Design of permanent magnet generator
The axial magnet motor is a terribly wasteful design; a magnetic path can be made short, and field leakage minimized, with iron pole parts (which they did
not employ).   For 3-phase current, you'll want to use a two-pole
magnet disk (one N, one S) and three-pole pickup; each pickup will be connected as one winding
of a WYE (and more important, each of the pickups will peak when the N
magnet approaches it, and trough when the S magnet approaches it...).  Six pickups
and four magnets will work, too, if you wire it correctly.

The eight poles in the illustration all align at the same time over the eight coils, it won't
generate more than two phases (from two possible magnet pole orientations) that way.

If the magnets were mounted on a steel disk, the flux from the side opposite the
coils will return in the rotating metal disk.   For most flux through the coils, a steel pole in the center of each coil, and a steel base under the coils, is recommended.