Mahmood,

I feel DC motors would be inappropriate here... plus you will still be moving a load mechanically, so the first (or higher) order stuff still stands.

In case anyone didnt get what I am trying to say, I meant that when you accelerate an object (to compensate for a disturbance, in Mahmood's case) you give it momentum...so even when you stop driving the motor, the inertia of the load may be high enough to keep the motor moving beyond that point. You may actually have to give some reverse torque to the motor to control that. Thats where frequency response and all that control theory rears its ugly head.

Doeblin makes a good reference for the basics of modelling mechanical things like spring-mass systems. You may find it useful. But this is just a hunch I have, not a professional opinion, of course... Maybe the mass of a camera will not be sufficient to generate enough inertia for you to worry about that.

If you could just give some basic details like where on the car you plan to mount it, and what sort of disturbances you wish to compensate (and along how many planes), maybe we could help you better.

kundi