RE: dx7 and the famous DS821 servos
a few on heli side of things have had probs with gears stripping in flight. I made sure there were no binds - its my 4th plane built so well aware of binding, etc. I was flying on low rates so binding was impossible during flight. i make sure before every flight that i do a preflight check on the surfaces, linkages and listen out for any binding from each servo and ensure it isn't trying to constantly drive.