If your still working on homopolar projects the simple principles are:

output is based on speed and total area disk saturation of flux in a uniform direction. If the field back tracks through the disk to complete the flux circuit to the magnets it will reverse the that amount of areas electrical polarity in proportion.

It is easier and cheaper to slap a large thin magnet between to mild steel discs instead of to over engineer a copper disk just get steel thats 4x thicker than copper.

last don't rotate a heavy wheel just rotate the brushes instead if you put a rim around the the disc just use centrifugal force to insure good contact.