Source: Finally a video showing that axial flux motors serpentine the magnetic field between the external magnetic rotors … offset between the magnetic field conductive material pads that are not permanent magnets. Truly brilliant design. Bob Wilson
Back if envelope, 1/3d material and closer to 99%. Although the magnetic conductivity material was not described, I suspect little to no expensive rare earths. This is the best motor architecture since induction motors. Perfect for aviation. Bob Wilson
Couldn't find any information but seeing as it is oil cooled itis doubtful that it is 99%, there is friction and heat from exciting the motor. The switched relcutance tesla motor has peak efficiency of 97% over a large rpm range. YASA seems to be saying lhigher power density in terms of power to weight and power to size, means it is more efficent as a system. That maybe. It currently is only going into super cars, which looks like maybe high costs, but perhaps low volumes and if volumes come then costs could come down. Would love some more information. Seems like a good choice for a motorcycle hub motor if costs can come down. YASA says it uses less magnetic material than PM, but this is similar to claims by most hybrid motors like the switched reluctance.
Axial flux motors can be made with or without permanent magnets. If you want to get rid of the rare earth magnetic material you need either excited field-rotor motors (serial, shunt, etc), induction motors, or pure reluctance motors. Of those reluctance motors are the most efficient but would likely need a transmission and multiple gears. The permanent-magnet-reluctance motors used in Teslas and Toyota hybrids (and perhaps others) have the advantage of having good torque over a large RPM range.