I am building an airplane for a friend and I am using MKS HV777 Servos for the first time. When I attempt to test a servo while mounted in the airframe I am only getting a small range of motion.

I am using a Hitec Optima 7 Receiver with a 7.4 Volt Lipo.

When I connect the servos to my tester I am able to get the full range of motion. What am I missing ?

You might have adjusted your travel in the transmitter , I have not heard of a conflict between Hitec and MKS

Yupp.. check your travels and maybe take a servo you have lying around and try it on the hitec rec and see if it does the same thing

... also try the problem servo in other channels. Or try it on a whole different model... using an existing model, or create one in the transmitter... Is it every MKS servo?, Do other brand servos respond in the same way?... etc..

Many ways to go about finding a solution. Just use the process of elimination in every configuration you can think of until you find the issue.

My best guess would also be a mix issue, or setting.