Bistable and switchable magnetic landing gear for UAV landings on curved surfaces

Abstract

An unmanned aerial vehicle (UAV) configured to land, take off, and magnetically perch on a ferromagnetic cylindrical surface is provided. The UAV includes a body and articulating magnetic legs configured to land and magnetically perch the UAV on the cylindrical surface. Each magnetic leg has a fixed portion coupled to the body and a pivot portion pivotally coupled to the fixed portion at a pivot axis. The pivot portion includes a switchable magnet and a single articulation joint that provides the pivot portion with a single degree of freedom about the pivot axis and passively orients the pivot portion inward and toward the cylindrical surface in response to the pivot portion contacting the cylindrical surface during landing and passively maintains the inward orientation of the pivot portion during takeoff.

Description

Technical Field

[0001] The present disclosure generally relates to a mechanical system design that enables an unmanned aerial vehicle (UAV or drone) to use switchable magnetic legs for magnetic landing or perching on a curved ferromagnetic surface such as a carbon steel pipe.

Background Art

[0002] One of the biggest challenges in the oil and gas industry is the regular inspection of high - elevation assets found in refineries, gas plants, offshore platforms, and other plants and facilities. These assets include high - elevation pipes and other structures that are difficult to access during inspection operations. In many cases, the practical way to inspect them is to erect scaffolding to allow inspectors to access the assets and perform manual inspections. Such scaffolding is expensive and not only poses a significant cost barrier for frequent inspections but also raises safety concerns mainly in the form of the risk of falls and trips.

Summary of the Invention

Problems to be Solved by the Invention

[0003] The present disclosure is directed to providing a technical solution for an effective UAV with bistable and switchable magnetic legs for landing on a curved ferromagnetic surface with respect to these and other problems in the art.

Means for Solving the Problems

[0004] According to a first aspect of the present disclosure, an unmanned aerial vehicle (UAV) is provided which is configured to land on, take off from, and magnetically perch on a ferromagnetic cylindrical surface. The UAV comprises a body and a plurality of articulated magnetic legs, the plurality of articulated magnetic legs configured to land the UAV on a ferromagnetic cylindrical surface and to magnetically perch the UAV on the ferromagnetic cylindrical surface after landing. Each magnetic leg has a fixed portion connected to the body and a pivot portion pivotably connected to the fixed portion on a pivot axis. The pivot portion comprises a switchable magnet and a single articulated joint, the articulated joint configured to provide the pivot portion with a single degree of freedom on a pivot axis, and to passively orient the pivot portion inward and in contact with the cylindrical surface in response to the pivot portion contacting the cylindrical surface during landing, and to passively maintain the inward orientation of the pivot portion during takeoff. The switchable magnet's magnetic properties are switched on at the end of landing and throughout the perch to magnetically attach the UAV to the ferromagnetic cylindrical surface, and switched off at the start of takeoff to magnetically detach the UAV from the ferromagnetic cylindrical surface.

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

[0006] In an embodiment consistent with the above, the UAV is further configured to land on and take off from a flat surface, and the articulated joints of each magnetic leg are further configured to provide a single degree of freedom of the pivot portion about a pivot axis, to passively orient the pivot portion flat and parallel to the flat surface in response to the pivot portion contacting the flat surface during landing on a flat surface, and to passively maintain the flat orientation of the pivot portion during takeoff from a flat surface.

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

[0008] In an embodiment consistent with the above, the pivot portion of each magnetic leg further includes a switch actuator, which is located above a switchable magnet and is configured to actuate the magnet to switch the magnet on and off, the center of gravity of the switch actuator is on the outward side of the pivot axis during takeoff from a cylindrical surface and on the inward side of the pivot axis during takeoff from a flat surface.

[0009] In an embodiment consistent with the above, each magnetic leg further includes an angular rotation sensor, which is configured to measure the amount of pivot movement of the pivot portion around the pivot axis after the pivot portion has come into contact with a cylindrical surface.

[0010] In an embodiment consistent with the above, the UAV further includes a control circuit configured to determine when to switch on the magnets of the magnetic leg at the end of landing, using a measured amount of pivot of the pivot portion of the magnetic leg.

[0011] In an embodiment consistent with the above, with respect to each magnetic leg, the pivot portion includes a switch actuator, which is coupled to the top of the magnet and configured to actuate the magnet to switch the magnet on and off, and the control circuit is further configured to control the switch actuator to switch the magnet on when the measured amount of pivot of the pivot portion of the magnetic leg is at the same inward angle.

[0012] In an embodiment consistent with the above, the UAV further includes a control circuit configured to determine the diameter of a cylinder corresponding to a cylindrical surface using a measured amount of pivoting of the pivot portion of the magnetic leg.

[0013] In an embodiment consistent with the above, the UAV further includes a control circuit configured to determine the distance from the main body to the cylindrical surface using the measured pivot amount of the pivot portion of the magnetic leg.

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

[0015] Another aspect of the present disclosure provides a method for landing, taking off, and magnetically perching an unmanned aerial vehicle (UAV) on a ferromagnetic cylindrical surface. The UAV comprises a body and a plurality of articulated magnetic legs, each of which has a fixed portion connected to the body and a pivot portion pivotably connected to the fixed portion on a pivot axis. The pivot portion includes a switchable magnet and a single articulated joint having a single degree of freedom about the pivot axis. The method includes the steps of landing the UAV on a ferromagnetic cylindrical surface using the magnetic legs; with respect to each magnetic leg using a single articulated joint having a single degree of freedom about the pivot axis, the steps of passively orienting the pivot portion inward and in contact with the cylindrical surface in response to the pivot portion contacting the cylindrical surface during landing; magnetically attaching the UAV to the ferromagnetic cylindrical surface at the end of landing by switching on a switchable magnet in each magnetic leg; and switching on each of the switchable magnets in the magnetic legs The process includes: using the magnetic legs, which remain switched on, to magnetically perch the UAV onto a ferromagnetic cylindrical surface after landing; magnetically detaching the UAV from the ferromagnetic cylindrical surface at the start of takeoff by switching off the switchable magnets in each magnetic leg; lifting the UAV off the cylindrical surface after the perching step; and, with respect to each magnetic leg using an articulated joint, passively maintaining the inward orientation of the pivot during takeoff, with the center of gravity of the pivot being outward from the pivot axis.

[0016] In embodiments consistent with the methods described above, the method further includes the step of limiting the inward rotation of the pivot portion during landing and takeoff with respect to each magnetic leg using an inward rotation limiter of the fixed portion of the magnetic leg.

[0017] In embodiments consistent with the methods described above, the method further includes the steps of: landing a UAV on a flat surface using magnetic legs; with respect to each magnetic leg using a single articulated joint having a single degree of freedom about a pivot axis, the steps of passively orienting the pivot portion flat and parallel to the flat surface in response to the pivot portion contacting the flat surface during landing on the flat surface; taking off the UAV from the flat surface; and with respect to each magnetic leg using an articulated joint, the steps of passively maintaining the flat orientation of the pivot portion during takeoff from the flat surface, with the center of gravity of the pivot portion being inward of the pivot axis.

[0018] In embodiments consistent with the methods described above, the method further includes, with respect to each magnetic leg using an outward rotation limiter on the fixed portion of the magnetic leg, the step of restricting the outward rotation of the pivot portion to a nearly flat orientation during landing on and taking off from a flat surface.

[0019] In embodiments consistent with the methods described above, the method further includes the step of measuring the amount of pivot of the pivot portion about the pivot axis with respect to each of the magnetic legs, after the pivot portion has come into contact with a cylindrical surface, using an angular rotation sensor of the magnetic leg.

[0020] In embodiments consistent with the methods described above, the method further includes the step of determining, by the control circuit of the UAV, when to switch on the magnets of the magnetic leg at the end of landing, using the measured amount of pivot of the pivot portion of the magnetic leg.

[0021] In an embodiment consistent with the method described above, for each of the magnetic legs, the method further includes operating the magnet by using a switch actuator of a pivotal portion connected to the top of the magnet to switch the magnet between on and off, and controlling the switch actuator by a control circuit to switch on the magnet when the measured pivotal amount of the pivotal portion of the magnetic leg is at the same inward angle.

[0022] In an embodiment consistent with the method described above, the method further includes determining, by a control circuit of the UAV, a diameter of a cylinder corresponding to a cylindrical surface by using the measured pivotal amount of the pivotal portion of the magnetic leg.

[0023] In an embodiment consistent with the method described above, the method further includes determining, by a control circuit of the UAV, a distance from the main body portion to the cylindrical surface by using the measured pivotal amount of the pivotal portion of the magnetic leg.

[0024] Any combination of the various embodiments and implementations disclosed herein can be used. These and other aspects and features can be understood from the following description of specific embodiments together with the accompanying drawings and the claims.

Brief Description of the Drawings

[0025] [Figure 1A] FIG. is an assembled view of an exemplary articulated magnetic leg for landing an unmanned aerial vehicle (UAV) or drone on a curved surface according to an embodiment. [Figure 1B] FIG. is an exploded view of an exemplary articulated magnetic leg for landing an unmanned aerial vehicle (UAV) or drone on a curved surface according to an embodiment. [Figure 2A] FIG. illustrates an exemplary UAV having articulated magnetic legs landing on a flat surface according to an embodiment. [Figure 2B]FIG. illustrating an exemplary UAV with articulated magnetic legs landing on a curved surface according to an embodiment. [Figure 3A] FIG. illustrating an exemplary articulated magnetic leg of a UAV making an initial contact with a curved surface (e.g., a pipe, etc.) according to an embodiment. [Figure 3B] FIG. illustrating an exemplary articulated magnetic leg of a UAV making a final contact with a curved surface (e.g., a pipe, etc.) according to an embodiment. [Figure 3C] FIG. illustrating the articulated magnetic legs of FIGS. 3A - 3B making an initial contact with a flat surface. [Figure 3D] FIG. illustrating the articulated magnetic legs of FIGS. 3A - 3B making a final contact with a flat surface. [Figure 4A] FIG. illustrating an exemplary articulated magnetic leg of a UAV before takeoff from a flat surface according to an embodiment. [Figure 4B] FIG. illustrating an exemplary articulated magnetic leg of a UAV before takeoff from a curved surface according to an embodiment. [Figure 5A] FIG. illustrating an exemplary UAV with articulated magnetic legs landing on a pipe in an aligned orientation according to an embodiment. [Figure 5B] FIG. illustrating the UAV of FIG. 5A landing on a pipe in a misaligned orientation and making an initial contact. [Figure 5C] FIG. illustrating the UAV of FIG. 5A landing on a pipe in a misaligned orientation and making a final contact. [Figure 6A] FIG. illustrating an exemplary UAV with articulated magnetic legs landing on a curved surface according to an embodiment. [Figure 6B] FIG. illustrating an exemplary UAV with articulated magnetic legs landing on a flat surface according to an embodiment. [Figure 7]This is a flow diagram of an exemplary method, according to an embodiment, for landing, taking off, and magnetically perching a UAV on a ferromagnetic cylindrical surface. [Modes for carrying out the invention]

[0026] It should be noted that the drawings are illustrative and not necessarily to scale, and that the same or similar features have the same or similar reference numbers throughout.

[0027] Exemplary embodiments of this disclosure are directed toward mechanical system designs that enable unmanned aerial vehicles (UAVs or drones) to use switchable magnetic legs to magnetically land or perch on both curved ferromagnetic surfaces (e.g., carbon steel pipes) and flat ferromagnetic surfaces (e.g., the tops of many structures such as home bases or operational bases, or storage tanks). Some such embodiments utilize switchable magnets and constrained joints to help improve stability, for example, during takeoff and landing, and reduce wobbling. In some such exemplary embodiments, these features provide a bistable design (e.g., exhibiting stability during takeoff and landing from both curved and flat surfaces). This bistable design provides 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 perching on a carbon steel pipe, for example.

[0028] As previously discussed, one of the biggest challenges in the oil and gas industry is the regular inspection of high-altitude assets found at refineries, gas plants, offshore platforms, and other plants and facilities. These assets include high-altitude pipes and structures that are difficult to access during inspection work. While UAVs can be used to aid in access, landing on such structures by UAVs presents its own set of obstacles. For example, these structures are often high-altitude pipes with relatively narrow diameters (e.g., 6 inches). Landing, taking off, and perching on such curved surfaces can be challenging tasks for UAVs.

[0029] Accordingly, in exemplary embodiments, systems and methods are provided for an effective method that enables a drone (e.g., a battery-powered drone or UAV) to magnetically land and perch on these assets in order to perform inspection tasks while conserving battery energy. In exemplary embodiments, the UAV includes switchable magnetic legs that enable the UAV to magnetically perch on a ferromagnetic surface after landing and before takeoff. This enables such a UAV to conserve its battery power by landing on a pipe instead of hovering during long-duration missions (e.g., gas leak monitoring or inspection), and to perform work that requires contact with the pipe, such as inspections (e.g., ultrasonic inspection, magnetic inspection) or light maintenance (e.g., coating), and to deliver a payload (e.g., a small sensing device and crawler) to the pipe, or to retrieve a sample (e.g., a corrosion test specimen). Exemplary embodiments provide for a UAV to land on operational assets (e.g., pipes, containers, and structures) found in oil and gas facilities. In some such embodiments, since most of these assets are made from carbon steel, magnetic mounting (e.g., switchable magnetic legs) is used by the UAV.

[0030] According to various embodiments, a UAV is provided having passively articulated landing gear with embedded switchable magnets. These magnets are selectively turned on or off, which facilitates easy removal from the pipe during takeoff by switching off the magnets. According to some embodiments, a magnetic perch mechanism is provided (e.g., as part of a UAV). The mechanism allows landing on various pipe diameters (e.g., 6 inches or more) and tolerates misalignment resulting from improper landings (e.g., up to 15° from the vertical, or in some cases, 20°). Since payload weight is a critical limitation for most UAVs, the mechanism uses lightweight landing gear (e.g., as light as possible or practical). Numerous variations of UAVs and articulated magnetic landing gear exist, and exemplary embodiments of these are illustrated in Figures 1A to 6B and described in the text that follows.

[0031] Figures 1A and 1B illustrate assembled and exploded views, respectively, of an exemplary articulated magnetic leg 110 for landing an unmanned aerial vehicle (UAV) or drone on a curved ferromagnetic surface (e.g., a carbon steel pipe). For example, a drone or UAV may have four or six such magnetic legs 110 (e.g., one for each propeller of the drone).

[0032] Referring to the exploded view in Figure 1B, the magnetic leg 110 includes a fixed portion 120, which normally remains fixed and attaches the magnetic leg 110 to the main body (or simply the body) of the UAV. The fixed portion 120 includes a fixed leg body 124, which is rigidly attached to the drone through a carbon fiber tube 122. The leg body 124 holds a rotating holder (also referred to as a pivot portion 130), which houses a switchable magnet 140 and acts as one of the drone's legs. A single degree of freedom (e.g., inward to outward relative to the drone's body) allows the magnetic leg 110 to conform to the curvature of any inward surface (e.g., 6 inches or more relative to the pipe) (including flat surfaces). For example, the pivot pin 144 can function as an inward-facing rotating shaft, which allows the pivot portion 130 to rotate inward by one degree of freedom around a pivot axis that coincides with the rotating shaft.

[0033] In one or more embodiments, the switchable magnet 140 includes two stacked disk magnets, one stationary and the other rotatable (e.g., an upper disk magnet). The rotatable disk magnet is rotated or oriented to one of two positions. In the first position, the rotatable disk magnet cancels out the magnetic field of the other disk magnet, effectively switching off the magnetism of the switchable magnet 140. In the second position (e.g., rotated 180° from the first position), the rotatable disk magnet is oriented in the same way as the magnetic field of the other disk magnet, thereby enhancing the total magnetism and switching on the switchable magnet 140.

[0034] An actuator, such as a servo motor 132, is used to perform this disk magnet rotation. The servo motor 132 can rotate the rotatable disk magnet through a mechanical coupling (e.g., a servo horn 134 and an adapter 136). A servo magnet holder 142 holds the upper disk magnet and has a rotation limiter embedded to restrict the rotatable disk magnet (e.g., the upper disk magnet) to 180 degrees. This limitation allows the servo motor rotation direction to be linked to switching on or off the switchable magnet 140. In some other embodiments, different types of switchable magnets are used (e.g., electromagnets or electric permanent magnets).

[0035] The switchable magnets 140 of each magnetic leg 110 are switched on at some point during the landing maneuver. For example, this switching can occur at the start of the landing while the UAV is approaching the landing target (e.g., a pipe), or at the end of the landing after the leg (e.g., pivot section 130) has settled down after touchdown on the pipe. To activate the switching, in one embodiment, an onboard controller (on the drone) is programmed or otherwise configured to send a signal to a servo motor 132 to allow the UAV to stick to (or magnetically perch on) the pipe. When it is time for takeoff (e.g., at the start of takeoff), the switchable magnets 140 are switched off (e.g., by the onboard controller which is further programmed to send such a signal to the servo motor 132). This makes the propeller work easier and avoids the need to overcome the magnetic pulling force during takeoff.

[0036] Figures 2A and 2B illustrate an exemplary UAV 200 having articulated magnetic legs 210, which land on a flat surface and a curved surface (e.g., the flat surface 60 and the pipe 20), respectively, according to an embodiment. The UAV 200 includes a body (or UAV body) 205, and the articulated magnetic legs 210 (in this case, four such legs) are attached to the body 205. The UAV 200 also includes a plurality of propellers 207 attached to the body 205. In different embodiments, the number of articulated magnetic legs can vary (e.g., six), and the number of propellers can 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 with respect to the longitudinal axis (e.g., lengthwise axis) of the UAV. For the sake of clarity throughout, the number of articulated magnetic legs of the UAV is four, the number of propellers of the UAV is four, and the articulated magnetic legs are arranged symmetrically with respect to the longitudinal axis of the UAV. Other embodiments are not necessarily limited in this way.

[0037] Figures 2A and 2B show the UAV 200 landed on two different surfaces, namely a flat surface 60 (e.g., a home base, or the top of a vertically positioned cylinder) and a curved pipe 20 (e.g., a carbon steel pipe, or the top of a horizontally positioned cylinder or the curved portion of a structure). Here, “top” is in relation to gravity, and the articulated magnetic legs 210 of the UAV 200 in Figure 2B are positioned symmetrically with respect to the top of the pipe 20 (e.g., with respect to the longitudinal axis of the top of the pipe 20). In some embodiments, the articulated magnetic legs 210 are adapted to allow landing on any pipe diameter greater than 6 inches. That is, the articulated magnetic legs 210 are adaptable to pipes of multiple diameters (e.g., all articulated magnetic legs 210 can reliably land).

[0038] Figures 3A and 3B illustrate an exemplary articulated magnetic leg 310 of a UAV (e.g., UAV200) making initial and final contact, respectively, with a curved surface 40 (e.g., a pipe 20, or other partially or fully cylindrical curved surface having a predetermined radius of curvature). Figures 3C and 3D illustrate the articulated magnetic leg 310 of Figures 3A and 3B making initial and final contact, respectively, with a flat surface 60. The articulated magnetic leg 310 includes a fixed portion 320 (connected to the body of the UAV) and a pivot portion 330 connected to the fixed portion 320 through a pivot point 350 (e.g., a pivot pin 144, which defines a single degree of freedom rotation of the pivot portion 330 relative to the fixed portion 320).

[0039] Referring here to Figures 3A and 3B, the pivot axis 350 is parallel to the longitudinal axis of the UAV in order to impart an inward (or outward) rotation of the pivot portion 330 relative to the curved surface 40, when the longitudinal axis of the UAV is aligned with or parallel to the longitudinal axis of the curved surface, such that the longitudinal axis of the UAV is aligned with or parallel to the longitudinal axis of the curved surface, such that the pivot axis 350 is parallel to the longitudinal axis of the UAV. Thus, the initial contact of the pivot portion 330 with the curved surface 40 causes a contact force 45 to be imparted to the pivot portion 330. This then 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 touches the curved surface 40 at the final contact between the pivot portion 330 and the curved surface 40.

[0040] In addition, and referring to Figures 3C to 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 causes a contact force 65 to be applied to the pivot portion 330. This then causes a corresponding counterclockwise rotation 360 (downward) of the pivot portion 330 around 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 in the final contact between the pivot portion 330 and the flat surface 60.

[0041] The landing gear 310 has one degree of freedom around the pivot axis 350 (or pivot point) shown in Figures 3A to 3D, allowing them to rotate and adapt to surfaces with different curvatures. When the landing gear 310 rotates to face a flat surface and makes contact, it retains its orientation even after detachment. Similarly, when the landing gear 310 rotates to face a curved surface or a small pipe, it retains its orientation even after detachment. This makes the joint stable in these two positions (e.g., bistable), reducing rocking and wobbling in the landing gear joint during flight.

[0042] More specifically, and referring to Figures 3A and 3B, when the leg portion 310 contacts the curved surface 40 at the contact point, the surface 40 pushes the leg portion 310 (and, in particular, the pivot portion 330) at the contact point. This causes the pivot portion 330 to rotate along or about its pivot axis 350 until it faces (for example, touches) the surface 40. The contact force 45 generates a rotational torque 360 ​​in the correct direction (clockwise in this case) due to the flat design of the bottom contact surface of the pivot portion 330 of the leg portion 310.

[0043] In contrast, and referring to Figures 3C to 3D, the leg portion 310 (and, in particular, the pivot portion 330) is in contact with a flat surface 60 at the contact point. In addition, the flat bottom of the pivot portion 330 is not parallel to the flat surface 60. Thus, the rotating portion 330 of the leg portion 310 rotates around or about its pivot axis 350 (counterclockwise in this case 365) until the flat bottom of the rotating portion 330 faces the flat surface 60. This is due to a pressing force 65 from the surface 60 at the contact point. This contact force 65 generates a (counterclockwise) rotational torque in the correct (counterclockwise) direction 365, due to the flat design of the bottom contact surface of the pivot portion 330 of the leg portion 310.

[0044] Figures 4A and 4B illustrate exemplary articulated magnetic legs 410 of a UAV (e.g., UAV200) prior to takeoff from a flat surface and a curved surface (e.g., a flat surface 60 and a curved surface 40), respectively, according to an embodiment. The legs 410 (more specifically, the pivot portion 430) have only one degree of freedom, i.e., a degree of freedom inward (e.g., clockwise or rotational 460 as shown in Figure 4B) or outward (e.g., counterclockwise or rotational 465 as shown in Figure 4A) around the pivot point 450 (or around the pivot axis), allowing the legs 410 to land flat on a flat surface or touch a curved surface. These curved surfaces can include pipes of different sizes (or diameters) having corresponding different curvatures (or radii of curvature).

[0045] The landing gear 410 has two stable positions and is therefore sometimes referred to as bistable. When the landing gear 410 rotates (for example, as shown in Figures 3C-3D) to face a flat surface, the landing gear 410 remains oriented in that direction during and after detachment (for example, as part of takeoff from a flat surface). Similarly, when the landing gear 410 rotates (for example, as shown in Figures 3A-3B) to face a curved surface or a small pipe, the landing gear 410 remains oriented in that direction during and after detachment (for example, as part of takeoff from a curved surface or a small pipe). This makes the joint (for example, the pivot part 430) stable in these two positions (bistable state), which helps reduce rocking and wobbling in the landing gear joint during flight.

[0046] More specifically, when landing on a flat surface, the leg 410 remains vertically oriented after takeoff (for example, the bottom of the pivot section 430 is parallel to the flat surface). This is due to the servo motor 432 being positioned off-center on the top of the pivot section 430. The servo motor 432 is off-center relative to the pivot axis 450, causing its center of gravity 485 to shift to the left of the pivot axis 450 (while the center of gravity of the rest of the pivot section 430 remains centered relative to the pivot axis 450). The leftward shift of the servo motor 432's center of gravity causes the leg 410 to rotate outward (counterclockwise 465 as illustrated in Figure 4A).

[0047] However, the fixed portion of the leg 410 (e.g., the leg frame) acts as a rotation limiter 475 to prevent the pivot portion 430 from rotating further in this direction. For example, the rotation limiter 475 prevents the pivot portion 430 from rotating more than a few degrees outward (e.g., 3 degrees or less or 5 degrees or less), effectively keeping the bottom of the pivot portion 430 nearly flat during takeoff from a flat surface. In some embodiments, the same effect is achieved by keeping the center of gravity of the pivot portion 430 inward of the pivot axis 450 when perching and taking off from a flat surface. Also in some such embodiments, the center of gravity of the pivot portion is above the pivot axis 450 when perching and taking off from a flat surface, where the direction such as “above” is relative to the direction of gravity.

[0048] Furthermore, when landing on a curved surface, the contact force from the surface to the bottom part of the leg 410 generates torque, which causes the leg 410 to rotate and achieve the rotated (inward) orientation shown in Figure 4B. The leg 410 remains in this orientation even after takeoff. This is because the center of gravity 480 of the servo motor 432 (or the center of gravity of the pivot part 430) is shifted outward from the pivot axis 450 (and, in some embodiments, upward from the pivot axis 450), causing the weight to generate a torque in the opposite direction (clockwise 460 as shown in Figure 4B), maintaining the pivot part 430 in this (inward) orientation. Here, the fixed part of the leg 410 (e.g., the leg body) also acts as a rotation range limiter 470 to prevent excessive (inward) rotation. For example, in some embodiments, the rotation limiter 470 limits inward rotation to 45° or less, while in some other embodiments, the rotation limiter 470 limits inward rotation to 60° or less.

[0049] Figure 5A illustrates an exemplary UAV 500 having articulated magnetic legs 510 landing on a pipe 20 in an aligned orientation according to an embodiment. Figures 5B–5C illustrate the UAV 500 of Figure 5A landing on the pipe 20 in an unaligned orientation, making initial and final contact, respectively. In some embodiments, measuring the rotation angle of the legs 510 due to their single degree of freedom before or after contact with a surface (e.g., pipe 20) is done through a rotation angle sensor, such as a 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 the UAV 500 relative to the surface. In some embodiments, the rotation angle sensor measures the angular rotation of the pivot portion of the leg 510 relative to gravity, while in some embodiments, the rotation angle sensor measures the angular rotation of the pivot 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 pivot portion of the leg 510 relative to both gravity and the fixed portion of the leg 510.

[0050] For example, in some embodiments, rotation angle sensors are mounted on the legs 510, and a control circuit is provided to signal whether they all have the same orientation (e.g., the same measured inward angle of their pivot parts) when landing on a surface, before switching on the switchable magnets of the magnetic legs 510. This helps to detect situations where one or more legs are not touching the surface or are not touching it at the appropriate (inward) angle (they indicate an inadequate or incomplete landing attempt on the surface). In some embodiments, this indication of the same inward angle is further combined with a level sensor in the body of the UAV500 to detect whether the body of the UAV500 is horizontal to gravity.

[0051] For example, in Figure 5B, the pivot portion of the leg 510 of the UAV500 is not rotating by the same angle, which indicates a problem in landing (in this case, the UAV500 is off-center relative to the top of the pipe 20). If the UAV500 continues to land in an attempt to force the pivot portion to have the same angle of rotation relative to at least the fixed portion, as in Figure 5C, the UAV500 will no longer be horizontal with respect to gravity. This can be detected, for example, by a level sensor in the body of the UAV500, or by a rotation angle sensor in the leg 510 that measures the angular rotation of the pivot portion relative to gravity. At this point, in some embodiments, an automatic control circuit is programmed to determine the amount of off-center and whether to retry the landing, or whether the amount of off-center is within a safe landing tolerance (e.g., 10, 15, or 20 degrees off-center).

[0052] Figures 6A and 6B illustrate an exemplary UAV 600 having articulated magnetic legs 610, which are landing on flat and curved surfaces (pipe 20 and flat surface 60), respectively, according to an embodiment. The legs 610 are connected to the UAV body 605. Here, a rotation angle sensor in the leg 610 is used to measure the curvature of the surface on which the leg 610 lands. In some embodiments, the measurement is used to determine the distance between the body 605 (or the top of the leg 610, or the bottom of the payload) and the surface. Based on this distance, it is possible to establish the amount by which the UAV 600's payload needs to be lowered to the surface (e.g., the distance 690 from the body 605 to, for example, pipe 20, or the distance 695 to the flat surface 60). Determining this distance can be particularly useful when a controller is used to deploy the payload through a feedback loop between the controller and the sensor (e.g., configured by code).

[0053] Referring to Figures 1A to 6B, several exemplary embodiments provide unmanned aerial vehicles (UAVs, e.g., UAV200, 500, or 600) that land on, take off from, and magnetically perch on ferromagnetic cylindrical surfaces (e.g., pipe 20 or curved surface 40). The UAV comprises a body (e.g., UAV body 205 or 605) and a plurality (e.g., four or six) articulated magnetic legs (e.g., articulated magnetic legs 110, 210, 310, 410, 510, or 610). The magnetic legs land the UAV on the ferromagnetic cylindrical surface and, after landing, magnetically perch the UAV on the ferromagnetic cylindrical surface. Each magnetic leg has a fixed portion (e.g., fixed portion 120 or 320) connected to the UAV body and a pivot portion (e.g., pivot portion 130, 330, or 430) pivotably connected to the fixed portion on a pivot axis (e.g., pivot pin 144 or pivot axis 305 or 405).

[0054] The pivot section includes a switchable magnet (e.g., switchable magnet 140), the magnetism of which is switched on to magnetically attach the UAV to the ferromagnetic cylindrical surface at the end of landing and throughout the perch, and switched off to magnetically detach the UAV from the ferromagnetic cylindrical surface at the start of takeoff. The pivot section further includes only a single articulated joint (e.g., pivot pin 144), the articulated joint providing the pivot section with only a single degree of freedom (e.g., inward and outward) about the pivot axis, and is configured to passively orient the pivot section inward and in contact with the cylindrical surface in response to the pivot section contacting the cylindrical surface during landing, and to passively maintain the inward orientation of the pivot section during takeoff. The single articulated joint with a single degree of freedom also passively maintains the inward orientation of the pivot section during takeoff.

[0055] In one embodiment, the fixed portion of each magnetic leg includes an inward rotation limiter (e.g., rotation limiter 470) that restricts the inward rotation of the pivot portion during landing and takeoff. In one embodiment, the UAV lands on a flat surface (e.g., flat surface 60) and takes off from a flat surface. In addition, the articulated joint of each magnetic leg provides the pivot portion with a single degree of freedom around the pivot axis, and is configured to passively orient the pivot portion flat and parallel to the flat surface in response to the pivot portion contacting the flat surface during landing on the flat surface. Furthermore, the articulated joint with a single degree of freedom also passively maintains the flat orientation of the pivot portion during takeoff from a flat surface.

[0056] 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 pivot portion to a nearly flat orientation (e.g., within a few degrees from flat, such as 3 degrees or 5 degrees from flat) during landing on and takeoff from a flat surface. In one embodiment, the pivot portion of each magnetic leg further includes a switch actuator (e.g., servo motor 132 or 432) on top of a switchable magnet. The switch actuator acts on the magnet to switch the magnet on and off. The center of gravity of the switch actuator is on the outward side of the pivot axis during takeoff from a cylindrical surface (e.g., center of gravity 480) and on the inward side of the pivot axis during takeoff from a flat surface (e.g., center of gravity 485).

[0057] In one embodiment, each magnetic leg further includes an angular rotation sensor, which measures the amount of pivot of the pivot portion about a pivot axis after the pivot portion has made contact with a cylindrical surface. In one embodiment, the UAV further includes a control circuit, which is configured to use the measured amount of pivot of the pivot portion of the magnetic leg to determine when to switch on the magnet of the magnetic leg at the end of landing (e.g., programmed by code). In one embodiment, with respect to each magnetic leg, the pivot portion includes a switch actuator, which is coupled to the top of the magnet and acts on the magnet to switch the magnet on and off. The control circuit is further configured to control the switch actuator to switch on the magnet when the measured amount of pivot of the pivot portion of the magnetic leg is at the same inward angle (e.g., by code for that purpose).

[0058] In one embodiment, the UAV further includes a control circuit, which consists of code for determining the diameter of a cylinder corresponding to a cylindrical surface using a measured pivot amount of the pivot portion of the magnetic leg. In another embodiment, the UAV further includes a control circuit, which consists of code or other programmable logic for determining the distance from the body to the cylindrical surface (e.g., distance 690) using a measured pivot amount of the pivot portion of the magnetic leg. In another embodiment, the ferromagnetic cylindrical surface is part of a carbon steel pipe or container (e.g., a storage tank).

[0059] The techniques described herein can be implemented using a combination of sensors, cameras, and other devices (including (e.g., programmed) computing or other logic circuits configured to perform their assigned tasks). These devices are positioned on or within (or otherwise in close proximity to) the body or legs of a UAV to perform the techniques. In some exemplary embodiments, the control logic is implemented as computer code configured to run on computing circuits (e.g., a microprocessor) to perform the control steps that are part of the techniques.

[0060] Figure 7 is a flow diagram of an exemplary method 700 according to an embodiment for landing, taking off, and magnetically perching a UAV (e.g., UAV 200, 500, or 600) on a ferromagnetic cylindrical surface (e.g., a pipe 20 or a curved surface 40). The UAV includes a body (e.g., UAV body 205 or 605) and a plurality of articulated magnetic legs (e.g., magnetic legs 110, 210, 310, 410, 510, or 610). Each leg has a fixed portion connected to the body (e.g., fixed portion 120 or 320) and a pivot portion pivotably connected to the fixed portion on a pivot axis (e.g., pivot axis 350 or 450). The pivot section 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) around the pivot axis.

[0061] Some or all of Method 700 can be carried out using the components and techniques illustrated in Figures 1A to 6B. In addition, parts of the Methods and other Methods disclosed herein can be carried out on or using custom or pre-programmed logic devices, circuits, or processors, such as programmable logic circuits (PLCs), computers, software, or other circuits (e.g., ASICs, FPGAs) configured by code or logic to perform their assigned tasks. The devices, circuits, or processors can be, for example, dedicated or shared hardware devices (e.g., laptop computers, single-board computers (SBCs), workstations, tablets, smartphones, parts of servers, or dedicated hardware circuits such as those in FPGAs or ASICs), or computer servers, or parts of server or computer systems. The devices, circuits, or processors can include non-temporary computer-readable media (such as CRM, e.g., read-only memory (ROM), flash drives, or disk drives) that store instructions causing parts of Method 700 (or other disclosed Methods) to be carried out when executed on one or more processors. It should be noted that in other embodiments, the order of operations can be changed, and some of the operations can be omitted. Also, some of the methods of method 700 can be implemented using logic, circuits, or processors positioned on or electrically communicating with a processing circuit configured by code to carry out these parts of method 700.

[0062] In Method 700, the process begins with step 710, which involves landing a UAV on a ferromagnetic cylindrical surface using magnetic legs. With respect to each magnetic leg, which uses a single articulated joint having a single degree of freedom about a pivot axis, Method 700 further includes step 720, which passively orients the pivot portion inward and in contact with the cylindrical surface in response to the pivot portion contacting the cylindrical surface during landing. See, for example, Figures 3A–3B. In addition, Method 700 includes step 730, which magnetically attaches the UAV to the ferromagnetic cylindrical surface at the end of the landing by switching on switchable magnets in each magnetic leg. In some embodiments, a servo motor (e.g., servo motor 132 or 432) is used to rotate the stacked disk magnets of the switchable magnets to turn on the switchable magnets.

[0063] Method 700 subsequently includes step 740 of using the magnetic legs to magnetically perch the UAV onto a ferromagnetic cylindrical surface after landing, with each of the switchable magnets in the magnetic legs remaining switched on. Method 700 further includes step 750 of magnetically detaching the UAV from the ferromagnetic cylindrical surface at the start of takeoff by switching off the switchable magnets in each of the magnetic legs, and step 760 of lifting the UAV off the cylindrical surface after the perching step. In addition, with respect to each magnetic leg using an articulated joint, Method 700 includes step 770 of passively maintaining the inward orientation of the pivot part during takeoff, with the center of gravity of the pivot part on the outward side of the pivot axis (for example, as shown in Figure 4B).

[0064] In some embodiments, Method 700 includes, with respect to each magnetic leg using an inward rotation limiter (e.g., rotation limiter 470) on the fixed portion of the magnetic leg, the step of limiting the inward rotation of the pivot portion during landing and takeoff. In some embodiments, Method 700 includes, with respect to each magnetic leg using a single articulated joint having a single degree of freedom about a pivot axis, the step of passively orienting the pivot portion flat and parallel to the flat surface in response to the pivot portion contacting the flat surface during landing on the flat surface (e.g., as shown in Figures 3C-3D), the step of taking off the UAV from the flat surface, and with respect to each magnetic leg using an articulated joint, the step of passively maintaining the flat orientation of the pivot portion during takeoff from the flat surface with the center of gravity of the pivot portion on the inward side of the pivot axis.

[0065] In some embodiments, Method 700 includes, with respect to each magnetic leg using an outward rotation limiter (e.g., rotation limiter 475) on the fixed portion of the magnetic leg, the step of limiting the outward rotation of the pivot portion to a nearly flat orientation (e.g., at most 3 degrees or at most 5 degrees) during landing on and taking off from a flat surface. In some embodiments, Method 700 includes, with respect to each magnetic leg, the step of measuring the amount of pivot of the pivot portion about the pivot axis using an angular rotation sensor of the magnetic leg after the pivot portion has made contact with a cylindrical surface. In some embodiments, Method 700 includes, by the step of the UAV's control circuit, determining when the magnets of the magnetic leg should be switched on at the end of landing, using the measured amount of pivot of the pivot portion of the magnetic leg.

[0066] In some embodiments, Method 700 includes, with respect to each magnetic leg, the step of activating the magnet using a switch actuator (e.g., a servo motor 132 or 432) on a pivot part connected to the top of the magnet to switch the magnet on and off, and the step of controlling the switch actuator by a control circuit to switch on the magnet when the measured pivot amount of the pivot part of the magnetic leg is at the same inward angle. In some embodiments, Method 700 includes, by the control circuit of the UAV, the step of using the measured pivot amount of the pivot part of the magnetic leg to determine the diameter of a cylinder (e.g., a pipe 20 with a radius of curvature or a cylindrically curved surface 40) corresponding to a cylindrical surface. In some embodiments, Method 700 includes, by the control circuit of the UAV, the step of using the measured pivot amount of the pivot part of the magnetic leg to determine the distance (e.g., a distance 690) from the body to the cylindrical surface.

[0067] The methods described herein can be partially implemented by software or firmware in a machine-readable form on a tangible (e.g., non-temporary) storage medium. For example, the software or firmware can be in the form of a computer program, comprising computer program code adapted to perform some of the steps of the methods described herein when the program is executed on a computer or a suitable hardware device (e.g., an FPGA), and when a computer program can be embodied on a computer-readable medium. Examples of tangible storage mediums include computer storage devices having a computer-readable medium (e.g., disks, thumb drives, and flash memory, etc.) and do not include propagated signals. Propagated signals may be present in a tangible storage medium, but propagated signals themselves are not examples of tangible storage mediums. The software may be suitable for execution on parallel or serial processors, and the method steps may be made possible in any suitable order or simultaneously.

[0068] It should be further understood that similar or analogous figures in the drawings represent similar or analogous elements across several drawings, and that not all components or steps described and illustrated with reference to the drawings are required for all embodiments or arrangements.

[0069] The technical terms used herein are for the purpose of describing specific embodiments and are not intended to limit the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context explicitly indicates otherwise. It will be further understood that the terms “comprises” and / or “comprising,” when used herein, identify the presence of the described features, integers, steps, actions, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, actions, elements, components, and / or groups thereof.

[0070] The terms of orientation are used herein solely for convention and reference purposes and should not be construed as limiting. However, it is acknowledged that these terms may be used relative to the viewer. Therefore, no limitation is implied or should be inferred. In addition, the use of ordinal numbers (e.g., first, second, third) is for distinction, not counting. For example, the use of "third" does not imply the existence of a corresponding "first" or "second." Furthermore, the expressions and terminology used herein are for illustrative purposes only and should not be considered limiting. The use herein of "including," "comprising," "having," "containing," "involving," and their variations means that they encompass the items listed thereafter and their equivalents, as well as any additional items.

[0071] The subject matter described above is provided solely for illustrative purposes and should not be construed as limiting. Various modifications and changes can be made to the subject matter described herein without following the exemplary embodiments and uses illustrated and described, and without departing from the true spirit and scope of the invention encompassed by this disclosure (which is defined by the set of descriptions in the following claims and by equivalent structures and functions or steps). [Explanation of symbols]

[0072] 20 pipes 40. Curved surface 45 Contact force 60 Flat surface 65 Contact force 110 Articulated Magnetic Legs 120 Fixed part 122 Carbon Fiber Tube 124 Leg main body 130 Pivoting part 132 Servo motors 134 Servo Horn 136 Adapter 140 Switchable Magnets 142 Servo Magnet Holder 144 Pivot pins 200 Unmanned Aerial Vehicle (UAV) 205 UAV main unit 207 Propeller 210 Articulated Magnetic Legs 310 Articulated Magnetic Legs 320 Fixed part 330 Pivoting part 350 pivot points 360 degrees of rotation 365 rotation directions 410 Articulated Magnetic Legs 430 Pivoting part 432 Servo motor 450 pivot points 460 rotation direction 465 Rotation direction 470 RPM limiter 475 RPM limiter 480 Servo motor center of gravity 485 Servo motor center of gravity 500 Unmanned Aerial Vehicle (UAV) 510 Articulated Magnetic Legs 600 Unmanned Aerial Vehicle (UAV) 605 UAV main unit 610 Articulated Magnetic Legs 690 Distance from the main body to the pipe surface 695 Distance from the main body to a flat surface

Claims

1. An unmanned aerial vehicle (UAV) configured to land on, take off from, and magnetically perch on a ferromagnetic cylindrical surface, wherein the UAV is The main body and A plurality of articulated magnetic legs, each configured to land the UAV on the ferromagnetic cylindrical surface, and to magnetically perch the UAV on the ferromagnetic cylindrical surface after landing, wherein each magnetic leg has a fixed portion connected to the main body and a pivot portion pivotably connected to the fixed portion along a pivot axis. Includes, The pivot portion has a center of gravity with respect to the pivot axis, The aforementioned pivot portion is A flat bottom contact surface that contacts the cylindrical surface during the landing and maintains contact with the cylindrical shape during the perch, A switchable magnet, wherein the magnetism of the switchable magnet is switched on at the end of the landing and throughout the perch to magnetically attach the UAV to the ferromagnetic cylindrical surface, and is switched off at the start of the takeoff to magnetically detach the UAV from the ferromagnetic cylindrical surface, A single articulated joint, the articulated joint is configured to provide the pivot portion and the center of gravity with a single degree of freedom about the pivot axis, and in response to the flat bottom contact surface contacting the cylindrical surface during landing, the articulated joint passively orients (1) the flat bottom contact surface inward and in contact with the cylindrical surface, and (2) the center of gravity outward from the pivot axis, and passively maintains the inward orientation of the flat bottom contact surface and the outward orientation of the center of gravity during takeoff. Includes, Each of the plurality of magnetic legs includes an angle rotation sensor, and the angle rotation sensor measures the amount of pivot movement of the pivot part around the pivot axis after the pivot part has come into contact with the cylindrical surface. The UAV further includes a control circuit, which is configured to determine, using the measured amount of pivoting of the pivot portion of the magnetic leg, (1) the diameter of the cylinder corresponding to the cylindrical shape, or (2) the distance from the main body to the surface of the cylindrical shape. Unmanned aerial vehicle (UAV).

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

3. The UAV is further configured to land on and take off from a flat landing surface, and the articulated joints of each magnetic leg are further configured to provide the pivot portion and the center of gravity with a single degree of freedom about the pivot axis, and in response to the flat bottom contact surface contacting the flat landing surface during the landing on the flat landing surface, (1) the flat bottom contact surface is passively oriented parallel to the flat landing surface, and (2) the center of gravity is passively oriented inward from the pivot axis, and in response to the flat bottom contact surface contacting the flat landing surface during the takeoff from the flat landing surface. The UAV according to claim 1.

4. 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 nearly flat orientation and to restrict the inward rotation of the center of gravity during landing on the flat landing surface and takeoff from the flat surface, The UAV according to claim 3.

5. Each of the pivot portions of the magnetic leg further includes a switch actuator, which is located above the switchable magnet and is configured to actuate the magnet to switch the magnet between on and off, and the center of gravity of the switch actuator is outside the pivot axis during takeoff from the cylindrical surface and inside the pivot axis during takeoff from the flat landing surface. The UAV according to claim 3.

6. An unmanned aerial vehicle (UAV) configured to land on, take off from, and magnetically perch on a ferromagnetic cylindrical surface, wherein the UAV is The main body and A plurality of articulated magnetic legs, each configured to land the UAV on the ferromagnetic cylindrical surface, and to magnetically perch the UAV on the ferromagnetic cylindrical surface after landing, wherein each magnetic leg has a fixed portion connected to the main body and a pivot portion pivotably connected to the fixed portion along a pivot axis. Includes, The pivot portion has a center of gravity with respect to the pivot axis, The aforementioned pivot portion is A flat bottom contact surface that contacts the cylindrical surface during the landing and maintains contact with the cylindrical shape during the perch, A switchable magnet, wherein the magnetism of the switchable magnet is switched on at the end of the landing and throughout the perch to magnetically attach the UAV to the ferromagnetic cylindrical surface, and is switched off at the start of the takeoff to magnetically detach the UAV from the ferromagnetic cylindrical surface, A single articulated joint, the articulated joint is configured to provide the pivot portion and the center of gravity with a single degree of freedom about the pivot axis, and in response to the flat bottom contact surface contacting the cylindrical surface during landing, the articulated joint passively orients (1) the flat bottom contact surface inward and in contact with the cylindrical surface, and (2) the center of gravity outward from the pivot axis, and passively maintains the inward orientation of the flat bottom contact surface and the outward orientation of the center of gravity during takeoff. Includes, Each magnetic leg includes an angle rotation sensor, which is configured to measure the amount of pivot movement of the pivot part around the pivot axis after the flat bottom contact surface has come into contact with the cylindrical surface. The UAV further includes a control circuit, which is configured to determine when to switch on the magnets of the magnetic legs at the end of the landing, using the measured amount of pivot of the pivot portion of the magnetic legs. Unmanned aerial vehicle (UAV).

7. With respect to each magnetic leg, the pivot portion includes a switch actuator, which is connected to the top of the magnet and is configured to actuate the magnet to switch the magnet on and off, and the control circuit is further configured to control the switch actuator to switch the magnet on when the respective rotation angles in the measured pivot amount of the pivot portion of the magnetic leg are the same. The UAV according to claim 6.

8. The ferromagnetic cylindrical surface is part of a carbon steel pipe or container. The UAV according to claim 1.

9. A method for landing, taking off, and magnetically perching an unmanned aerial vehicle (UAV) on a ferromagnetic cylindrical surface, wherein the UAV comprises a body and a plurality of articulated magnetic legs, each of which has a fixed portion connected to the body and a pivot portion pivotably connected to the fixed portion on a pivot axis, the pivot portion having a center of gravity on the pivot axis, the pivot portion comprising a flat bottom contact surface, a switchable magnet and a single articulated joint having a single degree of freedom around the pivot axis, and the method is as follows: The steps include: landing the UAV on the ferromagnetic cylindrical surface using the magnetic legs; With respect to each magnetic leg using the single articulated joint having the single degree of freedom around the pivot axis, in response to the flat bottom contact surface coming into contact with the cylindrical surface during landing, the steps include: (1) passively orienting the flat bottom contact surface inward and in contact with the cylindrical surface, and (2) passively orienting the center of gravity outward from the pivot axis; The steps include: switching on the switchable magnets in each of the magnetic legs to magnetically attach the UAV to the ferromagnetic cylindrical surface at the end of the landing; The steps include using the magnetic legs to magnetically perch the UAV on the ferromagnetic cylindrical surface after landing, with each of the switchable magnets of the magnetic legs remaining switched on, The steps include: magnetically detaching the UAV from the ferromagnetic cylindrical surface at the start of takeoff by switching off the switchable magnets in each of the magnetic legs, The steps include, following the perching step, taking off the UAV from the cylindrical surface, With respect to each magnetic leg using the aforementioned articulated joint, the steps include passively maintaining the inward orientation of the flat bottom contact surface and the outward orientation of the center of gravity during takeoff, with the center of gravity of the pivot portion located outside the pivot axis. Methods that include...

10. With respect to each magnetic leg using an inward rotation limiter of the fixed portion of the magnetic leg, the further step includes limiting the inward rotation of the flat bottom contact surface and the outward rotation of the center of gravity during landing and takeoff, The method according to claim 9.

11. The steps include: landing the UAV on a flat landing surface using the magnetic legs; With respect to each of the magnetic legs that uses the single articulated joint having the single degree of freedom around the pivot axis, in response to the flat bottom contact surface coming into contact with the flat landing surface during the landing on the flat landing surface, the steps include: (1) passively orienting the flat bottom contact surface parallel to the flat surface, and (2) passively orienting the center of gravity inward from the pivot axis; The steps include taking off the UAV from the flat landing surface, With respect to each of the magnetic legs using the articulated joint, the step of passively maintaining 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, with the center of gravity of the pivot portion located on the inward side of the pivot axis. Further including, The method according to claim 9.

12. With respect to each magnetic leg using the outward rotation limiter on the fixed portion of the magnetic leg, the steps include: (1) limiting the outward rotation of the flat bottom contact surface to a nearly flat orientation, and (2) limiting the inward rotation of the center of gravity, during the landing on the flat landing surface and the takeoff from the flat landing surface. The method according to claim 11.

13. With respect to each of the magnetic legs, the further step includes measuring the amount of pivot movement of the pivot portion around the pivot axis using an angle rotation sensor of the magnetic leg after the flat bottom contact surface has come into contact with the cylindrical surface. The method according to claim 9.

14. The control circuit of the UAV further includes the step of determining when to switch on the magnets of the magnetic legs at the end of the landing, using the measured amount of pivot of the pivot portion of the magnetic legs. The method according to claim 13.

15. With respect to each of the magnetic legs, the method further includes the steps of: operating the magnet using a switch actuator on the pivot portion connected to the top of the magnet to switch the magnet on and off; and controlling the switch actuator by the control circuit to switch the magnet on when the respective rotation angles in the measured pivot amount of the pivot portion of the magnetic leg are the same. The method according to claim 14.

16. The control circuit of the UAV further includes the step of determining the diameter of the cylinder corresponding to the surface of the cylindrical shape using the measured amount of pivot of the pivot portion of the magnetic leg, The method according to claim 13.

17. The control circuit of the UAV further includes the step of determining the distance from the main body to the cylindrical surface using the measured amount of pivot of the pivot portion of the magnetic leg, The method according to claim 13.

18. The fixed portion of each magnetic leg includes an inward rotation limiter to restrict the inward rotation of the flat bottom contact surface and the outward rotation of the center of gravity during landing and takeoff. The UAV according to claim 6.

19. The UAV is further configured to land on and take off from a flat landing surface, and the articulated joints of each magnetic leg are further configured to provide the pivot portion and the center of gravity with a single degree of freedom about the pivot axis, and in response to the flat bottom contact surface contacting the flat landing surface during the landing on the flat landing surface, (1) the flat bottom contact surface is passively oriented parallel to the flat landing surface, and (2) the center of gravity is passively oriented inward from the pivot axis, and in response to the flat bottom contact surface contacting the flat landing surface during the takeoff from the flat landing surface. The UAV according to claim 6.

20. 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 nearly flat orientation and to restrict the inward rotation of the center of gravity during landing on the flat landing surface and takeoff from the flat surface, The UAV according to claim 19.

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