o_lampe:
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.
Thanks for answering o_lampe.
I'd checked, there is no unused input pin in my code
tuxduino:
Never used a servo (yet), but if I remember correctly they shouldn't be controlled by pwm pins. This library has to (should) be used:
o_lampe:
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.
I don't understand o_lampe, I used standard Servo library like tuxduino mentioned before.
Can you explain how PWM has something to do with servo library?
Hi, tuxduino I was trying to post my code, but then my post exceeds 9500 character, which is not allowed. Sorry 
Jantje:
I would advice to use simplot http://www.negtronics.com/simplot (or something similar) to look at the values you are sending to the servo's.
At least then you know whether the problem is in your code or in the electronics/mechanics.
If you have a scope you can also read the signals send to the servo's. I would also check the voltage. I would not be surprised you have voltage spikes because you have 12 servo's.
Thanks alot Jantje. That's way above my level of knowledge.
I guess I need to learn from your link first..