Depends recessed can be sloted or reverse drill bitted out, above surface, Sears and others make extractors that will grab the head and have teeth that dig into bolt heads, some can have a stud welded to them and vise grips used to turn the welded stud or the one I hate the most is center drill the bolt and use an old fashion screw extractor, but most of these are not for rc stuff so a small pair of vise grips on those tiny screws or dremel with a cut off wheel to slot the head but you need a steady hand, I think they make small reverse drill bits or you can take a standard bit and grind the head to the opposite direction and run your drill backwards it should dig in and loosen them
