Transmission system of tandem double-rotor unmanned aerial vehicle

Abstract

The utility model relates to a tandem type double-rotor unmanned aerial vehicle transmission system, which is characterized in that reversing speed reduction units of a front rotor and a rear rotor are connected through a plurality of sections of synchronous long shafts, and the tandem type double-rotor unmanned aerial vehicle transmission system comprises a three-stage speed reduction structure, namely a first-stage synchronous belt speed reduction structure, a second-stage bevel gear speed reduction structure and a third-stage planetary gear train speed reduction structure, the second-stage bevel gear speed reduction realizes power transmission through a bevel gear, and the third-stage planetary gear train speed reduction transmits power to a rotor shaft through meshing of a planetary gear, a sun gear and a gear ring; the system solves the problems that a traditional tandem rotorcraft transmission system is single in structure, slow in clutch response, difficult in engine starting, insufficient in power, poor in emergency risk avoiding capacity and difficult to maintain, and the performance and reliability of the unmanned aerial vehicle are improved.

Description

A tandem dual-rotor UAV transmission system Technical Field

[0001] This utility model belongs to the field of aerospace technology and relates to a tandem dual-rotor UAV transmission system. In particular, it relates to a tandem dual-rotor UAV transmission system that uses a dual-piston engine power input and a three-stage reduction mechanism to work together, combines a centrifugal and overrunning clutch to achieve dynamic decoupling, and ensures that the front and rear rotors have the same speed through multiple synchronous long shafts. It has a redundant transmission topology and a lightweight design. Background Technology

[0002] In the aerospace field, the performance of a drone's transmission system directly affects its flight stability and mission execution capabilities. Traditional drone transmission systems mostly use a single engine, which is prone to insufficient power or single-point failure under complex operating conditions, making it difficult to meet the requirements of special scenarios such as heavy-load transportation and high-altitude patrol. Tandem-rotor drones, with their unique rotor layout, have significant advantages in hovering efficiency and vertical takeoff and landing flexibility. However, their transmission systems must achieve lightweight design and high reliability while ensuring efficient power transmission, which places higher demands on the design.

[0003] The transmission system of a tandem rotor UAV, as the core of power transmission, bears the critical task of rationally distributing engine power to the rotors. Existing transmission systems suffer from problems such as a simple deceleration structure and slow clutch response, leading not only to low transmission efficiency but also potential component damage due to inertial drag. Furthermore, the lack of redundancy design makes them highly susceptible to flight accidents should an engine fail. In addition, as UAV applications expand into extreme environments, the shortcomings of traditional transmission systems in terms of weight and ease of maintenance become increasingly apparent, making them unable to meet diverse mission requirements. Summary of the Invention

[0004] In view of this, in order to solve the problems of the current tandem rotorcraft transmission system, such as simple structure, slow clutch response, difficulty in starting piston engines, insufficient single-engine driving power, insufficient emergency avoidance capability, and difficulty in component maintenance, this utility model provides a tandem dual-rotor UAV transmission system.

[0005] To achieve the above objectives, this utility model provides the following technical solution:

[0006] A tandem dual-rotor UAV transmission system includes a front rotor reversing reduction unit and a rear rotor reversing reduction unit connected by multiple synchronous long shafts. Both units include a first-stage belt reduction small pulley and a first-stage belt reduction large pulley connected by synchronous belts. The first-stage belt reduction small pulley is connected to a piston engine via an engine output shaft. The first-stage belt reduction large pulley is connected to a second-stage reversing reduction output shaft via a first-stage large pulley output shaft and a second-stage reversing reduction input shaft. A second-stage reversing reduction input bevel gear is fixedly mounted on the second-stage reversing reduction input shaft, and a second-stage reversing reduction output gear is fixedly mounted on the second-stage reversing reduction output shaft. The second-stage reversing reduction output bevel gear meshes with the second-stage reversing reduction input bevel gear. The second-stage reversing reduction output shaft is connected to the sun gear of the third-stage planetary gear system. Multiple third-stage planetary gears are evenly distributed on the planetary carrier of the third-stage planetary gear system. The third-stage planetary gears mesh simultaneously with the sun gear and the ring gear of the third-stage planetary gear system. The ring gear of the third-stage planetary gear system is fitted over the multiple third-stage planetary gears. The rotor shaft is connected to the planetary carrier of the third-stage planetary gear system to realize the transmission of power to the rotor.

[0007] Furthermore, the output end of the piston engine is connected to the engine output shaft via a coupling, which is a flexible coupling.

[0008] Furthermore, the synchronous belt is a toothed belt, and an automatic tensioning device is installed on the outside of the synchronous belt. This device adopts a spring-guide wheel structure. The guide wheel is installed on an adjustable bracket through a sliding bearing. The adjustable bracket automatically adjusts the position of the guide wheel under the action of spring force according to the tension of the synchronous belt, so as to realize the real-time adaptive adjustment of the tension of the synchronous belt.

[0009] Furthermore, an overrunning clutch is provided between the first-stage belt reducer pulley and the first-stage belt reducer output shaft. The inner ring of the overrunning clutch is connected to the first-stage belt reducer output shaft, and the outer ring is fixedly connected to the first-stage belt reducer pulley, thereby realizing one-way engagement and disengagement between the first-stage belt reducer pulley and the first-stage belt reducer output shaft.

[0010] Furthermore, the first-stage large pulley output shaft and the second-stage reversing reduction input shaft are connected by a centrifugal clutch, and deep groove ball bearings are installed on the first-stage large pulley output shaft and the second-stage reversing reduction input shaft to provide support.

[0011] Furthermore, the second-stage reversing reduction input shaft and the second-stage reversing reduction input bevel gear, as well as the second-stage reversing reduction output shaft and the second-stage reversing reduction output bevel gear, are all integrated structures.

[0012] Furthermore, the sun gear of the third-stage planetary gear train is connected to the output shaft of the second-stage reversing reduction gear via a spline, ensuring the coaxiality and torque transmission accuracy between the sun gear and the output shaft of the second-stage reversing reduction gear.

[0013] Furthermore, the third-stage planetary gear reducer planetary carrier is fixedly mounted on the machine frame using double-row tapered roller bearings. The double-row tapered roller bearings are installed back-to-back, and appropriate preload is applied by preload nuts to improve the rigidity and rotational accuracy of the bearings, while effectively bearing the axial and radial forces generated during the planetary gear transmission process.

[0014] Furthermore, the third-stage planetary gear train reduction planetary carrier is connected to the rotor shaft via a spline, enabling the transmission of power to the rotor.

[0015] Furthermore, the synchronous long shaft includes a synchronous long shaft input shaft, a synchronous long shaft output shaft, and a diaphragm coupling for connecting the synchronous long shaft input shaft and the synchronous long shaft output shaft.

[0016] Furthermore, the synchronous long shaft output shafts are respectively located on one side near the front rotor reversing reduction unit and the rear rotor reversing reduction unit. The synchronous long shaft output bevel gears that mesh with the corresponding second-stage reversing reduction output bevel gears are fixedly installed on the synchronous long shaft output shafts. The synchronous long shaft output shafts and the synchronous long shaft output bevel gears are an integral structure.

[0017] Furthermore, the diaphragm coupling is connected to both the synchronous long shaft input shaft and the synchronous long shaft output shaft via splines, ensuring that the front and rear rotors maintain the same speed during operation.

[0018] The beneficial effects of this utility model are as follows:

[0019] 1. The tandem dual-rotor UAV transmission system disclosed in this utility model includes three-stage reduction gears in both the front and rear reducers: a first-stage synchronous belt reduction, a second-stage bevel gear reduction, and a third-stage planetary gear reduction. Each of the front and rear engines is connected to a piston engine. The engine output shaft transmits power to the first-stage output shaft via the first-stage synchronous belt reduction, then to the second-stage reversing reduction bevel gear output shaft, and finally to the planetary carrier via the third-stage planetary gear system, from which the power is then transmitted to the rotor shaft. This structure is more compact and has higher power utilization efficiency compared to traditional tandem transmission systems, significantly reducing system weight and structural size.

[0020] 2. The tandem dual-rotor UAV transmission system disclosed in this utility model has a first-stage reduction pulley mounted on the engine output shaft, a first-stage reduction pulley mounted on the first-stage large pulley output shaft, and the first-stage reduction pulley and the first-stage reduction pulley connected by a toothed synchronous belt. This system can reduce vibration during the operation of the piston engine, achieve smooth transmission, and provide overload protection.

[0021] 3. The tandem dual-rotor UAV transmission system disclosed in this utility model has an overrunning clutch installed between the first-stage reduction pulley and the output shaft of the first-stage large pulley. This allows the overrunning clutch to engage and disengage the engine when one engine fails. If the two engines rotate at different speeds at a certain moment, the speed difference between the first-stage large pulley and the first-stage reduction pulley on one side will be transmitted to the first-stage large pulley via the synchronous long shaft. At this time, the overrunning clutch can disengage. When the speed of the engine on this side increases and there is no speed difference between the two pulleys, the overrunning clutch will re-engage, and the speed difference between the engines can still satisfy the rotor shaft speed. This allows the overrunning clutch to disconnect the engine when it lands and shuts down, protecting the components from damage caused by inertial drag.

[0022] 4. The tandem dual-rotor UAV transmission system disclosed in this utility model uses a centrifugal clutch to separate and engage the first-stage large pulley output shaft and the second-stage reversing reduction input shaft. The piston engine has a small initial torque and low speed, so the centrifugal clutch is in the disengaged state. When a certain speed is reached, the centrifugal clutch automatically engages the two shafts to ensure the normal start-up of the piston engine. Compared with traditional clutch solutions, it does not require a pneumatic or hydraulic system, thus reducing the system weight.

[0023] 5. The tandem dual-rotor UAV transmission system disclosed in this utility model has an automatic tensioning device installed on the outer side of the toothed synchronous belt, which can adaptively adjust the tension in real time, avoid slippage and tooth skipping and abnormal wear, reduce maintenance frequency, ensure stable power transmission, improve the reliability and service life of the transmission system under different working conditions, and reduce the flight risk of UAV caused by transmission failure.

[0024] Other advantages, objectives, and features of this invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination and study, or may be learned from practice of this invention. The objectives and other advantages of this invention can be realized and obtained through the following description. Attached Figure Description

[0025] To make the objectives, technical solutions, and advantages of this utility model clearer, the preferred embodiments of this utility model will be described in detail below with reference to the accompanying drawings, wherein:

[0026] Figure 1 is a structural schematic diagram of the tandem dual-rotor UAV transmission system of this utility model;

[0027] Figure 2 is a schematic diagram of the front rotor reversing deceleration unit in the tandem dual-rotor UAV transmission system of this utility model.

[0028] Figure 3 is a schematic diagram of the synchronous long shaft in the tandem dual-rotor UAV transmission system of this utility model.

[0029] Figure 4 is a schematic diagram of the automatic tensioning device in the tandem dual-rotor UAV transmission system of this utility model.

[0030] Figure 5 is a schematic diagram of the transmission principle of the tandem dual-rotor UAV transmission system of this utility model.

[0031] Reference numerals: 1. Piston engine; 2. Coupling; 4. Engine output shaft; 5. First-stage belt reduction pulley; 6. Toothed synchronous belt; 7. First-stage belt reduction pulley; 8. Overrunning clutch; 9. First-stage large pulley output shaft; 10. Centrifugal clutch; 11. Second-stage reversing reduction input shaft; 13. Second-stage reversing reduction bevel gear; 15. Rotor shaft; 17. Third-stage planetary gear reducer planet carrier; 18. Third-stage planetary gear reducer planet gears; 19. Second-stage... The system includes: a reduction bevel gear 20, a synchronous long shaft output bevel gear 22, a synchronous long shaft output shaft 23, a third-stage planetary gear reducer sun gear 29, a second-stage reversing reduction output shaft 32, a long shaft 25, diaphragm couplings 26, 33, and 40, deep groove ball bearings 12, 28, 24, 27, 35, and 36, tapered roller bearings 21 and 34, cylindrical roller bearings 14 and 31, four-point contact ball bearings 3 and 37, double-row tapered roller bearings 16 and 30, a guide wheel 38, and a spring 39. Detailed Implementation

[0032] The following specific examples illustrate the implementation of this utility model. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification. This utility model can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this utility model.

[0033] As shown in Figures 1-5, a tandem dual-rotor UAV transmission system adopts a symmetrical layout, connecting the front rotor reversing reduction unit and the rear rotor reversing reduction unit via multiple synchronous long shafts 25. The front and rear rotor reversing reduction units are structurally symmetrical and each features a three-stage reduction system: a first-stage synchronous belt reduction, a second-stage bevel gear reduction, and a third-stage planetary gear reduction. The system is equipped with dual-piston engines, connected to the front and rear reduction units respectively, forming a dual-power input mode.

[0034] Both the front rotor reversing reduction unit and the rear rotor reversing reduction unit include a first-stage belt reduction small pulley 5 and a first-stage belt reduction large pulley 7 connected by a toothed synchronous belt 6. The first-stage belt reduction small pulley 5 is connected to the piston engine 1 through the engine output shaft 4. The first-stage belt reduction large pulley 7 is connected to the second-stage reversing reduction output shaft 32 through the first-stage large pulley output shaft 9 and the second-stage reversing reduction input shaft 11. A second-stage reversing reduction input bevel gear 13 is fixedly installed on the second-stage reversing reduction input shaft 11, and a gear meshing with the second-stage reversing reduction input bevel gear 13 is fixedly installed on the second-stage reversing reduction output shaft 32. The second-stage reversing reduction output bevel gear 20 is connected to the second-stage reversing reduction output shaft 32 and the third-stage planetary gear reducer sun gear 29. Multiple third-stage planetary gear reducer planetary gears 18 are evenly distributed on the third-stage planetary gear reducer planet carrier 17. The third-stage planetary gear reducer planetary gears 18, the third-stage planetary gear reducer sun gear 29, and the third-stage planetary gear reducer ring gear 19 mesh simultaneously. The third-stage planetary gear reducer ring gear 19 is fitted onto the multiple third-stage planetary gear reducer planetary gears 18. The rotor shaft 15 is connected to the third-stage planetary gear reducer planet carrier 17 to realize the transmission of power to the rotor.

[0035] The output end of the piston engine 1 is connected to the engine output shaft 4 via coupling 2, and the first-stage large pulley output shaft 9 and the second-stage reversing reduction input shaft 11 are connected via centrifugal clutch 10.

[0036] The combination of the first-stage reduction pulley 5, the toothed synchronous belt 6, and the first-stage reduction pulley 7 achieves the first-stage synchronous belt reduction of the front rotor reversing reduction unit.

[0037] Specifically, the output end of the piston engine 1 is connected to the engine output shaft 4 through the coupling 2. The coupling 2 is an elastic coupling, which absorbs the vibration and impact generated by the engine operation through elastic elements, so as to realize the flexible connection between the engine and the transmission system and the reliable power transmission.

[0038] The engine output shaft 4 is mounted with an interference fit on four-point contact ball bearings 3 and 37, which can simultaneously withstand radial and bidirectional axial loads, ensuring stable power output.

[0039] A first-stage belt reduction pulley 5 is coaxially mounted on one end of the engine output shaft 4 and fixed by a key connection to ensure that the first-stage belt reduction pulley 5 rotates synchronously with the engine output shaft 4. Simultaneously, a first-stage belt reduction pulley 7 is mounted on the first-stage large pulley output shaft 9. An overrunning clutch 8 is provided between the first-stage belt reduction pulley 7 and the first-stage large pulley output shaft 9. The inner ring of the overrunning clutch 8 is connected to the first-stage large pulley output shaft 9, and the outer ring is fixedly connected to the first-stage belt reduction pulley 7, realizing a one-way clutch function between the first-stage belt reduction pulley 7 and the first-stage large pulley output shaft 9.

[0040] The toothed synchronous belt 6 is a toothed belt. The toothed synchronous belt 6 is selected to connect the small pulley 5 and the large pulley 7 of the first-stage belt reduction. An automatic tensioning device is installed on the outside of the toothed synchronous belt 6. The device adopts a spring-guide wheel structure. The guide wheel 38 is installed on the adjustable bracket through a sliding bearing. The bracket automatically adjusts the position of the guide wheel 38 according to the tension of the toothed synchronous belt 6 under the action of the spring 39, so as to realize the real-time adaptive adjustment of the tension of the toothed synchronous belt 6.

[0041] A centrifugal clutch 10 is installed between the first-stage large pulley output shaft 9 and the second-stage reversing reduction input shaft 11. The driving disc of the centrifugal clutch 10 is fixedly connected to the first-stage large pulley output shaft 9, and the driven disc is connected to the second-stage reversing reduction input shaft 11. Deep groove ball bearings 12, 28, 35, and 36 are respectively installed on the first-stage large pulley output shaft 9 and the second-stage reversing reduction input shaft 11. The deep groove ball bearings 12, 28, 35, and 36 are fixedly installed on both sides, and the axial displacement of the bearings is restricted by the shaft shoulders and bearing end caps, providing radial support and a certain axial load capacity for the shaft.

[0042] The cooperation of the second-stage reversing reduction input bevel gear 13 and the second-stage reversing reduction output bevel gear 20 realizes the second-stage bevel gear reduction of the front rotor reversing reduction unit.

[0043] Specifically, the second-stage reversing reduction input shaft 11 and the second-stage reversing reduction input bevel gear 13 are integrated structures, as are the second-stage reversing reduction output shaft 32 and the second-stage reversing reduction output bevel gear 20. The second-stage reversing reduction input shaft 11 and the second-stage reversing reduction output shaft 32 are assembled to mesh the second-stage reversing reduction input bevel gear 13 and the second-stage reversing reduction output bevel gear 20. The meshing of the second-stage reversing reduction input bevel gear 13 and the second-stage reversing reduction output bevel gear 20 is achieved by adjusting the axial position of the two shafts using shims.

[0044] The coordination of the third-stage planetary gear reducer planet carrier 17, the third-stage planetary gear reducer planetary gear 18, the third-stage planetary gear reducer sun gear 29, and the third-stage planetary gear reducer ring gear 19 achieves the third-stage planetary gear reducer of the front rotor reversing reduction unit.

[0045] The third-stage planetary gear reducer sun gear 29 is connected to the second-stage reversing reduction output shaft 32 via a spline to ensure the coaxiality and torque transmission accuracy between the third-stage planetary gear reducer sun gear 29 and the second-stage reversing reduction output shaft 32.

[0046] Multiple third-stage planetary gears 18 are evenly distributed and mounted on the third-stage planetary gear carrier 17. The third-stage planetary gears 18 are connected to the third-stage planetary gear carrier 17 via cylindrical pins and bearings, ensuring that the third-stage planetary gears 18 can rotate flexibly. The third-stage planetary gears 18 mesh simultaneously with the third-stage planetary gear sun gear 29 and the third-stage planetary gear ring gear 19 to form a planetary gear transmission structure.

[0047] The third-stage planetary gear reducer planetary carrier 17 is fixedly mounted on the airframe via double-row tapered roller bearings 16 and 30. The double-row tapered roller bearings 16 and 30 are mounted back-to-back, and a suitable preload is applied using preload nuts to improve the bearing rigidity and rotational accuracy, while effectively bearing the axial and radial forces generated during planetary gear transmission. The third-stage planetary gear reducer planetary carrier 17 is connected to the rotor shaft 15 via a spline, enabling power transmission to the rotor.

[0048] The synchronous long shaft output shaft 23 is respectively set on one side near the front rotor reversing reduction unit and the rear rotor reversing reduction unit. The synchronous long shaft output bevel gear 22, which meshes with the corresponding second-stage reversing reduction output bevel gear 20, is fixedly installed on the synchronous long shaft output shaft 23. The tapered roller bearings 21 and 34 are connected to the synchronous long shaft output shaft 23 by interference fit, so as to realize the axial positioning and radial support of the synchronous long shaft output shaft 23 and suppress the axial movement and radial runout of the synchronous long shaft output end.

[0049] The cylindrical roller bearing 14 and the rotor shaft 15 are fitted with an interference fit to provide reliable circumferential positioning and facilitate disassembly. The bearing mainly bears radial loads, reducing operating losses and vibration. The cylindrical roller bearing 31 and the second-stage reversing reduction output shaft 32 are fixed with an interference fit to distribute stress concentration under alternating loads and ensure the stability of power transmission.

[0050] The synchronous long shaft consists of multiple long shaft segments 25 and diaphragm couplings 26 and 40 for connecting adjacent long shafts 25. The long shaft 25 is connected to the front reducer unit via a diaphragm coupling 33, which is splined to the output shaft 23 of the synchronous long shaft. The long shaft 25 is also splined to the diaphragm coupling 26. The diaphragm coupling 26 is bolted to the diaphragm coupling 40, and the diaphragm coupling 40 is splined to the next long shaft segment, ensuring that the front and rear rotors maintain consistent speeds during operation. Deep groove ball bearings 24 and 27 are interference-fitted onto the diaphragm coupling 33 and 40, respectively, providing dynamic stiffness to the long shaft 25.

[0051] This tandem dual-rotor UAV transmission system consists of a dual-piston engine, symmetrical front / rear reducers, a clutch mechanism, and a synchronous long shaft. Both the front and rear reducers feature three-stage reduction: a reduction and shock absorption system with bevel gear reversal, planetary gear speed regulation, and efficient rotor shaft drive. The symmetrical structure enhances balance and stability, and simplifies manufacturing and maintenance. A combination of centrifugal and overrunning clutches achieves dynamic decoupling; the former ensures smooth engine start-up, while the latter prevents inertial damage during idling or malfunctions. The synchronous long shaft ensures consistent rotor speeds. The system employs a redundant topology, maintaining dual-rotor drive even in the event of a single engine failure. Compared to traditional systems, this transmission system offers advantages such as light weight, high transmission efficiency, and ease of maintenance, making it suitable for complex scenarios such as heavy-load transport and high-altitude patrols, significantly enhancing the UAV's environmental adaptability and reliability.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of this utility model and are not intended to limit it. Although this utility model has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of this utility model without departing from the spirit and scope of this technical solution, and all such modifications or substitutions should be covered within the scope of the claims of this utility model.

Claims

1. A tandem dual-rotor unmanned aerial vehicle (UAV) transmission system, characterized in that, Both the front rotor reversing reduction unit and the rear rotor reversing reduction unit, which are connected by multiple synchronous long shafts, include a first-stage belt reduction small pulley (5) and a first-stage belt reduction large pulley (7) connected by a toothed synchronous belt (6). The first-stage belt reduction small pulley (5) is connected to the piston engine (1) through the engine output shaft (4). The first-stage belt reduction large pulley (7) is connected to the second-stage reversing reduction output shaft (32) through the first-stage large pulley output shaft (9) and the second-stage reversing reduction input shaft (11). The second-stage reversing reduction input shaft (11) is fixedly mounted with a second-stage reversing reduction bevel gear (13). The second-stage reversing reduction output shaft (32) is fixedly mounted with a bevel gear that is connected to the second-stage reversing reduction input gear. The second-stage reversing reduction output bevel gear (20) meshes with the wheel (13). The second-stage reversing reduction output shaft (32) is connected to the third-stage planetary gear reducer sun gear (29). Multiple third-stage planetary gear reducer planetary gears (18) are evenly installed on the third-stage planetary gear reducer planetary carrier (17). The third-stage planetary gear reducer planetary gears (18), the third-stage planetary gear reducer sun gear (29), and the third-stage planetary gear reducer ring gear (19) mesh simultaneously. The third-stage planetary gear reducer ring gear (19) is fitted outside the multiple third-stage planetary gear reducer planetary gears (18). The rotor shaft (15) is connected to the third-stage planetary gear reducer planetary carrier (17) to realize the transmission of power to the rotor.

2. The tandem dual-rotor UAV transmission system as described in claim 1, characterized in that, The toothed synchronous belt (6) is a toothed belt. An automatic tensioning device is installed on the outside of the toothed synchronous belt. The device adopts a spring-guide wheel structure. The guide wheel (38) is installed on the adjustable bracket through a sliding bearing. The adjustable bracket automatically adjusts the position of the guide wheel (38) under the force of the spring (39) according to the tightness of the toothed synchronous belt (6), so as to realize the real-time adaptive adjustment of the tension of the toothed synchronous belt (6).

3. The tandem dual-rotor UAV transmission system as described in claim 1, characterized in that, An overrunning clutch (8) is provided between the first-stage belt reducer pulley (7) and the first-stage pulley output shaft (9). The inner ring of the overrunning clutch (8) is connected to the first-stage pulley output shaft (9), and the outer ring is fixedly connected to the first-stage belt reducer pulley (7), thereby realizing one-way engagement and disengagement between the first-stage belt reducer pulley (7) and the first-stage pulley output shaft (9).

4. The tandem dual-rotor UAV transmission system as described in claim 1, characterized in that, The first-stage large pulley output shaft (9) and the second-stage reversing speed reduction input shaft (11) are connected by a centrifugal clutch (10). Deep groove ball bearings are installed on the first-stage large pulley output shaft (9) and the second-stage reversing speed reduction input shaft (11) to provide support.

5. The tandem dual-rotor UAV transmission system as described in claim 1, characterized in that, The second-stage reversing deceleration input shaft (11), the second-stage reversing deceleration input bevel gear (13), the second-stage reversing deceleration output shaft (32), and the second-stage reversing deceleration output bevel gear (20) are all integrated structures.

6. The tandem dual-rotor UAV transmission system as described in claim 1, characterized in that, The third-stage planetary gear reducer sun gear (29) is connected to the second-stage reversing reducer output shaft (32) via a spline, and the third-stage planetary gear reducer planet carrier (17) is connected to the rotor shaft (15) via a spline.

7. The tandem dual-rotor UAV transmission system as described in claim 1, characterized in that, The third-stage planetary gear reducer planet carrier (17) is fixedly installed on the machine frame by double-row tapered roller bearings, which are installed back-to-back.

8. The tandem dual-rotor UAV transmission system as described in claim 1, characterized in that, The synchronous long shaft includes a synchronous long shaft output shaft (23), multiple long shaft segments (25), and a diaphragm coupling for connecting the multiple long shaft segments.

9. The tandem dual-rotor UAV transmission system as described in claim 8, characterized in that, The synchronous long shaft output shaft (23) is respectively located on one side near the front rotor reversing deceleration unit and the rear rotor reversing deceleration unit. The synchronous long shaft output shaft (23) is fixedly installed with a synchronous long shaft output bevel gear (22) that meshes with the corresponding second-stage reversing deceleration output bevel gear (20). The synchronous long shaft output shaft (23) and the synchronous long shaft output bevel gear (22) are an integral structure.

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