Transmission mechanism of flapping-wing air vehicle with wings capable of being unfolded, folded and flapped

Abstract

The invention discloses a transmission mechanism of a flapping-wing air vehicle with foldable and flapping wings, and belongs to the field of design and manufacturing of air vehicles. The folding and unfolding mechanism comprises a rack set, a motor, a front side folding and unfolding gear set, a hinge four-bar linkage set and a rear side flapping bevel gear set. The front side folding and unfolding spur gear set and the hinge four-bar linkage form a crank rocker mechanism, and the front side folding and unfolding spur gear set rotates around a horizontal shaft in the front-back direction to drive the hinge four-bar linkage to achieve folding and vertical flapping of the flapping wing in the unfolding direction; and the rear side flapping bevel gear set steers the rotation motion output by the motor by 90 degrees, so that the hinge four-bar linkage is driven to realize the transverse flapping of the wing. According to the invention, the same-frequency coupling motion of spanwise folding, vertical flapping and transverse flapping of the flapping wing is realized at the same time.

Description

Technical Field

[0001] The invention relates to the field of aircraft design and manufacturing, and in particular to a transmission mechanism for a flapping-wing aircraft with wings that can be extended, retracted and flapped. Background Art

[0002] In recent years, drone technology has gradually matured. In addition to large drones, micro-aircraft with typical characteristics of "low, slow and small" have also become one of the research hotspots. Small birds such as hummingbirds and sparrows that fly efficiently and flexibly are natural micro-"aircraft" in nature. Scientists study and imitate these creatures to design bionic flapping-wing micro-aircraft. Bionic flapping-wing aircraft can achieve complex movements such as hovering, inverted flight, and instantaneous acceleration by simulating the flapping of bird wings.

[0003] At present, bionic flapping-wing aircraft developed at home and abroad are mainly divided into two categories: one is designed to imitate large birds such as falcons and eagles. This type of bionic flapping-wing aircraft is larger in size (meter-level), generates thrust through vertical flapping of wings, and generates efficient lift through flapping and gliding, which is suitable for long-distance and long-duration flight missions; the other is designed to imitate micro-flying creatures such as hummingbirds and insects, which are smaller in size, and use the nearly horizontal reciprocating flapping of wings and the principle of unsteady aerodynamics to achieve highly maneuverable and complex flight movements. Compared with small-scale insect-like and hummingbird-like micro-flapping-wing aircraft, bird-like configuration and larger-scale flapping-wing aircraft have been developed and applied faster.

[0004] Although the scales of bird-like flapping-wing aircraft are obviously different, flapping-wing aircraft simulating birds of different magnitudes mostly adopt the same overall wing structure, that is, the wings cannot be bent. However, most bird wings can be folded during movement. A few flapping-wing aircraft with foldable wings also imitate creatures such as albatrosses. The wings can move and fold in a single vertical plane. Such birds and flapping-wing aircraft designed based on them are large in size, with a large aspect ratio and high flight efficiency, but they also have a limited aspect ratio and a large volume, which makes it difficult to meet the requirements of miniaturization and rapid maneuverability of aircraft. For example, the invention patent "A flapping-wing aircraft that can make flapping wings flap-twist at the same frequency" (CN202410565560.5) designs a flapping-twist drive device for flapping wings, which realizes the lateral twisting and flapping of the wings while flapping vertically, so as to change the angle of attack of the wings in real time and obtain greater lift. This transmission mechanism has the characteristics of simple structure and strong variable amplitude drive capability, but it cannot realize the folding of the wings.

[0005] From the perspective of micro flapping-wing aircraft design, in addition to large birds, small flying birds such as sparrows are also worth learning from. Unlike albatrosses, sparrows have extremely complex wing movements when moving. In addition to vertical flapping of the wings and wing folding and spreading, there is also lateral expansion and retraction. The flapping-wing motion mechanisms in the past did not have these functions. For example, the invention patent "Bionic Flapping-Wing Aircraft Transmission Device" (CN202210180800.0) designed a hinged four-bar transmission mechanism, designed the wing folding and vertical flapping in the longitudinal plane, but the wing does not have lateral flapping outside the plane. In order to enrich the mechanism design scheme of micro flapping-wing aircraft, we should also explore the design and implementation of flapping-wing transmission mechanisms with multiple motion couplings of spanwise folding, vertical flapping and lateral flapping. Summary of the invention

[0006] In order to enrich the mechanism design scheme of micro flapping-wing aircraft and realize flapping-wing multi-degree of freedom, the present invention takes sparrow wings as bionic objects and proposes a flapping-wing aircraft transmission mechanism with wings that can be expanded, retracted and flapped. The transmission mechanism is small in size and can simultaneously realize the spanwise folding, vertical flapping and lateral flapping of the wings of the flapping-wing aircraft through the combination of the output end of the gear system and the hinge four-bar linkage.

[0007] The invention discloses a transmission mechanism for a flapping-wing aircraft with expandable and retractable wings, comprising a frame assembly, a motor, a front folding and unfolding spur gear assembly, two hinged four-bar linkages, and a rear flapping bevel gear assembly. The motor is a hollow cup double-headed motor, which is placed front and back; the output shaft at one end of the front side of the motor is connected to the front folding and unfolding spur gear assembly, the front folding and unfolding spur gear assembly and the hinged four-bar linkage constitute a crank rocker mechanism, the front folding and unfolding gear assembly rotates around a horizontal axis along the front-to-back direction, and drives the hinged four-bar linkage to achieve spanwise folding and vertical flapping of the flapping wings; the output shaft at one end of the rear side of the motor is connected to the rear flapping bevel gear assembly, and the rear flapping bevel gear assembly, on the one hand, turns the motor output rotational motion by 90°, and then drives the hinged four-bar linkage to achieve lateral flapping of the wings.

[0008] The frame group includes a frame mainboard, two left and right combination leaves, and two left and right wing hinge seats. The front folding spur gear group constitutes a two-stage reduction gear group, including a front driving gear, a front double-layer transmission gear, and two left and right output gears with the same number of teeth; the hinge four-bar linkage group includes a connecting rod, an inner upper wing rod, an inner lower wing rod, and an outer wing rod. The two hinge four-bar linkage groups are symmetrically distributed with respect to the frame group. The rear fanning bevel gear group includes a rear driving gear, a rear double-layer transmission gear, a reversing gear, two 90° bevel gears, and two reversing connecting rods. The rear fanning bevel gear group realizes two-stage reduction and reversing. In order to ensure the stability of the reversing transmission of the rear fanning bevel gear group, the reversing gear has the same number of teeth as the two 90° bevel gears. The rear fanning bevel gear group pulls the wing hinge seat laterally through the reversing connecting rod, so that the wing hinge seat generates a lateral flapping around the hinge shaft, thereby realizing the lateral flapping of the flapping wing rod.

[0009] The present invention decouples the composite spatial motion of the sparrow's wings into three single plane motions, namely, spanwise folding, vertical flapping and lateral flapping, and realizes the composite spatial motion in the vertical, lateral and folding directions by connecting the front folding and spreading spur gear set, the hinged four-bar linkage set and the rear fanning bevel gear set with the frame set and driven by a single motor. The components and functions of the transmission mechanism are introduced as follows.

[0010] The rack mainboard in the rack group is provided with mounting holes for all gears in the front folding spur gear group and the rear fan bevel gear group. Each gear is fixed to the corresponding mounting hole of the rack mainboard through a pin shaft. The rack mainboard is also provided with mounting holes for hinge fixing. The wing hinge seats on the left and right sides are respectively fixed to the rack mainboard through the left and right sets of leaves. In addition, a semi-cylindrical motor mounting groove is also provided on the rack mainboard to fix the motor.

[0011] The wing hinges on the left and right sides of the frame group are installed symmetrically relative to the frame mainboard. The wing hinges are also provided with mounting holes for hinge fixation. Each wing hinge is provided with spherical hinges on both the front and rear sides. The spherical hinge on the front side is used to connect the inner upper wing rod of the hinge four-bar linkage, and the spherical hinge on the rear side cooperates with the reversing connecting rod of the rear fan bevel gear group to achieve vertical flapping and span folding of the wing. The rotational motion output by the rear fan bevel gear group is transmitted to the wing hinge through the spherical hinge on the rear side of the wing hinge seat, and the wing hinge seat generates rotation around the hinge shaft, and then pulls the hinge four-bar linkage through the spherical hinge on the front side to achieve the flapping of the hinge four-bar linkage and the wing.

[0012] The front driving gear in the front folding spur gear set is connected to the output end of the front side of the motor and meshes with the lower layer of the front double-layer transmission gear. The upper layer of the front double-layer transmission gear meshes with an output gear. At the same time, this output gear also meshes with another output gear with the same number of teeth. There are through holes on both output gears to cooperate with the connecting rod of the hinge four-bar linkage to achieve the connection between the front folding spur gear set and the hinge four-bar linkage. The motor drives the hinge four-bar linkage through the secondary gear reduction to achieve folding and flapping movements. The transmission ratio of the front folding spur gear set is about 15 to 25.

[0013] Two spherical hinges are provided on the connecting rod in the hinged four-bar linkage, and each spherical hinge is respectively connected to one end of the inner upper and lower wing rods, so as to realize the spatial movement of the inner upper and lower wing rods relative to the connecting rod. The other ends of the inner upper and lower wing rods are connected to the outer wing rods through plane hinges to realize the vertical flapping and span-wise folding of the wing. The middle section of the inner upper wing rod in the hinged four-bar linkage is provided with a joint that cooperates with the front spherical hinge on the wing hinge seat. When the bevel gear of the rear fanning bevel gear set rotates, the wing hinge seat is pulled, and the wing hinge seat generates a lateral rotation around the hinge shaft. The inner upper wing rod is pulled through this joint to realize the lateral flapping movement of the hinged four-bar linkage.

[0014] The rear drive gear in the rear fanning bevel gear set is connected to the rear output end of the motor and meshes with the lower layer of the rear double-layer transmission gear. The upper layer of the rear double-layer transmission gear meshes with the reversing gear. At the same time, the left and right sides of this reversing gear respectively cooperate with two 90° bevel gears with the same number of teeth to realize the rotation of the bevel gear in the vertical plane. The 90° bevel gears on the left and right sides are provided with spherical hinges to cooperate with one end of the reversing connecting rod. The other end of the reversing connecting rod cooperates with the spherical hinges on the rear side of the left and right wing hinge seats. The reversing motion of the 90° bevel gear is output to the wing hinge seat through the reversing connecting rod. The wing hinge seat generates lateral fanning around the hinge shaft. The wing hinge seat motion is transmitted to the inner upper wing rod through the joint in the middle section of the inner upper wing rod, realizing the lateral fanning motion of the hinge four-bar linkage. In order to ensure that the angular velocity of the output rotation of the front folding spur gear group and the rear fanning bevel gear group is consistent, so that the motion cycles of the hinged four-bar group's spanwise folding, vertical flapping, and lateral fanning are consistent, it is necessary to ensure that the transmission ratio of the rear fanning bevel gear group is the same as the transmission ratio of the front folding spur gear group.

[0015] The motor is a coreless double-headed motor, and the output ends on both sides are respectively connected to the front driving gear and the rear driving gear in the front folding and spreading spur gear set and the rear fanning bevel gear set. The motor output drives the two gear sets simultaneously. The output gear of the front folding and spreading spur gear set outputs the rotational motion to the connecting rod of the hinge four-bar linkage set, realizing the spanwise folding and vertical flapping motion of the hinge four-bar linkage set; the 90° bevel gear of the rear fanning bevel gear set outputs the rotational motion to the wing hinge seat through the reversing connecting rod, and the wing hinge seat generates lateral flapping around the hinge shaft, and the wing hinge seat transmits the motion to the inner upper wing rod, realizing the lateral flapping motion of the hinge four-bar linkage set. The rotational motion of the two gear sets is jointly output to the hinge four-bar linkage set, so that the wing rod realizes the sparrow-like composite motion including spanwise folding, vertical flapping, and lateral flapping. When the hinged four-bar linkage flaps backward, the wing lever is folded and the wing lever is flapped upward at the same time; when the hinged four-bar linkage flaps forward, the wing lever is unfolded and the wing lever is flapped downward at the same time.

[0016] The beneficial effects of the present invention are:

[0017] 1. Different from the single drive module of the existing bionic aircraft transmission mechanism, the present invention adopts a separate drive gear set to achieve sparrow-like composite spatial motion by coupling multiple plane motions. The transmission form is novel and reliable, taking into account both superior flight performance and lightweight structure;

[0018] 2. The present invention adopts a separate driving gear set, which can adjust the relative phase of the folding and flapping movements according to specific movement requirements, realize the diversification of movement forms, and can adapt to complex scenes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a three-dimensional schematic diagram of a transmission mechanism of a flapping-wing aircraft with expandable and retractable wings when the wing rod is folded;

[0020] Figure 2 It is a three-dimensional schematic diagram of the front side of a frame assembly of a transmission mechanism of a flapping-wing aircraft with wings that can be extended, retracted and flapped according to the present invention;

[0021] Figure 3 It is a three-dimensional schematic diagram of the rear side of a frame assembly of a transmission mechanism of a flapping-wing aircraft with wings that can be extended, retracted and flapped according to the present invention;

[0022] Figure 4 It is a front three-dimensional schematic diagram of a transmission mechanism frame assembly, a motor and a front folding and unfolding spur gear assembly of a flapping-wing aircraft with wings that can be unfolded, retracted and flapped according to the present invention;

[0023] Figure 5 It is a three-dimensional schematic diagram of the rear side of a transmission mechanism frame assembly, a motor and a front side folding and unfolding spur gear assembly of a flapping-wing aircraft with wings that can be unfolded, retracted and flapped according to the present invention;

[0024] Figure 6 The invention discloses a three-dimensional schematic diagram of a hinged four-linkage group of a transmission mechanism of a flapping-wing aircraft with expandable, retractable and flapping wings.

[0025] Figure 7 The invention is a three-dimensional schematic diagram of a transmission mechanism frame group, a motor and a rear-flapping bevel gear group of a flapping-wing aircraft with expandable and retractable wings.

[0026] Figure 8 It is a three-dimensional schematic diagram of a transmission mechanism of a flapping-wing aircraft with expandable and retractable wings when the wing rod is deployed according to the present invention;

[0027] Fig. 9 It is a three-dimensional schematic diagram of the rear side of a transmission mechanism of a flapping-wing aircraft with expandable and retractable wings when the wing rod is folded;

[0028] Fig.10 It is a three-dimensional schematic diagram of the rear side of a transmission mechanism of a flapping-wing aircraft with expandable and retractable wings when the wing rod is deployed according to the present invention;

[0029] In the figure:

[0030] 1-frame 2-motor 3-front folding spur gear set

[0031] 4-Hinged four-link group 5-Rear fan bevel gear group 11-Rack main board

[0032] 12- Hinge 13- Wing hinge seat 14- Front ball hinge

[0033] 15- rear ball hinge 16- motor mounting slot 31- front drive gear

[0034] 32-front double-layer transmission gear 33-output gear 41-connecting rod

[0035] 42-inner upper wing bar 43-inner lower wing bar 44-outer wing bar

[0036] 45-ball hinge 51-rear driving gear 52-rear double-layer transmission gear

[0037] 53-reversing gear 54-90° bevel gear 55-spherical hinge

[0038] 56-Reversing connecting rod DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the specific implementation method of the present invention is described in detail below with reference to the accompanying drawings.

[0040] Figure 1The invention provides a transmission mechanism for a flapping-wing aircraft with expandable and retractable wings, comprising a frame assembly 1, a motor 2, a front folding and unfolding spur gear assembly 3, a hinged four-bar linkage assembly 4, and a rear flapping bevel gear assembly 5.

[0041] like Figure 2 and Figure 3 As shown, the frame assembly 1 is composed of a frame main board 11, hinges 12, wing hinge seats 13, front spherical hinges 14, rear spherical hinges 15 and motor mounting slots 16. The motor 2 is a coreless double-head motor.

[0042] like Figure 5 and Figure 4 As shown, the front folding spur gear set 3 is composed of a front driving gear 31 , a front double-layer transmission gear 32 , and an output gear 33 .

[0043] like Figure 6 As shown, the hinge four-bar linkage 4 is composed of a connecting rod 41 , an inner upper wing rod 42 , an inner lower wing rod 43 , an outer wing rod 44 and a spherical hinge 45 .

[0044] like Figure 7 As shown, the rear fan bevel gear set 5 is composed of a rear driving gear 51, a rear double-layer transmission gear 52, a reversing gear 53, a 90° bevel gear 54, a spherical hinge 55 and a reversing connecting rod 56.

[0045] The following introduces the components of the transmission mechanism of a flapping-wing aircraft with wings that can be extended, retracted and flapped according to the present invention.

[0046] In order to more accurately define the components of the transmission mechanism, the following conventions are made: Figure 1 As shown, the side where the rear fan bevel gear set 5 is located is the rear side of the transmission mechanism, and the other side is the front side. Figure 2 and 3 As shown, the frame mainboard 11 in the frame group 1 is provided with mounting holes for all gears of the front folding spur gear set 3 and the rear fanning bevel gear set 5. In addition, the frame mainboard 11 is also provided with a semi-cylindrical motor mounting groove 16 to fix the motor 2.

[0047] like Figure 2 , Figure 3 As shown, the wing hinge seats 13 on the left and right sides of the frame group 1 are symmetrically installed on the frame main board 11 through two sets of leaves 12, and the front and rear sides of each wing hinge seat 13 are respectively provided with a front spherical hinge 14 and a rear spherical hinge 15. The front spherical hinge 14 is used to connect the inner upper wing rod 42 of the hinge four-bar linkage 4, and the rear spherical hinge 15 is used to cooperate with the reversing connecting rod 56 of the rear fan bevel gear set 5, and the three-dimensional spatial movement of the hinge four-bar linkage 4 is realized by the joint action of the front folding spur gear set 3 and the rear fan bevel gear set 5.

[0048] like Figure 4 , Figure 5 As shown, in the front folding spur gear set 3, the number of teeth of the lower layer of the front double-layer transmission gear 32 is greater than that of the upper layer, the front driving gear 31 is connected to the front output end of the motor 2, and meshes with the lower layer of the front double-layer transmission gear 32, the upper layer of the front double-layer transmission gear 32 is meshed with an output gear 33, and at the same time, this output gear 33 is also meshed with another output gear 33 with the same number of teeth. There are through holes on both output gears 33, which are used to cooperate with the connecting rod 41 of the hinge four-bar linkage 4 to achieve the connection between the front folding spur gear set 3 and the hinge four-bar linkage 4, and then drive the hinge four-bar linkage 4 to move through the motor 2 to achieve the lateral flapping of the wing. The transmission ratio of the front folding spur gear set 3 is about 15 to 25, and the transmission ratio can be 20.

[0049] like Figure 1 , Figure 6 As shown, the two hinged four-bar linkages 4 are symmetrically distributed relative to the frame group 1. Two spherical hinges 45 are provided on the connecting rod 41 in each hinged four-bar linkage 4, and the upper and lower spherical hinges 45 are respectively connected to one end of the inner upper wing rod 42 and the inner lower wing rod 43, so as to realize the spatial movement of the inner upper wing rod 42 and the inner lower wing rod 43 relative to the connecting rod 41. The other ends of the inner upper wing rod 42 and the inner lower wing rod 43 are connected to the outer wing rod 44 through a plane hinge.

[0050] like Figure 1 and Figure 2 , Figure 6 As shown, the inner upper wing rod 42 cooperates with the front spherical hinge 14 of the wing hinge seat 13 through the joint of the middle section, so that the wing hinge seat 13 generates a lateral rotation around the rotating axis of the hinge leaf 12 under the action of the rotation of the 90° bevel gear 54 in the rear flap bevel gear set 5. The joint of the inner upper wing rod 42 pulls the inner upper wing rod 42 to realize the up and down flapping movement of the hinge four-bar linkage set 4.

[0051] like Figure 3 , Figure 7 As shown, in the rear fan bevel gear set 5, the number of teeth of the lower layer of the rear double-layer transmission gear 52 is greater than that of the upper layer, the rear drive gear 51 is connected to the output end of the rear side of the motor 2, and meshes with the lower layer of the rear double-layer transmission gear 52, and the upper layer of the rear double-layer transmission gear 52 is meshed with the reversing gear 53. The left and right sides of this reversing gear 53 are respectively matched with two 90° bevel gears 54 with the same number of teeth to achieve 90° reversing movement. In order to ensure the stability of the reversing transmission, the reversing gear 53 has the same number of teeth as the two 90° bevel gears 54, and the gear ratio is 1:1. In order to ensure that the angular velocity of the output rotation of the front folding spur gear set 3 and the rear fan bevel gear set 5 is consistent, so that the movement cycle of the hinge four-link set 4 is consistent in the folding, vertical flapping, and lateral fanning, the transmission ratio of the front folding spur gear set 3 and the rear fan bevel gear set 5 is the same.

[0052] like Figure 7 As shown, in the rear flapping bevel gear set 5, the 90° bevel gears 54 on the left and right sides of the reversing gear 53 are both provided with spherical hinges 55, which are used to cooperate with one end of the reversing connecting rod 56. The other end of the reversing connecting rod 56 cooperates with the rear spherical hinges 15 of the left and right wing hinge seats 13, and the reversing motion of the 90° bevel gear 54 is output to the wing hinge seat 13 through the reversing connecting rod 56, and the wing hinge seat 13 generates a lateral flapping around the rotating axis of the hinge leaf 12, and then the motion of the wing hinge seat 13 is transmitted to the inner upper wing rod 42 through the joint in the middle section of the inner upper wing rod 42, so as to realize the lateral flapping motion of the hinge four-bar linkage set 4.

[0053] The motor 2 is a coreless double-head motor, and the output ends at the front and rear sides are respectively connected to the front driving gear 31 in the front folding spur gear set 3 and the rear driving gear 51 in the rear fan bevel gear set 5.

[0054] Finally, the transmission method of the transmission mechanism of a flapping-wing aircraft with wings that can be extended, retracted and flapped is introduced. Figure 8 A three-dimensional schematic diagram of a transmission mechanism of a flapping-wing aircraft with expandable and retractable wings when the wing rod is deployed is given. Fig. 9 It is a three-dimensional schematic diagram of the rear side of a transmission mechanism of a flapping-wing aircraft with expandable and retractable wings when the wing rod is folded; Fig.10 It is a three-dimensional schematic diagram of the transmission mechanism of a flapping-wing aircraft with expandable and flapping wings of the present invention, when the wing bar is unfolded. As shown in the above figure, the motor 2 drives the front folding and unfolding spur gear set 3 and the rear side flapping bevel gear set 5 to rotate at the same time. The two output gears 33 of the front folding and unfolding spur gear set 3 output the rotational motion to the connecting rod 41 of the hinge four-bar linkage 4, realizing the spanwise folding and vertical flapping motion of the hinge four-bar linkage 4; the two 90° bevel gears 54 of the rear side flapping bevel gear set 5 output the rotational motion to the wing hinge seat 13 through the reversing connecting rod 56, and the wing hinge seat 13 generates lateral flapping around the rotating shaft of the hinge leaf 12, and the wing hinge seat 13 transmits the motion to the inner upper wing bar 42, realizing the lateral flapping motion of the hinge four-bar linkage 4.

[0055] The rotational motion of the two gear sets is jointly output to the hinged four-bar linkage 4, so that when the hinged four-bar linkage 4 flaps backward, the inner upper and lower wing rods 42, 43 and the outer wing rod 44 are relatively folded, and the inner and outer wing rods are flapped upward at the same time; when the hinged four-bar linkage 4 flaps forward, the inner and outer wing rods are relatively unfolded, and the inner and outer wing rods are flapped downward at the same time, thereby realizing a composite three-dimensional spatial motion including spanwise folding, vertical flapping, and lateral flapping.

Claims

1. A transmission mechanism for a flapping-wing aircraft with wings that can be extended, retracted and flapped, characterized in that: The transmission mechanism comprises a frame group, a motor, a front folding gear group, two hinged four-bar groups, and a rear fanning bevel gear group; The motor is a hollow cup double-head motor, which is placed front and back; the output shaft at one end of the front side of the motor is connected to the front side folding spur gear set, and the front side folding spur gear set and the hinge four-bar linkage form a crank rocker mechanism. The front side folding gear set rotates around the horizontal axis along the front and back direction, driving the hinge four-bar linkage to achieve span-wise folding and vertical flapping of the flapping wings; the output shaft at one end of the rear side of the motor is connected to the rear side fanning bevel gear set, and the rear side fanning bevel gear set, on the one hand, turns the motor output rotational motion by 90 degrees, thereby driving the hinge four-bar linkage to achieve lateral flapping of the wings; In order to make the movement cycles of the hinged four-bar linkage group's spanwise folding, vertical flapping, and lateral fanning consistent, the angular velocities of the output rotations of the front folding spur gear group and the rear fanning bevel gear group are consistent, and the transmission ratio of the rear fanning bevel gear group is the same as that of the front folding spur gear group.

2. A transmission mechanism for a flapping-wing aircraft with expandable and retractable wings as claimed in claim 1, characterized in that: The rack assembly comprises a rack mainboard, two left and right combination leaves, and two left and right wing hinge seats; The front folding spur gear set constitutes a two-stage reduction gear set, including a front driving gear, a front double-layer transmission gear, and two left and right output gears with the same number of teeth; The hinged four-bar linkage group includes a connecting rod, an inner upper wing rod, an inner lower wing rod, and an outer wing rod, and the two hinged four-bar linkage groups are symmetrically distributed relative to the frame group. The rear fanning bevel gear set includes a rear driving gear, a rear double-layer transmission gear, a reversing gear, two 90° bevel gears, and two reversing connecting rods. The rear fanning bevel gear set realizes secondary deceleration and reversing. In order to ensure the stability of the reversing transmission of the rear fanning bevel gear set, the reversing gear has the same number of teeth as the two 90° bevel gears; the rear fanning bevel gear set pulls the wing hinge seat laterally through the reversing connecting rod, so that the wing hinge seat produces lateral flapping around the hinge shaft, thereby realizing the lateral flapping of the flapping wing rod.

3. A transmission mechanism for a flapping-wing aircraft with expandable and retractable wings as claimed in claims 1 and 2, characterized in that: The rack mainboard in the rack group is provided with mounting holes for all the gears in the front folding spur gear group and the rear fanning bevel gear group, and each gear is fixed to the corresponding mounting hole of the rack mainboard through a pin shaft. The rack mainboard is also provided with mounting holes for hinge fixing, and the wing hinge seats on the left and right sides are respectively fixed to the rack mainboard through the left and right sets of leaves; The frame mainboard is also provided with a semi-cylindrical motor mounting groove for fixing the motor; The left and right wing hinges in the frame group are symmetrically installed relative to the frame main board, and the wing hinges are also provided with mounting holes for fixing hinges. Ball hinges are provided on the front and rear sides of each wing hinge. The front ball hinge is used to connect the inner upper wing rod of the hinge four-bar linkage group, and the rear ball hinge cooperates with the reversing connecting rod of the rear fan bevel gear group to realize vertical flapping and span-wise folding of the wing; the rotational motion output by the rear fan bevel gear group is transmitted to the wing hinge seat through the ball hinge on the rear side of the wing hinge seat, and the wing hinge seat generates a rotation around the hinge shaft, and then pulls the hinge four-bar linkage group through the ball hinge on the front side to realize the flapping of the hinge four-bar linkage group and the wing.

4. A transmission mechanism for a flapping-wing aircraft with expandable and retractable wings as claimed in claims 1 and 2, characterized in that: The front driving gear in the front folding and unfolding spur gear group is connected to the output end of the front side of the motor and meshes with the lower layer of the front double-layer transmission gear. The upper layer of the front double-layer transmission gear meshes with an output gear. At the same time, this output gear also meshes with another output gear with the same number of teeth. Both output gears are provided with through holes for cooperating with the connecting rod of the hinge four-bar linkage group to realize the connection between the front folding and unfolding spur gear group and the hinge four-bar linkage group. The motor drives the hinge four-bar linkage group through the secondary gear reduction to realize the folding and flapping movement.

5. A transmission mechanism for a flapping-wing aircraft with expandable and retractable wings as claimed in claims 1 and 2, characterized in that: Two spherical hinges are provided on the connecting rod of the hinged four-bar group, and each spherical hinge is respectively connected to one end of the inner upper and lower wing rods, so as to realize the spatial movement of the inner upper and lower wing rods relative to the connecting rod, and the other ends of the inner upper and lower wing rods are connected to the outer wing rod through a plane hinge to realize the vertical flapping and span-wise folding and unfolding of the wing; the middle section of the inner upper wing rod in the hinged four-bar group is provided with a joint that cooperates with the front spherical hinge on the wing hinge seat, and when the bevel gear of the rear fanning bevel gear group rotates, the wing hinge seat is pulled, and the wing hinge seat generates a lateral rotation around the hinge shaft, and the inner upper wing rod is pulled through this joint to realize the lateral flapping movement of the hinged four-bar group.

6. A transmission mechanism for a flapping-wing aircraft with expandable and retractable wings as claimed in claims 1 and 2, characterized in that: The rear driving gear in the rear fanning bevel gear group is connected to the rear output end of the motor and meshes with the lower layer of the rear double-layer transmission gear, and the upper layer of the rear double-layer transmission gear meshes with the reversing gear. At the same time, the left and right sides of this reversing gear respectively cooperate with two 90° bevel gears with the same number of teeth to realize the rotation of the bevel gear in the vertical plane; the 90° bevel gears on the left and right sides are provided with spherical hinges for cooperating with one end of the reversing connecting rod, and the other end of the reversing connecting rod cooperates with the spherical hinge on the rear side of the left and right wing hinge seats, and the reversing motion of the 90° bevel gear is output to the wing hinge seat through the reversing connecting rod, and the wing hinge seat generates lateral fanning around the hinge shaft, and the wing hinge seat motion is transmitted to the inner upper wing rod through the joint in the middle section of the inner upper wing rod, thereby realizing the lateral fanning motion of the hinge four-bar linkage.

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