Firstly, I have a question regarding voltage and amp output difference between using a coil using an iron core or an air coil... putting aside the cogging issue, if the coils are the same wire gauge, turns and dimensions other than one has a core and the other is air... which one will produce more power?
Air core PMG's are designed differently than iron core PMG's. In general, a 'soft magnetic core' will allow a PMG to be smaller, have a different mechanical arrangement and use less permanent magnetic material. However, a well designed and constructed air core machine eliminates core losses and can be very efficient.
When you say 'iron core' you need to be careful. Using an Iron core is very inefficient - you get huge losses from eddy currents. Most 'soft magnetic cores' are laminated silicon steel. The laminations and silicon content reduce the losses, and the alloy is designed to have high magnetic permeability and a high saturation point. There are many different types of core material; some need exotic annealing procedures to be effective and some are so delicate they need to be re-annealed after stamping.
You can make a soft magnetic core with iron powder and resin that reduces losses over pure iron, but its permeability and a saturation point won't be anywhere near a laminated core using electrical steel alloy. The material availability and manufacturing procedures for a laminated core are out of the reach of most home shops.
One alternative that may be within the capability of a home shop is Somaloy like materials - powered metals with high tech coatings. They can be pressed and sintered and make decent cores. you'd need some tooling, a press and a small kiln with good temperature control.
If I went through the effort of making a good magnetic core I'd probably use it to full advantage; to allow a single coil design, possibly a transverse flux or clawpole machine, with good cooling airflow as part of the design.
After a few hours of poking around the forums, I did find one item in regards to my 1st question that speculated that more output is generated from coils with iron cores because the entire winding is exposed to the passing magnet's induction compared to air core coils where just the part of the winding in the path of the magnet is induced... does this sound reasonable?
Yes, your output will rise with an iron core. So you could potentially use fewer turns. But then your stator will get hotter due to the core losses, your blade loading will increase and you'll get cogging and a new set of wicked mechanical vibrations that a cast resin core wasn't designed for. So it's a different design. Don't expect to modify a proven air core design in this way and have be trouble free. You'd need to do some R&D.
