High-Reliability UAV Heavy-Load Performance Test Platform with Matrix-Type Multi-Tensile Sensors

Abstract

The present invention discloses a high-reliability heavy-load performance test platform for a matrix multi-tensile force sensor unmanned aerial vehicle, which relates to the field of test devices and includes a test frame connecting plate. A fixed seat is installed on the top of the test frame connecting plate, and four groups of the first tensile and compressive force sensors are arranged on the top of the fixed seat. The four groups of the first tensile and compressive force sensors are distributed in a matrix on the top of the fixed seat. A bearing seat is installed on the top of the first tensile and compressive force sensor. In the present invention, the torque is indirectly measured by measuring the tensile force. The transmission shaft and the second tensile and compressive force sensor are at 90°. The bearing sleeve on the cross bar is in point contact with the second tensile and compressive force sensor and impacts the contact plate on the second tensile and compressive force sensor. The bearing eliminates the torque brought by the transmission shaft through rotation, so that the second tensile and compressive force sensor is only subjected to a single tensile force. Through the torque M = F * L, the torque generated by the operation of the unmanned aerial vehicle is calculated. Four first tensile and compressive force sensors are distributed in a matrix to jointly share the tensile force received.

Description

Technical Field

[0001] The present invention relates to the field of testing devices, and specifically to a high-reliability matrix multi-tensile sensor UAV heavy-load performance testing platform. Background Technique

[0002] Since 2022, the scale of the UAV market has been expanding year by year. The global UAV market has maintained rapid growth, and the industrial chain has been gradually improved, including fields such as UAV R & D, testing, production, sales, training, and maintenance. The application scenarios have gradually shifted from consumer UAVs to industrial UAVs, and the phenomenon of "low-altitude economy" has become increasingly obvious. In application fields such as agricultural plant protection, power line inspection, aerial mapping, police security, environmental monitoring, railway construction, and disaster relief, the market is in urgent need of heavy-load application UAVs. Solving the payload problem will become the key to its rapid development. After the UAV is produced, it needs to be tested. The UAV tensile and torsion load testing platform can test whether the UAV can meet the use standards.

[0003] In the current UAV tensile and torsion load testing platform, when the heavy-load motor runs, due to the large swing amplitude of the propeller blades up and down, the swaying force between the linear bearing and the stepped shaft is too large, and the stepped shaft is severely worn. The bearing for measuring torque is very easy to be damaged, and during repeated testing, the fluctuation range of the test data is very large, and the data consistency is very poor, which cannot well simulate the real flight state and poses a relatively large risk for market introduction. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a high-reliability matrix multi-tensile sensor UAV heavy-load performance testing platform to solve the technical problems mentioned in the above background technique.

[0005] To achieve the above object, the present invention provides the following technical solution: a high-reliability heavy-load performance test platform for a matrix multi-tensile force sensor unmanned aerial vehicle, including a test frame connecting plate, on the top of which a fixed seat is installed, and on the top of the fixed seat, four groups of the first tensile and compressive force sensors are arranged. The four groups of the first tensile and compressive force sensors are arranged in a matrix on the top of the fixed seat. On the top of the first tensile and compressive force sensor, a bearing seat is installed, and above the bearing seat, a fixing plate is arranged. On the top of the fixing plate, a transfer plate is installed, and on the top of the transfer plate, a motor is arranged. On the bottom of the test frame connecting plate, a fixed sleeve is installed, and inside the fixed sleeve, a transmission shaft is movably installed. On the outer wall of the transmission shaft, a rotor assembly is arranged, and the top of the transmission shaft is connected to the fixing plate. At the bottom of the transmission shaft, an installation rod is installed, and at the bottom of the installation rod, a transmission rod is fixed. The rotor assembly includes a rotating rod sleeved on the outer wall of the transmission shaft, and at one end of the rotating rod, a cross bar is movably installed. At the end of the cross bar, a first bearing is sleeved, and on the outer wall of the first bearing, a bearing sleeve is sleeved. At the end of the test frame connecting plate, two groups of the force-bearing seats are installed, and at the bottom of the force-bearing seat, a second tensile and compressive force sensor is movably installed.

[0006] By adopting the above technical solution, the torque is indirectly measured by measuring the tensile force. The transmission shaft and the second tensile and compressive force sensor are at 90°. The bearing sleeve on the cross bar is in point contact with the second tensile and compressive force sensor and impacts the contact plate on the second tensile and compressive force sensor. The bearing eliminates the torque brought by the transmission shaft through rotation, so that the second tensile and compressive force sensor is only subjected to a single tensile force. Through the torque M = F * L, the torque generated by the operation of the unmanned aerial vehicle is calculated. Four first tensile and compressive force sensors are arranged in a matrix to share the tensile force together. At the same time, the bearing seat can move up and down to reduce the high-frequency vibration of the load test and the yaw force of the propeller. The measurement accuracy is accurate to 0.1 Kg level. Two second bearings are used to fix the transmission shaft to reduce vibration. A linear bearing is used to fix the transmission shaft to transfer the vibration to the fixed seat, eliminating the interference of factors such as vibration on the test, and enabling the transmission shaft to axially slide and radially rotate freely within a small range, increasing the measurement accuracy and stability of the device. The rotating rod is sleeved on the outer wall of the installation rod, locked with two M10 screws, and fixed with a flat key to increase the structural stability, ensure the coaxiality between the bearing seat and the linear bearing sleeve and the fixed sleeve, ensure being on the same center line, increase the data accuracy, and prevent the influence of external interference.

[0007] The present invention is further arranged such that a fixed block is fixed on the top of the second tensile and compressive force sensor, and the top of the fixed block is attached to the bottom of the force-bearing seat. A screw rod is sleeved inside the fixed block, and the screw rod penetrates through the two fixed blocks and is movably connected to the force-bearing seat. The outer wall of the screw rod is provided with a positive and negative thread.

[0008] Preferably, it is convenient to adjust the distance between the two groups of second tension and compression sensors and the bearing sleeve, so as to achieve the purpose of clamping the bearing sleeve by the two groups of second tension and compression sensors.

[0009] The present invention is further configured such that a contact plate is installed on one side of the second tension and compression sensor, and the two contact plates are distributed on both sides of the bearing sleeve.

[0010] Preferably, the contact plate can reduce the contact area with the bearing sleeve, so as to ensure that the second tension and compression sensor is only subjected to a single tensile force.

[0011] The present invention is further configured such that a lead screw is fixed to the end of the cross bar, and a mounting hole is formed at one end of the rotating rod, and the mounting hole is in threaded connection with the lead screw.

[0012] Preferably, through the cooperation of the lead screw and the mounting hole, the installation of the cross bar can be realized, ensuring the fixation of the cross bar and the rotating rod.

[0013] The present invention is further configured such that a through hole is formed at the other end of the rotating rod, and limiting grooves are formed on both sides of the inner wall of the through hole. Vertical rods are fixed on both sides of the mounting rod, and the outer wall of the vertical rods is fitted with the inner wall of the limiting grooves.

[0014] Preferably, by providing the through hole, the rotating rod can be sleeved on the outer wall of the mounting rod, and the limiting groove and the vertical rod cooperate with each other, so that the rotating rod slides directionally on the outer wall of the mounting rod, facilitating the insertion of the M screw into the jack.

[0015] The present invention is further configured such that two jacks are formed on the outer wall of the mounting rod, and the rotating rod is connected to the mounting rod by bolts.

[0016] Preferably, the formed jacks facilitate the insertion of the M screw, and the rotating rod and the mounting rod are fixed by two M screws.

[0017] The present invention is further configured such that a linear bearing is installed at the end of the transmission rod. The bottom of the fixed sleeve is installed with a connecting plate by bolts, and a linear bearing sleeve is fixed on the top of the connecting plate, and the inner wall of the linear bearing sleeve is fitted with the outer wall of the linear bearing.

[0018] Preferably, the inner wall of the linear bearing sleeve is fitted with the outer wall of the linear bearing. The linear bearing fixes the bottom of the transmission shaft, transmits the vibration to the fixed seat, eliminates the interference of factors such as vibration on the test, and enables the transmission shaft to axially slide and radially rotate freely within a small range, ensuring the coaxiality between the bearing seat, the linear bearing sleeve and the fixed sleeve, ensuring being on the same center line, increasing the data accuracy, and preventing the influence of external interference.

[0019] The present invention is further configured such that a positioning block is fixed to one side of the second tensile and compressive force sensor, and a through hole is formed inside the positioning block. A fixing rod is fixed to one side of the force receiving seat, and the outer wall of the fixing rod is in fit with the inner wall of the through hole.

[0020] Preferably, through the cooperation of the formed positioning block and the fixing rod, the second tensile and compressive force sensor can be supported. When the screw rotates, under the action of the fixing rod, the second tensile and compressive force sensor can only move horizontally.

[0021] The present invention is further configured such that a handle is fixed to the end of the screw, and two sets of the second bearings are sleeved on the outer wall of the transmission shaft.

[0022] Preferably, the provided handle can facilitate personnel to rotate the screw, thereby adjusting the distance between the two sets of second tensile and compressive force sensors. The second bearings can fix the transmission shaft and reduce its vibration at the same time.

[0023] In summary, the present invention mainly has the following beneficial effects:

[0024] 1. The present invention is provided with a motor, a first tensile and compressive force sensor, a second tensile and compressive force sensor, a rotor assembly and a transmission shaft. By measuring the tensile force, the torque is indirectly measured. The transmission shaft and the second tensile and compressive force sensor are at 90°. The bearing sleeve on the cross bar is in point contact with the second tensile and compressive force sensor and impacts the contact plate on the second tensile and compressive force sensor. The bearing eliminates the torque brought by the transmission shaft through rotation, so that the second tensile and compressive force sensor is only subjected to a single tensile force. Through the torque M = F * L, the torque generated by the operation of the drone is calculated. Four first tensile and compressive force sensors are distributed in a matrix to jointly share the tensile force received. At the same time, the bearing seat can move up and down to reduce the high-frequency vibration of the load test and the yaw force of the propeller. The measurement accuracy is accurate to the 0.1 Kg level. Two second bearings are used to fix the transmission shaft to reduce vibration. A linear bearing is used to fix the transmission shaft to transfer the vibration to the fixed seat, eliminating the interference of factors such as vibration on the test, and enabling the transmission shaft to axially slide and radially rotate freely within a small range, increasing the measurement accuracy and stability of the device. The rotating rod is sleeved on the outer wall of the mounting rod, locked with two M10 screws, and fixed with a flat key to increase the structural stability, ensure the coaxiality between the bearing seat, the linear bearing sleeve and the fixed sleeve, ensure they are on the same center line, increase the data accuracy, and prevent external interference from affecting.

[0025] 2. The present invention is provided with a screw, a fixing block, a fixing rod and a positioning block, which facilitates adjusting the distance between the two sets of second tensile and compressive force sensors and the bearing sleeve, thereby achieving the purpose of clamping the bearing sleeve by the two sets of second tensile and compressive force sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1Schematic structural diagram of the present invention;

[0027] Figure 2 Schematic connection diagram of the rotor assembly and the transmission shaft of the present invention;

[0028] Figure 3 Schematic exploded view of the fixing sleeve and the connecting plate of the present invention;

[0029] Figure 4 Schematic exploded view of the rotor assembly of the present invention;

[0030] Figure 5 Schematic connection diagram of the force-bearing seat and the second tension and compression sensor of the present invention.

[0031] Explanation of reference numerals:

[0032] 1. Test frame connecting plate; 2. Fixed seat; 3. Bearing seat; 4. First tension and compression sensor; 5. Fixed plate; 51. Adapter plate; 6. Motor; 7. Fixing sleeve; 71. Connecting plate; 72. Linear bearing sleeve; 8. Rotor assembly; 81. Cross bar; 82. First bearing; 83. Bearing sleeve; 84. Rotating rod; 85. Mounting hole; 86. Through hole; 87. Limiting groove; 88. Lead screw; 89. Stopper; 9. Transmission shaft; 91. Second bearing; 92. Mounting rod; 93. Jack; 94. Vertical rod; 95. Transmission rod; 96. Linear bearing; 10. Second tension and compression sensor; 11. Force-bearing seat; 12. Fixed block; 13. Screw; 14. Handle; 15. Contact plate; 16. Fixed rod; 17. Threaded hole; 18. Positioning block; 19. Through hole. Detailed implementation manners

[0033] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. The embodiments described below by referring to the accompanying drawings are exemplary and are only used to explain the present invention and should not be construed as limiting the present invention.

[0034] Next, the embodiments of the present invention will be described according to the overall structure of the present invention.

[0035] Please refer to Figures 1-5, including a test frame connecting plate 1, a fixed seat 2 is installed on the top of the test frame connecting plate 1, and four groups of first tensile and pressure sensors 4 are arranged on the top of the fixed seat 2, and the four groups of first tensile and pressure sensors 4 are distributed in a matrix on the top of the fixed seat 2, and a bearing seat 3 is installed on the top of the first tensile and pressure sensors 4, and a fixed plate 5 is arranged above the bearing seat 3, an adapter plate 51 is installed on the top of the fixed plate 5, and a motor 6 is arranged on the top of the adapter plate 51, a fixed sleeve 7 is installed on the bottom of the test frame connecting plate 1, and a transmission shaft 9 is movably installed inside the fixed sleeve 7, a rotor assembly 8 is arranged on the outer wall of the transmission shaft 9, and the top of the transmission shaft 9 is connected to the fixed plate 5, and the bottom of the transmission shaft 9 A mounting rod 92 is installed, and a transmission rod 95 is fixed to the bottom of the mounting rod 92. The rotor assembly 8 includes a rotating rod 84 sleeved on the outer wall of the transmission shaft 9, and a cross bar 81 is movably installed on one end of the rotating rod 84. A stopper 89 is movably installed on the end of the cross bar 81. The set stopper 89 can limit the first bearing 82 sleeved on the outer wall of the cross bar 81, thereby avoiding the problem of the first bearing 82 being separated from the cross bar 81. The end of the cross bar 81 is sleeved with the first bearing 82, and the outer wall of the first bearing 82 is sleeved with a bearing sleeve 83. Two groups of force seats 11 are installed on the end of the test frame connecting plate 1, and a second tension and pressure sensor 10 is movably installed on the bottom of the force seat 11.

[0036] In the above embodiment, please refer to Figure 2 and Figure 5 A fixed block 12 is fixed on the top of the second tension and pressure sensor 10, and the top of the fixed block 12 is in contact with the bottom of the force seat 11. A screw 13 is sleeved inside the fixed block 12, and the screw 13 passes through the two groups of fixed blocks 12, and the screw 13 is movably connected to the force seat 11. The outer wall of the screw 13 is provided with positive and negative threads. When the screw 13 rotates, according to the screw principle, the screw 13 rotates to adjust the distance between the two groups of second tension and pressure sensors 10, so that the contact plate 15 on one side of the two groups of second tension and pressure sensors 10 contacts the bearing sleeve 83.

[0037] In the above embodiment, please refer to Figure 5 A contact plate 15 is installed on one side of the second tension and pressure sensor 10. Two groups of contact plates 15 are distributed on both sides of the bearing sleeve 83. The contact plate 15 can reduce the contact area with the bearing sleeve 83, thereby ensuring that the second tension and pressure sensor 10 is only subjected to a single tensile force.

[0038] In the above embodiment, please refer to Figure 4 A screw rod 88 is fixed to the end of the cross bar 81, and a mounting hole 85 is opened at one end of the rotating rod 84, and the mounting hole 85 is threadedly connected to the screw rod 88. The screw rod 88 cooperates with the mounting hole 85 to realize the installation of the cross bar 81 and ensure that the cross bar 81 and the rotating rod 84 are fixed.

[0039] In the above embodiments, specifically, please refer to Figure 4 , a through hole 86 is formed at the other end of the rotating rod 84, and limiting grooves 87 are formed on both sides of the inner wall of the through hole 86. Vertical rods 94 are fixed on both sides of the mounting rod 92, and the outer wall of the vertical rod 94 is attached to the inner wall of the limiting groove 87. By forming the through hole 86, the rotating rod 84 can be sleeved on the outer wall of the mounting rod 92, and the limiting groove 87 and the vertical rod 94 cooperate with each other, so that the rotating rod 84 slides directionally on the outer wall of the mounting rod 92, facilitating the insertion of the M10 screw into the jack 93.

[0040] In the above embodiments, specifically, please refer to Figure 4 , two groups of jacks 93 are formed on the outer wall of the mounting rod 92, and the rotating rod 84 is connected to the mounting rod 92 by bolts. The formed jacks facilitate the insertion of the M10 screw, and the rotating rod 84 and the mounting rod 92 are fixed by two M10 screws.

[0041] In the above embodiments, specifically, please refer to Figure 3 , a linear bearing 96 is installed at the end of the transmission rod 95. The bottom of the fixed sleeve 7 is installed with a connecting plate 71 by bolts, and a linear bearing sleeve 72 is fixed on the top of the connecting plate 71. The inner wall of the linear bearing sleeve 72 is attached to the outer wall of the linear bearing 96. The linear bearing 96 fixes the bottom of the transmission shaft 9, transmits the vibration to the fixed seat 2, eliminates the interference of factors such as vibration on the test, and enables the transmission shaft 9 to axially slide and radially rotate freely within a small range, ensuring the coaxiality between the bearing seat 3, the linear bearing sleeve 72, and the fixed sleeve 7, ensuring they are on the same center line, increasing the data accuracy, and preventing the influence of external interference.

[0042] In the above embodiments, specifically, please refer to Figure 5 , a positioning block 18 is fixed on one side of the second tensile and compressive force sensor 10, and a through hole 19 is formed inside the positioning block 18. A fixed rod 16 is fixed on one side of the force receiving seat 11, and the outer wall of the fixed rod 16 is attached to the inner wall of the through hole 19. By the cooperation of the formed positioning block 18 and the fixed rod 16, the second tensile and compressive force sensor 10 can be supported. When the screw 13 rotates, under the action of the fixed rod 16, the second tensile and compressive force sensor 10 can only move horizontally.

[0043] In the above embodiments, specifically, please refer to Figure 3 and Figure 4 , a handle 14 is fixed at the end of the screw 13, and two groups of second bearings 91 are sleeved on the outer wall of the transmission shaft 9. By providing the handle 14, it is convenient for personnel to rotate the screw 13, thereby adjusting the distance between the two groups of second tensile and compressive force sensors 10. The second bearings 91 can fix the transmission shaft 9 and reduce its vibration at the same time.

[0044] When the present invention is working specifically: When working, the motor 6 is started. The motor drives the adapter plate 51 to rotate when it works, thereby driving the transmission shaft 9 to rotate. The torque is indirectly measured by measuring the pulling force (known, M = F * L, the length of the force arm L = 0.250 m, the range of the tension and compression sensor is 500 Kg, and the maximum measurable torque is theoretically 1250 N.m). The transmission shaft 9 and the second tension and compression sensor 10 are at 90°. The bearing sleeve 83 sleeved on the cross bar 8 is in point contact with the second tension and compression sensor 10 (reducing the stress area, accurately determining the length of the force arm, and reducing the internal interference factors), and impacts the contact plate on the second tension and compression sensor 10. The first bearing 82 eliminates the torque brought by the transmission shaft 9 through rotation, so that the second tension and compression sensor 10 is only subjected to a single pulling force. Through the torque M = F * L, the torque generated by the operation of the drone is calculated. Four first tension and compression sensors 4 (range 500 Kg) are distributed in a matrix to share the pulling force together. At the same time, the bearing seat 3 can move up and down (due to the matrix distribution of the tension and compression sensors, the radial pulling force is excluded), reducing the high-frequency vibration of the load test and the yaw force of the propeller, and the measurement accuracy is accurate to the 0.1 Kg level. Two second bearings 91 are used to fix the transmission shaft 9 to reduce vibration. A linear bearing 96 is used to fix the bottom of the transmission shaft 9, and the vibration is transmitted to the fixed seat 2, excluding the interference of factors such as vibration on the test, and enabling the transmission shaft 9 to axially slide and radially rotate freely within a small range, increasing the measurement accuracy and stability of the device. The rotating rod 84 is sleeved on the outer wall of the mounting rod 92, locked with two M10 screws, and fixed with a flat key to increase the structural stability, ensure the coaxiality between the bearing seat 3, the linear bearing sleeve 72, and the fixed sleeve 7, ensure they are on the same center line, increase the data accuracy, and prevent external interference from affecting.

[0045] ​

Claims

1. Matrix multi-tensile sensor high-reliability UAV heavy-load performance test platform, including a test rack connection plate (1), characterized in that: A fixing seat (2) is installed on the top of the test rack connecting plate (1), and four groups of first tension and compression sensors (4) are arranged on the top of the fixing seat (2). The four groups of first tension and compression sensors (4) are distributed in a matrix on the top of the fixing seat (2). A bearing seat (3) is installed on the top of the first tension and compression sensor (4), and a fixing plate (5) is arranged above the bearing seat (3). A transfer plate (51) is installed on the top of the fixing plate (5), and a motor (6) is arranged on the top of the transfer plate (51). A fixing sleeve (7) is installed on the bottom of the test rack connecting plate (1), and a transmission shaft (9) is movably installed inside the fixing sleeve (7). A rotor assembly (8) is arranged on the outer wall of the transmission shaft (9), and the top of the transmission shaft (9) is connected to the fixing plate (5). An installation rod (92) is installed at the bottom of the transmission shaft (9), and a transmission rod (95) is fixed to the bottom of the installation rod (92). The rotor assembly (8) includes a rotating rod (84) sleeved on the outer wall of the transmission shaft (9), and a cross bar (81) is movably installed at one end of the rotating rod (84). A first bearing (82) is sleeved at the end of the cross bar (81), and a bearing sleeve (83) is sleeved on the outer wall of the first bearing (82). Two groups of force receiving seats (11) are installed at the end of the test rack connecting plate (1), and a second tension and compression sensor (10) is movably installed at the bottom of the force receiving seat (11).

2. The matrix multi-tensile sensor high-reliability UAV heavy-load performance test platform according to claim 1, characterized in that: A fixing block (12) is fixed to the top of the second tension and compression sensor (10), and the top of the fixing block (12) is in contact with the bottom of the force receiving seat (11). A screw rod (13) is sleeved inside the fixing block (12), and the screw rod (13) penetrates through the two fixing blocks (12), and the screw rod (13) is movably connected to the force receiving seat (11). A positive and negative thread is arranged on the outer wall of the screw rod (13).

3. The matrix multi-tensile sensor high-reliability UAV heavy-load performance test platform according to claim 1, characterized in that: A contact plate (15) is installed on one side of the second tension and compression sensor (10), and the two contact plates (15) are distributed on both sides of the bearing sleeve (83).

4. The high-reliability UAV heavy-load performance test platform with a matrix multi-tensile sensor according to claim 1, characterized in that: A lead screw (88) is fixed to the end of the cross bar (81), and a mounting hole (85) is opened at one end of the rotating rod (84), and the mounting hole (85) is threadedly connected to the lead screw (88).

5. The matrix multi-tensile sensor high-reliability UAV heavy-load performance test platform according to claim 1, characterized in that: A through hole (86) is opened at the other end of the rotating rod (84), and limiting grooves (87) are opened on both sides of the inner wall of the through hole (86). Vertical rods (94) are fixed to both sides of the installation rod (92), and the outer walls of the vertical rods (94) are in contact with the inner walls of the limiting grooves (87).

6. The matrix multi-tensile sensor high-reliability UAV heavy-load performance test platform according to claim 1, characterized in that: Two groups of jacks (93) are opened on the outer wall of the installation rod (92), and the rotating rod (84) is connected to the installation rod (92) through bolts.

7. The matrix multi-tensile sensor high-reliability UAV heavy-load performance test platform according to claim 1, characterized in that: A linear bearing (96) is installed at the end of the transmission rod (95). A connecting plate (71) is installed at the bottom of the fixing sleeve (7) through bolts, and a linear bearing sleeve (72) is fixed to the top of the connecting plate (71). The inner wall of the linear bearing sleeve (72) is in contact with the outer wall of the linear bearing (96).

8. The high-reliability UAV heavy-load performance test platform with a matrix multi-tensile sensor according to claim 2, characterized in that: A positioning block (18) is fixed to one side of the second tensile and compressive force sensor (10), and a through hole (19) is formed inside the positioning block (18). A fixing rod (16) is fixed to one side of the force-bearing seat (11), and the outer wall of the fixing rod (16) is in fit with the inner wall of the through hole (19).

9. The matrix multi-tensile sensor high-reliability UAV heavy-load performance test platform according to claim 2, wherein: A handle (14) is fixed to the end of the screw rod (13), and two groups of second bearings (91) are sleeved on the outer wall of the transmission shaft (9).

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