ABSTRACT
This chapter introduces the basics of feedback control. The purpose of feedback is to make the output insensitive to plant parameter variations and disturbances. Negative, positive, and large feedback are defined and discussed along with sensitivity and disturbance rejection. The notions of frequency response, the Nyquist diagram, and the Nichols chart are introduced. The system of regulating aircraft-control surfaces using joysticks and servos was termed “fly by wire” when it was first introduced to replace bulky mechanical gears and cables. The telecommunication link between the control box and the servo can certainly also be wireless. The sum of sinusoidal signals of the same frequency is a sinusoidal signal with the same frequency. Disturbances are signals that enter the feedback system at the input or output of the plant or actuator and cause undesirable signals at the system output.
