Cross-medium coaxial dual-rotor unmanned aerial vehicle with foldable propellers and control method of cross-medium coaxial dual-rotor unmanned aerial vehicle

Abstract

The invention provides a cross-medium coaxial double-rotor unmanned aerial vehicle with foldable propellers and a control method of the cross-medium coaxial double-rotor unmanned aerial vehicle. The unmanned aerial vehicle comprises a main fuselage module, a vector motor base module, a coaxial propeller power module, a foldable propeller module, a waterproof sealing module and electronic equipment. According to the cross-medium power system, by folding the propellers, the effective area of the propellers is reduced, the influence of different working media of the cross-medium unmanned aerial vehicle on the efficiency of the propellers is fundamentally reduced, the capacity loss is reduced, and the endurance time is prolonged; the number of actuators is reduced, a complex gear structure is omitted, the weight of the unmanned aerial vehicle is reduced, the reliability of the unmanned aerial vehicle is improved, finally, control codes suitable for the cross-medium coaxial double-rotor unmanned aerial vehicle are designed, and automatic control over the rotating speed of motors and folding of propellers of the unmanned aerial vehicle under different working media are achieved. And the power distribution of the unmanned aerial vehicle in the cross-medium task is more reasonable.

Description

Technical Field

[0001] The present invention relates to the fields of underwater propulsion technology and aviation technology, and in particular to a cross-medium coaxial twin-rotor UAV with foldable propellers and a control method thereof. Background Art

[0002] In recent years, with the continuous development of UAV technology, scholars at home and abroad have begun to be keen on the research of cross-media UAVs. After a period of research and development, the research on water UAVs and submarine-launched UAVs has become relatively mature. Since cross-media aircraft have both air flight capabilities and underwater diving capabilities, they have good maneuverability and concealment. Therefore, cross-media aircraft have a wider range of activities and can obtain more air and underwater enemy information. However, cross-media UAVs have the disadvantages of high energy consumption and limited operating space, which can no longer meet people's needs to perform cross-media operations in complex environments. Therefore, it is necessary to develop new cross-media UAVs. Cross-media UAVs can be divided into fixed-wing aircraft and rotorcraft according to the classification of aircraft wings. According to the different navigation methods in the water, they can be divided into water UAVs, submarine-launched UAVs and submersible UAVs.

[0003] The characteristic of water drones is that they are equipped with floats or other devices that can provide buoyancy at the bottom, so that they can be moored or glide on the water surface, and can realize independent operation. The propeller or rotor provides lift or thrust, so that the drone can take off or glide on the water surface. For example, the Soviet Union's LPL plan has a huge buoy at the bottom that allows the drone to float on the water surface. At the same time, the propeller generates thrust and the fixed wing generates lift, so that the drone can take off, land and glide on the water surface. In addition, there is the GULL36 developed by the British Warrior Air and Sea Technology Research and Development Co., Ltd., which adopts an upper wing layout. There is no buoyancy device such as a buoy at the bottom, but its fuselage is cylindrical, which is itself a huge buoy. The upper wing layout allows the power unit to be on the water surface to provide thrust so that the drone can take off, land and glide on the water surface. From the summary and analysis of some existing water drones, it cannot achieve cross-medium navigation, and can only float on the water surface at most. In essence, it is not a complete cross-medium drone.

[0004] The characteristic of submarine-launched drones is that they have a simple structure. The propeller or rotor alone can provide the power required underwater and in the air, but they cannot operate independently. They usually need to be carried on submarines and launched when they are needed. Therefore, it only has the ability to cross the medium once and cannot sail in the water for a long time. For example, the Cormorant UAV developed by Lockheed Martin, after being launched from the submarine, relies on its own buoyancy to float to the surface, and then takes off through the rotor to achieve a single cross-medium operation. When it is recovered, it does not have the ability to move underwater, and needs to be captured and recovered by an underwater robot, so it will have a certain impact on the concealment and safety of the submarine. In addition, there is the Switchblade UAV proposed by the United States. The Switchblade uses a launch tube for catapult takeoff. When it is ejected into the air, the folded wings unfold, and the motor-driven propeller is started for propulsion. When performing a mission, the launch tube is thrown out, the launch device floats to the surface, and then the launch command is executed. The launch process is the land launch method. It also does not have the ability to sail underwater. Through the analysis and summary of some existing submarine-launched UAVs, although it can achieve a single cross-medium flight, it has the disadvantages of troublesome recovery, poor maneuverability and concealment.

[0005] The characteristics of a submersible drone are that it has the ability to cross media multiple times and can operate independently. For fixed-wing submersible drones, the power in the air and underwater is provided by the rotor, and a combined power system is used, which makes the weight lighter and the structure simpler. However, since the water resistance is much greater than the air resistance, the energy consumption is very large. At the same time, the wing will also produce more water resistance underwater, resulting in greater energy consumption. Therefore, fixed-wing submersible drones mostly adopt a more complex variable sweep configuration. For example, the Dipper drone developed by the Zurich Institute of Technology adopts a fixed-wing configuration. When in the air, the wing is unfolded to provide lift. Under water, the wing sweep angle is increased to reduce the wing water resistance, but the variable sweep mechanism also brings a larger weight and a more complex structure to the drone. For some multi-rotor submersible drones, they have an air power system and an underwater power system. The air power system is used to provide power when flying in the air, and the underwater power system is used to provide power when sailing underwater. Although this balances the energy consumption of the power system in the air and underwater, the weight of the drone increases significantly and the structure becomes more complex. For example, Loon Copter uses four different propellers in air and underwater media. The depth control system consists of a water depth sensor and a variable flow buoyancy device. During the water exit process, the aircraft first floats on the water surface by adjusting the depth control system, and then takes off like a seaplane. During the water entry process, the aircraft first lands on the water surface and floats, and then sinks into the water by adjusting the depth control system. Due to the heavy weight of the two power systems, the endurance is poor, so multi-rotor diving drones mostly use a combined power system, that is, a power system is shared in the air and in the water. The advantages of this are light weight, simple structure, and high flexibility, but the water resistance of the rotor underwater will be very large, and the load on the motor is very large. For example, Naviator, jointly developed by Rutgers University and the Office of Naval Research in the United States, is a four-rotor diving drone using a combined power system. The four-rotor control strategy is the same in the air and in the water. During the water exit process, the drone relies on pulling the throttle to take off from underwater. However, this way of navigation leads to large water resistance on the rotor when underwater, so the problems of energy loss and shortened endurance will still be exposed.

[0006] In summary, existing cross-medium aircraft have the following main defects that need to be improved urgently: When sailing underwater, the power efficiency is low, the energy consumption is high, and the endurance performance is poor; The fuselage structure has poor impact resistance when crossing the medium; The coaxial knot mechanism is complex in design, and has low safety and reliability; There are a large number of actuators, the mechanical structure is complex, the weight is large, and the flexibility and reliability are low. Summary of the invention

[0007] In order to solve the problems of the prior art, the present invention provides a cross-medium coaxial twin-rotor UAV with foldable propellers and a control method thereof, which reduces the influence of the different working media of the cross-medium UAV on the propeller efficiency, reduces the power loss, and prolongs the flight time. It can be applied to maritime patrol, diving reconnaissance, communication relay, water quality monitoring, marine resource exploration, biological observation, hydrological and meteorological measurement and other mission scenarios, and has important significance and value in the future.

[0008] The present invention provides a cross-medium coaxial twin-rotor UAV with foldable propellers, which is characterized by comprising a main body module and a coaxial propeller power module, wherein a vector motor seat module and a foldable propeller module are fixed inside the main body module, and the coaxial propeller power module is fixedly connected to the main body module through the vector motor seat module; The vector motor seat module comprises a motor seat, a universal joint, a reinforced fixed frame, a steering gear fixing part, a steering gear, and a pipe clamp, wherein the reinforced fixed frame is fixedly connected to the main body module through the pipe clamp, the top of the reinforced fixed frame is connected to the motor seat through a universal joint, the bottom is fixedly connected to the steering gear fixing part, the steering gear fixing part is connected to the steering gear, and the steering gear is connected to the motor seat through a ball joint connecting rod and controls the motor seat to perform pitch or roll movements; The coaxial propeller power module comprises a reversing motor stator, a reversing motor rotor, a forward motor stator, a forward motor rotor, a motor bracket, a reversing motor output shaft, a forward propeller, a reversing propeller, a forward motor rotor connector, a forward propeller fixing part, a reversing motor output shaft connector, a reversing propeller fixing part, a propeller clamp, and a top screw. The motor bracket is fixedly connected to the vector motor seat module, the reversing motor stator is connected to the bottom of the motor bracket by an interference fit, and the forward motor stator is connected to the top of the motor bracket by an interference fit; one end of the reversing motor output shaft passes through the forward motor stator, the forward motor rotor and the reversing propeller. The stator of the reversing motor is fixed with the reversing motor rotor by a top screw, the other end of the reversing motor output shaft is connected with the reversing motor output shaft connecting piece by a propeller clamp, the reversing motor output shaft connecting piece is connected with the reversing propeller fixing piece by a cylindrical pin, the reversing propeller fixing piece is connected with the reversing propeller, the reversing motor rotor drives the reversing motor output shaft to rotate, thereby driving the reversing propeller to rotate; the forward motor rotor is connected with the forward motor rotor connecting piece, the forward motor rotor connecting piece is fixedly connected with the forward propeller fixing piece by a cylindrical pin, the forward propeller fixing piece is connected with the forward propeller, and the rotation of the forward motor rotor drives the forward propeller to rotate; The folding propeller module includes a push rod fixing part, a push rod, a stretching stator, a stretching rotor, a reverse stretching rotor, a forward stretching rotor, a pull rod structure, a Kevlar rope, a pipe clamp, a cylindrical pin, a spring pin, and a hook, wherein the push rod fixing part is fixedly connected to the main body module through the pipe clamp, and the push rod is connected to the push rod fixing part through the cylindrical pin; one end of the stretching stator is connected to the motor seat through the spring pin, and the other end is connected to the push rod through the Kevlar rope and the hook, and the push rod moves up and down to drive the stretching stator to move up and down; the stretching rotor is connected to the stretching stator through a bearing, and the stretching rotor rotates around the stretching stator; the outer ring of the forward stretching rotor The pull rod structure is used to fix the stretching rotor through interference fit, and the inner ring is fixed to the output shaft of the reversing motor through a bearing through clearance fit, and the forward stretching rotor rotates and moves up and down around the output shaft of the reversing motor; the forward stretching rotor is connected to the forward propeller fixing piece through the pull rod structure, and the up and down movement of the forward stretching rotor drives the forward propeller to fold; the reversing stretching rotor is connected to the forward stretching rotor through a deep groove ball bearing, and the reversing stretching rotor rotates around the forward stretching rotor but cannot move relatively; the reversing stretching rotor is connected to the reversing propeller fixing piece through the pull rod structure, and the up and down movement of the reversing stretching rotor drives the reversing propeller to fold.

[0009] Further improvements, the ball joint connecting rod in the vector motor seat module includes a ball joint and a carbon rod, and the two sections of the carbon rod are respectively connected with a ball joint by interference fit to form a ball joint connecting rod structure with ball joints at both ends, the ball joint at one end is connected to the motor seat, and the ball joint at the other end is connected to the rudder arm, and the rudder arm is connected to the servo through a spline.

[0010] According to a further improvement, the servo comprises a pitch servo and a roll servo, and the installation angles of the pitch servo and the roll servo differ by 90°.

[0011] As a further improvement, the tie rod structure of the folding propeller module includes a tie rod head and a carbon rod, and tie rod heads are respectively connected to both ends of the carbon rod to form a tie rod structure with tie rod heads at both ends.

[0012] According to further improvements, the main fuselage module includes a streamlined fuselage structure consisting of a fuselage front beam, a fuselage rear beam, a cabin left section, a cabin right section and a cabin lower section, and a landing gear is connected to the bottom of the fuselage structure.

[0013] Further improvement, the main body module is provided with a waterproof sealing module, and electronic equipment is placed inside the waterproof sealing module. The waterproof sealing module includes a sealed cavity composed of a sealed cabin, a sealed box cover, and a sealed box bottom. The sealed cabin and the main body module are fixed by interference fit, the sealed box cover is movably connected to the sealed cabin and sealed by a sealing ring, and the sealed box bottom is fixedly connected to the sealed cabin and sealed by a sealing ring. The electronic equipment includes a flight control, an electronic speed regulator, a battery, a receiver, a power module, a step-down module, a wifi data transmission module, and a GPS positioning module. The flight control is used to automatically control the stable flight of the aircraft, the electronic speed regulator is used to power the brushless motor and adjust the speed, the battery is used to power the power system and control system of the entire aircraft, the receiver is used to receive the signal of the remote control, the power module is used to measure the voltage of the battery and power the flight control, the electronic speed regulator, and the step-down module, the step-down module is used to power the steering gear, the wifi data transmission module is used to communicate with the ground station and send and receive mission instruction information, the GPS positioning module is used to receive GPS satellite information, and locate and navigate the aircraft.

[0014] The present invention also provides a control method for a cross-medium coaxial dual-rotor UAV with foldable propellers, including a flight mode, an underwater mode and a cross-medium mode; The flight modes of the UAV include control methods for forward and backward movement, control methods for lifting movement, control methods for rolling movement, and control methods for yaw movement; the control method for forward and backward movement refers to that the pitch vector servo controls the coaxial propeller motor to tilt forward and backward, drives the coaxial propeller power module to generate a longitudinal horizontal component of force, and moves the aircraft forward and backward; the control method for lifting movement refers to that the coaxial propeller motor synchronously increases or decreases power, so that the aircraft generates acceleration in the vertical direction, thereby realizing lifting movement; the control method for rolling movement refers to that the roll vector servo controls the coaxial propeller motor to tilt left and right, generates a rolling torque, and gradually tilts the fuselage to one side to realize rolling movement; the rolling movement generates a lateral horizontal component of force, thereby driving the aircraft to realize lateral movement; the control method for yaw movement refers to that the forward motor and the reverse motor in the coaxial propeller power module differentially increase or decrease power, generate a yaw torque, and thereby realize yaw movement; The UAV in underwater mode includes pitch attitude change, yaw attitude change, rolling motion control method, forward motion control method and folding propeller motion; the pitch attitude change refers to that the pitch vector servo controls the coaxial propeller motor to tilt up and down, drives the coaxial propeller power module to generate a longitudinal horizontal component, thereby generating a pitch torque, so that the UAV pitches; the yaw attitude change refers to that the yaw vector servo controls the coaxial propeller motor to tilt left and right, drives the coaxial propeller power module to generate a lateral horizontal component, thereby generating a yaw torque, so that the UAV yaws; the rolling motion control method refers to that the forward motor and the reverse motor in the coaxial propeller power module increase or decrease power differentially, generate a rolling torque, and then realize the rolling motion; the forward motion control method refers to that the motor in the coaxial propeller power module increases or decreases power synchronously, so that the UAV generates acceleration in the horizontal direction, thereby accelerating or decelerating the UAV; the folding propeller motion refers to that the push rod drives the propeller to fold or unfold, so that the effective area of ​​the propeller is reduced, thereby reducing the resistance of the propeller rotating underwater; The UAV cross-medium mode includes changing from flight mode to underwater mode and from underwater mode to flight mode; the control method for changing from flight mode to underwater mode refers to detecting whether a remote control water entry command is received in flight mode. When the command is received, the propeller begins to fold and the motor speed automatically switches to a low-speed mode. At this time, the UAV enters the water. When it is detected that the UAV is completely immersed in the water, it is switched to underwater mode, and the navigation attitude is switched from longitudinal to transverse to complete the cross-medium process; the control method for changing from underwater mode to flight mode refers to that when the UAV receives a remote control cross-medium command, the navigation attitude is switched from transverse to longitudinal, and the propeller begins to unfold. At this time, the motor is still in a low-speed mode. When it is detected that the UAV is completely out of water, the motor speed automatically switches to a high-speed mode to complete the cross-medium process and enter flight mode.

[0015] Further improvements, in the underwater motion mode, there are a total of five actuators, including two vector tilt servos, two propeller motors and a push rod. The vector tilt servos change the direction of the motor thrust to achieve changes in navigation attitude, specifically changes in pitch attitude and yaw attitude. The two propeller motors provide thrust for the drone's underwater navigation to control the forward and roll of the drone. The push rod folds the propeller to reduce the propeller's resistance underwater; in the aerial flight mode, there are a total of four actuators, including two vector tilt servos and two propeller motors. The change of flight attitude is achieved by changing the direction of the propeller motor's pulling force.

[0016] The beneficial effects of the present invention are: The propeller of the UAV adopts a foldable propeller design, combined with a low Reynolds number propeller, which minimizes the propeller's resistance underwater while ensuring its efficiency in the air. This fundamentally reduces the impact of the different working media of cross-medium UAVs on propeller efficiency, reduces capacity loss, and extends flight time. The spacing between the two pairs of propellers in the coaxial system has been optimized, reducing the interference of the upper propeller on the start-up of the lower propeller, further improving the propeller's propulsion efficiency and extending the flight time; The slender cylindrical fuselage design makes the drone more resistant to interference and impact, and enables rapid entry and exit of water. A combined coaxial propeller power system was designed to reduce the number of actuators, simplify the mechanical structure and control algorithm, facilitate inspection and maintenance, reduce the weight of the UAV, and improve the safety and reliability of the UAV structure; The motor suitable for coaxial propellers is designed, which eliminates the complicated gear transmission mechanism and improves the reliability of the UAV; The code for controlling the motor speed of the UAV under different working media is designed to make the power distribution of the UAV more reasonable in cross-media missions; Drones can be used in mission scenarios such as maritime patrol, diving reconnaissance, communication relay, water quality monitoring, marine resource exploration, biological observation, hydrological and meteorological measurement, and will have important significance and value in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 This is a perspective view of the overall structure of the cross-medium coaxial twin-rotor UAV with foldable propellers of the present invention; Figure 2 This is a front view of the overall structure of the cross-medium coaxial twin-rotor UAV with foldable propellers of the present invention; Figure 3 It is a side view and a top view of the appearance of the cross-medium coaxial twin-rotor UAV with foldable propellers of the present invention; Figure 4 It is a partial cross-sectional view of the front view of the cross-medium coaxial twin-rotor UAV with foldable propellers of the present invention; Figure 5 This is a structural diagram of the main body module of the cross-medium coaxial twin-rotor UAV with foldable propellers of the present invention; Figure 6This is a structural diagram of a vector motor seat module of a cross-medium coaxial twin-rotor UAV with foldable propellers of the present invention; Figure 7 This is a structural diagram of a coaxial propeller power module of a cross-medium coaxial twin-rotor UAV with foldable propellers according to the present invention; Figure 8 This is a structural diagram of a folding propeller module of a cross-medium coaxial twin-rotor UAV with foldable propellers according to the present invention; Fig. 9 This is a structural diagram of a waterproof sealing module of a cross-medium coaxial twin-rotor UAV with foldable propellers of the present invention; Fig.10 It is a schematic diagram of an electronic device of a cross-medium coaxial twin-rotor UAV with foldable propellers of the present invention; Fig.11 It is a schematic diagram of the cross-medium process of the cross-medium coaxial twin-rotor UAV with foldable propellers of the present invention.

[0019] In the attached drawings: 1. Main fuselage module; 2. Vector motor seat module; 3. Coaxial propeller power module; 4. Folding propeller module; 5. Waterproof sealing module; 6. Electronic equipment; 101. Right section of cabin; 102. Rear beam b of fuselage; 103. M3 nut; 104. M3 screw; 105. Lower section of fuselage; 106. Landing gear; 107. Rear beam a of fuselage; 108. Left section of cabin; 109. Front beam a of fuselage; 110. Front beam b of fuselage; 201. Motor seat; 202. Universal joint; 203. Strengthening fixed frame; 204. Pipe clamp; 205. Rudder arm; 206. Servo a; 207. Stud M2; 208. Screw M2; 209. Servo fixing piece; 210. Servo b; 211. Ball joint; 212. Carbon rod; 213. Nut M2; 301. Reverse propeller; 302. First screw M4; 303. Reverse propeller fixing piece; 304. Reverse motor output shaft connecting piece; 305. Second screw M2; 306. Forward motor rotor connecting piece; 307. Reverse motor output shaft; 308. Forward motor rotor; 309. Forward motor stator; 310. The third screw M3; 311. The top screw; 312. The reversing motor rotor; 313. The reversing motor stator; 314. The motor bracket; 315. The forward propeller; 316. The forward propeller fixing piece; 317. The first cylindrical pin; 318. The propeller clamp; 401. The pull rod head; 402. The second carbon rod; 403. The reverse stretching rotor; 404. 6800V deep groove ball bearing; 405. MR63.ZZ bearing; 406. The forward stretching rotor; 407. The bearing 50x62x6; 408. The stretching rotor; 409. The pull rod head; 410. The second carbon rod; 411. The second carbon rod; 412. The second carbon rod; 413. The second carbon rod; 414. The second carbon rod; 415. The second carbon rod; 416. The second carbon rod; 417. The second carbon rod; 418. The second carbon rod; 419. The second carbon rod; 420. The second carbon rod; 421. The second carbon rod; 422. The second carbon rod; 423. The second carbon rod; 424. The second carbon rod; 425. The second carbon rod; 426. The second carbon rod; 427. The second carbon rod; 428. The second carbon rod; 429. The second carbon rod; 430. The second carbon rod; 431. The second carbon rod; 432. The second carbon rod; 433. The second carbon rod; 434. The second carbon rod; 435. The second carbon rod; 436. The second carbon rod; 437. The second carbon rod; 438. The second carbon rod; 439. The second carbon rod; 440. The second Extend the stator; 410. Spring pin; 411. Push rod; 412. Second cylindrical pin M3; 413. Push rod fixing piece; 414. Second pipe clamp; 415. Second screw M2; 416. Kevlar rope; 417. Hook; 418. Third cylindrical pin M2; 501. Third screw M2; 502. Sealed box cover; 503. Sealing ring; 504. Sealed cabin; 505. Sealed box bottom; 506. Second nut M2; 601. Flight control; 602. Step-down module; 603. WiFi data transmission module; 604. GPS positioning module; 605. Power module; 606. Electronic speed regulator; 607. Receiver; 608. Battery. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] The present invention provides a cross-medium coaxial twin-rotor UAV with foldable propellers, comprising a main body module 1, a vector motor seat module 2, a coaxial propeller power module 3, a folding propeller module 4, a waterproof sealing module 5 and an electronic device 6.

[0022] The main fuselage module 1 includes a fuselage front beam a109, a fuselage front beam b110, a fuselage rear beam a107, a fuselage rear beam b102, a cabin left section 108, a cabin right section 101, a cabin lower section 105, a landing gear 106, screws 104, nuts 103, etc. The fuselage front beam a109 is connected to the cabin left section 108 by interference fit, the fuselage front beam b110 is connected to the cabin right section 101 by interference fit, the fuselage rear beam a107 is connected to the cabin left section 108 by interference fit, the fuselage rear beam b102 is connected to the cabin right section 101 by interference fit, the cabin left section 108 is connected to the cabin right section 101 by screws 104 and nuts 103, the screws 104 pass through the screw holes of the cabin left section and the cabin right section respectively, and then are fixed by the nuts 103. The fuselage front beam a109, the fuselage front beam b110, the fuselage rear beam a107, the fuselage rear beam b102 and the cabin lower section 105 are connected by interference fit, and the cabin lower section 105 and the cabin left section 108 are connected by the screws 104 and the nuts 103, and the screws 104 pass through the screw holes of the cabin lower section 105 and the cabin left section 108, respectively, and then are fixed by the nuts 103. The cabin lower section 105 and the cabin right section 101 are connected by the screws 104 and the nuts 103, and the screws 104 pass through the screw holes of the cabin lower section and the cabin right section, respectively, and then are fixed by the nuts 103, which play the role of fixing the fuselage front beam a109, the fuselage front beam b110, the fuselage rear beam a107, and the fuselage rear beam b102. In this way, a complete streamlined fuselage is assembled.

[0023] The vector motor seat module 2 includes a motor seat 201, a universal joint 202, a reinforced fixed frame 203, a servo fixing part 209, a servo a 206, a servo b 210, a rudder arm 205, a ball joint 211, a carbon rod 212, a screw M2 208, a stud M2 207, a pipe clamp 204, etc. The motor seat 201 is connected to the universal joint 202 by the screw M2 208, and the screw M2 208 is respectively fixed through the screw holes of the motor seat and the universal joint. The universal joint 202 is connected to the reinforced fixed frame 203 by the screw M2 208, and the screw M2 208 is respectively fixed through the screw holes of the universal joint 202 and the reinforced fixed frame 203. The reinforced fixed frame 203 is connected to the pipe clamp 204 by the screw M2 208, and the screw M2 208 is respectively fixed through the screw holes of the reinforced fixed frame and the pipe clamp. The pipe clamp 204 is fixed to the fuselage front beam a, fuselage front beam b, fuselage rear beam a, and fuselage rear beam b through interference fit, so that the reinforced fixed frame 203 is fixed to the main fuselage module. The motor seat 201 is connected to the ball joint 211 through the screw M2 208, and the screw M2 208 is fixed through the screw holes of the motor seat and the ball joint respectively. The ball joint 211 is fixed to the carbon rod 212 through interference fit, and the other side of the carbon rod is fixed to the ball joint 211 through interference fit to form a pull rod with ball joints at both ends. The ball joint 211 is connected to the rudder arm 205 through the screw M2 208, and the screw M2 208 is fixed through the screw holes of the rudder arm and the ball joint respectively. The rudder arm 205 is connected to the steering gear a206 through a spline. The steering gear a206 is connected to the steering gear fixing part 209 through the screw M2 208. After installation, the rotation of the steering gear a can drive the motor seat to pitch. The installation method of the servo b210 is exactly the same as that of the servo a206, except that it is installed by rotating 90° counterclockwise to control the rolling motion of the motor seat. The servo fixing part 209 is connected to the reinforced fixed frame 203 through the stud M2 207 and the screw M2 208. The servo fixing part 209 is connected below the stud M2 207 by screws, and the reinforced fixed frame 203 is connected above the stud by screws, so that the servo fixing part 209 is connected to the reinforced fixed frame 203. The above parts are assembled together to form a vector motor seat module.

[0024] The coaxial propeller power module 3 includes a reversing motor stator 313, a reversing motor rotor 312, a forward motor stator 309, a forward motor rotor 308, a motor bracket 314, a reversing motor output shaft 307, a forward propeller 315, a reversing propeller 301, a forward motor rotor connector 306, a forward propeller fixing member 316, a reversing motor output shaft connector 304, a reversing propeller fixing member 303, a propeller clamp 318, a top screw 311, a second screw M2 305, a screw M3 310, a first screw M4 302, a first cylindrical pin 317, etc. The reversing motor stator 313 is connected to the motor bracket 314 by interference fit, and the reversing motor stator 313 is connected below the motor bracket 314. The forward motor stator 309 is connected to the motor bracket 314 by interference fit, and the forward motor stator 309 is connected above the motor bracket 314. The reverse motor output shaft 307 passes through the forward motor stator 309, the forward motor rotor 308, and the reverse motor stator 313, and is fixed to the reverse motor rotor 312 through the top screw 311, so that the reverse motor rotor rotates and drives the reverse motor output shaft to rotate. The forward motor rotor connector 306 is connected to the forward motor rotor 308 through the second screw M2 305, and the second screw M2 305 is respectively fixed through the screw holes of the forward motor rotor connector and the forward motor rotor. The forward propeller fixing member 316 is fixed to the forward motor rotor connector 306 through the first cylindrical pin 317, and the first cylindrical pin 317 is respectively fixed through the cylindrical pin holes of the forward propeller fixing member and the forward motor rotor connecting member through interference fit. The forward propeller 315 and the forward propeller fixing member 316 are fixed by the first screw M4 302, and the first screw M4 302 is respectively fixed through the screw holes of the forward propeller and the forward propeller fixing member, so that the forward motor rotor rotates and the forward propeller rotates. The reverse motor output shaft 307 and the reverse motor output shaft connecting member 304 are fixed by the propeller clamp 318, so that the reverse motor output shaft rotates and the reverse motor output shaft connecting member rotates. The reverse propeller fixing member 303 and the reverse motor output shaft connecting member 304 are fixed by the first cylindrical pin 317, and the first cylindrical pin 317 is respectively fixed by the cylindrical pin holes on the reverse propeller fixing member and the reverse motor output shaft connecting member through interference fit. The reverse propeller 301 and the reverse propeller fixing member 303 are connected by the first screw M4 302, and the first screw M4 302 is respectively fixed through the screw holes on the reverse propeller and the reverse propeller fixing member, so that the reverse motor rotor rotates and the reverse propeller rotates. The above parts are assembled together to form a coaxial propeller power module.The coaxial propeller power module is connected to the vector motor seat module through the motor bracket 314 through the third screw M3 310, and the third screw M3 310 is fixed through the screw holes of the motor bracket and the vector motor seat module respectively.

[0025] The folding propeller module 4 includes a push rod fixing part 413, a push rod 411, a stretching stator 409, a stretching rotor 407, a bearing 50x62x6 407, a 6800V deep groove ball bearing 404, an MR63.ZZ bearing 405, a reverse stretching rotor 403, a forward stretching rotor 406, a pull rod head 401, a second carbon rod 402, a Kevlar rope 416, a second pipe clamp 414, a second screw M2 415, a third cylindrical pin M2 418, a second cylindrical pin M3 412, a spring pin 410, a hook 417, etc. The push rod 411 is connected to the push rod fixing part 413 through the second cylindrical pin M3 412, and the second cylindrical pin M3 412 passes through the cylindrical pin holes of the push rod and the push rod fixing part and is fixed by interference fit. The push rod fixing part 413 is connected to the second pipe clamp 414 through the second screw M2 415, and the second screw M2 415 is respectively fixed through the screw holes of the push rod fixing part and the pipe clamp. The second pipe clamp 414 is fixed to the fuselage front beam a, the fuselage front beam b, the fuselage rear beam a, and the fuselage rear beam b through interference fit, so that the push rod fixing part 413 and the push rod 411 are fixed to the fuselage. The stretching stator 409 is connected to the motor seat 201 through the spring pin 410, and the bottom of the spring pin 410 is connected to the motor seat through interference fit, and the head of the spring pin passes through the positioning groove of the stretching stator and is connected to the stretching stator, so that the stretching stator is fixed on the motor seat. The stretching stator 409 is connected to the push rod 411 through the Kevlar rope 416 and the hook 417. One end of the Kevlar rope 416 is connected to the hook, and then the hook is hooked into the hook hole at the lower end of the stretching stator, so that one end of the Kevlar rope 416 is connected to the lower end of the stretching stator. The other end of the Kevlar rope 416 passes around the round hole of the push rod head and is bonded with 502 glue, so that the Kevlar rope 416 is connected to the push rod, so that the push rod moves up and down to drive the stretching stator to move up and down. The stretching rotor 407 is connected to the stretching stator 409 via the bearing 50x62x6 407. The outer ring of the bearing 50x62x6 407 is fixed to the stretching rotor via interference fit, thereby preventing the bearing 50x62x6 407 from moving up and down relative to the stretching rotor 408. The inner ring of the bearing 50x62x6 407 is connected to the stretching stator via interference fit, thereby preventing the bearing from moving up and down relative to the stretching stator. In this way, the stretching rotor 407 can rotate around the stretching stator 409 but cannot move linearly.The forward-rotating stretching rotor 406 is connected to the stretching rotor 408 through the pull rod head 401, the second carbon rod 402, and the third cylindrical pin M2 418. The pull rod head 401 and the second carbon rod 402 are bonded with 502 glue to form a pull rod. One end of the pull rod is connected to the forward-rotating stretching rotor through the third cylindrical pin M2 418. The third cylindrical pin M2 418 is respectively fixed through the cylindrical pin holes of the pull rod head and the forward-rotating stretching rotor. The other end of the pull rod is also connected to the stretching rotor through the cylindrical pin M2. The third cylindrical pin M2 418 is respectively fixed through the cylindrical pin holes of the pull rod head and the stretching rotor. In this way, the forward-rotating stretching rotor and the stretching rotor are fixed. The forward-rotating stretching rotor 406 is connected to the output shaft of the reversing motor through the MR63.ZZ bearing 405. The outer ring of the MR63.ZZ bearing 405 is fixed to the forward-rotating stretching rotor 406 through an interference fit, and the inner ring of the MR63.ZZ bearing 405 is fixed to the output shaft of the reversing motor through a clearance fit, so that the forward-rotating stretching rotor can only rotate around the output shaft of the reversing motor and move up and down. The forward-rotating stretching rotor 406 is also connected to the forward-rotating propeller fixing part 316 through a pull rod composed of the pull rod head 401 and the second carbon rod 402. One end of the pull rod is connected to the forward-rotating stretching rotor through the third cylindrical pin M2 418, and the third cylindrical pin M2 418 is respectively fixed through the cylindrical pin holes of the pull rod head and the forward-rotating stretching rotor. The other end of the pull rod is connected to the forward-rotating propeller fixing part through the third cylindrical pin M2 418, and the third cylindrical pin M2 418 is respectively fixed through the cylindrical pin holes of the pull rod head and the forward-rotating propeller fixing part, thereby playing the role of driving the forward-rotating propeller to fold when the forward-rotating stretching rotor moves up and down. The reverse stretching rotor 403 is connected to the forward stretching rotor 406 via the 6800V deep groove ball bearing 404. The outer ring of the 6800V deep groove ball bearing 404 is fixed to the reverse stretching rotor via an interference fit. The inner ring of the 6800V deep groove ball bearing 404 is fixed to the forward stretching rotor via an interference fit, so that the reverse stretching rotor can rotate around the forward stretching rotor but cannot translate relative to it. The inverted stretching rotor 403 is connected to the inverted propeller fixing part 303 through a pull rod composed of the pull rod head 401 and the second carbon rod 402. One end of the pull rod is connected to the inverted stretching rotor through the third cylindrical pin M2 418. The third cylindrical pin M2 418 passes through the cylindrical pin holes of the pull rod head and the inverted stretching rotor respectively and is fixed. The other end of the pull rod is connected to the inverted propeller fixing part through the third cylindrical pin M2 418. The third cylindrical pin M2 418 passes through the inverted propeller fixing part and the pull rod head respectively and is fixed, so that the inverted stretching rotor moves up and down to drive the inverted propeller to fold.The above parts cooperate together to form a folding propeller module, which plays the role of the push rod moving up and down to drive the stretching stator to move up and down, thereby driving the stretching rotor to move up and down, thereby driving the forward stretching rotor and the reverse stretching rotor to move up and down, thereby driving the reverse propeller and the forward propeller to fold.

[0026] The waterproof sealing module 5 includes a sealed cabin 504, a sealed box cover 502, a sealed box bottom 505, a third screw M2 501, a sealing ring 503, a second nut M2 506, etc. The sealed cabin 504 is fixed to the fuselage front beam a, the fuselage front beam b, the fuselage rear beam a, and the fuselage rear beam b through interference fit, which plays a role in fixing the sealed cabin on the fuselage. The sealed box cover 502 is connected to the sealed cabin 504 through the third screw M2 501 and the second nut M2 506. The third screw M2 501 is fixed through the screw holes of the sealed box cover and the sealed cabin respectively. The sealing ring 503 is sandwiched between the sealed box cover and the sealed cabin to play a role in waterproof sealing. The sealed box bottom 505 is connected to the sealed cabin 504 by the third screw M2 501 and the second nut M2 506. The third screw M2 501 is respectively fixed through the screw holes of the sealed box bottom and the sealed cabin. The sealing ring 503 is sandwiched between the sealed cabin and the sealed box bottom to play a waterproof and sealing role. In this way, a complete waterproof sealing module is assembled.

[0027] The electronic device includes a flight control 601, an electronic speed regulator 606, a battery 608, a receiver 607, a power module 605, a voltage reduction module 602, a wifi data transmission module 603, a GPS positioning module 604, etc. The flight control 601 is used to automatically control the stable flight of the aircraft. The electronic speed regulator 606 is used to power the brushless motor and adjust the speed. The battery 608 is used to power the power system and control system of the entire aircraft. The receiver 605 is used to receive signals from the remote control. The power module 605 is used to measure the voltage of the battery and power the flight control, electronic speed regulator, and voltage reduction module. The voltage reduction module 602 is used to power the steering gear. The wifi data transmission module 603 is used to communicate with the ground station and send and receive mission instruction information. The GPS positioning module 604 is used to receive GPS satellite information and locate and navigate the aircraft.

[0028] The present invention also provides a control method for a cross-medium coaxial twin-rotor UAV with foldable propellers. The main feature of the UAV described in the present invention is that it can realize air and underwater navigation and has the ability to enter and exit the water multiple times. Specifically, it can realize rapid maneuvering and stable movement underwater, and can also realize stable flight in the air and the ability to enter and exit the water quickly. In the underwater motion mode, there are five actuators, including two vector tilting servos, two propeller motors and a push rod. The main function of the vector tilting servos is to change the direction of the motor thrust to achieve the change of navigation attitude, specifically the change of pitch attitude and yaw attitude. The main function of the two propeller motors is to provide thrust for the underwater navigation of the UAV to control the forward and rolling of the UAV. The main function of the push rod is to fold the propeller to reduce the resistance of the propeller underwater. In the air flight mode, there are four actuators, including two vector tilting servos and two propeller motors. The change of flight attitude is achieved by changing the direction of the propeller motor pulling force, specifically the control of pitch attitude, yaw attitude and roll attitude.

[0029] When the drone is in flight mode, the control method for forward and backward movement refers to that the pitch vector servo controls the coaxial propeller motor to tilt forward and backward, drives the coaxial propeller power module to generate a longitudinal horizontal component, and moves the aircraft forward and backward. The control method for lifting movement refers to that the coaxial propeller motor increases or decreases power synchronously, so that the aircraft generates acceleration in the vertical direction, thereby realizing lifting movement. The control method for rolling movement refers to that the roll vector servo controls the coaxial propeller motor to tilt left and right, generates a rolling torque, and gradually tilts the fuselage to one side to realize rolling movement. The rolling motion will generate a lateral horizontal component, thereby driving the aircraft to achieve lateral movement. The control method for yaw motion refers to that the forward motor and the reverse motor in the coaxial propeller power module differentially increase or decrease power to generate a yaw torque, thereby realizing yaw motion.

[0030] When the drone is in underwater mode, the pitch attitude change refers to that the pitch vector servo controls the coaxial propeller motor to tilt up and down, drives the coaxial propeller power module to generate a longitudinal horizontal component, thereby generating a pitch torque, so that the drone pitches. The yaw attitude change refers to that the yaw vector servo controls the coaxial propeller motor to tilt left and right, drives the coaxial propeller power module to generate a lateral horizontal component, thereby generating a yaw torque, so that the drone yaws. The control method of the rolling motion refers to that the forward motor and the reverse motor in the coaxial propeller power module increase or decrease power differentially, generate a rolling torque, and then realize the rolling motion. The control method of the forward motion refers to that the motor in the coaxial propeller power module increases or decreases power synchronously, so that the drone generates acceleration in the horizontal direction, thereby accelerating or decelerating the drone. The folding propeller motion refers to that the push rod drives the propeller to fold or unfold, so that the effective area of ​​the propeller is reduced, thereby reducing the resistance of the propeller to rotate underwater.

[0031] The drone can complete the transition from flight mode to underwater mode and from underwater mode to flight mode in the cross-medium mode. The control method for changing the flight mode to underwater mode refers to detecting whether a remote control water entry command is received in the flight mode. When the command is received, the propeller begins to fold, and the motor speed automatically switches to a low-speed mode. At this time, the drone enters the water. When it is detected that the drone is completely in the water, it is switched to underwater mode, and the navigation attitude is switched from longitudinal to transverse, completing the cross-medium process. The control method for changing the underwater mode to flight mode refers to that when the drone receives a cross-medium command from the remote control, the navigation attitude is switched from transverse to longitudinal, and the propeller begins to unfold. At this time, the motor is still in a low-speed mode. When it is detected that the drone is completely out of the water, the motor speed automatically switches to a high-speed mode, completing the cross-medium process and entering the flight mode.

[0032] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the device embodiment, the above is only a preferred embodiment of the present invention. Since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited to this. Any technician familiar with the technical field is within the technical scope disclosed by the present invention. For ordinary technicians in the technical field, changes or replacements that can be easily thought of should be covered within the protection scope of the present invention without departing from the principle of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A cross-medium coaxial twin-rotor UAV with foldable propellers, characterized in that: It includes a main body module and a coaxial propeller power module. A vector motor seat module and a folding propeller module are fixed inside the main body module. The coaxial propeller power module is fixedly connected to the main body module through the vector motor seat module. The vector motor seat module comprises a motor seat, a universal joint, a reinforced fixed frame, a steering gear fixing part, a steering gear, and a pipe clamp, wherein the reinforced fixed frame is fixedly connected to the main body module through the pipe clamp, the top of the reinforced fixed frame is connected to the motor seat through a universal joint, the bottom is fixedly connected to the steering gear fixing part, the steering gear fixing part is connected to the steering gear, and the steering gear is connected to the motor seat through a ball joint connecting rod and controls the motor seat to perform pitch or roll movements; The coaxial propeller power module comprises a reversing motor stator, a reversing motor rotor, a forward motor stator, a forward motor rotor, a motor bracket, a reversing motor output shaft, a forward propeller, a reversing propeller, a forward motor rotor connector, a forward propeller fixing part, a reversing motor output shaft connector, a reversing propeller fixing part, a propeller clamp, and a top screw. The motor bracket is fixedly connected to the vector motor seat module, the reversing motor stator is connected to the bottom of the motor bracket by an interference fit, and the forward motor stator is connected to the top of the motor bracket by an interference fit; one end of the reversing motor output shaft passes through the forward motor stator, the forward motor rotor and the reversing propeller. The stator of the reversing motor is fixed with the reversing motor rotor by a top screw, the other end of the reversing motor output shaft is connected with the reversing motor output shaft connecting piece by a propeller clamp, the reversing motor output shaft connecting piece is connected with the reversing propeller fixing piece by a cylindrical pin, the reversing propeller fixing piece is connected with the reversing propeller, the reversing motor rotor drives the reversing motor output shaft to rotate, thereby driving the reversing propeller to rotate; the forward motor rotor is connected with the forward motor rotor connecting piece, the forward motor rotor connecting piece is fixedly connected with the forward propeller fixing piece by a cylindrical pin, the forward propeller fixing piece is connected with the forward propeller, and the rotation of the forward motor rotor drives the forward propeller to rotate; The folding propeller module includes a push rod fixing part, a push rod, a stretching stator, a stretching rotor, a reverse stretching rotor, a forward stretching rotor, a pull rod structure, a Kevlar rope, a pipe clamp, a cylindrical pin, a spring pin, and a hook, wherein the push rod fixing part is fixedly connected to the main body module through the pipe clamp, and the push rod is connected to the push rod fixing part through the cylindrical pin; one end of the stretching stator is connected to the motor seat through the spring pin, and the other end is connected to the push rod through the Kevlar rope and the hook, and the push rod moves up and down to drive the stretching stator to move up and down; the stretching rotor is connected to the stretching stator through a bearing, and the stretching rotor rotates around the stretching stator; the outer ring of the forward stretching rotor The pull rod structure is used to fix the stretching rotor through interference fit, and the inner ring is fixed to the output shaft of the reversing motor through a bearing through clearance fit, and the forward stretching rotor rotates and moves up and down around the output shaft of the reversing motor; the forward stretching rotor is connected to the forward propeller fixing piece through the pull rod structure, and the up and down movement of the forward stretching rotor drives the forward propeller to fold; the reversing stretching rotor is connected to the forward stretching rotor through a deep groove ball bearing, and the reversing stretching rotor rotates around the forward stretching rotor but cannot move relatively; the reversing stretching rotor is connected to the reversing propeller fixing piece through the pull rod structure, and the up and down movement of the reversing stretching rotor drives the reversing propeller to fold.

2. The cross-medium coaxial twin-rotor UAV with foldable propellers according to claim 1, characterized in that: The ball joint connecting rod in the vector motor seat module includes a ball joint and a carbon rod. The two sections of the carbon rod are respectively connected with ball joints by interference fit to form a ball joint connecting rod structure with ball joints at both ends. The ball joint at one end is connected to the motor seat, and the ball joint at the other end is connected to the rudder arm, and the rudder arm is connected to the steering gear through a spline.

3. The cross-medium coaxial twin-rotor UAV with foldable propellers according to claim 1 or 2, characterized in that: The servos include a pitch servo and a roll servo, and the installation angles of the pitch servo and the roll servo differ by 90°.

4. The cross-medium coaxial twin-rotor UAV with foldable propellers according to claim 1, characterized in that: The tie rod structure of the folding propeller module comprises a tie rod head and a carbon rod, and the two ends of the carbon rod are respectively connected to the tie rod heads to form a tie rod structure with tie rod heads at both ends.

5. The cross-medium coaxial twin-rotor UAV with foldable propellers according to claim 1, characterized in that: The main fuselage module comprises a streamlined fuselage structure consisting of a fuselage front beam, a fuselage rear beam, a cabin left section, a cabin right section and a cabin lower section, and a landing gear is connected to the bottom of the fuselage structure.

6. The cross-medium coaxial twin-rotor UAV with foldable propellers according to claim 1, characterized in that: A waterproof sealing module is arranged inside the main body module, and electronic equipment is placed inside the waterproof sealing module.

7. The cross-medium coaxial twin-rotor UAV with foldable propellers according to claim 6, characterized in that: The waterproof sealing module includes a sealed cavity composed of a sealed cabin, a sealed box cover, and a sealed box bottom. The sealed cabin and the main body module are fixed by interference fit. The sealed box cover and the sealed cabin are movably connected and sealed by a sealing ring. The sealed box bottom and the sealed cabin are fixedly connected and sealed by a sealing ring.

8. The cross-medium coaxial twin-rotor UAV with foldable propellers according to claim 6 or 7, characterized in that: The electronic device includes a flight control, an electronic speed regulator, a battery, a receiver, a power module, a step-down module, a wifi data transmission module, and a GPS positioning module. The flight control is used to automatically control the stable flight of the aircraft, the electronic speed regulator is used to power the brushless motor and adjust the speed, the battery is used to power the power system and control system of the entire aircraft, the receiver is used to receive signals from the remote control, the power module is used to measure the voltage of the battery and power the flight control, the electronic speed regulator, and the step-down module, the step-down module is used to power the servo, the wifi data transmission module is used to communicate with the ground station and send and receive mission instruction information, and the GPS positioning module is used to receive GPS satellite information and locate and navigate the aircraft.

9. A control method for a cross-medium coaxial twin-rotor UAV with foldable propellers as claimed in any one of claims 1 to 8, characterized in that: Including flight mode, underwater mode and cross-media mode; The flight modes of the UAV include control methods for forward and backward movement, lifting and lowering movement, rolling movement, and yaw movement; The control method for forward and backward movement refers to that the pitch vector servo controls the coaxial propeller motor to tilt forward and backward, drives the coaxial propeller power module to generate a longitudinal horizontal component force, and moves the aircraft forward and backward; the control method for lifting and lowering movement refers to that the coaxial propeller motor increases and decreases power synchronously, so that the aircraft generates acceleration in the vertical direction, thereby realizing lifting and lowering movement; the control method for rolling movement refers to that the roll vector servo controls the coaxial propeller motor to tilt left and right, generates a rolling torque, and gradually tilts the fuselage to one side to realize rolling movement; the rolling movement generates a lateral horizontal component force, thereby driving the aircraft to realize lateral movement; the control method for yaw movement refers to that the forward motor and the reverse motor in the coaxial propeller power module differentially increase and decrease power, generate a yaw torque, and thereby realize yaw movement; The UAV in underwater mode includes pitch attitude change, yaw attitude change, rolling motion control method, forward motion control method and folding propeller motion; the pitch attitude change refers to that the pitch vector servo controls the coaxial propeller motor to tilt up and down, drives the coaxial propeller power module to generate a longitudinal horizontal component, thereby generating a pitch torque, so that the UAV pitches; the yaw attitude change refers to that the yaw vector servo controls the coaxial propeller motor to tilt left and right, drives the coaxial propeller power module to generate a lateral horizontal component, thereby generating a yaw torque, so that the UAV yaws; the rolling motion control method refers to that the forward motor and the reverse motor in the coaxial propeller power module increase or decrease power differentially, generate a rolling torque, and then realize the rolling motion; the forward motion control method refers to that the motor in the coaxial propeller power module increases or decreases power synchronously, so that the UAV generates acceleration in the horizontal direction, thereby accelerating or decelerating the UAV; the folding propeller motion refers to that the push rod drives the propeller to fold or unfold, so that the effective area of ​​the propeller is reduced, thereby reducing the resistance of the propeller rotating underwater; The UAV cross-medium mode includes changing from flight mode to underwater mode and from underwater mode to flight mode; the control method for changing from flight mode to underwater mode refers to detecting whether a remote control water entry command is received in flight mode. When the command is received, the propeller begins to fold and the motor speed automatically switches to a low-speed mode. At this time, the UAV enters the water. When it is detected that the UAV is completely immersed in the water, it is switched to underwater mode, and the navigation attitude is switched from longitudinal to transverse to complete the cross-medium process; the control method for changing from underwater mode to flight mode refers to that when the UAV receives a remote control cross-medium command, the navigation attitude is switched from transverse to longitudinal, and the propeller begins to unfold. At this time, the motor is still in a low-speed mode. When it is detected that the UAV is completely out of water, the motor speed automatically switches to a high-speed mode to complete the cross-medium process and enter flight mode.

10. The control method of the cross-medium coaxial twin-rotor UAV with foldable propellers according to claim 9, characterized in that: In the underwater motion mode, there are five actuators, including two vector tilt servos, two propeller motors and a push rod. The vector tilt servos change the direction of the motor thrust to achieve changes in the navigation attitude, specifically changes in the pitch attitude and yaw attitude. The two propeller motors provide thrust for the drone's underwater navigation to control the forward and roll of the drone. The push rod folds the propeller to reduce the propeller's resistance underwater; in the aerial flight mode, there are four actuators, including two vector tilt servos and two propeller motors. The change of flight attitude is achieved by changing the direction of the propeller motor's pulling force.

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