ORIGINAL: MJD
I have a pair of HS-625's on the elevons which ought to do just fine. They move easily and are sealed. I have three rates set up, e.g. elevator - 100%, 65%, 40%, with decreasing negative expo as you go through the three.
Mike, there are two servos that I won’t touch with a ten foot pole, the HS-625MG and the JR ST125MG. The 625 has poor centering and excessive back lash or it soon will have, and the pots go bad quickly. If you insist on using those servos, give them the mechanical advantage (shorter arms) this will help reduce the first two issues with it at the expense of control surface travel and speed.
The ST125s have killed at least 4 planes and almost one of mine at my field that I know of. These servos had a very narrow dead band, so much so they eat up batteries or the electrical noise they generated blinded the receiver.
I can only speak from my own personal observations. These two types of servos were early models and may have had these issues resolved, but I won’t take the chance.
Hitec and JR make great stuff and I have a lot of both, every brand has some dogs.
For launch on my Diamond Dust I set the aileron expo at a very low level with moderate rate of throws. Once it’s tracking and before it’s up to speed, I switch to 100% expo with high rates. I have found this eliminated a vicious over correcting cycle that I had from time to time at launch. The elevator settings are left same from start to finish with 100% expo with high rates. You may wish to reduce the rates at first or for other users. I launch at 45* with the right wing down a bit and I feed in just a bit of right aileron. Mr. Connor may have a different or better way for a Demon to leave its nest.
Have fun with it Mike!