I would like to build, from scratch, a small generator to be driven by a small windmill, for experimental purposes. One such generator on the internet has 8 NIB disk magnets (about the size of a quarter coin), flat sides facing out, mounted around a plastic rotor, with axes aligned along the radii, and 8 air core coils in Series around a stator, with axes aligned along the radii, surrounding the rotor. It is a simple, easy to build generator, with easy to wind air core coils, about 1/2 inch in diameter and 1/2 inch in length, on plastic bobbins. It appears the idea for air core was to eliminate the pull or resistance to rotation that iron cores would have. This allows the rotor to be spun easier, and faster, without the magnets getting "stuck" in alignment with the coils. It appears to lower the starting torque required to initiate rotation. Is this an acceptably efficient type of generator, or is there a significantly more efficient design, that is still easy to build, with very low start-up torque?