I am in the process of rewinding a model motor to make an alternator. I can make a 12v 50w alternator you can hide in your closed hand. I am only concerned about heat. It is being wound for much lower RPM operation than as a motor and no propeller to cool with. I will put a fan on it to see if I can keep it cool. Also it is an open frame and debris must be kept out, especially steel that can stick to the magnets and jamb the works.