Stopping Servo Jitter
When my one (or more) servo(s) is connected, it jitters. Even when it is not receiving any command, it seems to wiggle, move, and make strange sounds. The behavior is constant.
In my case, I had 4 servos attached to the Sparkfun Spectacle Motion Board. They were incredibly jittery and made a strange sound, but did function as expected upon command (pressing a button). However, they did move out of sync because they were so jittery.
The servo is not being supplied with sufficient power. In my case on the Spectacle system, I was only powering everything via the battery pack plugged into the Director Board, rather than powering the servos directly by using an additional battery pack connected to the Motion Board.
Supply the servo with more power. In my case, I just needed to plug in an extra battery pack to the Motion Board. This immediately resolved the jitter problem and improved the synchronization of the servo movement.