(Conversion) Basic knowledge of quad-rotor aircraft

Because we are currently working on a quad-rotor project. So I searched for some information on the Internet and transferred the following article about the four-rotor entry-level knowledge.

1. Structure
The rotor is symmetric distributed in the four directions of the front and back of the body, left and right. The four rotor is in the same height plane, and the structure and radius of the four rotor are the same. The four motors are installed in the bracket of the aircraft, flight control computers and external devices are placed in the center space of the bracket. The structure 1.1 is shown in.

 

. Working Principle

The four-rotor aircraft adjusts the rotation speed of the four motors to change the rotation speed of the rotor, and changes the lift to control the attitude and position of the aircraft. A quad-rotor is a vertical elevator with six degrees of freedom. It has only four input forces and six output States. Therefore, it is an underdriven system.

 

The motor 1 and the motor 3 rotate clockwise at the same time, and the motor 2 and the motor 4 rotate clockwise. Therefore, when the aircraft balance flight, the gyro effect and Aerodynamic Torque effect are both offset.

In the middle, the motor 1 and the motor 3 rotate clockwise, and the motor 2 and the motor 4 rotate clockwise. The forward motion is called forward motion, the arrow above the motion plane of the rotor indicates that the motor speed is increased, and below it indicates that the motor speed is decreased.

(1) vertical motion: At the same time, the output power of the four motors is increased, and the increase of the rotor speed increases the overall tension. When the total tension is sufficient to overcome the weight of the whole machine, the four-rotor aircraft rises vertically from the ground; on the contrary, the output power of the four motors is reduced at the same time, and the quad-rotor aerial vehicles are vertically reduced until the balance is implemented, achieving vertical motion along the Z axis. When the external disturbance volume is zero, when the lift produced by the rotor is equal to the weight of the aircraft, the aircraft remains in the hovering state.

(2) pitching motion: In Figure (B), the rotation speed of motor 1 increases, and the rotation speed of motor 3 decreases (the size of the change should be equal ), the speed of motor 2 and motor 4 remains unchanged. As the lift of rotor 1 rises, the lift of rotor 3 decreases, and the unbalanced torque generated allows the fuselage to rotate around Y axis. Similarly, when the rotation speed of motor 1 decreases, the rotation speed of motor 3 increases, the fuselage rotates around the Y axis to the other direction to achieve the aerial movement.

(3) rolling movement: the same principle as Figure B. In Figure C, the rotation speed of motor 2 and motor 4 is changed to keep the rotation speed of motor 1 and motor 3 unchanged, it allows the fuselage to rotate around the X axis (forward and backward) to achieve rolling of the aircraft.

(4) Yaw movement: In the rotor rotation process, the opposite anti-torque will be formed due to the air resistance. In order to overcome the impact of the anti-torque, two of the four rotor may be in normal rotation, the rotation direction of each rotor on the diagonal line is the same. The anti-torque is related to the rotor speed. When the four motors rotate at the same speed, the anti-torque generated by the four rotor is balanced with each other, and the four rotor aircraft do not rotate; when the speed of the four motors is not completely the same, the unbalanced anti-torque will cause the four-rotor aircraft to rotate. In Figure D, when the speed of motor 1 and motor 3 increases and the speed of motor 2 and motor 4 decreases, the anti-torque of rotor 1 and rotor 3 is greater than the anti-torque of rotor 2 and rotor 4, and the body rotates around the Z axis with the surplus anti-torque, achieve the yaw movement of the aircraft. The steering is opposite to the steering of motor 1 and motor 3.

(5) front-and-back motion: to realize the movement of an aircraft before, after, and left in the plane, a certain amount of force must be applied to the aircraft in the plane. In Figure E, increase the motor speed by 3 to increase the tension, reduce the motor speed by 1, and reduce the tension. At the same time, the rotation speed of the other two motors remains unchanged, and the anti-torque should still be balanced. According to the theory in Figure B, the aircraft first skews to a certain extent, so that the rotor tension generates a horizontal component. Therefore, the aircraft can be moved forward. Backward Flight is the opposite of forward flight. (In Figure B, Figure C, the aircraft produces horizontal motion along the X and Y axes while generating the pitching and rolling motion .)

(6) tendency motion: In Figure F, due to the symmetric structure, the tendency to flight works exactly the same as the movement before and after.

 

 

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