1. The problem statement, all variables and given/known data I am trying to understand the Proportinal controller, used as a cruise controll for a car. I do understand how it works as long as there are no overshoot. 2. Relevant equations 3. The attempt at a solution The reason why I do not understand overshoot is because the error then gets negative and then the output also gets negative (out=Kp*error). This means negative thrust? You can never give less thrust than 0, so what is actually happening when the error gets negative?