheel on the axis of the VAWT .
Thanks for the infmn on the frenergy.com site and the calculator.
Subramanian