How would you make the dynamics in the cruise control example more realistic?
The cruise control example gives a controller that causes the force of the engine to go to zero when the car's velocity matches the desired velocity. In a real system, there is always some engine force when the velocity of the car is non-zero. This force that is needed to keep the speed constant is necessary because of friction, drag, and other dissapative forces. These are not modeled in the dynamical equation for the car, but the controller as given would account for them, albeit inefficiently. As the speed decreases from the desired speed due to the disturbances, the engine force would become non-zero until the speed increases to the desired speed again. We'll learn later how to design better controllers for this problem (like including integral and/or derivative control or using a feed-forward term).
--Julia Braman 17:24, 29 September 2008 (PDT)