Hi there,
Cool robot.
Not sure about the servo stutter though. I do get a slight stutter on the servos of the pan/tilt unit we sell, but I'd assumed that that was just the motor controller seeking to the target angle.
There is the possiblity, that there is some bug in the Arduino sketch I wrote for the mini driver. Could you try programming your mini driver with one of the Servo examples from the Arduino IDE like servo sweep or servo knob to see if they cause servo jitter also? If you have access to an oscilloscope then it would be good to have a look at the generated PWM signals to see if you can see jitter on those signals.
Regards
Alan