Axial flux alternators and motors design?

[Artlav]

Axial flux alternator is an easy to make pancake of stationary coils between spinning permanent magnets.
Having made one and played with it, i ended up with a few questions.

Would it make a good motor?
There are axial flux motors for sale, and my alternator spins nicely when hooked up to a BLDC driver.
How does it compare with other brushless motor designs, and what should be altered (if anything) to make it a more efficient motor?

Are air core coils good, or should there be iron in them?
I was looking at BLDC motor designs, and the coils are always winded on iron "horns" of the stator. However, all designs for axial flux motors or alternators i found on the internet use just air core coils.
Would it help to put a piece of iron inside them?

 

[Baluncore]

The forces on windings are very high. They must be held tightly to prevent them being torn out of the machine. That is difficult to do with pancakes, but it is easy to do with bundled coils on magnetic pole pieces, (your “horns”).

Magnetic material sets the path for the magnetic “circuit” a bit like the way copper wire makes a path for electrons in a conductive circuit. Flat pancake coils are inefficient without a magnetic core, but they couple OK because they can be close when face to face. Copper is expensive. Whatever you do, more copper wire is needed to make pancake coils than traditional windings. Axial flux machines will always cost more than the equivalent performance traditional design because of the copper cost.

You cannot use solid iron for an alternator core, it must be laminated and oriented parallel with the coil axis, that way the magnetic field can get into all the core material. A laminated core is difficult to make with flat pancake coils. You could use an iron powder or ferrite core material, but the copper will still be more expensive.

 

[Artlav]

I see, thanks.

Two things i found experimenting:
-An axial flux alternator does make a motor, however the windings good for a motor aren't as good for the generator, and vice-versa (at the same voltages),

-Glue the magnets down. :) The motor mode spins much faster, and their mutual attraction is no longer sufficient to hold them in place against the centrifugal force.

The forces on windings are very high. They must be held tightly to prevent them being torn out of the machine.

Interesting.
Are they more likely to deform, rather than being torn out completely, being usually encased into some material?
But yes, no matter what you do you can't beat the security of coils wrapped around steel poles.