Emergency landing control method for quadcopter

Abstract

The application discloses a quad-rotor unmanned plane emergency landing control method, which comprises the following steps: step S1, unmanned plane kinematics analysis, step S2, unmanned plane mathematical model establishment, step S3, task demand design, step S4, unmanned plane main body manufacturing, step S5, unmanned plane emergency landing simulation experiment and step S6, emergency landing attitude control; step S1: through the kinematics analysis of the unmanned plane, the flight principle of the quad-rotor unmanned plane is analyzed, that is, the quad-rotor unmanned plane is an under-actuated system, the quad-rotor unmanned plane has four inputs and six outputs, the six outputs include three position variables and three attitude angle variables, the application relates to the XX technical field, and the emergency landing method of the quad-rotor unmanned plane is realized based on a variable double-Y configuration unmanned plane, so that the problem that the quad-rotor unmanned plane cannot balance the balance of the fuselage itself when a single or multiple motors are damaged at the present stage is solved, thereby the difficulty of unmanned plane landing and the control difficulty are increased.

Description

Technical Field

[0001] This invention relates to the field of XX technology, specifically to an emergency landing control method for a quadcopter unmanned aerial vehicle. Background Technology

[0002] In response to the above issues, in-depth research was conducted, leading to this case. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the present invention provides a name and solves the existing background art problems.

[0004] To achieve the above objectives, the present invention is implemented through the following technical solution: a quadcopter unmanned aerial vehicle (UAV) emergency landing control method, comprising the following steps: step S1, UAV kinematic analysis; step S2, UAV mathematical model establishment; step S3, mission requirement design; step S4, UAV main body manufacturing; step S5, UAV emergency landing simulation experiment; and step S6, emergency landing attitude control.

[0005] Step S1: By analyzing the kinematics of the UAV, the flight principle of the quadcopter UAV is analyzed. The quadcopter UAV is an underactuated system. The quadcopter UAV has 4 inputs and 6 outputs. The 6 outputs include 3 position variables and 3 attitude angle variables. By changing the rotation speed of the brushless motor that drives the UAV rotor, the torque direction between the UAV rotors changes, thereby realizing the flight attitude control of the UAV.

[0006] Step S2: Establish a mathematical model of the quadcopter drone based on the flight principle of the drone, and define the required coordinate system and attitude angles: Let x, y, z represent the position information with the center of mass of the quadcopter drone as the origin, and let α, β, γ be the attitude angles of the quadcopter drone.

[0007] α is the turning angle, which is the angle between the UAV's forward motion direction and the X-axis direction of the geodetic coordinate system on the horizontal plane;

[0008] β is the pitch angle, which is the angle between the two-dimensional plane containing the X and Y axes of the UAV body coordinate system and the two-dimensional plane containing the X and Y axes of the geodetic coordinate system, with the downward direction as the positive reference direction.

[0009] γ is the roll angle, which is the angle between the two-dimensional plane containing the Z and X axes of the UAV body coordinate system and the two-dimensional plane containing the X and Y axes of the geodetic coordinate system, with the rightward rotation of the UAV as the positive reference direction.

[0010] By calculating the rotation matrix between the UAV's body coordinate system and the geodetic coordinate system, the transformation formula between the quadrotor UAV's body coordinate system and the geodetic coordinate system is obtained, and then the position and attitude dynamics model of the quadrotor UAV is built in the Simulink simulation tool.

[0011] Step S3: Using the existing selected UAV hardware, given the basic parameters of the UAV power system, calculate the working capacity value of the quadcopter UAV through reverse derivation. The parameters to be calculated include, but are not limited to, propeller lift, motor speed, propeller torque, equivalent current of the motor, equivalent voltage of the motor, and hovering time.

[0012] Step S4: Based on the reverse-derived data results, select the flight controller, onboard computer, four servos, four brushless motors, and matching propellers. Construct the main body of the UAV according to the variable double-Y configuration. The normal operating condition of the UAV main body is a quadcopter configuration. The flight controller is preferably the Pixhawk4 flight controller. The onboard computer is preferably the NVIDIA Jetson Nano onboard computer. The servos are preferably the PDI-1181MG18g metal gear digital servos.

[0013] The variable double-Y configuration UAV demonstrated by the above method still maintains the main structure of a traditional quadcopter UAV when performing normal flight missions. Only in emergency situations will it actively change its configuration to a double-Y configuration. Since the UAV body changes from a quadcopter to a tri-rotor or tandem dual-rotor after the configuration change, the flight control system needs to support the control of tri-rotor and tandem dual-rotor UAV configurations.

[0014] Step S5: Using the simulation scheme of PX4 flight controller + Gazebo simulation + MAVROS communication control system, simulate various flight attitudes that the quadcopter drone needs to achieve during flight in a complex environment. And build the emergency landing trigger conditions required by the drone through this simulation environment. Simulate the drone attitude under emergency landing conditions, and correct the drone attitude control code based on the feedback data of the drone attitude. The drone emergency landing experiment simulation requires running the corresponding simulation file in the Ubuntu system, opening the Gazebo environment, loading the simulation environment, including the quadcopter drone model and landing platform, inputting the command to unlock the drone and make it fly normally to a certain altitude, and then giving the drone an emergency landing trigger signal. The drone first stabilizes its own flight status, and then maintains its flight status to land slowly.

[0015] Step S6: During the emergency landing of the variable double-Y configuration UAV designed above, the onboard computer identifies the emergency landing signal. When one or more brushless DC motors are damaged, the circuit where the damaged motor is located is either open-circuited and does not generate current, or short-circuited and generates overload current. Therefore, the onboard computer officially determines whether an emergency situation has occurred by identifying this current change and generates a signal to change the double-Y configuration. The two servos divide the four brushless DC motors into two groups. According to the onboard computer, when one or more motors are damaged, one group of motors will rotate through the servos. The usable motors rotate vertically upward, and the damaged motors rotate downward accordingly, ensuring that the usable motors provide upward lift for the UAV. Then, the flight controller controls the UAV to make an emergency landing. The emergency landing of the UAV is divided into three working conditions depending on whether a single brushless motor or multiple brushless motors cannot work properly.

[0016] Step S6.1: When a single brushless DC motor of the UAV fails to work properly, the onboard computer controls the corresponding servo motor to change the orientation of the brushless DC motor and the propeller. Then, the servo motor changes the position of the Y-shaped propeller on one side of the motor, so that the quadcopter UAV is transformed into a tri-rotor UAV. Then, the flight controller changes the flight strategy to complete the emergency landing.

[0017] Step S6.2: When the two brushless DC motors of different groups of the UAV fail to work properly, after the emergency landing condition is triggered, the quadcopter UAV begins to change into a double Y configuration. After the configuration change, it becomes a tandem dual-rotor UAV. The flight controller controls the UAV according to the tandem dual-rotor flight strategy to complete the emergency landing.

[0018] Step S6.3: When two or three brushless DC motors in the same group of the UAV fail to work properly, after the emergency landing condition is triggered, the quadcopter UAV begins to change into a double Y configuration. Then, the flight controller issues a command to increase the speed of the available motors as much as possible, so that the available motors can provide as much lift as possible to achieve an emergency landing.

[0019] A variable double-Y configuration unmanned aerial vehicle includes a main body and landing gear, wherein the landing gear is mounted on the bottom of the main body and the main body integrates a flight controller, an onboard computer and a communicator.

[0020] The main body is provided with a pair of variable configuration Y-shaped wings on both sides, and the pair of variable configuration Y-shaped wings are arranged symmetrically;

[0021] The variable configuration Y-wing includes a connecting beam mounted on one side of the main body. A control component is mounted on the connecting beam. An wing control seat is connected to the end of the connecting beam. A pair of rotating shafts are symmetrically arranged on the wing control seat. Arms are movably connected to the pair of rotating shafts. A pair of movable motor rotating seats are provided at the ends of the pair of arms. A pair of brushless motors are provided on the pair of motor rotating seats. A pair of rotors are mounted on the drive ends of the pair of brushless motors.

[0022] The pair of motor rotating bases can rotate in conjunction with the control components.

[0023] The control assembly includes a servo motor. The wing control base is movably connected to the connecting beam via a rotating cylinder. The servo motor is mounted on the wing control base, and the servo motor and the rotating cylinder are linked by a gear set.

[0024] The drive end of the servo motor is equipped with a rudder, and a traction rope is connected to the rudder. The traction rope is arranged along the inner axis of the arm. A nylon core striker is provided in the middle section of the traction rope. A slot is provided on the motor rotating seat to engage with the nylon core striker, and one end of the traction rope is tied to the motor rotating seat. The motor rotating seat is movably connected to the end of the arm.

[0025] The servo motor does not work under normal operating conditions. In the event of an accident, the servo motor controls the arm, which is normally operating with a brushless motor, to rotate upwards.

[0026] Two pairs of limiting clips are provided on both sides of the wing control seat corresponding to a pair of arms. The two pairs of limiting clips are used to limit the range of motion of a pair of arms.

[0027] Beneficial effects

[0028] This invention provides an emergency landing control method for a quadcopter drone. It offers the following advantages: This emergency landing method for a quadcopter drone is based on a variable double-Y configuration drone, solving the problem that current quadcopter drones cannot maintain their own balance when one or more motors fail, thus increasing the difficulty of landing and control. Specifically, it has the following advantages:

[0029] ① When designing a variable double-Y configuration UAV, the design is based on maintaining the traditional quadcopter UAV configuration under normal flight conditions. By analyzing the flight principles and mathematical models of quadcopter and tricopter UAVs, a double-Y design with the ability to change configuration is introduced when designing the main structural frame of the UAV. The calculation is accurate and the design is ingenious.

[0030] ② When performing normal flight missions, this variable double-Y configuration UAV still maintains the main structure of a traditional UAV. During normal flight, it adopts traditional flight control technology, which is mature and simple to control, making it easy for users to operate. At the same time, the flight control also takes into account the flight control technology of tri-rotor UAVs, which can effectively assist the pilot in operating the UAV during emergency landing operations.

[0031] ③ This variable double-Y configuration UAV will actively unlock and change configuration only in emergency situations, changing from a quadcopter to a tri-rotor, dual-rotor, or even a single-rotor layout, to stabilize the UAV body as much as possible, maintain the stability of the aerodynamic center of the aircraft, and improve the success rate of emergency landing;

[0032] ④ The orientation of the arm and brushless motor is controlled by a servo motor linked with a traction rope and gear set. The onboard computer detects the signal of the brushless motor. In case of emergency, the onboard computer directly controls the servo motor. It is not only fast and easy to control, but also simple and compact in structure, which is convenient for the production and processing of UAVs. Attached Figure Description

[0033] Figure 1 This is a Simulink attitude dynamics model of a quadrotor UAV for the emergency landing control method of the quadrotor UAV described in this invention.

[0034] Figure 2 This is a Simulink model of the position and dynamics of a quadrotor UAV, representing the emergency landing control method for quadrotor UAVs described in this invention.

[0035] Figure 3 This is a flowchart illustrating the reverse engineering derivation of the emergency landing control method for a quadcopter UAV described in this invention.

[0036] Figure 4 This is a simulated emergency landing trajectory diagram of a quadcopter UAV according to the emergency landing control method of the present invention.

[0037] Figure 5 This is a flowchart of the emergency landing system of the quadcopter UAV emergency landing control method described in this invention.

[0038] Figure 6 This is a flowchart of the single motor damage response strategy in the emergency landing control method for quadcopter UAVs described in this invention.

[0039] Figure 7 This is a flowchart illustrating the multiple motor damage response strategy of the emergency landing control method for quadcopter UAVs described in this invention.

[0040] Figure 8 This is a schematic diagram of the three-dimensional unfolded state of a variable double-Y configuration UAV according to the present invention.

[0041] Figure 9 This is a schematic diagram of the three-dimensional folded-up structure of a variable double-Y configuration UAV according to the present invention.

[0042] Figure 10 This is a partial three-dimensional cross-sectional view of a variable double-Y configuration UAV according to the present invention.

[0043] Figure 11 This is a schematic diagram of the single-sided configuration change structure of a variable double-Y configuration UAV according to the present invention.

[0044] Figure 12 This is a partial cross-sectional view of the variable double-Y configuration UAV described in this invention.

[0045] Figure 13 This is a schematic diagram illustrating the operating principle of the motor rotating base of a variable double-Y configuration UAV as described in this invention.

[0046] In the diagram: 1. Main body; 2. Landing gear; 3. Flight controller; 4. Onboard computer; 5. Communicator; 6. Connecting beam; 7. Control components; 8. Wing control mount; 9. Rotating shaft; 10. Arm; 11. Motor swivel mount; 12. Brushless motor; 13. Rotor; 14. Limiting clip; 15. Rotating cylinder; 701. Servo; 702. Gear set; 703. Rudder; 704. Towing rope; 705. Nylon core striker. Detailed Implementation

[0047] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] Please see Figure 1-12 This invention provides an implementation scheme: Addressing the current problem that quadcopter drones cannot effectively perform emergency landings when one or more motors fail, this application first determines the flight attitude principle of the quadcopter drone, then establishes a mathematical model of the quadcopter drone based on this principle, and then calculates the main design scheme of the quadcopter drone using data through a reverse calculation method. Finally, a simulation experiment is conducted, resulting in a variable double-Y configuration drone. Based on this variable double-Y configuration drone, an emergency landing control method is disclosed, as follows:

[0049] Example 1: Design and simulation experiments of the overall scheme of the UAV.

[0050] (I) First, we need to understand the flight principle of a quadcopter drone: First, a quadcopter drone is an underactuated system. A quadcopter drone has 4 inputs and 6 outputs. The 6 outputs include 3 position variables and 3 attitude angle variables.

[0051] Specifically, the flight principle of a quadcopter drone involves changing the output power of its four brushless motors, which alters the rotational speed of the corresponding rotors. This changes the drone's torque, thereby altering its flight attitude.

[0052] Specifically, taking hovering as an example: when the four brushless DC motors rotate at the same speed or the horizontal torque generated by the diagonal motors cancels each other out, and the upward force provided by the four brushless DC motors is equal to the weight of the quadcopter drone itself, the drone will be in a hovering state.

[0053] 4F f =MG

[0054] In the formula F f M is the pulling force provided by a single brushless DC motor, M is the mass of the quadcopter drone, and G is the local gravitational acceleration.

[0055] For example, consider pitch motion: Keeping the rotational speed and direction of one diagonally opposite set of brushless motors in the four brushless motors constant, increasing the rotational speed of one of the remaining diagonally opposite brushless motors while decreasing the rotational speed of the other motor in that set generates surplus torque, allowing the quadcopter drone to achieve pitch motion, and vice versa. In other words, the lift provided by the four brushless DC motors satisfies the following relationship to achieve pitch motion:

[0056] F f1 >F f2 =F f4 >=F f3

[0057] In the formula F fi The pulling force provided for a single brushless DC motor.

[0058] (II) Establishing a mathematical model for the quadcopter UAV. To facilitate the calculation and establishment of the mathematical model for the quadcopter UAV, we assume:

[0059] (1) The drone installation is a standard installation, meaning that there is no error or the error is negligible during installation.

[0060] (2) The four rotors are located on the same horizontal line and are in dynamic equilibrium.

[0061] (3) Whether flying or stationary, the UAV is a rigid body and does not produce deformation or the deformation is negligible.

[0062] (4) The center of gravity and the center of mass of the UAV coincide, and it is located at the origin of the spatial coordinate system.

[0063] Quadrone drone body coordinate system: First, determine the drone's center of gravity as the origin of the coordinate system, parallel to the two-dimensional plane where the four rotors are located. Take the forward motion direction of the quadrotor drone as the positive X-axis, and the direction of the left side of the quadrotor drone body as the positive Y-axis. The positive Z-axis of the drone body coordinate system is determined to be vertically upward by the right-hand rule.

[0064] Geodetic coordinate system: The origin of the geodetic coordinate system, which is fixed to the body, is located at the center of the quadcopter UAV. The positive half-axis of the x-axis is the direction in which the quadcopter UAV turns α=0, the positive half-axis of the y-axis is the direction in which the turning angle β=90, and the positive half-axis of the z-axis is the direction in which the center of gravity of the UAV is vertically upward.

[0065] When the counterclockwise direction is taken as the positive direction, the rotation matrix of the quadrotor UAV's body coordinate system internally rotated along the z, y, and x axes (each rotation axis is a certain axis after the previous rotation) to the geodetic coordinate system fixed to the quadrotor UAV body is:

[0066]

[0067] This leads to the transformation formula between the quadcopter UAV's body coordinate system and the geodetic coordinate system:

[0068] X E =RX b

[0069] X b =RTX E

[0070] Then, further calculations are performed based on the Newton-Euler equations. Since the designed quadcopter drone operates at low altitude and low speed, the drone's angular velocity can be approximated as equal to the Euler angular velocity, resulting in:

[0071]

[0072] Remember u f =δ1-δ2+δ3-δ4, The final equations of motion for the quadcopter UAV are:

[0073]

[0074] As per the instruction manual Figure 1-2 As shown, the position and attitude dynamics model of the quadcopter UAV is built in the Simulink simulation tool according to the above formula.

[0075] (III) According to the appendix to the instruction manual Figure 3As can be seen, the construction of a quadcopter drone requires reverse engineering, thus necessitating the calculation of various airframe capabilities. This design is a single-rotor top-mounted quadcopter drone, model X, with a total weight of 1.5kg (including payload). The primary flight mission area has an altitude of 50m and a local temperature of 25℃. The formulas for calculation are as follows:

[0076] Calculate the thrust, based on the total weight of the machine, by calculating the thrust generated by a single propeller:

[0077]

[0078] In the formula, T is the thrust generated by each propeller, G is the total mass of the machine, and n r This represents the number of propellers.

[0079] Calculate the motor speed N and propeller torque M based on the propeller model, and calculate the atmospheric pressure based on the flight altitude and the temperature of the flight environment at the time of flight.

[0080]

[0081] In the formula P a where h is atmospheric pressure and T is altitude. t The ambient temperature during flight.

[0082] Calculate the air density in the flight environment based on atmospheric pressure:

[0083]

[0084] In the formula, ρ is the air density in the flight environment, and ρ0 is the pressure at point P. a ambient air density at that time

[0085] Given the air density and propeller parameters, the motor speed can be obtained:

[0086]

[0087] In the formula, N is the rotational speed of the motor, and D p C is the diameter of the propeller. T The pulling coefficient of the motor

[0088] The propeller torque is obtained by incorporating the motor speed:

[0089]

[0090] In the formula, M is the propeller torque, and C is the torque of the propeller. M drag coefficient

[0091] Calculate the equivalent current I of the motor based on the motor model. m and equivalent voltage U m :

[0092] Equivalent current:

[0093]

[0094] In the formula U m0 and I m0 These represent the input voltage and input current, respectively, R m K is the equivalent resistance. V0 This indicates the increase in motor speed for every 1 volt increase in motor voltage.

[0095] Equivalent voltage:

[0096]

[0097] Calculate the ESC throttle input command, ESC input current, and ESC input voltage.

[0098]

[0099] I e =σI m

[0100] U e =U b -I b R b

[0101] In the formula, σ represents the ESC input command, and I e and U e R represents the ESC input current and ESC input voltage. e For the electrically adjustable internal resistance, U b Battery voltage

[0102] Hovering time calculated based on the battery model:

[0103] Calculate battery capacity I b :

[0104] I b =n r I e +I other

[0105] In the formula I b I is the battery current. oth er为 Other load current

[0106] The minimum capacity is set at 15% of the total capacity, resulting in the hovering time T. b for

[0107]

[0108] In the formula T b For hovering time, C bC represents the total battery capacity. min This is 15% of the total battery capacity.

[0109] Then, based on the mission requirements of the drone, the basic values ​​of the drone body are calculated using CopterSim software.

[0110] (iv) Based on the reverse-derived data results, select the flight controller, onboard computer, 4 servo motors, 4 brushless motors and matching propellers, and construct the main body of the UAV according to the variable double Y configuration. The normal working condition of the UAV main body is a quadcopter configuration.

[0111] The flight controller uses the Pixhawk4 (hereinafter referred to as PX4) flight controller, which integrates multiple electronic maps. Designers can choose according to their needs. The Pixhawk4 has a computing frequency of 168MHz and uses a Cortex-M4 microcontroller as the control chip. Its main processor is a 32-bit STM32F427, and the fault protection coprocessor is a 32-bit STM32F103. It also has two built-in gyroscope and accelerometer MEMS sensors. The Pixhawk4 also has a three-axis magnetic field sensor inside and an external three-axis magnetic field sensor interface. It can also connect two GPS sensors, one main and one backup. The firmware with open source PX4 is selected as the flight controller and secondary development is carried out in conjunction with the Pixhawk4 hardware.

[0112] The onboard computer is used to meet the emergency processing needs of drones for data information in case of emergencies. Therefore, the NVIDIA Jetson Nano onboard computer, which has strong computing power and low price, is used.

[0113] The servo motor uses a PDI-1181MG18g metal gear digital servo motor, which receives PWM signals to control its rotation angle, thereby realizing the configuration change of the quadcopter drone.

[0114] (v) The simulation scheme using PX4 flight controller + Gazebo simulation + MAVROS communication control provides a highly similar physical environment, which can effectively simulate various flight attitudes that quadcopter UAVs need to achieve during flight in complex environments. Furthermore, this simulation environment can also be used to build the emergency landing triggering conditions required by the UAV.

[0115] After successfully configuring the ROS system, first create a folder to install PX4. Then, open a terminal in the corresponding folder and enter the command `make px4fmu-v5_default` to download the script to your local file. If there are no red error messages after the configuration is complete, it means the script file has been configured successfully.

[0116] Similarly, open the terminal again in the relevant folder and enter the command roslaunch px4.launch. We will see a display prompt indicating that PX4 is launching.

[0117] Next, install the drone simulator Gazebo. Open a terminal in the previously created folder, and first enter the commands `sudo apt-get update` and `sudo apt-get install lsb-release wget gnupg` to install the necessary tools. Then modify and update the source, and finally enter `sudo apt-get install gazebo` to install Gazebo.

[0118] To enable communication between ROS and PX4 firmware, a protocol conversion is required. Since PX4 emulation uses the MAVLink protocol, the communication between ROS and PX4 firmware uses MAVROS. Enter the following code to complete the installation of MAVROS.

[0119] (1)git clone https: / / github.com / mavlink / mavros.git cd mavros gitcheckout-b v1.4.0tags / v1.4.0

[0120] (2)sudo apt-get install python-catkin-tools python-rosinstall-generator-y rosdep install--from-paths src--ignore-src--rosdistro melodic-y

[0121] (3)catkin build source devel / setup.bash

[0122] Finally, add the landing platform and drone model required for the simulation experiment to Gazebo to complete the setup of the simulation environment. The procedure is shown below:

[0123] (1)sudo apt install-y ninja-build exiftool python-argparse python-empy python-toml python-numpy python-yaml python-dev python-pip ninja-buildprotobuf-compiler libeigen3-dev genromfs xmlstarlet libgstreamer1.0-devlibgstreamer-plugins-base1.0-dev

[0124] (2)pip install pandas jinja2 pyserial cerberus pyulog numpy tomlpyquaternion-i https: / / pypi.tuna.tsinghua.edu.cn / simple

[0125] Based on the established simulation environment, a drone landing simulation experiment was conducted. First, the corresponding simulation file was run on the Ubuntu system, and the Gazebo environment was opened. At this point, the simulation environment, including the quadcopter drone model and the landing platform, was loaded.

[0126] Input the command to unlock the drone and allow it to fly normally to a certain altitude. Then, give the drone an emergency landing trigger signal. The drone will first stabilize its flight status and then maintain its flight status to descend slowly. The simulated emergency landing drone flight trajectory is shown in the attached instruction manual. Figure 4 As shown.

[0127] Based on the above simulation experiment, the flight control code of the UAV was further modified. The UAV obtained based on the above steps (I)-(V) is a variable double Y configuration UAV.

[0128] Example 2: Based on the above demonstration and calculation, a variable double-Y configuration UAV is obtained. The variable double-Y configuration UAV is unique from ordinary quadcopter UAVs in that the UAV's arms are not directly connected to the UAV's fuselage, but are indirectly connected through a servo motor. In order to reduce the redundancy of flight control, the servo motor circuit is directly connected to the onboard computer. When the motor damage signal is triggered, the onboard computer issues a command to directly control the rotation of the servo motor of the unit where the damaged motor is located.

[0129] A specific variable double-Y configuration UAV includes a main body 1 and landing gear 2. The landing gear 2 is mounted on the bottom of the main body 1. During landing, the landing gear 2 plays the role of buffering and supporting the main body 1. The main body 1 is made of aviation plastic and has an approximately rectangular structure. The main body 1 integrates a flight controller 3, an onboard computer 4, and a communicator 5. The flight controller 3 is used to control the flight attitude of the UAV and plan the flight strategy. The onboard computer 4 can detect the current of the brushless motor 12 of the UAV and then control the servo motor 701 to change the configuration of the UAV. The communicator 5 transmits the pilot's control commands through a wireless communication protocol.

[0130] Furthermore, in order to enable the UAV to change its configuration in an emergency landing state, a pair of variable configuration Y-wings are set on both sides of the main body 1; the four arms 10 of the quadcopter 13 UAV are divided into two groups according to the configuration requirements, and a pair of arms 10 in one group are mounted on the same variable configuration Y-wing. The pair of variable configuration Y-wings are arranged symmetrically to ensure the stability of the aerodynamic center of the UAV during normal flight.

[0131] According to the instruction manual Figure 8-10 It can be seen that the above-mentioned variable configuration Y-shaped wing includes a connecting beam 6, which is installed on one side of the main body 1. A control component 7 is provided on the connecting beam 6. The end of the connecting beam 6 is connected to the wing control seat 8. A pair of rotating shafts 9 are symmetrically arranged on the wing control seat 8. Arms 10 are movably connected to the pair of rotating shafts 9. A pair of movable motor rotating seats 11 are provided at the ends of the pair of arms 10. A pair of brushless motors 12 are provided on the pair of motor rotating seats 11. A pair of rotors 13 are installed on the drive ends of the pair of brushless motors 12.

[0132] In the specific implementation process, the wing control seat 8 is connected to the connecting beam 6. The wing control seat 8 is used to mount the arm 10, and the arm 10 is movably connected to the rotation axis. The servo motor 701 in the control component 7 provides control power. When one or more brushless motors 12 fail to work, the movable parts of the connecting beam 6 and the wing control seat 8 are linked by the control component 7, causing the wing control seat 8 to rotate. This causes the arm 10, which is working normally with the brushless motors 12, to rotate upward, changing the configuration of the UAV. At the same time, a pair of motor rotating seats 11 can rotate in conjunction with the control component 7. This changes the orientation of the brushless motor 12 and the wings, so that the lift direction of the functional brushless motor 12 is upward. With the configuration change, it can provide lift, changing the configuration from a quadcopter 13 drone to a tri-rotor 13 drone or a biplane tandem drone, maintaining flight power and providing operability for emergency landing. It should be noted that this variable double Y configuration drone is only designed for brushless motors 12 with 1-3 damaged rotors 13. When all rotors 13 of the drone are not working, there is basically no existing technology that can guarantee the emergency landing of the drone.

[0133] Furthermore, according to the instruction manual appendix Figure 11-12 It can be seen that the control component 7 includes a servo motor 701, the wing control seat 8 is movably connected to the connecting beam 6 through the rotating cylinder 15, the servo motor 701 is installed on the wing control seat 8, and the servo motor 701 and the rotating cylinder 15 are linked through the gear set 702.

[0134] In the specific implementation process, the control component 7 is powered by the servo motor 701. The wing control seat 8 and the connecting beam 6 are axially connected through the rotating cylinder 15, so that the wing control seat 8 can rotate around the rotating beam. Furthermore, the drive end of the servo motor 701 is linked with the rotating cylinder 15 through the gear set 702. On the one hand, it provides the power for the rotation of the wing control seat 8 to complete the configuration change. On the other hand, it does not use direct connection but uses gears to transmit power and angle changes, avoiding damage to the servo motor 701 caused by the flight sway of the UAV body.

[0135] Furthermore, a rudder 703 is provided on the drive end of the servo motor 701, and a traction rope 704 is connected to the rudder 703. The traction rope 704 is arranged inside the arm 10, and a nylon core striker 705 is provided in the middle section of the traction rope 704. The motor rotating seat 11 is engaged with the nylon core striker 705, and one end of the traction rope 704 is tied to the motor rotating seat 11. The motor rotating seat 11 is movably connected to the end of the arm.

[0136] In the specific implementation process, in order to keep the lift direction of the brushless motor 12 facing upward during the rotation of the wing control seat 8, it is necessary to change the direction of the brushless motor 12 and the rotor 13 when the configuration is changed.

[0137] The arm 10 is designed to be hollow, with a built-in traction rope 704. The traction rope 704 is a high-strength fiber rope. The head of the traction rope 704 is connected to the rudder 703 of the servo motor 701, and a nylon core striker 705 is tied to the middle. In the quadcopter 13 state, the nylon core striker 705 is engaged in the shaft groove of the motor rotating seat 11. This part of the mechanism becomes a self-locking mechanism. In the flight state of the quadcopter 13, this mechanism is a rigid body. Only when it changes to a double Y configuration, the nylon core striker 705 is pulled backward by the fiber rope connected to the servo motor 701. At this time, the mechanism is released from the self-locking state. And under the action of the nylon rope pulling the protruding part below the tail of the motor (the length of the extension tube of the servo motor 701 is equal to the length of the protruding part below the tail of the motor), the orientation of the entire rotor 13 will rotate 90°. This changes the orientation of the brushless motor 12 and the rotor 13, keeping the lift direction of the rotor 13 of the drone upward.

[0138] Furthermore, two pairs of limiting clips 14 are provided on both sides of the wing control seat 8 corresponding to a pair of arms 10. The two pairs of limiting clips 14 are used to limit the range of motion of a pair of arms 10 and play a role in fixing the arms 10 when the drone is retracted.

[0139] When performing normal flight missions, the variable double-Y configuration UAV maintains the main structure of a traditional quadcopter 13 UAV. Only in emergency situations will it actively change its configuration to a double-Y configuration. Since the UAV body changes from a quadcopter 13 to a tri-rotor 13 or a tandem dual-rotor 13 after the configuration change, the flight control system needs to support the control of tri-rotor 13 and tandem dual-rotor 13 configuration UAVs.

[0140] Example 3: Based on the above-mentioned variable double-Y configuration UAV, this application discloses an emergency landing method for the UAV under different operating conditions.

[0141] According to the instruction manual Figure 5As can be seen, during the emergency landing of the variable double-Y configuration UAV using the above design, the onboard computer identifies the emergency landing signal. When one or more brushless DC motors are damaged, the circuit where the damaged motor is located is either open-circuited and does not generate current, or short-circuited and generates overload current. Therefore, the onboard computer identifies this current change to determine whether an emergency has occurred and generates a signal to change the double-Y configuration. The two servos divide the four brushless DC motors into two groups. According to the onboard computer, when one or more motors are damaged, one group of motors will rotate through the servos. The usable motors rotate vertically upward, and the damaged motors rotate downward accordingly, ensuring that the usable motors provide upward lift for the UAV. Then, the flight controller controls the UAV to make an emergency landing. The emergency landing of the UAV is divided into three working conditions depending on whether a single brushless motor or multiple brushless motors cannot work properly.

[0142] Example 3.1: According to the appendix to the instruction manual Figure 6 It can be seen that when a single brushless DC motor fails to operate in a drone, the execution process is as follows:

[0143] (1) The onboard computer identifies emergency landing signals. When one or more brushless DC motors are damaged, the circuit containing the damaged motor is either open-circuited and does not generate current, or short-circuited and generates overload current. Therefore, the onboard computer identifies this current change to determine whether an emergency has occurred and generates a switch to the dual-Y configuration signal. The switch configuration signal is:

[0144]

[0145] In the formula, H is the trigger signal for the configuration change; I i I represents the current in the circuit containing the damaged motor. min I max These are the motor's effective minimum and maximum currents, respectively.

[0146] (2) The onboard computer determines the location of motor failure. In addition to the four brushless DC motors, the quadcopter UAV designed in this project is also equipped with two servo motors. Through these two servo motors, we divide the four brushless DC motors into two groups, namely motor group A and motor group B.

[0147] Therefore, when a motor is damaged, a set of motors will rotate via the servo motor. Based on the configuration change signal generated by the above formula, we will rotate the damaged motor vertically downward and the available motor vertically upward, ensuring that the available motor provides upward pull for the drone.

[0148] (3) The flight controller Pixhawk4 starts the tri-rotor flight mode. After the configuration is changed, the UAV changes from a quadcopter to a tri-rotor. Therefore, the conventional quadcopter flight mode cannot meet the flight mission after the configuration is changed. So, by using the mathematical model of the previous double Y configuration design, the flight control of the UAV is changed at this time to ensure that the UAV can land stably.

[0149] (4) Emergency landing: When the UAV completes the configuration change, the flight controller Pixhawk4 is also in tri-rotor flight mode. The UAV begins to correct its flight status and achieves a slow landing.

[0150] It should be noted that although the motion control of a tri-rotor UAV is more complex, since the tri-rotor configuration in this application is only used for emergency landing, it does not involve the complex aerodynamic formulas of the tri-rotor, but only calculates the formula relationship between the tri-rotor UAV and the geodetic coordinate system.

[0151] Pitch angle θ: The angle between the X-axis of the three-rotor UAV and the X-axis of the geodetic coordinate system is defined as the pitch angle. The positive direction of the UAV's motion is taken as the upward tilt of the UAV. The domain is [-90°, 90°].

[0152] Roll angle φ: The angle between the Z-axis of the three-rotor UAV and the Z-axis of the geodetic coordinate system is defined as the roll angle. The rightward yaw of the UAV is taken as the positive direction of human-machine motion, and the domain is [-180°, 180°].

[0153] Turning angle ψ: The angle between the Y-axis of the three-rotor UAV and the Y-axis of the geodetic coordinate system is defined as the turning angle. The leftward deflection of the UAV is taken as the positive direction of the UAV's motion. The domain is [0°, 360°].

[0154] The drone's body coordinate system can be transformed into a geodetic coordinate system by rotating it three times around its coordinate axes. b Axis, Y b Axis, Z b Rotating the axes yields the geodetic coordinate system, and the corresponding rotation matrix R around the x, y, and z axes. ψ R θ R φ They are as follows:

[0155]

[0156] The transformation matrix R3 between the body coordinate system and the geodetic coordinate system of the tri-rotor UAV can be derived from the three rotation matrices above:

[0157] R3 = R ψ ·R θ ·R φ

[0158] Finally, we obtained the attitude angle formula for the tri-rotor UAV as follows:

[0159]

[0160] For ease of explanation, the transformation rotation matrix from the UAV body coordinate system to the geodetic coordinate system can be redefined as R3, which will facilitate subsequent calculations:

[0161]

[0162] Finally, through calculation, we obtained the Euler angles for the tri-rotor UAV:

[0163]

[0164] Embedding the above data into the drone's flight controller enables the drone to perform flight strategy control based on the data when changing to a tri-rotor configuration, increasing the chances of landing.

[0165] Example 3.2: According to the appendix of the instruction manual Figure 7 It can be seen that when the two brushless DC motors of different groups of the drone fail to work properly, after triggering the emergency landing condition, the quadcopter drone begins to change into a double Y configuration. After changing the configuration, it becomes a tandem dual-rotor drone. The flight controller controls the drone according to the tandem dual-rotor flight strategy to complete the emergency landing.

[0166] Example 3.3: When two or three brushless DC motors in the same group of the UAV fail to work properly, after the emergency landing condition is triggered, the quadcopter UAV begins to change into a double Y configuration. At this time, no matter what configuration the UAV changes into, it is impossible to maintain the stability of the UAV's aerodynamic center and center of gravity. Therefore, the flight controller needs to issue a command to increase the speed of the available motors as much as possible, so that the available motors can provide as much lift as possible, reduce the descent speed, and achieve an emergency landing.

[0167] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An emergency landing control method for a quadcopter unmanned aerial vehicle, characterized in that, The process includes the following steps: Step S1, UAV kinematic analysis; Step S2, UAV mathematical model establishment; Step S3, mission requirement design; Step S4, UAV main body manufacturing; Step S5, UAV emergency landing simulation experiment; and Step S6, emergency landing attitude control. Step S1: By analyzing the kinematics of the UAV, the flight principle of the quadcopter UAV is analyzed. The quadcopter UAV is an underactuated system. The quadcopter UAV has 4 inputs and 6 outputs. The 6 outputs include 3 position variables and 3 attitude angle variables. By changing the rotation speed of the brushless motor that drives the UAV rotor, the torque direction between the UAV rotors changes, thereby realizing the flight attitude control of the UAV. Step S2: Establish a mathematical model of the quadcopter drone based on the flight principle of the drone, and define the required coordinate system and attitude angles: Let x, y, z represent the position information with the center of mass of the quadcopter drone as the origin, and let α, β, γ be the attitude angles of the quadcopter drone. By calculating the rotation matrix between the drone body coordinate system and the geodetic coordinate system, the transformation formula between the quadcopter drone body coordinate system and the geodetic coordinate system is obtained. Then, the position and attitude dynamics model of the quadcopter drone is built in the Simulink simulation tool. Step S3: Using the existing selected UAV hardware, given the basic parameters of the UAV power system, calculate the working capacity value of the quadcopter UAV through reverse derivation. Step S4: Based on the reverse-derived data results, select the flight controller, onboard computer, 4 servos, 4 brushless motors, and matching propellers. Construct the main body of the UAV according to the variable double-Y configuration. The normal operating condition of the UAV main body is a quadcopter configuration. Step S5: Use Gazebo simulation to simulate various flight attitudes that the quadcopter drone needs to achieve during flight in a complex environment. And use this simulation environment to build the emergency landing trigger conditions required by the drone. Simulate the drone attitude under emergency landing conditions and correct the drone attitude control code based on the feedback data of the drone attitude. Step S6: During the emergency landing of the variable double-Y configuration UAV designed above, the onboard computer identifies the emergency landing signal. When one or more brushless DC motors are damaged, the circuit where the damaged motor is located is either open-circuited and does not generate current, or short-circuited and generates overload current. Therefore, the onboard computer officially determines whether an emergency situation has occurred by identifying this current change and generates a signal to change the double-Y configuration. The two servos divide the four brushless DC motors into two groups. According to the onboard computer, when one or more motors are damaged, one group of motors will rotate through the servos. The usable motors rotate vertically upward, and the damaged motors rotate downward accordingly, ensuring that the usable motors provide upward lift for the UAV. Then, the flight controller controls the UAV to make an emergency landing. The emergency landing of the UAV is divided into three working conditions depending on whether a single brushless motor or multiple brushless motors cannot work properly. Step S6.1: When a single brushless DC motor of the UAV fails to work properly, the onboard computer controls the corresponding servo motor to change the orientation of the brushless DC motor and the propeller. Then, the servo motor changes the position of the Y-shaped propeller on one side of the motor, so that the quadcopter UAV is transformed into a tri-rotor UAV. Then, the flight controller changes the flight strategy to complete the emergency landing. Step S6.2: When the two brushless DC motors of different groups of the UAV fail to work properly, after the emergency landing condition is triggered, the quadcopter UAV begins to change into a double Y configuration. After the configuration change, it becomes a tandem dual-rotor UAV. The flight controller controls the UAV according to the tandem dual-rotor flight strategy to complete the emergency landing. Step S6.3: When two or three brushless DC motors in the same group of the UAV fail to work properly, after the emergency landing condition is triggered, the quadcopter UAV begins to change into a double Y configuration. Then, the flight controller issues a command to increase the speed of the available motors as much as possible, so that the available motors can provide as much lift as possible to achieve an emergency landing.

2. The emergency landing control method for a quadcopter UAV according to claim 1, characterized in that, In step S2, α is the turning angle, which is the angle between the forward motion direction of the UAV and the X-axis direction of the geodetic coordinate system on the horizontal plane. β is the pitch angle, which is the angle between the two-dimensional plane containing the X and Y axes of the UAV body coordinate system and the two-dimensional plane containing the X and Y axes of the geodetic coordinate system, with the downward direction as the positive reference direction. γ is the roll angle, which is the angle between the two-dimensional plane containing the Z and X axes of the UAV's body coordinate system and the two-dimensional plane containing the X and Y axes of the geodetic coordinate system, with the rightward rotation of the UAV as the positive reference direction.

3. The emergency landing control method for a quadcopter UAV according to claim 2, characterized in that, The parameters to be calculated in step S3 include, but are not limited to, propeller lift, motor speed, propeller torque, equivalent current of the motor, equivalent voltage of the motor, and hovering time.

4. The emergency landing control method for a quadcopter UAV according to claim 3, characterized in that, In step S4, the flight controller is preferably a Pixhawk4 flight controller, the onboard computer is preferably an NVIDIA Jetson Nano onboard computer, and the servo is preferably a PDI-1181MG18g metal gear digital servo.

5. The emergency landing control method for a quadcopter UAV according to claim 4, characterized in that, The simulation scheme used in step S5 is PX4 flight controller + Gazebo simulation + MAVROS communication control system. The UAV emergency landing experiment simulation requires running the corresponding simulation file in the Ubuntu system, opening the Gazebo environment, loading the simulation environment, including the quadcopter UAV model and landing platform, inputting the command to unlock the UAV and make it fly normally to a certain altitude, and then giving the UAV an emergency landing trigger signal. The UAV first stabilizes its own flight status, and then maintains its flight status to slowly land.

6. The emergency landing control method for a quadcopter unmanned aerial vehicle according to claim 5, characterized in that, The variable double-Y configuration UAV maintains the main structure of a traditional quadcopter UAV during normal flight missions. It will only actively change its configuration to double-Y configuration in emergency situations. Since the UAV body changes from a quadcopter to a tricopter or a tandem dual-rotor after the configuration change, the flight control system needs to support the control of tricopter and tandem dual-rotor UAV configurations.

7. A variable dual-Y configuration unmanned aerial vehicle (UAV) for use in the emergency landing control method for a quadcopter UAV as described in any one of claims 1-7, characterized in that, It includes a main body (1) and landing gear (2), the landing gear (2) being mounted on the bottom of the main body (1), and the main body (1) integrating a flight controller (3), an onboard computer (4) and a communicator (5); The main body (1) is provided with a pair of variable configuration Y-shaped wings on both sides, and the pair of variable configuration Y-shaped wings are arranged symmetrically. The variable configuration Y-wing includes a connecting beam (6), which is installed on one side of the main body (1). A control component (7) is provided on the connecting beam (6). The end of the connecting beam (6) is connected to a wing control seat (8). A pair of rotating shafts (9) are symmetrically arranged on the wing control seat (8). An arm (10) is movably connected to the pair of rotating shafts (9). A pair of movable motor rotating seats (11) are provided at the ends of the pair of arms (10). A pair of brushless motors (12) are provided on the pair of motor rotating seats (11). A pair of rotors (13) are installed on the drive end of the pair of brushless motors (12). The pair of motor rotating bases (11) can rotate in conjunction with the control component (7).

8. A variable double-Y configuration UAV according to claim 7, characterized in that, The control component (7) includes a servo motor (701), the wing control seat (8) is movably connected to the connecting beam (6) through a rotating cylinder (15), the wing control seat (8) is provided with a servo motor (701), and the servo motor (701) and the rotating cylinder (15) are linked through a gear set (702); The drive end of the servo motor (701) is provided with a rudder (703), and a traction rope (704) is connected to the rudder (703). The traction rope (704) is arranged along the inner axis of the arm (10). A nylon core striker (705) is provided in the middle section of the traction rope (704). A slot is provided on the motor rotating seat (11) to engage with the nylon core striker (705), and one end of the traction rope (704) is tied to the motor rotating seat (11). The motor rotating seat (11) is movably connected to the end of the arm.

9. A variable double-Y configuration UAV according to claim 8, characterized in that, The servo motor (701) does not work under normal operating conditions. Only when the brushless motor (12) is detected to be not working, the servo motor (701) controls the arm (10) with the brushless motor (12) working normally to rotate upward.

10. A variable double-Y configuration UAV according to claim 9, characterized in that, The wing control seat (8) has two pairs of limiting clips (14) on both sides corresponding to a pair of arms (10). The two pairs of limiting clips (14) are used to limit the range of motion of a pair of arms (10).

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