Unmanned aerial vehicle bionic folding foot stand

Abstract

The application discloses an unmanned aerial vehicle bionic folding foot support and relates to the technical field of unmanned aerial vehicle auxiliary equipment. The bionic joint module comprises at least two connecting rods, adjacent two connecting rods are connected through a rotating shaft to form a folding structure; an elastic driving module comprises a carbon fiber tendon and a rudder machine, the carbon fiber tendon is arranged along the connecting rod, and the rudder machine acts on the carbon fiber tendon under the control of a flight control system; a terrain adapting module is installed at the end of the bionic joint module and comprises a pressure sensor and a damper, and the attitude of the foot support is adjusted according to ground feedback.

Description

Technical Field

[0001] This invention relates to the field of unmanned aerial vehicle (UAV) auxiliary equipment technology. Background Technology

[0002] Most existing drone tripods use a fixed or simple folding structure, which has the following problems:

[0003] 1. The wind resistance is relatively large during flight. Even if it can be folded, the folded size is still large, which affects the flight speed.

[0004] 2. The servo output shaft is fixed to a connecting rod, forming a rigid connection, which results in poor landing gear flexibility. Furthermore, rigid landing can easily cause fuselage vibration and damage to precision loads.

[0005] 3. The angle cannot be adjusted, making it difficult to adapt to complex terrains such as slopes and sandy areas;

[0006] 4. The joints are very prone to damage after repeated take-off and landing operations, posing a great threat to the safety of the drone. Summary of the Invention

[0007] The purpose of this invention is to solve or alleviate the above problems by providing a biomimetic folding tripod for drones.

[0008] The biomimetic folding landing gear for unmanned aerial vehicles (UAVs) of the present invention includes: a biomimetic joint module comprising at least two connecting rods, with adjacent connecting rods connected by a rotating shaft to form a folding structure; an elastic drive module comprising carbon fiber tendons and servos, the carbon fiber tendons being arranged along the connecting rods, and the servos acting on the carbon fiber tendons under the control of a flight control system; and a terrain adaptation module installed at the end of the biomimetic joint module, comprising a pressure sensor and a damper, for adjusting the landing gear attitude based on ground feedback.

[0009] Optionally, the bionic joint module includes a first link, a second link, a third link, and a bottom support structure; the first link is fixed to the bottom of the UAV, and the first link, the second link, the third link, and the bottom support structure are rotatably connected in sequence, with a servo motor arranged at the connection point. The carbon fiber tendon is arranged along the second link and the third link, and the servo motor is used to drive the carbon fiber tendon to contract / extract, thereby causing the connection point to bend / extend.

[0010] Optionally, the elastic drive module further includes two pulleys arranged at the connection between the second link and the third link; the number of servos is three, wherein the first servo is arranged at the connection between the first link and the second link, the second servo is arranged at the connection between the second link and the third link, and the third servo is arranged at the connection between the third link and the bottom support structure; the number of carbon fiber tendons is two, one end of which is fixed to the first servo and the other end passes over a pulley and is fixed to the middle of the third link, and one end of which is fixed to the third servo and the other end passes over another pulley and is fixed to the middle of the second link; the second servo is used to drive the two pulleys to rotate in opposite directions.

[0011] Optionally, the bottom support structure is X-shaped.

[0012] Optionally, the connection between the third link and the bottom support structure is located at the center of the bottom support structure.

[0013] Optionally, the pressure sensor is used to detect the pressure from the ground when the drone lands.

[0014] Optionally, the oil pressure of the damper is regulated by a PID algorithm.

[0015] Optionally, the bottom of the bottom support structure is a non-slip rubber pad.

[0016] This invention mimics the kinematics of bird legs, using carbon fiber tendons to drive connecting rods, achieving a biomimetic drone landing gear design. This improves the landing gear's flexibility, and combined with sensors and dampers, enables the drone to achieve a "soft landing." Compared to traditional landing gear structures, this invention reduces landing impact by 50%, providing excellent protection for onboard equipment. To adapt to different surface conditions, the landing gear can adaptively adjust the degree of rod folding and the toe grip angle, accommodating slopes from -30° to 30°. These features make this invention particularly suitable for drones requiring rapid folding, impact resistance, and terrain adaptability.

[0017] In addition, the thickness of the drone landing gear of this invention is reduced by 80% when folded, which reduces the drone's flight drag; the use of lightweight connecting rods, small servos, and small-diameter carbon fiber tendons effectively controls the weight of the landing gear and extends the drone's flight time. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a biomimetic folding tripod for a drone according to an embodiment of this application;

[0019] Figure 2 This is a schematic diagram of the cross-sectional structure of the connecting rod according to an embodiment of this application;

[0020] Figure 3 This is a schematic diagram of the tripod control process according to an embodiment of this application;

[0021] Figure 4 This is a schematic diagram of a damper control method according to an embodiment of this application. Detailed Implementation

[0022] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention 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 the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0023] As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context indicates otherwise. It should be further understood that the terms “comprising,” “including,” indicate the presence of the stated feature, operation, element, component, item, kind, and / or group, but do not preclude the presence, occurrence, or addition of one or more other features, operations, elements, components, items, kinds, and / or groups. The terms “or” and “and / or” as used herein are to be interpreted inclusively, or mean any one or any combination thereof. Thus, “A, B, or C” or “A, B, and / or C” means any of the following: A; B; C; A and B; A and C; B and C; A, B, and C. Exceptions to this definition occur only when the combination of elements, functions, or operations is inherently mutually exclusive in some way.

[0024] To address the aforementioned problems in the prior art, this invention provides a biomimetic folding tripod for drones, which can reduce the volume after folding, has strong flexibility, facilitates angle adjustment, adapts to various complex terrains, and provides cushioning during landing to prevent damage to the drone.

[0025] The biomimetic folding tripod for drones in this application includes a biomimetic joint module, an elastic drive module, and a terrain adaptation module.

[0026] The bionic joint module includes at least two links, with adjacent links connected by a rotation axis to form a folding structure.

[0027] The elastic drive module includes carbon fiber tendons and servos. Under the control of the flight control system, the servos act on the carbon fiber tendons to provide the driving force for the deployment / folding of the landing gear. The carbon fiber tendons are artificial tendons made of carbon fiber material, typically consisting of bundles or bands of thousands of extremely fine carbon filaments. This structure forms a porous support, giving carbon fiber extremely high strength, even exceeding that of metals such as steel and iron, while remaining extremely lightweight, making it ideal for withstanding enormous tensile forces during movement. The carbon fiber tendons can store energy through elastic deformation. In this embodiment, carbon fiber tendons are applied to the folding landing gear of a UAV, providing cushioning and tensile / compressive resistance during landing, protecting joints (in this embodiment, joints refer to the connection points between adjacent links and between the link and the bottom support structure) and other physical components. The servos are preferably small-volume, high-power servos. The servos receive commands from the flight control system via a signal line connected to the system, enabling the free retraction of the landing gear. To better adapt to the outdoor flight environment, the servos are covered with dust covers.

[0028] In this embodiment, the carbon fiber tendon serves as the transmission medium, bypassing the joint rotation center, much like a human tendon bypassing a joint. Two adjacent links form a group, one being the proximal link and the other the distal link. The servo motor is fixed to the proximal link. When the servo motor rotates, it coils or releases the tendon, applying tension to the tendon to pull the distal link, thus producing flexion or extension movements. The two tendons work as "antagonistic muscles," one contracting and the other releasing, thereby achieving bidirectional joint movement.

[0029] The terrain adaptation module includes pressure sensors and dampers, which adjust the tripod attitude based on ground feedback.

[0030] Figure 1 A specific structure for a biomimetic folding tripod for drones is provided.

[0031] like Figure 1 As shown, the bionic joint module includes three links (first link 1, second link 2, and third link 3) and a bottom support structure 4. The first link 1 is fixed to the bottom 12 of the drone and is parallel to the bottom of the drone. One end of the second link 2 is mounted on the first link 1, for example, in the middle of the first link 1, and the second link 2 can rotate around the connection point. The other end of the second link 2 is rotatably connected to one end of the third link 3. The other end of the third link 3 is rotatably connected to the bottom support structure 4, preferably at the center of the bottom support structure 4.

[0032] The elastic drive module includes two carbon fiber tendons (first carbon fiber tendon 8 and second carbon fiber tendon 9) and three servos (first servo 5, second servo 6 and third servo 7).

[0033] The first servo motor 5 is installed at the connection between the first link 1 and the second link 2; the second servo motor 6 is installed at the connection between the second link 2 and the third link 3; and the third servo motor 7 is installed at the connection between the third link 3 and the bottom support structure 4. Two carbon fiber tendons are arranged along the second link 2 and the third link 3.

[0034] Pressure sensors and dampers are arranged on the bottom support structure. During the landing process of the UAV, the pressure sensors sense the pressure from the ground and transmit the pressure data to the flight control system. The flight control system dynamically adjusts the oil pressure of the damper according to the pressure data, so that the damper increases the damping coefficient at the moment the UAV lands.

[0035] As a preferred embodiment of this application, such as Figure 1 As shown, a pulley or pin is also provided at the connection between the first link 1 and the second link 2, preferably a pulley. Specifically, two pulleys (first pulley 10 and second pulley 11) are provided at the connection between the first link 1 and the second link 2.

[0036] One end of the first carbon fiber tendon 8 is fixed to the first servo motor 5, and the other end passes over the first pulley 10 and is fixed to the middle of the third link 3 (as shown at point B in the figure). One end of the second carbon fiber tendon 9 is fixed to the third servo motor 7, and the other end passes over the second pulley 11 and is fixed to the middle of the second link 2 (as shown at point A in the figure).

[0037] In one implementation, the output shaft of the second servo motor 6 is connected to the central shaft of the first pulley 10 and the central shaft of the first gear. The second gear meshes with the first gear, and the central shaft of the second gear is connected to the central shaft of the second pulley 11. When the output shaft of the second servo motor 6 rotates, it can drive the first pulley 10 and the second pulley 11 to rotate, and the two pulleys rotate in opposite directions.

[0038] by Figure 1 Taking the structure shown as an example, the first carbon fiber tendon 8 acts as an extensor. During the process of the first servo motor 5 tightening the first carbon fiber tendon 8, the first carbon fiber tendon 8 generates a pulling force to the upper left on point B of the third link 3, causing the third link 3 to rotate clockwise around the connecting axis C of the second link 2 and the third link 3, and the tripod opens. The second carbon fiber tendon 9 acts as an adductor. During the process of the third servo motor 7 tightening the second carbon fiber tendon 9, the second carbon fiber tendon 9 generates a pulling force to the lower left on point A of the second link 2, causing the third link 3 to rotate counterclockwise around the axis C, and the tripod retracts.

[0039] The first servo motor 5 and the third servo motor 7 are the main drive servos. Their main task is to contract and release the tendons, directly generating the tension that allows the joint to flex (bend) and extend (straighten). The first servo motor 5 and the third servo motor 7 usually operate in an "antagonistic" mode, one contracting and the other releasing. The second servo motor 6 is the tension servo motor. It does not directly participate in driving joint movement, but is responsible for adjusting the overall preload (i.e., basic tension) of the two tendons to prevent the two tendons from becoming loose.

[0040] This application provides a specific design scheme for a biomimetic folding tripod for a 2kg quadcopter drone.

[0041] Step 1: Design and Material Preparation.

[0042] 1. Linkage Design

[0043] The second link 2 and the third link 3 are made of aluminum alloy. The joint (the connection between the second link 2 and the third link 3) is designed with a pulley or a pin. The pulley is a better choice because it can reduce the friction and wear of the tendon. The diameter of the pulley should be as large as possible to reduce the bending stress on the tendon.

[0044] (1) Landing impact

[0045] The greatest load on a drone landing gear does not come from its static weight, but from the impact upon landing. A safety factor is typically used to cover this dynamic load. For drone landing gear, the safety factor is usually between 3 and 5; this application uses 4 as the calculation standard in its embodiment.

[0046] (2) Load distribution

[0047] Taking bipedal drones as an example, the maximum dynamic load that each leg needs to withstand. for:

[0048] =(Total mass) gravitational acceleration Safety factor) / Number of feet = (2kg) 9.8 m / s² 4) / 2 40N

[0049] For ease of calculation, this application uses 50 N (approximately 5 kgf) as the design load for a single leg, which is a crucial conservative estimate.

[0050] (3) Hazardous working conditions

[0051] For drone tripods, there are two most dangerous operating conditions: one is when the tripod is fully extended, in which case the impact force is entirely compressed along the axial direction of the connecting rod; the other is when the impact force is perpendicular to the bending direction of the connecting rod. In fact, the impact force perpendicular to the bending direction of the connecting rod is the more dangerous and more common operating condition.

[0052] (4) Calculation of key parameters of aluminum alloy connecting rod

[0053] This application embodiment calculates some key parameters of the aluminum alloy connecting rod from three dimensions: thickness, width, and length.

[0054] a. Bending resistance

[0055] Bending resistance is key to preventing connecting rods from bending and breaking. Simplifying the connecting rod as a cantilever beam, the root stress at the fixed end is the greatest.

[0056] Assuming the connecting rod is made of 6061-T6 aluminum alloy, its yield strength =275 MPa; Link length L=80mm (a reasonable bionic tripod length); Force F=50N acting perpendicularly on the end of the link.

[0057] Maximum bending stress of the connecting rod for:

[0058]

[0059] Where M is the maximum bending moment. c is the distance from the center point of the connecting rod's cross-section to the edge. For a rectangular cross-section, c is equal to half the thickness of the connecting rod, and for a circular cross-section, c is equal to the radius of the circular cross-section. I is the moment of inertia of the cross-section.

[0060] Assuming the connecting rod has a rectangular cross-section, such as Figure 2 As shown, the width of the rectangular section is w=10mm. The thickness t of the connecting rod is calculated below.

[0061]

[0062] Moment of inertia , The stress formula is:

[0063]

[0064] Increase working stress Material yield strength ,So,

[0065]

[0066]

[0067]

[0068]

[0069] Therefore, for a 6061 aluminum connecting rod that is 10mm wide and 80mm long, its thickness needs to be at least 3mm to withstand an end impact load of 50N.

[0070] In practical applications, the width and length of the connecting rod can be determined based on biomimetic design and UAV dimensions, with the length typically between 50mm and 120mm. Length is the most critical factor affecting stability and bending stress, and should be minimized during design. In rectangular cross-sections, width also has a linear impact on resistance to bending, due to... Increasing the width is more effective than increasing the thickness. The width of the rectangular section can be set between 8mm and 15mm to ensure good lateral stability and prevent twisting at the joint.

[0071] b. Compression and Bending Analysis

[0072] In addition to bending resistance, this application also considers link stability verification, i.e., analysis of compressive bending resistance. When the leg is extended and bearing weight, the leg mainly bears compressive stress, and there is a risk of buckling (compressive bending). For slender rods, their bending resistance must be checked.

[0073] Calculate the critical buckling load using Euler's formula. :

[0074]

[0075] Where K is the length coefficient, assuming that both ends of the link are hinged (rotatable) to other components, K=1; L is the length of the link, which is taken as 0.08 m here; E is the elastic modulus, which is 69 GPa for 6061 aluminum; For the minimum moment of inertia, for the aforementioned 10mm 3mm rectangular bar:

[0076]

[0077] Based on the above parameters, the following can be calculated: .

[0078] Since 266,000 N is much greater than the design load of 50 N, it indicates that the connecting rod in the embodiment of this application is very safe in terms of resistance to compressive bending.

[0079] Taking into account bending strength, weight, and manufacturability, the final connecting rod parameters are shown in Table 1.

[0080] Table 1. Linkage Parameters

[0081]

[0082] Based on the above calculations and analysis, for a drone with a total weight of 2kg, a safe and reasonable dimension for the aluminum alloy connecting rod of its bionic tripod is: 80mm in length. 10mm wide Thickness 3mm.

[0083] 2. Servo selection and mounting

[0084] The servo motor in this embodiment is a small servo motor. During the design process, it is necessary to calculate parameters such as the servo motor's torque, speed, size and weight, type, and voltage.

[0085] a. Torque

[0086] use Figure 1 For the structure shown, the torque is approximately equal to the required pulling force multiplied by the pulley radius.

[0087] Design and fabricate a servo bracket and securely mount it to the base link (i.e., the first link).

[0088] The total mass of the drone is Q = 2kg (equivalent to a large racing drone or a small aerial photography drone), the number of tripods is N = 2 (imitating bird feet, two independent feet), and the safety factor is 2.5.

[0089] Single-leg load This means that each tripod needs to be able to stably support approximately 2.5 kg of force.

[0090] In the worst-case scenario (when the leg is about to straighten), the arm of gravity... =30mm=0.03m.

[0091] pulley radius A radius of 5mm is used. The smaller the pulley radius, the greater the tension effect of the tendon, and the less torque is required from the servo motor.

[0092] The rudder radius r is set to 10mm.

[0093] Based on the above data, the tensile force F required for the carbon fiber tendon can be calculated as follows:

[0094]

[0095] The carbon fiber tendon needs to provide 150 Newtons of tensile force, which is about 15 kilograms of force, more than enough strength.

[0096] Servo torque .

[0097] Therefore, in this embodiment, a servo motor with a torque of at least 1.5 Nm (approximately equal to 15 kg·cm) is selected.

[0098] The effects of various drone parameters on torque are as follows: the heavier the drone, the greater the required torque; gravity arm The longer the leg (i.e., the wider the leg design), the greater the torque required; the larger the pulley radius, the smaller the torque required. The pulley radius is one of the key design points, but the pulley cannot be too large, otherwise it will affect the stretching and contraction of the carbon fiber tendon; the smaller the servo disk radius r, the smaller the torque required, but the servo disk radius cannot be too small, otherwise it will lead to higher requirements for servo rotation accuracy and smaller extension and retraction stroke.

[0099] During the design process, the servo torque can be calculated using the above method based on the specific parameters of the UAV. Generally, for small and medium-sized UAVs, small servos with a torque of 2.0-3.0 Nm (20-30 kg.cm) or higher can be selected, which provides sufficient margin for uncertainty and safety.

[0100] b. Speed

[0101] The tripod's extension and retraction speed doesn't need to be very high; typically, completing the action within 0.5 seconds is sufficient. Servo motors with excessively high speeds are usually more expensive and have lower torque. Therefore, a speed of 0.15-0.25 sec / 60 is recommended. A servo motor will suffice.

[0102] c. Dimensions and weight

[0103] Tripods suitable for small drones, with dimensions controllable to 40mm. 20mm Within 40mm, weighing around 50g.

[0104] d. Servo and gear types

[0105] This application embodiment selects a digital servo motor, which has higher holding torque, faster response speed and higher position control accuracy, and is especially suitable for application scenarios that need to be "locked" at a certain angle;

[0106] The embodiments of this application use metal gears, which can provide higher reliability under landing impact and high load scenarios.

[0107] e. Voltage

[0108] Common servo motors operate at 6V or 7.4V. It is required that the UAV's electronic speed controller can provide a stable voltage and sufficient current, as the operating current of a single servo motor may exceed 500mA.

[0109] In summary, the servo parameters selected in the embodiments of this application are shown in Table 2. The servo motors are preferably industrial-grade or robotic servo motors with higher reliability.

[0110] Table 2 Servo Parameters

[0111]

[0112] 3. Tendon selection

[0113] In this embodiment, a high-strength plastic-coated carbon fiber rope is selected as the carbon fiber tendon. The plastic-coated carbon fiber rope has high strength, light weight, and is not easily stretched, making it suitable as a "tendon" that needs to be bent. Based on the required tensile force, this embodiment selects a high-quality carbon fiber rope with a diameter of 2mm.

[0114] 4. Preparation of fasteners

[0115] The fasteners are used to securely fix both ends of the tendon to the rudder and the distal connecting rod. In this embodiment, the fasteners are miniature cable clamps and locking screws.

[0116] Step 2: Mechanical Assembly

[0117] 1. Install the joint shaft

[0118] Two aluminum alloy connecting rods are connected by a pin or bearing, allowing the two aluminum alloy connecting rods to rotate freely. The pin or bearing serves as the rotation center of the joint.

[0119] 2. Install pulleys

[0120] An idler wheel, serving as a guide, is installed at the center of joint rotation. This idler wheel, also known as the first pulley, ensures smooth rotation between the first pulley and the connecting rod. Another idler wheel, serving as a guide, is installed on the third connecting rod near the center of joint rotation. This second idler wheel is the second pulley. In this embodiment, a pulley with a low coefficient of friction, such as an aluminum wheel with ball bearings, is selected. The ratio of the pulley diameter (D) to the tendon diameter (d) (D / d) should be as large as possible. A ratio that is too small will drastically increase the bending fatigue of the tendon, leading to the breakage of its internal fibers. In this embodiment, a pulley with a diameter of 23 mm is selected.

[0121] 3. Fixed servo motor

[0122] The servo motor is fixed to the base linkage via a bracket, with the servo motor's output shaft facing the joint direction.

[0123] 4. Arrange tendon pathways

[0124] The second carbon fiber tendon 9 acts as a flexor muscle, with one end fixed to a hole in the servo disk of the third servo 7, and the other end passing around the outside of the second pulley 11 and fixed at point A in the middle of the second connecting rod 2.

[0125] It should be noted that, in this embodiment of the application, the pulley is oriented in the bending direction of the connecting rod ( Figure 1 The side indicated by the middle arrow is the inner side, and the direction opposite to the bending direction of the connecting rod is the outer side. Figure 1 For example, the outer side of the pulley is the left side, and the inner side of the pulley is the right side.

[0126] The first carbon fiber tendon 8 acts as an extensor muscle, with one end fixed at point B in the middle of the third link 3, usually symmetrical to point A. It then goes upward around the outside of the first pulley 10 at the joint and finally connects upward to a hole on the servo disk of the first servo 5.

[0127] It should be noted that the paths of the two tendons must be symmetrical about the joint center and their lengths must be precisely matched. Accordingly, the distance from point A to joint C should be equal to the distance from point B to joint C.

[0128] Step 3: Tendon Tensioning and Fixation

[0129] 1. Initial fixation:

[0130] Fix one end of each of the two tendons to the corresponding connecting rod.

[0131] 2. Connect the steering wheel

[0132] After passing the other ends of the two tendons around the corresponding pulleys, tighten them slightly and temporarily fix them to the corresponding servo disc.

[0133] 3. Adjust the tension

[0134] Manually adjust the angle between the second and third links to 120 degrees, and fix the joint in this position or hold it in place with a clamp. Adjust the fixed position of the two tendons on the servo head so that they are both slightly taut, and the servo is also in the 90-degree neutral position, i.e., the "zero position". When a signal greater than 90 degrees is sent to the servo, the servo will tighten the extensor tendons and relax the adductor tendons, and the tripod will open from the 120-degree position; when a signal less than 90 degrees is sent to the servo, the servo will tighten the adductor tendons and relax the extensor tendons, and the tripod will retract from the 120-degree position.

[0135] 4. Final tightening

[0136] Use cable clamps or locking screws to secure the tendon firmly to the rudder, ensuring that the tendon will not slip under maximum tension.

[0137] Step 4: Integration with the control system

[0138] 1. Servo control

[0139] Write control code using Arduino, STM32, etc.

[0140] 2. Antagonistic control mode:

[0141] Bending mode: The servo rotates in the direction of "winding up the second carbon fiber tendon" while releasing an equal amount of the first carbon fiber tendon.

[0142] Extension mode: The servo rotates in the direction of "winding up the first carbon fiber tendon" while releasing an equal amount of the second carbon fiber tendon.

[0143] It is important to note that you should avoid simultaneously and forcefully coiling two tendons. Doing so can cause the servo to stall, tendon overload and rupture, or structural damage. The procedure should ensure that while one tendon is coiling, the other tendon is released in equal amounts.

[0144] Step 5: Design and installation of the toe section

[0145] The toe portion of the biomimetic folding landing gear for drones in this embodiment refers to the bottom support structure. Unlike traditional bottom support structures, the toe portion in this embodiment is an active shock absorption system that integrates a pressure sensor (located at the bottom of the bottom support structure) and a damper (preferably a magnetorheological fluid damper) into the bottom support structure. This enables real-time adjustment based on impact force, greatly improving the landing stability and adaptability of the drone.

[0146] The pressure sensor is directly mounted on the bearing plate at the bottom of the toes (X-shaped bottom support structure), where it contacts the ground. The sensor's pressure-sensing surface faces downwards, allowing it to directly sense all or most of the impact force. This embodiment selects a miniature thin-film pressure sensor or a FlexiForce thin-film force sensor. These two sensors are very thin, can conform to the surface of the foot, and have a range of 100N, capable of handling a maximum dynamic load of 50N. The sensor output signal is preferably an analog voltage output or an I2C / SPI digital output for easy reading by the microcontroller. The X-shaped bottom support structure is made of aluminum alloy. A flat mounting groove is milled into the bottom surface of the X-shaped bottom support structure, and the thin-film sensor is fixed within it with a small amount of silicone rubber. A wear-resistant and hard foot pad is then placed over the surface of the thin-film sensor. This embodiment uses a carbon fiber plate or Teflon plate as the foot pad to protect the pressure sensor and ensure effective force transmission. Replaceable anti-slip rubber pads are placed at other points of contact between the toes and the ground to improve the stability of the toes' grip.

[0147] The pressure sensor is connected to the flight controller's ADC (analog-to-digital converter) pin or I2C / SPI interface via a signal conditioning circuit.

[0148] The damper is the core actuator of the active damping system. Traditional mechanical dampers cannot be adjusted in real time; therefore, this embodiment selects a magnetorheological fluid damper. The magnetorheological fluid damper is filled with magnetorheological fluid, which can change from a free-flowing liquid to a semi-solid within milliseconds under the action of a magnetic field, thereby changing the damping force. During use, the damping force can be precisely controlled by changing the magnitude of the input current. In this embodiment, the magnetorheological fluid damper is installed at the joint between the third link and the bottom support structure. Specifically, two universal ball bearing seats are designed; one universal ball bearing seat connects one end of the damper to the third link, and the other universal ball bearing seat connects the other end of the damper to the X-shaped bottom support structure. This structure can prevent the damper from jamming or being damaged by lateral forces, ensuring that it only bears pure tension and compression.

[0149] One end of the magnetorheological fluid damper is connected to the third link, close to the body, and the other end is connected to the bottom support structure, i.e., the toe area. The magnetorheological fluid damper and the second carbon fiber tendon work in parallel. The tendon provides active contraction and extension driving force, while the damper provides passive, adjustable buffering resistance.

[0150] The flight controller drives the coil of the magnetorheological fluid damper through a power drive circuit (H-bridge or constant current source). Specifically, under the control of the flight controller, the power drive circuit provides a drive current of 1-2A to the magnetorheological fluid damper.

[0151] When the drone's main flight controller I / O and computing power have sufficient margin, the flight controller in this embodiment can be the drone's main flight controller, such as Pixhawk, Arduino, STM32, etc. Alternatively, a separate MCU can be used to implement landing control, such as ESP32 or STM32F103. The task of this MCU is to continuously read sensor data, run control algorithms, and output PWM or DAC signals to the corresponding drive circuits.

[0152] like Figure 3 As shown, the control of the landing gear during the drone landing process includes several aspects: perception, processing and decision-making, control, and execution.

[0153] (1) Perception

[0154] The pressure sensor measures the impact force in real time when it comes into contact with the ground.

[0155] (2) Processing and Decision Making

[0156] The flight controller reads data from the pressure sensor to determine the magnitude and trend of the impact force. Based on a preset PID algorithm or a lookup table method, the flight controller obtains the ideal damping value that the damper needs to provide.

[0157] (3) Control

[0158] The flight controller sends corresponding control signals to the magnetorheological fluid damper through the power drive circuit based on the ideal damping value.

[0159] (4) Execution

[0160] The damper adjusts its damping coefficient based on control signals received from the flight controller, making it "harder" or "softer" to absorb impact energy. It actively adjusts the angle and speed of joint bending between the third link and the bottom support structure, achieving a smooth, rebound-free landing. The inertial measurement unit (IMU) provides the UAV's attitude angles, while lidar or ultrasonic sensors measure downward distances. By comparing values ​​from multiple measurement points, such as the front, rear, left, and right of the fuselage, the relative tilt of the ground beneath the UAV can be calculated. The flight controller fuses the IMU data (flight attitude) with the ground sensor data (relative ground tilt) to calculate the absolute tilt angle of the ground in the world coordinate system. The ankle joint damper's "hardness" is dynamically adjusted based on the real-time impact force (F) and its rate of change (dF / dt). By controlling the speed and ease of joint bending, the damper influences the final equilibrium angle, achieving all-terrain adaptive cushioning.

[0161] like Figure 4 As shown, after the system is powered on and initialized, the flight controller's control method for the damper (hereinafter referred to as the damping control method) includes the following six steps.

[0162] Step S1: Read the pressure value F output by the pressure sensor in real time.

[0163] Step S2: Calculate the rate of change of the impact force from the ground, dF / dt, based on the collected pressure value F.

[0164] Step S3: Determine whether the pressure value F is greater than the preset quiet threshold.

[0165] Step S4: When the pressure value F is greater than the quiet threshold, determine the landing stage and calculate the impact intensity based on the impact force F and the impact force change rate dF / dt.

[0166] A complete intelligent landing process can typically be divided into four stages, as shown in Table 3. The judgment of each stage is mainly based on the pressure sensor reading (F) and its rate of change (dF / dt), and in some cases, it is also necessary to combine the altitude sensor and time information. The core significance of judging the landing stage is to enable the control system to understand the current physical process and thus take the most appropriate and timely control strategy. This is the key to upgrading from reactive control to predictive / situational control.

[0167] Table 3. Criteria for Judging Each Stage of the Landing Process

[0168]

[0169] 1. Phase 0, Pre-landing / Preparation Phase:

[0170] Basis: The drone entered the landing procedure and its altitude continued to decrease. At this time, the landing gear had been deployed but had not yet touched the ground, and the pressure sensor reading was zero or a very low noise value (i.e., F < quiet threshold).

[0171] During this phase, the flight controller can preset the damper to an initial state (e.g., medium damping) to prepare for the upcoming impact.

[0172] 2. Phase 1, Initial Contact / Compression Phase:

[0173] Trigger: When F > quiet threshold (e.g., 5N), it marks the first time the foot is confirmed as having made a valid ground contact.

[0174] Key characteristic: dF / dt > 0. A positive derivative indicates that the impact force is increasing and the mechanism and damper are being compressed.

[0175] This is the stage where impact energy begins to be injected into the system. The control system needs to start working immediately, determining how to resist or comply with this compression process based on the real-time values ​​of F and dF / dt.

[0176] 3. Stage 2, Peak Impact / Energy Dissipation Stage:

[0177] Judgment criteria: This is an instantaneous state, and the criterion is the change in the sign of dF / dt. When dF / dt decreases from a positive value to zero, it means that the impact force has reached its instantaneous maximum value. Subsequently, dF / dt turns negative.

[0178] At this point, the tripod is compressed to its lowest point, the elastic potential energy stored in the springs (tendons and structures) reaches its maximum, and the downward kinetic energy of the drone has been basically absorbed.

[0179] This stage marks a watershed moment in control strategies. Before this point, the goal is to suppress the impact; after this point, the goal is to suppress the rebound.

[0180] 4. Stage 3, Springback Stabilization / Static Load Stage:

[0181] Judgment basis: dF / dt 0 (fluctuating within a very small dead zone near zero), and the value of F is stable near the static load value (body weight / number of feet).

[0182] During this phase, the tripod, under the action of damping, smoothly rebounds to a static equilibrium position, all oscillations cease, and the drone lands steadily on the ground. This phase marks the end of the active buffering process. The damper can then return to a low-energy holding state or adjust to a new mode based on subsequent commands (such as walking).

[0183] The judgment results at each stage directly determine the control law and parameters for damping adjustment. Table 4 shows a typical application of judging each stage.

[0184] Table 4 Damping Adjustment Strategies at Each Stage

[0185]

[0186] Step S5: Determine the ideal damping value that the damper needs to provide based on the impact intensity and the rate of change of the pressure value.

[0187] Step S6: Convert the ideal damping value into a control signal and send the control signal to the drive circuit of the damper so that the damper outputs the corresponding damping value under the drive of the drive circuit.

[0188] Step S6 first determines the required current I based on the ideal damping value, then generates a PWM signal based on the current I, and outputs the PWM signal to the drive circuit so that the drive circuit converts the PWM signal into a current signal for driving the damper.

[0189] Before executing the above method, the damping value of the damper can be set to a medium value in advance. In this embodiment, it is set to 5N to cope with the expected impact.

[0190] The pressure sensor collects pressure data from the ground in real time. It's important to note that "ground" here refers to the surface in contact with the bottom of the drone's landing gear. When the sensor reading F exceeds a preset quiet threshold, it's considered the start of ground contact, and the control loop immediately activates. The control loop adjusts the damping value in two modes: incremental and decremental. When both F and dF / dt are very large, it indicates a severe impact. In this case, the incremental adjustment mode should be entered, significantly increasing the current to instantly stiffen the damper and quickly absorb the peak force. When F has experienced the peak impact and begins to decrease, and dF / dt becomes negative, the decremental adjustment mode should be entered, reducing the current and lowering the damping to allow the landing gear to gently rebound and straighten, preparing for ground contact.

[0191] In one implementation, steps S4 to S6 can determine the current I using a lookup table. Based on the damper's performance parameters, a table corresponding to (F, dF / dt) and current I is established in advance. The required current I can be quickly obtained by looking up the table using the current F value and the current dF / dt value.

[0192] In another implementation, step S5 calculates the ideal damping value that the damper needs to provide through the PID control algorithm. The PID control algorithm can calculate the accurate ideal damping value based on the values ​​of F and dF / dt, making the control of the damper more precise and providing the most suitable buffer force for the UAV landing process.

[0193] The biomimetic folding landing gear of this application embodiment enables the drone to sense the strength of the impact the moment it touches the ground, just like a bird, and instantly "tighten" or "relax" its ankles to achieve truly intelligent adaptive landing.

[0194] The MCU embedded damping control module in this application embodiment includes a data acquisition unit, an impact force calculation unit, a judgment unit, an impact strength calculation unit, a damping calculation unit, and a control unit. These five units are used to control the damper.

[0195] The data acquisition unit is suitable for real-time reading of the pressure value F output by the pressure sensor;

[0196] The impact force calculation unit is suitable for calculating the rate of change of impact force from the ground, dF / dt, based on the collected pressure value F.

[0197] The judgment unit is adapted to determine whether the pressure value F is greater than the quiet threshold.

[0198] The impact intensity calculation unit is adapted to determine the landing phase and calculate the impact intensity when the pressure value F is greater than the quiet threshold.

[0199] The damping calculation unit is adapted to determine the ideal damping value that the damper needs to provide based on the rate of change of the impact intensity and the pressure value.

[0200] The control unit is adapted to convert the ideal damping value into a control signal and send the control signal to the drive circuit of the damper, so that the damper outputs a corresponding damping value under the drive of the drive circuit.

[0201] Converting the ideal damping value into a control signal includes:

[0202] The required current is determined based on the ideal damping value;

[0203] It is adapted to output a PWM signal to the drive circuit according to the current I, so that the drive circuit converts the PWM signal into a current signal for driving the damper.

[0204] The damping control module described above is capable of performing each step of the damping control method described above.

[0205] This application utilizes biomimetic principles, applying the energy storage mechanism of bird leg tendons to the drone's landing gear: artificial biomimetic tendons are used in mechanical structural connections. The carbon fiber tendon-driven aluminum alloy connecting rod joints achieve high-performance, lightweight, high-strength, and compliant biomimetic motion effects. The tendon's flexibility absorbs some impact and vibration, protecting not only the servo gears but also closely resembling the working mechanism of biological joints, allowing for a degree of passive compliance. Furthermore, this application also incorporates an active shock absorption system, using sensor-based closed-loop control of the buffering force. These features enable the drone to adapt to landings on various terrains, such as flat surfaces, slopes, and uneven surfaces.

[0206] As a preferred embodiment of this application, the aforementioned biomimetic folding tripod of the drone is embedded with RFID electronic tags, which can be identified via smart mobile terminals (such as NFC-enabled mobile phones or matching readers). For example, in scenarios where multiple drones operate simultaneously, drones can be quickly identified and located via mobile phones, enabling automatic identification and management of large numbers of drones. Taking the logistics industry as an example, during last-mile delivery, automatic docking and positioning between drones and express delivery lockers can be achieved via mobile phones. Furthermore, the RFID electronic tags can store corresponding drone files, including manufacturing dates, detailed parameters, maintenance records, and other information, greatly facilitating drone management.

Claims

1. A biomimetic folding tripod for unmanned aerial vehicles, characterized in that, include: A biomimetic joint module includes at least two connecting rods, with adjacent connecting rods connected by a rotation axis to form a folding structure; The elastic drive module includes a carbon fiber tendon and a servo motor, wherein the carbon fiber tendon is arranged along the connecting rod, and the servo motor acts on the carbon fiber tendon under the control of the flight control system. A terrain adaptation module, installed at the end of the bionic joint module, includes a pressure sensor and a damper, which adjusts the tripod posture based on ground feedback.

2. The biomimetic folding tripod for drones as described in claim 1, characterized in that, The bionic joint module includes a first link, a second link, a third link, and a bottom support structure; The first link is fixed to the bottom of the drone. The first link, the second link, the third link and the bottom support structure are rotatably connected in sequence, and a servo motor is arranged at the connection. The carbon fiber tendon is arranged along the second link and the third link. The servo motor is used to drive the carbon fiber tendon to contract / extension, thereby causing the connection to bend / straighten.

3. The biomimetic folding tripod for drones as described in claim 2, characterized in that, The elastic drive module also includes two pulleys, which are arranged at the connection between the second link and the third link; The number of servo motors is three, wherein the first servo motor is arranged at the connection between the first link and the second link, the second servo motor is arranged at the connection between the second link and the third link, and the third servo motor is arranged at the connection between the third link and the bottom support structure; The number of carbon fiber tendons is two. One end of the carbon fiber tendon is fixed to the first servo, and the other end passes over a pulley and is fixed to the middle of the third link. One end of the other carbon fiber tendon is fixed to the third servo, and the other end passes over another pulley and is fixed to the middle of the second link. The second servo is used to drive the two pulleys to rotate in opposite directions.

4. The biomimetic folding tripod for drones as described in claim 2, characterized in that, The bottom support structure is X-shaped.

5. The biomimetic folding tripod for drones as described in claim 4, characterized in that, The connection between the third link and the bottom support structure is located at the center of the bottom support structure.

6. The biomimetic folding tripod for drones as described in claim 1, characterized in that, The pressure sensor is used to detect the pressure from the ground when the drone lands.

7. The biomimetic folding tripod for drones as described in claim 1, characterized in that, The oil pressure of the damper is regulated by a PID algorithm.

8. The biomimetic folding tripod for drones as described in claim 1, characterized in that, The bottom of the bottom support structure is a non-slip rubber pad.

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