At least it seems to work!
It looks like the input-readings are distorted.
Check the sketch for unused (but defined as input) pins and make them outputs or attach a pullup resistor on the inputs.
But don't expect too much:
the Arduino has only 256 different PWM steps per channel. A servo only 'understands' PWM signals from lets say 20% to 80% duty cycle ( wild guesssing here )
Both facts limit accuracy on the electronics side. Add mechanical inaccury and you see a trembling robot.
Probably a bit smoothing/averaging of the input-signals make it calm down, but at the same time it gets slower.