Yes, a brush-less motor can be made to produce electricity just as a brushed motor would, though it will be less efficient than a mini generator if you could find such a thing. Though the hardest part is to make sure it polarizes every time before you can start producing electricity. For example a many battery powered drills don't have permanent magnets, and you need to apply a small amount of electricity before you can produce electricity by turning the chuck, where a AC drill (with a cord) has permanent magnets and you can turn the chuck and produce DC volts without first applying any electricity.What about a mini wind turbine , so as the quad flies it charges the battery , Here a question for you can a brush-less motor be converted to charge a battery ?