Tried this many years ago -- thinking that the faster the mags pass the coils, the more current made , and a fellow by the name of "Smokey Yunic", made a very large one, many years ago -- it was featured in Popular Mechanics magazine..
Mine worked pretty well -- but, because the mags are so far out on the blades -- it took a twenty knot wind to get it going, and about the same to keep it going !!!
Many of us have experienced problems with "cogging", preventing our mills from operating in light and even moderate winds -- thus, the farther out you put the mags, the greater the effect at startup..
This is not to say, it won,t work, I,m just pointing out, a major problem with this type of mill...
Keep thinking and experimenting, you might succeed, where others have failed, Bill H.....