Bistable and switchable magnetic legs for drone landing on curved surfaces

Abstract

An unmanned aerial vehicle (UAV) configured to land, take off, and magnetically rest on a ferromagnetic cylindrical surface is provided. The UAV includes a body and articulated magnetic legs configured to cause the UAV to land and magnetically rest on the cylindrical surface. Each magnetic leg has a fixed portion coupled to the body and a pivoting portion pivotably coupled to the fixed portion at a pivot axis. The pivoting portion includes a switchable magnet and a single articulating joint that provides the pivoting portion with a single degree of freedom about the pivot axis to passively cause the pivoting portion to assume an inward and tangential orientation to the cylindrical surface in response to contact of the pivoting portion with the cylindrical surface during landing, and to passively maintain the inward orientation of the pivoting portion during takeoff.

Description

Technical Field

[0001] This disclosure generally relates to a mechanical system design that enables unmanned aerial vehicles (UAVs) to magnetically land or remain on curved ferromagnetic surfaces such as carbon steel pipes using switchable magnetic legs. Background Technology

[0002] One of the biggest challenges facing the oil and gas industry is the regular inspection of elevated assets in refineries, gas plants, offshore platforms, and other facilities. These assets include elevated pipelines and other structures that are difficult to access during inspections. Often, the only feasible method for inspecting them is to erect scaffolding to allow inspectors access to the asset for manual inspection. Such scaffolding is not only expensive and a significant cost barrier for frequent inspections, but it also creates safety problems primarily in the form of falls and tripping hazards.

[0003] In view of these and other problems in the art, this disclosure aims to provide a technical solution for an effective unmanned aerial vehicle with dual-stabilized and switchable magnetic legs for landing on curved ferromagnetic surfaces. Summary of the Invention

[0004] According to a first aspect of this disclosure, an unmanned aerial vehicle (UAV) is provided configured to land, take off, and magnetically remain on a ferromagnetic cylindrical surface. The UAV includes a body and a plurality of articulated magnetic legs configured to land the UAV on the ferromagnetic cylindrical surface and, after landing, magnetically remain on the ferromagnetic cylindrical surface. Each magnetic leg has a fixed portion coupled to the body and a pivoting portion pivotally coupled to the fixed portion at a pivot axis. The pivoting portion includes a switchable magnet and a single articulated joint configured to provide a single degree of freedom about the pivot axis, passively aligning the pivoting portion in an inward and tangential orientation to the cylindrical surface in response to contact with the cylindrical surface during landing, and passively maintaining the inward orientation of the pivoting portion during takeoff. The magnetism of the switchable magnet is activated at the end of landing and throughout the remainder to magnetically attach the UAV to the ferromagnetic cylindrical surface, and deactivated at the start of takeoff to magnetically detach the UAV from the ferromagnetic cylindrical surface.

[0005] In one embodiment consistent with the above embodiments, the fixed portion of each magnetic leg includes an inward rotation limiter configured to restrict inward rotation of the pivot portion during landing and takeoff.

[0006] In one embodiment consistent with the above embodiments, the UAV is further configured to land on and take off from a flat surface, and the articulation joint of each magnetic leg is further configured such that the pivot portion provides a single degree of freedom about the pivot axis to passively orient the pivot portion in a flat and parallel-to-the-flat orientation in response to contact between the pivot portion and the flat surface during landing on the flat surface, and to passively maintain the flat orientation of the pivot portion during takeoff from the flat surface.

[0007] In one embodiment consistent with the above embodiments, the fixed portion of each magnetic leg includes an outward rotation limiter to restrict the outward rotation of the pivot portion to a generally flat orientation during landing on and takeoff from a flat surface.

[0008] In an embodiment consistent with the above embodiments, the pivoting portion of each magnetic leg further includes a switch actuator located on top of a switchable magnet, the switch actuator being configured to actuate the magnet to switch the magnet between on and off states. During takeoff from a cylindrical surface, the center of gravity of the switch actuator is located outside the pivot axis, while during takeoff from a flat surface, the center of gravity of the switch actuator is located inside the pivot axis.

[0009] In an embodiment consistent with the above embodiments, each magnetic leg further includes a rotation sensor configured to measure the angle of pivoting of the pivot portion about the pivot axis after the pivot portion contacts the cylindrical surface.

[0010] In one embodiment consistent with the above embodiments, the drone further includes control circuitry configured to determine when to engage the magnets of the magnetic legs by measuring the pivoting of the pivoting portion of the magnetic legs at the end of landing.

[0011] In one embodiment consistent with the above embodiments, for each magnetic leg, the pivoting portion includes a switching actuator coupled to the top of the magnet and configured to actuate the magnet to switch the magnet between on and off states, and the control circuit is further configured to control the switching actuator to turn on the magnet when the measured pivoting of the pivoting portion of the magnetic leg is the same inward angle.

[0012] In one embodiment consistent with the above embodiments, the drone further includes control circuitry configured to determine the diameter of a cylinder corresponding to a cylindrical surface by measuring the pivoting of the pivoting portion of the magnetic leg.

[0013] In one embodiment consistent with the above embodiments, the drone further includes control circuitry configured to determine the distance from the body to the cylindrical surface using measured pivoting of the pivoting portion of the magnetic legs.

[0014] In one embodiment consistent with the above embodiments, the ferromagnetic cylindrical surface is part of a carbon steel pipe or container.

[0015] According to another aspect of this disclosure, a method is provided for enabling an unmanned aerial vehicle (UAV) to land, take off, and magnetically hover on a ferromagnetic cylindrical surface. The UAV includes a body and a plurality of articulated magnetic legs, each magnetic leg having a fixed portion coupled to the body and a pivoting portion pivotally coupled to the fixed portion at a pivot axis. The pivoting portion includes a switchable magnet and a single articulated joint having a single degree of freedom about the pivot axis. The method includes: using magnetic legs to land a drone on a ferromagnetic cylindrical surface; for each magnetic leg using a single articulated joint with a single degree of freedom around a pivot axis, passively aligning the pivot portion in an inward and tangential orientation to the cylindrical surface in response to contact between the pivot portion and the cylindrical surface during landing; at the end of landing, magnetically attaching the drone to the ferromagnetic cylindrical surface by activating a switchable magnet in each magnetic leg; after landing, magnetically holding the drone on the ferromagnetic cylindrical surface using the magnetic legs while keeping their respective switchable magnets activated; at the start of takeoff, magnetically separating the drone from the ferromagnetic cylindrical surface by deactivating the switchable magnets in each magnetic leg; after holding, taking off from the cylindrical surface; and, for each magnetic leg using an articulated joint and the center of gravity of the pivot portion being outside the pivot axis, passively maintaining the inward orientation of the pivot portion during takeoff.

[0016] In one embodiment consistent with the above method, the method further includes: for each magnetic leg using an inward rotation limiter of the fixed portion of the magnetic leg, restricting the inward rotation of the pivot portion during landing and takeoff.

[0017] In one embodiment consistent with the above method, the method further includes: using magnetic legs to land the drone on a flat surface; for each magnetic leg using a single articulated joint having a single degree of freedom around a pivot axis, passively aligning the pivot portion in a flat and parallel orientation to the flat surface in response to contact with the flat surface during landing; taking off the drone from the flat surface; and, for each magnetic leg using an articulated joint and the center of gravity of the pivot portion being located inside the pivot axis, passively maintaining the flat orientation of the pivot portion during takeoff from the flat surface.

[0018] In one embodiment consistent with the above method, the method further includes: for each magnetic leg using an outward rotation limiter of the fixed portion of the magnetic leg, limiting the outward rotation of the pivot portion to a generally flat orientation during landing on and takeoff from the flat surface.

[0019] In one embodiment consistent with the above method, the method further includes, for each magnetic leg, after the pivoting portion contacts the cylindrical surface, using an angle rotation sensor of the magnetic leg to measure the pivoting of the pivoting portion about the pivot axis.

[0020] In one embodiment consistent with the above method, the method further includes determining, by the control circuitry of the UAV, when to engage the magnet of the magnetic leg at the end of landing using measured pivoting of the pivoting portion of the magnetic leg.

[0021] In one embodiment consistent with the above method, the method further includes: for each magnetic leg, using a switch actuator of the pivot portion coupled to the top of the magnet to actuate the magnet to switch the magnet between on and off, and controlling the switch actuator to turn on the magnet by a control circuit when the measured pivot of the pivot portion of the magnetic leg is the same inward angle.

[0022] In one embodiment consistent with the above method, the method further includes determining the diameter of the cylinder corresponding to the cylindrical surface by means of measured pivoting of the pivoting portion of the magnetic leg using the control circuitry of the UAV.

[0023] In one embodiment consistent with the above method, the method further includes determining the distance from the body to the cylindrical surface by using measured pivoting of the pivoting portion of the magnetic leg via the control circuitry of the UAV.

[0024] Any combination of the various embodiments and implementations disclosed herein can be used. These and other aspects and features can be understood by reading the description of some embodiments below, along with the accompanying drawings and claims. Attached Figure Description

[0025] Figures 1A-1B show an assembly diagram and an exploded view of an exemplary articulated magnetic leg for landing a drone (UAV) or unmanned aerial vehicle on a curved surface, according to one embodiment.

[0026] Figures 2A-2B respectively illustrate the landing of an exemplary drone with articulated magnetic legs on a flat surface and a curved surface.

[0027] Figures 3A-3B respectively illustrate the initial and final contact of an exemplary articulated magnetic leg of a drone in one embodiment with a curved surface (e.g., a pipe).

[0028] Figures 3C-3D show the initial and final contact of the articulated magnetic leg of Figures 3A-3B with the flat surface, respectively.

[0029] Figures 4A-4B respectively illustrate exemplary articulated magnetic legs of a drone in one embodiment before the drone takes off from a flat surface and a curved surface.

[0030] Figure 5A illustrates an example of an unmanned aerial vehicle with articulated magnetic legs landing on a pipe in a centered orientation.

[0031] Figures 5B-5C show the initial and final contact scenarios when the UAV in Figure 5A lands on the pipe with a non-centered orientation.

[0032] Figures 6A-6B respectively illustrate the landing of an exemplary drone with articulated magnetic legs on a flat surface and a curved surface, respectively.

[0033] Figure 7 This is a flowchart illustrating an exemplary method for landing, taking off, and magnetically docking a drone on a ferromagnetic cylindrical surface, according to one embodiment.

[0034] It should be noted that the accompanying drawings are exemplary and not necessarily drawn to scale, and that the same or similar features have the same or similar reference numerals in all the drawings. Detailed Implementation

[0035] Exemplary embodiments of this disclosure relate to a mechanical system design that enables unmanned aerial vehicles (UAVs) to magnetically land or dock on curved ferromagnetic surfaces (e.g., carbon steel pipes) and flat ferromagnetic surfaces (e.g., home or operational bases, or the top of various structures such as tanks) using switchable magnetic legs. Some such embodiments utilize switchable magnets and restrained joints to help improve stability and reduce swaying during takeoff and landing. In some such exemplary embodiments, these features provide a bistabilization design (e.g., exhibiting stability during takeoff from and landing on curved and flat surfaces). This bistabilization results in less oscillation during flight. In some exemplary embodiments, one or more angular rotation sensors are provided to determine the pipe diameter after contact when landing or docking on a carbon steel pipe.

[0036] As mentioned earlier, one of the biggest challenges facing the oil and gas industry is the regular inspection of elevated assets in refineries, gas plants, offshore platforms, and other facilities. These assets include elevated pipelines and structures that are difficult to access during inspections. While drones can be used to aid access, landing a drone on such structures presents a number of obstacles. For example, these structures are often elevated pipelines with narrow diameters (e.g., 6 inches). Landing, taking off, and hovering on such curved surfaces can be a difficult task for drones.

[0037] Therefore, in exemplary embodiments, a system and method are provided to enable unmanned aerial vehicles (UAVs) to magnetically land and remain on these assets to perform inspection tasks, etc., while conserving battery energy. In exemplary embodiments, the UAV includes switchable magnetic legs that allow the UAV to magnetically remain on a ferromagnetic surface after landing and before takeoff. For example, this allows such a UAV to conserve its battery power by landing on a pipeline instead of hovering during long-duration tasks (e.g., monitoring or detecting gas leaks), performing work requiring contact with the pipeline (e.g., inspections (e.g., ultrasonic, magnetic inspections) or light maintenance (e.g., painting)), and delivering payloads (e.g., small sensing devices and crawlers) to the pipeline or retrieving samples (e.g., corrosion strips). Exemplary embodiments enable UAVs to land on operational assets (e.g., pipelines, containers, and structures) in oil and gas facilities. In some such embodiments, the UAV employs magnetic attachments (e.g., switchable magnetic legs) because these assets are largely made of carbon steel.

[0038] According to various embodiments, a drone with passive articulated landing legs having embedded switchable magnets is provided. These magnets are selectively turned on or off, which facilitates easy separation during removal from the pipe by turning off the magnets. According to some embodiments, a magnetic landing mechanism is provided, for example, as part of the drone. This mechanism allows landing on pipes of various diameters (e.g., 6 inches or larger), and misalignment due to imperfect landings (e.g., deviations from vertical by up to 15°, or in some cases 20°). The mechanism uses lightweight (e.g., as light or practical as possible) landing legs, as payload weight is a major limitation for most drones. Numerous variations of the drone and articulated magnetic legs are available, exemplary embodiments of which are shown in Figures 1A-6B and described below.

[0039] Figures 1A-1B respectively show an assembly diagram and an exploded view of an exemplary articulated magnetic leg 110 for landing a drone (UAV) or unmanned aerial vehicle on a curved ferromagnetic surface (e.g., a carbon steel pipe) according to one embodiment. For example, the drone or UAV may have four or six such magnetic legs 110, such as one for each propeller of the drone.

[0040] Referring to the exploded view of Figure 1B, the magnetic leg 110 includes a fixed portion 120 that is generally held stationary and attaches the magnetic leg 110 to the body (or simply the fuselage) of the drone. The fixed portion 120 includes a fixed leg body 124 rigidly attached to the drone via a carbon fiber tube 122. The leg body 124 holds a rotating support (also referred to as a pivot portion 130) that houses a switchable magnet 140 and serves as one foot of the drone. A single degree of freedom (e.g., from the inside out relative to the drone's fuselage) allows the magnetic leg 110 to adapt to any inward surface curvature (e.g., for a six-inch or larger pipe), including flat surfaces. For example, a pivot pin 144 can serve as an inward axis of rotation, allowing the pivot portion 130 to rotate inward with one degree of freedom about a pivot axis coinciding with the axis of rotation.

[0041] In one or more embodiments, the switchable magnet 140 includes two stacked disk magnets, one of which is static and the other is rotatable (e.g., a top disk magnet). The rotatable disk magnet is rotated to or toward one of two positions. In a first position, the rotatable disk magnet cancels out the magnetic field of the other disk magnet, effectively turning off the magnetism of the switchable magnet 140. In a second position (e.g., rotated 180° from the first position), the rotatable disk magnet is oriented in the same manner as the magnetic field of the other disk magnet, which enhances the overall magnetism and turns the switchable magnet 140 on.

[0042] To achieve this rotation of the disc magnet, an actuator, such as a servo motor 132, is used. The servo motor 132 is capable of rotating the rotatable disc magnet via mechanical coupling (e.g., servo horn 134 and adapter 136). A servo magnet holder 142 holds the top disc magnet and has embedded rotational restraints to limit the rotatable disc magnet (e.g., the top disc magnet) to 180 degrees. This restraint allows the servo motor's rotation direction to be associated with turning the switchable magnet 140 on or off. In some other embodiments, different types of switchable magnets are used, such as electromagnets or electro-permanent magnets.

[0043] The switchable magnet 140 of each magnetic leg 110 is engaged at some point during the landing maneuver. For example, this switching can occur at the start of landing as the UAV approaches the landing target (e.g., a pipe), or at the end of landing after landing on the pipe and the feet (e.g., the pivot portion 130) have been positioned. To activate the switching, in one embodiment, an onboard controller (on the UAV) is programmed or otherwise configured to send signals to the servo motors 132 to allow the UAV to attach to (or magnetically remain on) the pipe. When takeoff time arrives (e.g., at the start of takeoff), the switchable magnet 140 is deactivated (e.g., by the onboard controller, which is also programmed to send such signals to the servo motors 132). This makes propeller operation easier and avoids the need to overcome magnetic pull during takeoff.

[0044] Figures 2A-2B illustrate an exemplary drone 200 of one embodiment, which has articulated magnetic legs 210 that land on a flat surface and a curved surface (e.g., flat surface 60 and pipe 20), respectively. The drone 200 includes a body (or UAV body) 205 to which the articulated magnetic legs 210 (four such legs in this case) are attached. The drone 200 also includes a plurality of propellers 207 attached to the body 205. In different embodiments, the number of articulated magnetic legs may vary (e.g., six), and the number of propellers may vary (e.g., six). In some embodiments, the number of articulated magnetic legs is the same as the number of propellers. In some embodiments, the articulated magnetic legs are arranged symmetrically about the longitudinal (e.g., length direction) axis of the drone. For ease of illustration, the drone has four articulated magnetic legs, four propellers, and the articulated magnetic legs are arranged symmetrically about the longitudinal axis of the drone. Other embodiments are not necessarily limited to this.

[0045] Figures 2A-2B illustrate drones 200 that have landed on two different surfaces: a flat surface 60 (e.g., a home base or the top of a vertically arranged cylinder) and a curved pipe 20 (e.g., a carbon steel pipe, the top of a horizontally arranged cylinder, or a cylindrical curved section of a structure). Here, "top" refers to gravity, and the articulated magnetic legs 210 of the drone 200 in Figure 2B are arranged symmetrically about the top of the pipe 20 (e.g., about the longitudinal axis of the top of the pipe 20). In some embodiments, the articulated magnetic legs 210 are adapted to allow landing on pipes of any diameter greater than 6 inches. That is, the articulated magnetic legs 210 can accommodate pipes of various diameters (e.g., all articulated magnetic legs 210 can be used for safe landing).

[0046] Figures 3A-3B illustrate an exemplary articulated magnetic leg 310 of a drone (e.g., drone 200) of one embodiment, which makes initial and final contact with a curved surface 40 (e.g., a pipe or other partially or entirely cylindrical curved surface with a radius of curvature, such as in pipe 20). Figures 3C-3D illustrate the articulated magnetic leg 310 of Figures 3A-3B when it makes initial and final contact with a flat surface 60. The articulated magnetic leg 310 includes a fixed portion 320 (coupled to the body of the drone) and a pivot portion 330 coupled to the fixed portion 320 via a pivot point 350 (e.g., a pivot axis defining a single degree of freedom of rotation of the pivot portion 330 relative to the fixed portion 320, such as in pivot pin 144).

[0047] Referring here to Figures 3A-3B, the pivot axis 350 is parallel to the longitudinal axis of the UAV, causing the pivot portion 330 to rotate inward (or outward) relative to the curved surface 40 when the longitudinal axis of the UAV is aligned or parallel to the longitudinal axis of the pipe or other cylindrical curved surface. Therefore, the initial contact between the pivot portion 330 and the curved surface 40 results in a contact force 45 being applied to the pivot portion 330. This, in turn, causes a corresponding clockwise rotation 360 (inward) of the pivot portion 330 about the pivot axis 350. The inward rotation 360 continues until the pivot portion (or more specifically, the bottom of the pivot portion) 330 is tangent to the curved surface 40 at the point of final contact between the pivot portion 330 and the curved surface 40.

[0048] Furthermore, referring to Figures 3C-3D, the pivot axis is parallel to the flat surface 60. Therefore, the initial contact between the pivot portion 330 and the flat surface 60 results in a contact force 65 being applied to the pivot portion 330. This, in turn, causes a corresponding counterclockwise rotation 360 (downward) of the pivot portion 330 about the pivot axis 350. The downward rotation 360 continues until the pivot portion (or more specifically, the bottom of the pivot portion) 330 aligns with the flat surface 60 at the point of final contact between the pivot portion 330 and the flat surface 60.

[0049] Legs 310 have one degree of freedom about a pivot axis 350 (or pivot point) shown in Figures 3A-3D, allowing them to rotate and adapt to surfaces with different curvatures. Upon contact, when legs 310 rotate to face a flat surface, they remain pointing in that direction even after separation. Similarly, when legs 310 rotate to face a curved surface or a small pipe, they remain pointing in that direction even after separation. This stabilizes the joint in both positions (e.g., bi-stabilization), thereby reducing oscillations and wobble of the leg joints during flight.

[0050] More specifically, referring to Figures 3A-3B, when leg 310 contacts the curved surface 40 at the contact point, surface 40 pushes leg 310 (especially pivot portion 330) at the contact point. This causes pivot portion 330 to rotate along or about its pivot axis 350 until pivot portion 330 faces surface 40 (e.g., tangential to surface 40). Due to the flat design of the bottom contact surface of pivot portion 330 of leg 310, contact force 45 generates rotational torque in the correct direction (clockwise in this case) 360.

[0051] In contrast, referring to Figures 3C-3D, leg 310 (especially the pivoting portion 330) contacts the flat surface 60 at the contact point. Furthermore, the flat bottom of the pivoting portion 330 is not parallel to the flat surface 60. Therefore, the rotating portion 330 of leg 310 rotates about its pivot axis 350 (in this case, counterclockwise 365) until the flat bottom of the rotating portion 330 faces the flat surface 60. This is caused by a thrust 65 from surface 60 at the contact point. Due to the flat design of the bottom contact surface of the pivoting portion 330 of leg 310, this contact force 65 generates a (counterclockwise) rotational torque in the correct (counterclockwise) direction 365.

[0052] Figures 4A-4B respectively illustrate the state of an exemplary articulated magnetic leg 410 of a drone (e.g., drone 200) before takeoff from a flat surface and a curved surface (e.g., flat surface 60 and curved surface 40) according to one embodiment. The leg 410 (more specifically, the pivoting portion 430) has only one degree of freedom, namely, pivoting inward (e.g., clockwise or rotational direction 460 as shown in Figure 4B) or outward (e.g., counterclockwise or rotational direction 465 as shown in Figure 4A) about a pivot point (or about a pivot axis) 450 to allow the leg 410 to lie flat on the flat surface or tangentially to the curved surface. These curved surfaces may include pipes of different sizes (or diameters) with correspondingly different curvatures (or radii of curvature).

[0053] Leg 410 has two stable positions, and is therefore sometimes referred to as bi-stable. When leg 410 rotates to face a flat surface (e.g., as shown in Figures 3C-3D), leg 410 remains pointing in that direction even during and after separation (e.g., as part of takeoff from a flat surface). Similarly, when leg 410 rotates to face a curved surface or a small pipe (e.g., as shown in Figures 3A-3B), leg 410 remains pointing in that direction even during and after separation (e.g., as part of takeoff from a curved surface or a small pipe). This makes the joint (e.g., pivoting portion 430) stable in both positions (bi-stable), which helps reduce oscillations and wobble of the leg joint during flight.

[0054] More specifically, when landing on a flat surface, even after takeoff, the leg 410 maintains a vertical orientation (e.g., the bottom of the pivot portion 430 is parallel to the flat surface). This is due to the servo motor 432 being eccentrically positioned at the top of the pivot portion 430. The eccentricity of the servo motor 432 relative to the pivot axis 450 causes the center of gravity 485 of the servo motor to shift to the left of the pivot axis 450 (while the center of gravity of the rest of the pivot portion 430 remains centered relative to the pivot axis 450). This leftward shift of the center of gravity of the servo motor 432 causes the leg 410 to rotate outward (along a counterclockwise direction 465 as shown in Figure 4A).

[0055] However, the fixed portion of leg 410 (e.g., leg frame) acts as a rotation limiter 475 to prevent further rotation of pivot portion 430 along this direction. For example, rotation limiter 475 prevents pivot portion 430 from rotating outward by more than a few degrees (e.g., no more than three degrees, or no more than five degrees), thereby effectively keeping the bottom of pivot portion 480 substantially flat during takeoff from the flat portion. In some embodiments, the same effect is achieved when hovering and taking off on a flat surface by keeping the center of gravity of pivot portion 430 inside pivot axis 450. In some such embodiments, the center of gravity of pivot portion is also above pivot axis 450 when hovering and taking off from a flat surface. Here, direction (e.g., "above") is relative to the direction of gravity.

[0056] Furthermore, upon landing on a curved surface, the contact force from the surface of the bottom portion of leg 410 generates a torque that causes leg 410 to rotate and achieve the rotational (inward) orientation shown in FIG. 4B. Even after takeoff, leg 410 remains in this orientation because the center of gravity 480 of servo motor 432 (or the center of gravity of pivot portion 430) has shifted to the outside of pivot axis 450 (in some embodiments, above pivot axis 450), causing the weight to generate a counter-torque (along clockwise direction 460 as shown in FIG. 4B), thereby holding pivot portion 430 in this (inward) orientation. Here, the fixed portion of leg 410 (e.g., leg body) also serves as a rotation range limiter 470 to prevent excessive (inward) rotation. For example, in some embodiments, rotation limiter 470 limits inward rotation to no more than 45°, while in some other embodiments, rotation limiter 470 limits inward rotation to no more than 60°.

[0057] Figure 5A illustrates an exemplary drone 500 with articulated magnetic legs 510 landing on pipe 20 in a centered orientation according to one embodiment. Figures 5B-5C illustrate the drone 500 of Figure 5A landing on pipe 20 in a non-centered orientation and making initial and final contact, respectively. In some embodiments, due to the single degree of freedom of the legs 510 before or after contact with a surface (e.g., pipe 20), measuring the rotation angle of the legs 510 is accomplished by a rotation angle sensor (e.g., potentiometer, rotary encoder, or shaft encoder) in each magnetic leg 510. Determining the rotation angle of each leg 510 helps determine the orientation of the legs 510 or drone 500 relative to the surface. In some embodiments, the rotation angle sensor measures the angular rotation of the pivoting portion of the leg 510 relative to gravity, while in some embodiments, the rotation angle sensor measures the angular rotation of the pivoting portion of the leg 510 relative to the fixed portion of the leg 510. In some such embodiments, the rotation angle sensor measures the angular rotation of the pivoting portion of the leg 510 relative to both gravity and the fixed portion of the leg 510.

[0058] For example, in some embodiments, rotation angle sensors are mounted on the legs 510, and control circuitry is provided that, upon landing on a surface, a signal is emitted if the legs all have the same orientation (e.g., their pivot portions have the same measured inward angle) before the switchable magnets of the magnetic legs 510 are activated. This helps detect situations where one or more legs are not in contact with the surface or are not in contact with the surface at the appropriate (inward) angle, indicating that the landing attempt on the surface is incomplete or imperfect. In some embodiments, this indication of the same inward angle is also combined with a level sensor in the body of the drone 500 to detect that the body of the drone 500 is horizontal relative to gravity.

[0059] For example, if the pivoting portions of the legs 510 of the drone 500 in Figure 5B are not at the same rotation angle, this indicates a problem with the landing (in this case, the drone 500 is off-center relative to the top of the pipe 20). If the drone 500 continues to descend in an attempt to force the pivoting portions to have at least the same rotation angle relative to the stationary portion (as shown in Figure 5C), the drone 500 is no longer horizontal relative to gravity. This can be detected, for example, by a level sensor in the body of the drone 500 or a rotation angle sensor in the legs 510 that measures the angle of rotation of the pivoting portions relative to gravity. In this regard, in some embodiments, the automatic control circuitry is programmed to determine the amount of off-center, whether to re-attempt the landing, or whether the amount of off-center is within the permissible error range for a safe landing (e.g., 10, 15, or 20 degrees off-center).

[0060] Figures 6A-6B illustrate, respectively, the landing of an exemplary drone 600 with articulated magnetic legs 610 on a flat surface and a curved surface (pipe 20 and flat surface 60) according to one embodiment. The legs 610 are coupled to the drone body 605. Here, a rotation angle sensor in the legs 610 is used to measure the curvature of the surface on which the legs 610 land. In some embodiments, this measurement is used to determine the distance between the body 605 (or the top of the legs 610, or the bottom of the payload) and the surface. Based on this distance, it is possible to determine the amount by which the payload of the drone 600 needs to be lowered towards the surface (e.g., from the body 605, for example, a distance 690 to pipe 20 or a distance 695 to flat surface 60). Determining this distance can be particularly useful when deploying the payload using a controller (e.g., configured by code) via a feedback loop between the controller and the sensors.

[0061] Referring to Figures 1A-6B, in some exemplary embodiments, a drone (UAV, e.g., drone 200, 500, or 600) is provided that lands, takes off, and magnetically rests on a ferromagnetic cylindrical surface (e.g., pipe 20 or curved surface 40). The drone includes a body (e.g., drone body 205 or 605) and multiple (e.g., four or six) articulated magnetic legs (e.g., articulated magnetic legs 110, 210, 310, 410, 510, or 610). The magnetic legs allow the drone to land on the ferromagnetic cylindrical surface and, after landing, magnetically rest on the ferromagnetic cylindrical surface. Each magnetic leg has a fixed portion (e.g., fixed portion 120 or 320) coupled to the drone body and a pivoting portion (e.g., pivoting portion 130, 330, or 430) pivotally coupled to the fixed portion at a pivot axis (e.g., pivot pin 144 or pivot axis 305 or 405).

[0062] The pivoting section includes a switchable magnet (e.g., switchable magnet 140) that is turned on at the end of landing and throughout the stay to magnetically attach the UAV to the ferromagnetic cylindrical surface, and turned off at the start of takeoff to magnetically detach the UAV from the ferromagnetic cylindrical surface. The pivoting section also includes a single hinge joint (e.g., pivot pin 144) that provides the pivoting section with a single degree of freedom (e.g., inward and outward) about a pivot axis to passively orient the pivoting section inward and tangential to the cylindrical surface in response to contact during landing. During takeoff, the single hinge joint with the single degree of freedom also passively maintains the inward orientation of the pivoting section.

[0063] In one embodiment, the fixed portion of each magnetic leg includes an inward rotation limiter (e.g., rotation limiter 470) that restricts inward rotation of the pivoting portion during landing and takeoff. In one embodiment, the drone lands and takes off on a flat surface (e.g., flat surface 60). Furthermore, the articulation joint of each magnetic leg provides a single degree of freedom about a pivot axis to passively orient the pivoting portion in a flat and parallel-to-the-flat-surface orientation in response to contact with the flat surface during landing. Additionally, during takeoff from the flat surface, the single-degree-of-freedom articulation joint also passively maintains the flat orientation of the pivoting portion.

[0064] In one embodiment, the fixed portion of each magnetic leg includes an outward rotation limiter (e.g., rotation limiter 475) to restrict the outward rotation of the pivoting portion to a substantially flat orientation (e.g., within a few degrees of flatness, deviating from the flat orientation by no more than 3 degrees or 5 degrees). In one embodiment, the pivoting portion of each magnetic leg also includes a switching actuator (e.g., servo motor 132 or 432) located on top of a switchable magnet. This switching actuator actuates the magnet to switch it between on and off states. Furthermore, during takeoff from a cylindrical surface, the center of gravity of the switching actuator is outside the pivot axis (e.g., center of gravity 480), while during takeoff from a flat surface, this center is inside the pivot axis (e.g., center of gravity 485).

[0065] In one embodiment, each magnetic leg further includes an angle rotation sensor that measures the pivoting of the pivoting portion about a pivot axis after the pivoting portion contacts the cylindrical surface. In one embodiment, the drone also includes control circuitry configured (e.g., programmed by code) to determine, at the end of landing, when to activate the magnet of the magnetic leg using the measured pivoting of the pivoting portion of the magnetic leg. In one embodiment, for each magnetic leg, the pivoting portion includes a switch actuator coupled to the top of the magnet, which actuates the magnet to switch it between on and off. The control circuitry is also configured (e.g., programmed by code) to control the switch actuator to activate the magnet when the measured pivoting of the pivoting portion of the magnetic leg is the same inward angle.

[0066] In one embodiment, the drone further includes control circuitry configured by code to determine the diameter of a cylinder corresponding to a cylindrical surface using measured pivoting of the pivoting portion of the magnetic legs. In another embodiment, the drone further includes control circuitry configured by code or other programmable logic to determine a distance (e.g., distance 690) from the body to the cylindrical surface using measured pivoting of the pivoting portion of the magnetic legs. In one embodiment, the ferromagnetic cylindrical surface is part of a carbon steel pipe or container (e.g., a storage tank).

[0067] The techniques described herein can be implemented using a combination of sensors, cameras, and other devices, including computing or other logic circuitry configured (e.g., programmed) to perform tasks assigned to them. These devices are located on or within (or otherwise close to) the body or legs of the drone to perform these techniques. In some example embodiments, the control logic is implemented as computer code configured to execute on computing circuitry (e.g., a microprocessor) to perform control steps as part of the techniques.

[0068] Figure 7 This is a flowchart of an exemplary method 700 for landing, taking off, and magnetically hovering a drone (e.g., drone 200, 500, or 600) on a ferromagnetic cylindrical surface (e.g., pipe 20 or curved surface 40). The drone includes a body (e.g., drone body 205 or 605) and multiple articulated magnetic legs (e.g., magnetic legs 110, 210, 310, 410, 510, or 610). Each leg has a fixed portion (e.g., fixed portion 120 or 320) coupled to the body and a pivoting portion (e.g., pivoting portion 130, 330, or 430) pivotally coupled to the fixed portion at a pivot axis (e.g., pivot axis 350 or 450). The pivoting portion includes a switchable magnet (e.g., switchable magnet 140) and a single articulated joint (e.g., pivot pin 144) having a single degree of freedom (e.g., inward or outward) about the pivot axis.

[0069] A portion or all of method 700 may be performed using the components and techniques shown in Figures 1A-6B. Furthermore, portions of this and other methods disclosed herein may be executed on or using custom or pre-programmed logic devices, circuits, or processors, such as programmable logic circuits (PLCs), computers, software, or other circuits configured by code or logic (e.g., ASICs, FPGAs) to perform tasks assigned to them. The devices, circuits, or processors may be, for example, dedicated or shared hardware devices (e.g., laptops, single-board computers (SBCs), workstations, tablets, smartphones, part of a server, or dedicated hardware circuitry (e.g., in FPGAs or ASICs)), or computer servers, or part of a server or computer system. The devices, circuits, or processors may include a non-transitory computer-readable medium (CRM) (e.g., read-only memory (ROM), flash memory drive, or disk drive) storing instructions that, when executed on one or more processors, cause portions of method 700 (or other disclosed methods) to be executed. It should be noted that in other embodiments, the order of operations may be changed, and some operations may be omitted. A portion of method 700 may also be executed using logic, circuitry, or a processor located on or in electrical communication with the processing circuitry, the processing circuitry being coded to execute these portions of method 700.

[0070] In method 700, the process begins at step 710, which involves using magnetic legs to land the drone on a ferromagnetic cylindrical surface. Method 700 further includes the step of passively aligning, for each magnetic leg using a single articulated joint having a single degree of freedom about a pivot axis, the pivot portion in an inward and tangential orientation to the cylindrical surface in response to contact with the cylindrical surface during landing. See, for example, Figures 3A-3B. Furthermore, method 700 includes step 730, at the end of landing, magnetically attaching the drone to the ferromagnetic cylindrical surface by activating a switchable magnet in each magnetic leg. In some embodiments, a servo motor (e.g., servo motor 132 or 432) is used to rotate a stacked disk of switchable magnets to activate the switchable magnets.

[0071] Furthermore, method 700 includes step 740 of using magnetic legs to magnetically hold the drone on the ferromagnetic cylindrical surface after landing, while their respective switchable magnets remain engaged. Method 700 also includes step 750 of magnetically separating the drone from the ferromagnetic cylindrical surface at takeoff start by deactivating the switchable magnets in each magnetic leg, and step 760 of taking the drone off the cylindrical surface after holding. Additionally, method 700 includes the step of passively maintaining the inward orientation of the pivoting portion 770 during takeoff, in the case where each magnetic leg uses an articulated joint and the center of gravity of the pivoting portion is outside the pivot axis (e.g., as shown in FIG. 4B).

[0072] In some embodiments, method 700 includes the steps of: restricting inward rotation of the pivot portion during landing and takeoff for each magnetic leg using an inward rotation restriction (e.g., rotation restriction 470) of the fixed portion of the magnetic leg. In some embodiments, method 700 includes the steps of: landing the drone on a flat surface (e.g., flat surface 60) using the magnetic leg; passively aligning the pivot portion in a flat and parallel orientation to the flat surface (e.g., as shown in Figures 3C-3D) in response to contact with the flat surface during landing of the pivot portion on the flat surface for each magnetic leg using a single articulated joint with a single degree of freedom around the pivot axis; taking off from the flat surface for the drone; and passively maintaining the flat orientation of the pivot portion during takeoff from the flat surface for each magnetic leg using an articulated joint and the center of gravity of the pivot portion being inside the pivot axis.

[0073] In some embodiments, method 700 includes the step of: for each magnetic leg using an outward rotation restriction (e.g., rotation restriction 475) on a fixed portion of the magnetic leg, restricting the pivoting portion to rotate outward to a generally flat orientation (e.g., at most 3 degrees or at most 5 degrees) during landing on and takeoff from a flat surface. In some embodiments, method 700 includes the step of: for each magnetic leg, after the pivoting portion contacts a cylindrical surface, measuring the pivoting of the pivoting portion about a pivot axis using an angle rotation sensor of the magnetic leg. In some embodiments, method 700 includes the step of using the measured pivoting of the pivoting portion of the magnetic leg by the control circuitry of the UAV to determine when the magnet of the magnetic leg is engaged at the end of landing.

[0074] In some embodiments, method 700 includes the following steps: for each magnetic leg, actuating the magnet using a switching actuator (e.g., servo motor 132 or 432) coupled to the top of the magnet via a pivoting portion to switch the magnet between on and off, and controlling the switching actuator to turn on the magnet via control circuitry when the measured pivoting of the pivoting portion of the magnetic leg is the same inward angle. In some embodiments, method 700 includes the step of determining, by the control circuitry of the UAV, the diameter of a cylinder (e.g., pipe 20 or a cylindrical curved surface 40 having a radius of curvature) corresponding to a cylindrical surface using the measured pivoting of the pivoting portion of the magnetic leg. In some embodiments, method 700 includes the step of determining, by the control circuitry of the UAV, the distance from the body to the cylindrical surface (e.g., distance 690) using the measured pivoting of the pivoting portion of the magnetic leg.

[0075] The methods described herein can be implemented in part by software or firmware in a machine-readable form on a tangible (e.g., non-transitory) storage medium. For example, the software or firmware can be in the form of a computer program containing computer program code adapted to perform some steps of any of the methods described herein when run on a computer or suitable hardware device (e.g., an FPGA), and the computer program can be contained on a computer-readable medium. Examples of tangible storage media include computer storage devices having computer-readable media, such as disks, thumb drives, flash memory, etc., and do not include propagated signals. Propagated signals can exist in tangible storage media, but the propagated signals themselves are not instances of tangible storage media. The software can be adapted to execute on a parallel or serial processor, such that the method steps can be executed in any suitable order or simultaneously.

[0076] It should also be understood that the same or similar reference numerals in the accompanying drawings indicate the same or similar elements in multiple drawings, and not all embodiments or arrangements require reference to all parts or steps described and shown in the accompanying drawings.

[0077] The terminology used in this disclosure is for illustrative purposes only and does not constitute any limitation. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described,” as used herein, also include the plural forms. It should also be understood that the term “comprising” as used herein means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0078] The directional terms used herein are for convention and reference purposes only and should not be construed as restrictive. However, it should be recognized that these terms may be used by the observer as a reference. Therefore, no limitation is implied or inferred from them. Furthermore, the use of ordinal numbers (e.g., first, second, third) is for distinction rather than counting. For example, the use of “third” does not imply the existence of a corresponding “first” or “second”. In addition, the wording or terms used herein are for illustrative purposes only and should not be considered restrictive. The use of the terms “comprising,” “including,” or “having,” and their variations thereof, in this document means to encompass the items listed thereafter, as well as their equivalents and additional items.

[0079] The foregoing subject matter is merely exemplary and should not be considered limiting. Various modifications and variations can be made to the subject matter described herein without following the exemplary embodiments and applications shown and described, without departing from the true spirit and scope of the invention as covered by this disclosure, which is limited only by a set of the following claims and the structures, functions or steps equivalent to those claims.

Claims

1. An unmanned aerial vehicle (UAV) configured to land, take off, and magnetically hover on a ferromagnetic cylindrical surface, the UAV comprising: main body; as well as Multiple articulated magnetic legs are configured to allow the drone to land on a ferromagnetic cylindrical surface and, after landing, to magnetically remain on the ferromagnetic cylindrical surface. Each magnetic leg has a fixed portion coupled to a body and a pivoting portion pivotally coupled to the fixed portion at a pivot axis, the pivoting portion having a center of gravity relative to the pivot axis and including: A flat bottom contact surface for contacting the cylindrical surface during landing and maintaining contact with the cylindrical surface throughout the stay; A switchable magnet, whose magnetism is activated at the end of landing and throughout the stay to magnetically attach the drone to a ferromagnetic cylindrical surface, and deactivated at the start of takeoff to magnetically detach the drone from the ferromagnetic cylindrical surface; and A single articulated joint, configured such that the pivoting portion and the center of gravity provide a single degree of freedom about the pivot axis, passively (1) oriented the flat bottom contact surface in an inward and tangential orientation to the cylindrical surface, and (2) oriented the center of gravity outward of the pivot axis, in response to contact between the flat bottom contact surface and the cylindrical surface during landing, and passively maintaining the inward orientation of the flat bottom contact surface and the outward orientation of the center of gravity during takeoff. Each magnetic leg includes an angle rotation sensor configured to measure the pivoting of the pivoting portion about a pivot axis after the flat bottom contact surface contacts the cylindrical surface. The drone also includes a control circuit configured to determine (1) the diameter of the cylinder corresponding to the cylindrical surface or (2) the distance from the body to the cylindrical surface using the measured pivoting of the pivoting portion of the magnetic leg.

2. The drone of claim 1, wherein the fixed portion of each magnetic leg includes an inward rotation limiter configured to restrict inward rotation of the flat bottom contact surface and outward rotation of the center of gravity during landing and takeoff.

3. The drone of claim 1, wherein the drone is further configured to land on and take off from a flat landing surface, and the articulation joint of each magnetic leg is further configured to provide a single degree of freedom about a pivot axis for the pivot portion and the center of gravity, in response to contact between the flat bottom contact surface and the flat landing surface during landing on the flat landing surface, to passively (1) position the flat bottom contact surface in an orientation parallel to the flat landing surface, and (2) orient the center of gravity toward the inside of the pivot axis, and passively maintain the flat orientation of the flat bottom contact surface and the inward orientation of the center of gravity during takeoff from the flat landing surface.

4. The drone of claim 3, wherein the fixed portion of each magnetic leg includes an outward rotation limiter to restrict the outward rotation of the flat bottom contact surface to a generally flat orientation and to limit the inward rotation of the center of gravity during landing on and takeoff from the flat landing surface.

5. The drone of claim 3, wherein the pivoting portion of each magnetic leg further includes a switch actuator located on top of a switchable magnet, the switch actuator being configured to actuate the magnet to switch the magnet between on and off states, wherein during takeoff from a cylindrical surface, the center of gravity of the switch actuator is located outside the pivot axis, and during takeoff from a flat landing surface, the center of gravity of the switch actuator is located inside the pivot axis.

6. The drone of claim 1, wherein the ferromagnetic cylindrical surface is part of a carbon steel pipe or container.

7. An unmanned aerial vehicle (UAV) configured to land, take off, and magnetically hover on a ferromagnetic cylindrical surface, the UAV comprising: main body; as well as Multiple articulated magnetic legs are configured to allow the drone to land on a ferromagnetic cylindrical surface and, after landing, to magnetically remain on the ferromagnetic cylindrical surface. Each magnetic leg has a fixed portion coupled to a body and a pivoting portion pivotally coupled to the fixed portion at a pivot axis, the pivoting portion having a center of gravity relative to the pivot axis and including: A flat bottom contact surface for contacting the cylindrical surface during landing and maintaining contact with the cylindrical surface throughout the stay; A switchable magnet, whose magnetism is activated at the end of landing and throughout the stay to magnetically attach the drone to a ferromagnetic cylindrical surface, and deactivated at the start of takeoff to magnetically detach the drone from the ferromagnetic cylindrical surface; and A single articulated joint, configured such that the pivoting portion and the center of gravity provide a single degree of freedom about the pivot axis, passively (1) oriented the flat bottom contact surface in an inward and tangential orientation to the cylindrical surface, and (2) oriented the center of gravity outward of the pivot axis, in response to contact between the flat bottom contact surface and the cylindrical surface during landing, and passively maintaining the inward orientation of the flat bottom contact surface and the outward orientation of the center of gravity during takeoff. Each magnetic leg includes an angle rotation sensor configured to measure the pivoting of the pivoting portion about a pivot axis after the flat bottom contact surface contacts the cylindrical surface. The drone also includes control circuitry configured to determine when to engage the magnets of the magnetic legs by measuring the pivoting of the pivoting portion of the magnetic legs at the end of landing.

8. The drone as described in claim 7, wherein, For each magnetic leg, the pivoting portion includes a switching actuator coupled to the top of the magnet and configured to actuate the magnet to switch the magnet between on and off states, and the control circuit is further configured to control the switching actuator to turn on the magnet when the measured pivoting of the pivoting portion of the magnetic leg is the same inward angle.

9. The drone of claim 7, wherein the fixed portion of each magnetic leg includes an inward rotation limiter configured to restrict inward rotation of the flat bottom contact surface and outward rotation of the center of gravity during landing and takeoff.

10. The drone of claim 7, wherein the drone is further configured to land on and take off from a flat landing surface, and the articulation joint of each magnetic leg is further configured to provide a single degree of freedom about a pivot axis for the pivot portion and the center of gravity, in response to contact between the flat bottom contact surface and the flat landing surface during landing on the flat landing surface, to passively (1) position the flat bottom contact surface in an orientation parallel to the flat landing surface, and (2) orient the center of gravity toward the inside of the pivot axis, and passively maintain the flat orientation of the flat bottom contact surface and the inward orientation of the center of gravity during takeoff from the flat landing surface.

11. The drone of claim 10, wherein the fixed portion of each magnetic leg includes an outward rotation limiter to restrict the outward rotation of the flat bottom contact surface to a generally flat orientation and to limit the inward rotation of the center of gravity during landing on and takeoff from the flat landing surface.

12. A method for enabling an unmanned aerial vehicle (UAV) to land, take off, and magnetically hover on a ferromagnetic cylindrical surface, said UAV comprising a body and a plurality of articulated magnetic legs, each magnetic leg having a fixed portion coupled to the body and a pivoting portion pivotally coupled to the fixed portion at a pivot axis, the pivoting portion having a center of gravity relative to the pivot axis and including a flat bottom contact surface, a switchable magnet, and a single articulated joint having a single degree of freedom about the pivot axis, said method comprising: Magnetic legs are used to land the drone on a ferromagnetic cylindrical surface; For each magnetic leg using a single articulated joint with a single degree of freedom around the pivot axis, in response to the contact between the flat bottom contact surface and the cylindrical surface during landing, the flat bottom contact surface is passively (1) oriented inward and tangent to the cylindrical surface, and (2) the center of gravity is oriented outward of the pivot axis. At the end of the landing, the drone is magnetically attached to the ferromagnetic cylindrical surface by activating the switchable magnet in each magnetic leg. After landing, the magnetic legs are used to magnetically hold the drones on the ferromagnetic cylindrical surface, while keeping their respective switchable magnets connected. At the start of takeoff, the drone is magnetically separated from the ferromagnetic cylindrical surface by shutting off the switchable magnets in each magnetic leg. After pausing, the drone takes off from the cylindrical surface; as well as For each magnetic leg using an articulated joint and with the center of gravity of the pivot portion located outside the pivot axis, the inward orientation of the flat bottom contact surface and the outward orientation of the center of gravity are passively maintained during takeoff.

13. The method of claim 12, further comprising: For each magnetic leg using an inward rotation limiter on the fixed portion of the magnetic leg, the inward rotation of the flat bottom contact surface and the outward rotation of the center of gravity are limited during landing and takeoff.

14. The method of claim 12, further comprising: Magnetic legs are used to land the drone on a flat landing surface; For each magnetic leg using a single articulated joint with a single degree of freedom around the pivot axis, in response to the contact of the flat bottom contact surface with the flat landing surface during landing on the flat landing surface, the flat bottom contact surface is passively (1) oriented parallel to the flat landing surface, and (2) the center of gravity is oriented to the inside of the pivot axis. Enables drones to take off from flat landing surfaces; as well as For each magnetic leg using an articulated joint and with the center of gravity of the pivoting portion located inside the pivot axis, the flat orientation of the flat bottom contact surface and the inward orientation of the center of gravity are passively maintained during takeoff from a flat landing surface.

15. The method of claim 14, further comprising: For each magnetic leg using the outward rotation limiting member of the fixed part of the magnetic leg, during landing on and takeoff from the flat landing surface, (1) the outward rotation of the flat bottom contact surface is limited to a generally flat orientation, and (2) the outward rotation of the center of gravity is limited.

16. The method of claim 12, further comprising: For each magnetic leg, after the flat bottom contact surface contacts the cylindrical surface, the rotation of the pivoting portion around the pivot axis is measured using the angle rotation sensor of the magnetic leg.

17. The method of claim 16, further comprising: The control circuitry of the drone uses the measured pivoting of the pivoting section of the magnetic leg to determine when the magnet of the magnetic leg is engaged at the end of landing.

18. The method of claim 17, wherein, For each magnetic leg, the method further includes using a switch actuator coupled to the top of the magnet via a pivot portion to actuate the magnet to switch the magnet between on and off states, and controlling the switch actuator to turn on the magnet via a control circuit when the measured pivot of the pivot portion of the magnetic leg is the same inward angle.

19. The method of claim 16, further comprising determining the diameter of the cylinder corresponding to the cylindrical surface by means of a measured pivoting of the pivoting portion of the magnetic leg by the control circuitry of the UAV.

20. The method of claim 16, further comprising determining the distance from the body to the cylindrical surface by means of measured pivoting of the pivoting portion of the magnetic leg by the control circuitry of the UAV.

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