Multirotors are 2,3,4,6 or 8 rotor aircrafts which are aerodynamically imbalanced. They need a flight controller to balance them with help of multiple sensors. Ideally only gyroscopes on 3 axis are required but to get more control and functions today's flight controllers are equipped with Gyros, Accelerometers(Level), Magnetometer(Heading/direction), Barometer(Altitude), GPS (Position control and navigation) etc. They also need to have radio control (transmitter and receiver) to control various functions of aircraft manually and Li-Po battery for power supply.