I've been developing an inspection rover with two miniature cameras on two dual axis gimbals. I've tried analog, digital and now brushless servos from various R/C parts makers and all of them eventually develop a flutter or shake. I am getting ready to step up to a more expensive servo that will be almost 30X more expensive than the typical $30 R/C servos I started with. The loads seem to be easily controlled at first but after a few weeks the shaking starts and just gets worse until I replace the servo. I've tried two different R/C controllers and that hasn't helped and I can't seem to control by programming my Spektrum DX-9 controller. Any suggestions?
It means that your servos are too weak to handle load. After some time gears and electronics usage is getting worse, so PID of servos is not set properly anymore. That causes flickering.
What exactly servos were You using? From my experience, I'd recommend Dynamixel servos, since they are strong, compact and programmable.
If you dont want to spend that much, KDS servos are also an option. They are designed for 3D helicopters, thus have great rotational speed (0,07s/60°) and are powerful.