Hi! watch out for burning the pots out on 6v. make sure nothing binds. at all. have used hs-81's for a long time, are good servos, but be sure that they are not touching the case to anything, as the pots will wear out due to vibration. also, if it flutters at all they are gone! having said that, have used them on ailerons on a fun design. routinely use them on my 25 size ferroplanes at over 120 m.p.h. have used hs-85 m.g. on rudder of an omp 540. don't get the nylon hs-85! but really, hs-225 m.g. are better suited to fun fly stuff. VERY rugged, very fast, hold up to 6v well, and still a little lighter than standards with more torque! a little pricey, but you won't regret using them. but you can use 81's, just be careful on your setup, as noted!