And the white zone is for loading and unloading . <| sep |> It ' s been a long time since I ' ve done any controls , so i ' m a little rusty . If I remember correctly , you have to move at a rate 1 order higher than your input in order to converge on the solution . If you fed r and y into the controller K , with r being a position , it ' s going to perform an integral designed to close the gap between r and y . As your error increase or decreases , the gain should also follow . The integration in this controller is what turns your static position into a velocity . The velocity is output to the antenna G and handled accordingly . The output of the antenna is a new position , which loops back to K and repeats . In this situation , the antenna G is using your input to adjust itself . y is always position , which would be a zero order . As for the torque and acceleration part it ' s the same answer . Your r input isn ' t a constant , but a function . So if your input is velocity and position ry , the integrator in the controller outputs a signal that represents kiry 2 kpry , which would represent acceleration .