Thanks Allan. This is exactly my point. Take a look at the magnets used on the rotor here: http://www.otherpower.com/listeraxialflux.shtml
They are 2" in diameter, and therefore would not ever be on a "neutral" position between the legs of a coil. I am wondering why he used such wide magnets, considering that the same guy used bar magnets here: http://otherpower.com/steamengine.shtml
These are only 1.5" wide, and would most likely be in a near neutral position.
Having said that, the round magnet unit seems to perform quite well, and is basically what I want to build, once I decide the best configuration and components to use.
I would also ask if you know why he used 4 strands of 15g wire, instead of 1 strand of thicker wire?
Phill, the world is not a perfect place. Danb has introduced some cancellation by way of design sizing for the following reason.
RESISTANCE!...... and layout constraints...
(A):
Resistance is the killer for an axial flux. Dan has deliberately gone inside the magnet size with his coil because not all the turns are linked by the flux at the same time in this flat coil design. (with iron core slots, we can link them all at once as the field flips from tooth to tooth) Because of this, we can use quite a bit of the hole for winding a few more turns... I have used up to 15% of the hole in this manner. You don't get quite the volts/turn you get with coils outside the magnet diameter, but you do have a lot less resistance introduced, as the turns are made up of shorter length turns.
So what he lost due to slight cancellation compared to the same turns outside the magnet diameter, he makes up for with less resistance per turn, and wack in a few extra to make up for the less than perfect volts per turn by being inside the magnet diameter...... in the real world he wins.... (it won't help with the waveform however.... delta could become problematic)
This is a game of diminishing returns, and filling the hole is only good for so much. At some point, the cancellation effects outweigh the shorter wire resistance gains. It is a balancing thing.
He wins two ways. He will probably have more turns, but less resistance for the same/better emf at X rpm, and the coil may be made to fit in a less than desirable space.....
(B):
Wire in hand. ......1 lump of wire that will replace 4x#15 will be a difficult thing to wind,... or even bend, and secondly, the thicker wire will likely get into difficulty with eddy currents..... so easier to wind, and avoids eddy currents.
An interesting game I played was to use 500grams of #13 wire, and wound it in all kinds of hole size etc, and tested each one for EMF@ Xrpm. The differences are published on this site somewhere, but I would no longer be able to find them here now.... but the gains are worthwhile using the hole a bit. (from memory 42mm for a 50mm magnet was starting to be the useful limit.... down hill from there. I call it volts/gram)
.............oztules