UAV flight control refers to the control system that can stabilize the flight attitude of the UAV and control the autonomous or semi-autonomous flight of the UAV. The core system of the drone, known as the brain of the drone, is one of the core technologies of the drone. Flight control generally includes three parts: sensors, onboard computers and servo drive equipment. Its main function is to automatically maintain the normal flight attitude of the aircraft, including geomagnetic induction, ultrasonic sensor, optical flow sensor, control circuit, accelerometer, air pressure, etc. It consists of sensors, GPS module and gyroscope. This article will tell us how the flight controller controls the drone?

Among various UAVs, the flight control of fixed-wing UAVs usually includes control surfaces such as ailerons, direction, throttle, lift and flaps. The surface of the wing of the aircraft is changed by the steering gear, which produces a corresponding torque to control the aircraft. Turn, climb, dive, roll and other actions. The multi-rotor drone controls the attitude of the drone by controlling the rotation speed of each shaft blade.

For fixed-wing UAVs, when the attitude is stable, controlling the rudder will change the heading of the aircraft, usually causing a certain roll angle. In a stabilized plane, it looks like a car turning on the ground. Call it a slip test. The rudder is the most common method of automatically controlling turns. The disadvantage of rudder turning is that the turning radius is relatively large, and the maneuverability is slightly lower than that of aileron turning. The function of the ailerons is to control the roll of the aircraft.

When a fixed-wing aircraft rolls, it turns in the direction of the roll and descends a certain altitude at the same time. The function of the elevator is to control the pitch of the aircraft, the pull rod is raised and the push rod is lowered. When the stick is pulled, the plane rises and climbs, and the conversion of kinetic energy to potential energy reduces speed. Therefore, airspeed should be monitored during control to avoid stalling due to excessive stick pull. The function of the throttle rudder is to control the speed of the aircraft engine. Increasing the amount of throttle will increase the aircraft’s power, acceleration or climb, and vice versa. And in the elevator and throttle control. The lowest speed per hour for a fixed-wing aircraft is called the stall speed. At speeds below this speed, the rudder effect fails, as the vehicle cannot gain enough lift and the vehicle loses control. The current airspeed of the aircraft can be known in real time through the airspeed sensor of the aircraft. As the airspeed decreases, the airplane must lose altitude by increasing the throttle or stick in exchange for an increase in airspeed. Altitude in exchange for airspeed reduction. Therefore, the fixed-wing aircraft has two different control modes, and the user can choose according to the actual situation:

The first control method is, according to the set target airspeed, when the actual airspeed is higher than the target airspeed, control the elevator joystick, and vice versa; the airspeed affects the altitude, so the throttle is used to control the altitude of the aircraft, When the flight altitude is higher than the target altitude, reduce the throttle, otherwise increase the throttle.

When flying, if the altitude is lower than the target altitude, the throttle of the flight control will increase, causing the airspeed to increase, and then pull the flight control stick to make the aircraft rise; when the altitude of the aircraft is higher than the target altitude, the throttle of the flight control will decrease, causing the airspeed to drop. So the flight controller controls the push stick again to lower the altitude. The advantage of this control method is that the aircraft is always controlled with airspeed as the first factor, thereby ensuring flight safety, especially in the event of abnormal situations such as engine flame out, the aircraft can continue to maintain safety until the altitude is lowered to the ground. The disadvantage of this method is that the altitude control is controlled indirectly, so there may be some lag or fluctuation in the altitude control.

The second control method is to set the angle of attack when the aircraft is in level flight. When the flight altitude is above or below the target altitude, the PID is set according to the difference between the altitude and the target altitude according to the horizontal flight angle of attack. The limited-amplitude climb angle output by the controller is controlled by the deviation between the current pitch angle and the climb angle of the aircraft to control the surface of the elevator, so that the aircraft can quickly reach this climb angle and complete the elimination of the altitude deviation as soon as possible.

However, when the altitude of the aircraft increases or decreases, it will inevitably cause a change in airspeed. Therefore, the throttle is used to control the airspeed of the aircraft, that is, when the airspeed is lower than the target airspeed, the throttle is increased on the basis of the current throttle, and the current airspeed is higher. After the target airspeed, reduce the throttle according to the current throttle. The advantage of this method of control is that it responds immediately to changes in altitude, so altitude control is better. Maximum elevation angle eventually stalled due to lack of power.

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