Bistable and Switchable Magnetic Legs for UAV Landing 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 to magnetically land or perch on curved ferromagnetic surfaces, such as carbon steel pipes. [Background technology]

[0002] One of the greatest challenges in the oil and gas industry is the regular inspection of elevated assets found in refineries, gas plants, offshore platforms, and other plants and facilities. These assets include elevated pipes and other structures that are difficult to access during inspection operations. Often, the only 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 poses a significant cost barrier for frequent inspections, as well as safety concerns, primarily in the form of fall and trip hazards. Summary of the Invention [Problem to be solved by the invention]

[0003] The present disclosure addresses these and other problems in the art by providing a technical solution for an effective UAV with bistable, switchable magnetic legs for landing on curved ferromagnetic surfaces. [Means for solving the problem]

[0004] According to a first aspect of the present disclosure, there is provided an unmanned aerial vehicle (UAV) configured to land, take off, and magnetically perch on a ferromagnetic cylindrical surface. The UAV includes a body and a plurality of articulating magnetic legs configured to land the UAV on the ferromagnetic cylindrical surface and to magnetically perch the UAV on the ferromagnetic cylindrical surface after landing. 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 configured to provide the pivot portion with a single degree of freedom about the pivot axis, and to passively orient the pivot portion inwardly and toward 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 magnetic field of the switchable magnet is switched on to magnetically attach the UAV to the ferromagnetic cylindrical surface at the end of landing and throughout the perch, and is switched off to magnetically detach the UAV from the ferromagnetic cylindrical surface at the beginning of takeoff.

[0005] In embodiments consistent with the above, the fixed portion of each magnetic leg includes an inward rotation limiter configured to limit inward rotation of the pivoting 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 joint of each magnetic leg is further configured to provide the pivot portion with a single degree of freedom 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 the flat surface, and to passively maintain the flat orientation of the pivot portion during takeoff from the flat surface.

[0007] In an embodiment consistent with the above, the fixed portion of each magnetic leg includes an outward rotation limiter for limiting the outward rotation of the pivoting portion to a nearly flat orientation during landing on and take-off from a flat surface.

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

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

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

[0011] In an embodiment consistent with the above, for each magnetic leg, the pivoting portion includes a switch actuator, the switch actuator coupled to a top of the magnet and configured to actuate the magnet to switch the magnet between on and off, and the control circuitry further configured to control the switch actuator to switch on the magnet when the measured pivoting amounts of the pivoting portions of the magnetic legs are at the same inward angle.

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

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

[0014] In embodiments consistent with the above, the ferromagnetic cylindrical surface is a portion of a carbon steel pipe or vessel.

[0015] According to another aspect of the present disclosure, a method for landing, taking off, and magnetically perching an unmanned aerial vehicle (UAV) on a ferromagnetic cylindrical surface is provided. The UAV includes a body portion and a plurality of articulating magnetic legs, each of the plurality of articulating magnetic legs having a fixed portion coupled to the body portion 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 having a single degree of freedom about the pivot axis. The method includes the steps of: landing the UAV on the ferromagnetic cylindrical surface using the magnetic legs; for each magnetic leg using a single articulation joint having a single degree of freedom about the pivot axis, passively orienting the pivot portion inward and toward the cylindrical surface in response to the pivot portion contacting the cylindrical surface during landing; magnetically attaching the UAV to the ferromagnetic cylindrical surface upon completion of landing by switching on a switchable magnet in each magnetic leg; and switching on a switchable magnet in each magnetic leg. magnetically perching the UAV on the ferromagnetic cylindrical surface after landing using the magnetic legs while they remain switched on; magnetically detaching the UAV from the ferromagnetic cylindrical surface at the start of takeoff by switching off the switchable magnets in each magnetic leg; taking off the UAV from the cylindrical surface after the perching step; and, for each magnetic leg using an articulated joint, passively maintaining an inward orientation of the pivoting portion during takeoff with the center of gravity of the pivoting portion on an outward side of the pivot axis.

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

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

[0018] In embodiments consistent with the methods described above, the method further includes limiting the outward rotation of the pivoting portion to a nearly flat orientation during landing on and take-off from a flat surface for each magnetic leg using an outward rotation limiter in the fixed portion of the magnetic leg.

[0019] In an embodiment consistent with the methods described above, the method further includes, for each of the magnetic legs, measuring the amount of pivoting of the pivoting portion about the pivot axis using an angular rotation sensor in the magnetic leg after the pivoting portion contacts the cylindrical surface.

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

[0021] In an embodiment consistent with the methods described above, the method further includes, for each of the magnetic legs, activating the magnet using a switch actuator of a pivoting portion coupled to an upper portion of the magnet to switch the magnet between on and off, and controlling by a control circuit the switch actuator to switch on the magnet when the measured pivoting amounts of the pivoting portions of the magnetic legs are at the same inward angle.

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

[0023] In an embodiment consistent with the methods 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 using the measured pivot amount of the pivoting portion of the magnetic leg.

[0024] Any combination of the various embodiments and implementations disclosed herein may be used. These and other aspects and features may be understood from the following description of specific embodiments, taken in conjunction with the accompanying drawings and claims. [Brief explanation of the drawings]

[0025] [Figure 1A] FIG. 1 illustrates an assembly diagram of an exemplary articulating magnetic leg for landing an unmanned aerial vehicle (UAV) or drone on a curved surface, according to an embodiment. [Figure 1B] FIG. 1 illustrates an exploded view of an exemplary articulating magnetic leg for landing an unmanned aerial vehicle (UAV) or drone on a curved surface, according to an embodiment. [Figure 2A] FIG. 1 illustrates an exemplary UAV with articulating magnetic legs landing on a flat surface, according to an embodiment. [Figure 2B]FIG. 1 illustrates an exemplary UAV with articulating magnetic legs landing on a curved surface, according to an embodiment. [Figure 3A] 1 illustrates an exemplary articulating magnetic leg of a UAV making initial contact with a curved surface (e.g., a pipe), according to an embodiment. [Figure 3B] 1 illustrates an exemplary articulating magnetic leg of a UAV making final contact with a curved surface (e.g., a pipe, etc.), according to an embodiment. [Figure 3C] FIG. 3C illustrates the articulating magnetic leg of FIGS. 3A-3B making initial contact with a flat surface. [Figure 3D] FIG. 3C illustrates the articulating magnetic leg of FIGS. 3A-3B making final contact with a flat surface. [Figure 4A] 1 illustrates an exemplary articulating magnetic leg of a UAV prior to takeoff from a flat surface, according to an embodiment. [Figure 4B] 1 illustrates an exemplary articulating magnetic leg of a UAV prior to takeoff from a curved surface, according to an embodiment. [Figure 5A] FIG. 1 illustrates an exemplary UAV with articulating magnetic legs landing in a centered orientation on a pipe, according to an embodiment. [Figure 5B] FIG. 5B illustrates the UAV of FIG. 5A landing in a non-centered orientation on a pipe and making initial contact. [Figure 5C] FIG. 5B illustrates the UAV of FIG. 5A landing in an off-center orientation on a pipe and making final contact. [Figure 6A] FIG. 1 illustrates an exemplary UAV with articulating magnetic legs landing on a curved surface, according to an embodiment. [Figure 6B] FIG. 1 illustrates an exemplary UAV with articulating magnetic legs landing on a flat surface, according to an embodiment. [Figure 7]1 is a flow diagram of an exemplary method for landing, taking off, and magnetically perching a UAV on a ferromagnetic cylindrical surface, according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

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

[0027] Exemplary embodiments of the present disclosure are directed to 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., home or operating bases, or the tops of many structures, such as storage tanks). Some such embodiments utilize switchable magnets and constrained joints, for example, to help improve stability and reduce wobble during takeoff and landing. 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 bistability provides less wobble during flight. In some exemplary embodiments, one or more angular rotation sensors are provided to determine the pipe diameter after contact, for example, when landing or perching on a carbon steel pipe.

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

[0029] Thus, in exemplary embodiments, systems and methods are provided for an effective way to enable drones (e.g., battery-powered drones or UAVs) to magnetically land and perch on these assets, for example, 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 ferromagnetic surfaces after landing and before takeoff. This allows such UAVs to conserve their battery power by landing on pipes instead of hovering during missions requiring long periods of time (e.g., gas leak surveillance or monitoring), perform tasks requiring contact with the pipe, such as inspections (e.g., ultrasonic inspections, magnetic inspections) or light maintenance (e.g., coatings), deliver payloads (e.g., small sensing devices and crawlers, etc.) to the pipes, or retrieve samples (e.g., corrosion specimens, etc.). Exemplary embodiments provide for UAVs landing on operational assets (e.g., pipes, vessels, structures, etc.) found in oil and gas facilities. In some such embodiments, magnetic attachment (eg, switchable magnetic legs) is used by the UAV since most of these assets are made from carbon steel.

[0030] According to various embodiments, a UAV is provided with passively articulating landing legs with embedded switchable magnets. These magnets are selectively turned on or off, which facilitates easy detachment during takeoff from a pipe by switching off the magnets. According to some embodiments, a magnetic perch mechanism is provided (e.g., part of a UAV). The mechanism tolerates landing on various pipe diameters (e.g., 6 inches or larger) and misalignment due to imperfect landing (e.g., up to 15° from vertical, or in some cases, 20° off vertical). Because payload weight is a significant limitation for most UAVs, the mechanism uses lightweight landing legs (e.g., as light as possible or practical). Numerous variations of UAVs and articulating magnetic legs exist, example embodiments of which are illustrated in FIGS. 1A-6B and described in the text that follows.

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

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

[0033] In one or more embodiments, the switchable magnet 140 includes two stacked disc magnets, one stationary and one rotatable (e.g., the top disc magnet). The rotatable disc magnet is rotated or oriented to one of two positions. In the first position, the rotatable disc magnet cancels the magnetic field of the other disc magnet, which effectively switches off the magnetism of the switchable magnet 140. In the second position (e.g., rotated 180° from the first position), the rotatable disc magnet is oriented the same as the magnetic field of the other disc magnet, which reinforces the total magnetic field and switches on the switchable magnet 140.

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

[0035] The switchable magnets 140 of each magnetic leg 110 are switched on at some point in the landing maneuver. For example, this switching can occur at the beginning of landing while the UAV is approaching a landing target (e.g., a pipe) or at the end of landing after the foot (e.g., the pivoting portion 130) settles after touching down on the pipe. To activate the switching, in one embodiment, an on-board controller (on the drone) is programmed or otherwise configured to send a signal to the servo motors 132 to allow the UAV to cling to (or magnetically perch on) the pipe. When it's time for takeoff (e.g., at the beginning of takeoff), the switchable magnets 140 are switched off (e.g., by the on-board controller being further programmed to send such a signal to the servo motors 132). This makes the propellers easier to work with and avoids the need to overcome magnetic pull forces during takeoff.

[0036] 2A-2B illustrate an exemplary UAV 200 having articulating magnetic legs 210 landing on a flat surface and a curved surface (e.g., flat surface 60 and pipe 20), respectively, according to an embodiment. UAV 200 includes a body portion (or UAV body portion) 205, and articulating magnetic legs 210 (in this case, four such legs) are attached to body portion 205. UAV 200 also includes multiple propellers 207 attached to body portion 205. In different embodiments, the number of articulating magnetic legs can vary (e.g., six, etc.), and the number of propellers can vary (e.g., six, etc.). In some embodiments, the number of articulating magnetic legs is the same as the number of propellers. In some embodiments, the articulating magnetic legs are arranged symmetrically about a longitudinal (e.g., length) axis of the UAV. For ease of explanation throughout, the number of articulating magnetic legs of the UAV is four, the number of propellers of the UAV is four, and the articulating magnetic legs are symmetrically arranged about the longitudinal axis of the UAV, although other embodiments are not necessarily so limited.

[0037] 2A-2B show UAV 200 landing on two different surfaces: a flat surface 60 (e.g., a home base or the top of a vertically oriented cylinder) and a curved pipe 20 (e.g., a carbon steel pipe or the top of a horizontally oriented cylinder or a cylindrically curved portion of a structure). Here, "top" refers to gravity, and the articulating magnetic legs 210 of UAV 200 in FIG. 2B are symmetrically positioned 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 articulating magnetic legs 210 are adapted to enable landing on any pipe diameter greater than 6 inches. That is, the articulating magnetic legs 210 are adaptable to pipes of multiple diameters (e.g., all articulating magnetic legs 210 are capable of reliably landing).

[0038] 3A-3B illustrate an exemplary articulating magnetic leg 310 of a UAV (such as UAV 200) making initial and final contact, respectively, with a curved surface 40 (such as a pipe or other partially or fully cylindrically curved surface having a predetermined radius of curvature, such as pipe 20), according to an embodiment. FIGS. 3C-3D illustrate the articulating magnetic leg 310 of FIGS. 3A-3B making initial and final contact, respectively, with a flat surface 60. The articulating magnetic leg 310 includes a fixed portion 320 (coupled to a body portion of the UAV) and a pivoting portion 330 coupled to the fixed portion 320 through a pivot point 350 (e.g., a pivot axis that defines a single degree of freedom of rotation of the pivoting portion 330 relative to the fixed portion 320, such as pivot pin 144).

[0039] 3A-3B, when the longitudinal axis of the UAV is aligned with or parallel to the longitudinal axis of a pipe or other cylindrically curved surface, pivot axis 350 is parallel to the longitudinal axis of the UAV to impart inward (or outward) rotation of pivot portion 330 relative to curved surface 40. Thus, initial contact of pivot portion 330 with curved surface 40 causes contact force 45 to be applied to pivot portion 330, which in turn causes a corresponding clockwise rotation 360 (inward) of pivot portion 330 about pivot axis 350. Inward rotation 360 continues until pivot portion 330 (or, more specifically, the bottom of pivot portion) 330 abuts curved surface 40 upon final contact between pivot portion 330 and curved surface 40.

[0040] 3C-3D, the pivot axis is parallel to the flat surface 60. Thus, 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, 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 is aligned with the flat surface 60 upon final contact between the pivot portion 330 and the flat surface 60.

[0041] Legs 310 have one degree of freedom about pivot axis 350 (or pivot point) shown in Figures 3A-3D, allowing them to rotate and conform to surfaces with different curvatures. When legs 310 rotate to face a flat surface and make contact, they continue to point in that direction even after detachment. Similarly, when legs 310 rotate to face a curved surface or a small pipe, they continue to point in that direction even after detachment. This makes the joint stable (e.g., bistable) in these two positions, reducing rocking and wobbling in the leg joints during flight.

[0042] 3A-3B, when leg 310 contacts curved surface 40 at the contact point, surface 40 pushes against leg 310 (and, in particular, 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 (e.g., touches) surface 40. Contact force 45 generates a rotational torque in the correct direction (clockwise in this case) 360 due to the flat design of the bottom contact surface of pivot portion 330 of leg 310.

[0043] 3C-3D, leg 310 (and, in particular, pivoting portion 330) contacts flat surface 60 at a contact point. In addition, the flat bottom of pivoting portion 330 is not parallel to flat surface 60. Thus, rotating portion 330 of leg 310 rotates about or about its pivot axis 350 (in this case, counterclockwise 365) until the flat bottom of rotating portion 330 faces flat surface 60. This is due to a pushing force 65 from 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 pivoting portion 330 of leg 310.

[0044] 4A-4B illustrate exemplary articulating magnetic legs 410 of a UAV (e.g., UAV 200) prior to takeoff from flat and curved surfaces (e.g., flat surface 60 and curved surface 40), respectively, according to an embodiment. Legs 410 (more specifically, pivoting portions 430) have only one degree of freedom—i.e., inward (e.g., clockwise or rotational direction 460 as shown in FIG. 4B ) or outward (e.g., counterclockwise or rotational direction 465 as shown in FIG. 4A )—about pivot point 450 (or about a pivot axis), allowing legs 410 to land flat on the flat surface or against a curved surface. These curved surfaces can include pipes of different sizes (or diameters) with correspondingly different curvatures (or radii of curvature).

[0045] The legs 410 have two stable positions and are therefore sometimes referred to as bistable. When the legs 410 rotate to face a flat surface (e.g., as shown in FIGS. 3C-3D), the legs 410 continue to face that direction during and after detachment (e.g., as part of takeoff from a flat surface). Similarly, when the legs 410 rotate to face a curved surface or a small pipe (e.g., as shown in FIGS. 3A-3B), the legs 410 continue to face that direction during and after detachment (e.g., as part of takeoff from a curved surface or a small pipe). This makes the joints (e.g., pivot portions 430) stable (bistable) in these two positions, which helps reduce rocking and wobbling in the leg joints during flight.

[0046] More specifically, when landing on a flat surface, leg 410 remains in a vertical orientation after takeoff (e.g., the bottom of pivot portion 430 is parallel to the flat surface). This is due to servo motor 432 being positioned off-center at the top of pivot portion 430. Servo motor 432 is off-center with respect to pivot axis 450, causing servo motor center of gravity 485 to be shifted to the left of pivot axis 450 (while the center of gravity of the remainder of pivot portion 430 remains centered with respect to pivot axis 450). The leftward shift of servo motor 432's center of gravity causes leg 410 to rotate outward (in counterclockwise direction 465 as shown in FIG. 4A ).

[0047] However, a fixed portion of the leg 410 (e.g., the leg frame) acts as a rotation limiter 475 to prevent the pivoting portion 430 from rotating further in this direction. For example, the rotation limiter 475 prevents the pivoting portion 430 from rotating more than a few degrees in the outward direction (e.g., no more than 3 degrees or no more than 5 degrees), effectively maintaining the bottom of the pivoting portion 430 nearly flat during takeoff from a flat surface. In some embodiments, the same effect is achieved by maintaining the center of gravity of the pivoting portion 430 on the inward side 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 pivoting portion is above the pivot axis 450 when perching and taking off from a flat surface. Here, directions such as "upward" are with respect to the direction of gravity.

[0048] Furthermore, when landing on a curved surface, the contact force from the surface on the bottom part of the leg 410 generates a torque that causes the leg 410 to rotate and achieve the rotated (inward) orientation shown in FIG. 4B . The leg 410 remains in this orientation even after takeoff because the center of gravity 480 of the servo motor 432 (or the center of gravity of the pivoting portion 430) shifts outward from the pivot axis 450 (and, in some embodiments, above the pivot axis 450), causing the weight to generate an opposing torque (in the clockwise direction 460, as shown in FIG. 4B ) that maintains the pivoting portion 430 in this (inward) orientation. Here, the fixed portion 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, 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°.

[0049] FIG. 5A illustrates an exemplary UAV 500 with articulating magnetic legs 510 landing in a centered orientation on a pipe 20, according to an embodiment. FIGS. 5B-5C illustrate the UAV 500 of FIG. 5A landing in a non-centered orientation on a pipe 20, making initial contact and final contact, respectively. In some embodiments, measuring the rotational angle of the legs 510 due to their single degree of freedom before or after contacting a surface (e.g., pipe 20) is performed through a rotational angle sensor, such as a potentiometer, rotary encoder, or shaft encoder, in each magnetic leg 510. Determining the rotational angle of each leg 510 helps determine the orientation of the leg 510 or UAV 500 relative to the surface. In some embodiments, the rotational angle sensor measures the angular rotation of a pivoting portion of the leg 510 relative to gravity, while in some embodiments, the rotational angle sensor measures the angular rotation of a pivoting portion of the leg 510 relative to a 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 .

[0050] For example, in some embodiments, rotation angle sensors are mounted on the legs 510, and control circuitry is provided to signal whether all of the magnetic legs 510 have the same orientation (e.g., the same measured inward angle of their pivoting portions) when landing on a surface before switching on the switchable magnets of the magnetic legs 510. This helps detect situations where one or more legs are not touching the surface or are not touching it at the proper (inward) angle, which indicates an insufficient or incomplete attempt to land 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 UAV 500 to detect when the body of the UAV 500 is level with respect to gravity.

[0051] For example, the pivoting portions of the legs 510 of the UAV 500 in FIG. 5B are not at the same angular rotation, indicating a problem with landing (in this case, the UAV 500 is off-center relative to the top of the pipe 20). If the UAV 500 continues landing, attempting to force the pivoting portions to have the same angular rotation, at least relative to a fixed portion, as in FIG. 5C, the UAV 500 will no longer be level with respect to gravity. This can be detected, for example, by a level sensor in the body of the UAV 500 or by a rotation angle sensor in the legs 510 that measures the angular rotation of the pivoting portions 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] 6A-6B illustrate an exemplary UAV 600 having articulating magnetic legs 610 landing on flat and curved surfaces (a pipe 20 and a flat surface 60), respectively, according to an embodiment. The legs 610 are coupled to a UAV body 605. Here, rotational angle sensors in the legs 610 are used to measure the curvature of the surface on which the legs 610 land. In some embodiments, the measurements are 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, the amount the payload of the UAV 600 needs to be lowered to the surface (e.g., distance 690 from the body 605 to the pipe 20 or distance 695 to the flat surface 60, for example) can be established. Determining this distance can be particularly useful when a controller is used (e.g., configured by code) to deploy the payload through a feedback loop between the controller and the sensor.

[0053] 1A-6B , in some exemplary embodiments, an unmanned aerial vehicle (UAV, such as UAV 200, 500, or 600) is provided that lands, takes off, and magnetically perches on a ferromagnetic cylindrical surface (such as a pipe 20 or a curved surface 40). The UAV includes a main body (such as UAV main body 205 or 605) and a plurality of articulating magnetic legs (such as four or six articulating magnetic legs 110, 210, 310, 410, 510, or 610). The magnetic legs land the UAV on the ferromagnetic cylindrical surface and magnetically perch the UAV on the ferromagnetic cylindrical surface after landing. 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) pivotally connected to the fixed portion at a pivot axis (e.g., pivot pin 144 or pivot axis 305 or 405).

[0054] The pivoting portion includes a switchable magnet (such as switchable magnet 140) that is switched on to magnetically attach the UAV to the ferromagnetic cylindrical surface at the end of landing and throughout the perch, and that is switched off to magnetically detach the UAV from the ferromagnetic cylindrical surface at the beginning of takeoff. The pivoting portion further includes only a single articulation joint (such as pivot pin 144) that provides the pivoting portion with only a single degree of freedom (e.g., inward and outward) about a pivot axis and is adapted to passively orient the pivoting portion inward and toward the cylindrical surface in response to the pivoting portion contacting the cylindrical surface during landing, and is adapted to passively maintain the inward orientation of the pivoting portion during takeoff. The single articulation joint with a single degree of freedom also passively maintains the inward orientation of the pivoting portion during takeoff.

[0055] In one embodiment, the fixed portion of each magnetic leg includes an inward rotation limiter (such as rotation limiter 470) that limits inward rotation of the pivoting portion during landing and takeoff. In one embodiment, the UAV lands on and takes off from a flat surface (such as flat surface 60). In addition, the articulation joint of each magnetic leg further provides the pivoting portion with a single degree of freedom about the pivot axis so as to passively orient the pivoting portion flat and parallel to the flat surface in response to the pivoting portion contacting the flat surface during landing on the flat surface. Furthermore, the articulation joint with a single degree of freedom also passively maintains the flat orientation of the pivoting portion during takeoff from the flat surface.

[0056] In one embodiment, the fixed portion of each magnetic leg includes an outward rotation limiter (e.g., rotation limiter 475, etc.) to limit the outward rotation of the pivoting portion to a nearly flat orientation (e.g., within a few degrees of flat, such as no more than 3 degrees or no more than 5 degrees from flat) during landing on and takeoff from a flat surface. In one embodiment, the pivoting portion of each magnetic leg further includes a switch actuator (e.g., servo motor 132 or 432, etc.) on top of the switchable magnet. The switch actuator actuates the magnet to switch it between on and off. The center of gravity of the switch actuator is on the outward side of the pivot axis (e.g., center of gravity 480, etc.) during takeoff from a cylindrical surface and on the inward side of the pivot axis (e.g., center of gravity 485, etc.) during takeoff from a flat surface.

[0057] In some embodiments, each magnetic leg further includes an angular rotation sensor that measures the amount of pivoting of the pivot portion about the pivot axis after the pivot portion contacts the cylindrical surface. In some embodiments, the UAV further includes control circuitry that is configured (e.g., programmed by code, etc.) to use the measured amount of pivoting 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. In some embodiments, for each magnetic leg, the pivot portion includes a switch actuator that is coupled to the top of the magnet and actuates the magnet to switch the magnet between on and off. The control circuitry is further configured (e.g., by code therefor, etc.) to control the switch actuator to switch on the magnet when the measured amount of pivoting of the pivot portion of the magnetic leg is at the same inward angle.

[0058] In one embodiment, the UAV further includes control circuitry configured with code for using the measured pivoting amount of the pivoting portion of the magnetic legs to determine a diameter of a cylinder corresponding to the cylindrical surface. In one embodiment, the UAV further includes control circuitry configured with code or other programmable logic for using the measured pivoting amount of the pivoting portion of the magnetic legs to determine a distance from the body portion to the cylindrical surface (e.g., distance 690, etc.). In one embodiment, the ferromagnetic cylindrical surface is a portion of a carbon steel pipe or vessel (e.g., a storage tank, etc.).

[0059] 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 their assigned tasks. These devices are positioned on or within (or otherwise in close proximity to) the body or legs of the UAV to perform the techniques. In some exemplary embodiments, control logic is implemented as computer code configured to run on computing circuitry (e.g., a microprocessor, etc.) to perform the control steps that are part of the techniques.

[0060] 7 is a flow diagram of an exemplary method 700 for landing, taking off, and magnetically perching a UAV (e.g., UAV 200, 500, or 600, etc.) on a ferromagnetic cylindrical surface (e.g., pipe 20 or curved surface 40, etc.) according to an embodiment. The UAV includes a body portion (e.g., UAV body portion 205 or 605, etc.) and a plurality of articulating magnetic legs (e.g., magnetic legs 110, 210, 310, 410, 510, or 610, etc.). Each leg has a fixed portion (e.g., fixed portion 120 or 320, etc.) coupled to the body portion and a pivot portion (e.g., pivot portion 130, 330, or 430, etc.) pivotally coupled to the fixed portion at a pivot axis (e.g., pivot axis 350 or 450, etc.). The pivot portion includes a switchable magnet (such as, for example, switchable magnet 140) and a single articulation joint (such as, for example, pivot pin 144) having a single degree of freedom (e.g., inward or outward) about a pivot axis.

[0061] Some or all of method 700 can be implemented using the components and techniques illustrated in FIGS. 1A-6B. Additionally, portions of this and other methods disclosed herein can be implemented on or using custom or preprogrammed logic devices, circuits, or processors, such as programmable logic circuits (PLCs), computers, software, or other circuits (e.g., ASICs, FPGAs), configured with code or logic to perform their assigned tasks. The device, circuit, or processor can be, for example, a dedicated or shared hardware device (e.g., a laptop computer, a single-board computer (SBC), a workstation, a tablet, a smartphone, part of a server, or a dedicated hardware circuit such as in an FPGA or ASIC), or a computer server, or part of a server or computer system. The device, circuit, or processor can include a non-transitory computer-readable medium (e.g., a read-only memory (ROM), a flash drive, or a disk drive) that stores instructions that, when executed on one or more processors, cause portions of method 700 (or other disclosed methods) to be performed. It should be noted that in other embodiments, the order of the operations may be changed and some of the operations may be omitted. Also, some of the method 700 may be implemented using logic, circuitry, or a processor located on or in electronic communication with a processing circuit configured by code to perform those portions of the method 700.

[0062] In method 700, processing begins with step 710 of landing a UAV on a ferromagnetic cylindrical surface using magnetic legs. Method 700 further includes step 720, for each magnetic leg using a single articulation joint having a single degree of freedom about a pivot axis, passively orienting the pivot portion inward and toward the cylindrical surface in response to the pivot portion contacting the cylindrical surface during landing. See, for example, FIGS. 3A-3B. Additionally, method 700 includes step 730 of magnetically attaching the UAV to the ferromagnetic cylindrical surface upon completion of landing by switching on a switchable magnet in each magnetic leg. In some embodiments, a servo motor (e.g., servo motor 132 or 432) is used to rotate stacked disk magnets of the switchable magnets, causing the switchable magnets to turn on.

[0063] Subsequently, method 700 includes step 740 of magnetically perching the UAV on the ferromagnetic cylindrical surface after landing using the magnetic legs with the switchable magnets of each of 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 taking off the UAV from the cylindrical surface after the perching step. Additionally, method 700 includes step 770 of passively maintaining an inward orientation of the pivoting portion during takeoff with the center of gravity of the pivoting portion on the outward side of the pivot axis (e.g., as in FIG. 4B ) for each magnetic leg using an articulation joint.

[0064] In some embodiments, method 700 includes, for each magnetic leg, limiting inward rotation of a pivoting portion during landing and takeoff using an inward rotation limiter (e.g., rotation limiter 470) in a fixed portion of the magnetic leg. In some embodiments, method 700 includes landing the UAV on a flat surface (e.g., flat surface 60) using the magnetic legs, and, for each magnetic leg using a single articulation joint having a single degree of freedom about a pivot axis, passively orienting the pivoting portion flat and parallel to the flat surface in response to the pivoting portion contacting the flat surface during landing on the flat surface (e.g., as shown in FIGS. 3C-3D ), taking off the UAV from the flat surface, and, for each magnetic leg using an articulation joint, passively maintaining a flat orientation of the pivoting portion during takeoff from the flat surface with the center of gravity of the pivoting portion on the inward side of the pivot axis.

[0065] In some embodiments, method 700 includes, for each magnetic leg using an outward rotation limiter (e.g., rotation limiter 475) on a fixed portion of the magnetic leg, limiting the outward rotation of the pivoting portion to a nearly flat (e.g., at most 3 degrees or at most 5 degrees) orientation during landing on and takeoff from a flat surface. In some embodiments, method 700 includes, for each magnetic leg, measuring the amount of pivoting of the pivoting portion about a pivot axis using an angular rotation sensor on the magnetic leg after the pivoting portion contacts the cylindrical surface. In some embodiments, method 700 includes, by a control circuit of the UAV, using the measured amount of pivoting of the pivoting portion of the magnetic leg to determine when to switch on the magnets of the magnetic leg at the end of landing.

[0066] In some embodiments, method 700 includes, for each magnetic leg, actuating the magnet using a switch actuator (e.g., servo motor 132 or 432, etc.) of a pivoting portion coupled to the top of the magnet to switch the magnet between on and off, and controlling, by control circuitry, the switch actuator to switch the magnet on when the measured pivoting amount of the pivoting portion of the magnetic leg is at the same inward angle. In some embodiments, method 700 includes determining, by control circuitry of the UAV, the diameter of a cylinder (e.g., pipe 20 having a radius of curvature or cylindrically curved surface 40, etc.) corresponding to the cylindrical surface using the measured pivoting amount of the pivoting portion of the magnetic leg. In some embodiments, method 700 includes determining, by control circuitry of the UAV, the distance from the body to the cylindrical surface (e.g., distance 690, etc.) using the measured pivoting amount of the pivoting portion of the magnetic leg.

[0067] The methods described herein may be implemented in part by software or firmware in machine-readable form on a tangible (e.g., non-transitory) storage medium. For example, the software or firmware may be in the form of a computer program comprising computer program code adapted to perform some of the steps of any of the methods described herein when the program is executed on a computer or suitable hardware device (e.g., FPGA), and where the computer program may be embodied on a computer-readable medium. Examples of tangible storage media include computer storage devices having computer-readable media (e.g., disks, thumb drives, flash memory, etc.), but do not include propagated signals. While a propagated signal may reside in a tangible storage medium, the propagated signal itself is not an example of a tangible storage medium. The software may be suitable for execution on a parallel processor or a serial processor, such that the method steps can be performed in any suitable order or simultaneously.

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

[0069] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0070] Orientational terms are used herein merely for purposes of convention and reference and should not be construed as limiting. However, it is recognized that these terms may be used relative to the viewer. Therefore, no limitation is implied or inferred. Additionally, the use of ordinal numbers (e.g., first, second, third) is for purposes of distinction and not for purposes of counting. For example, the use of "third" does not imply the presence of a corresponding "first" or "second." Also, the phraseology and terminology used herein is for purposes of description and should not be considered limiting. The use of "including," "comprising," "having," "containing," "involving," and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof, as well as additional items.

[0071] The subject matter described above is provided merely as an illustration 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 applications shown 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 claims below, and by structures and functions or steps equivalent to those descriptions). [Explanation of symbols]

[0072] 20 Pipe 40 curved surfaces 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 motor 134 Servo Horn 136 Adapter 140 Switchable Magnets 142 Servo Magnet Holder 144 Pivot pin 200 Unmanned Aerial Vehicle (UAV) 205 UAV main body 207 Propeller 210 Articulated Magnetic Legs 310 Articulated Magnetic Legs 320 Fixed part 330 Pivoting part 350 pivot points 360 rotation direction 365 rotation direction 410 Articulated Magnetic Legs 430 Pivoting part 432 Servo Motor 450 pivot points 460 Rotation Direction 465 Rotation Direction 470 rev limiter 475 rev 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 body 610 Articulated Magnetic Legs 690 Distance from the main body to the pipe surface 695 Distance from the body to a flat surface

Claims

1. 1. An unmanned aerial vehicle (UAV) configured to land, take off, and magnetically perch on a ferromagnetic cylindrical surface, the UAV comprising: A main body portion, a plurality of articulating magnetic legs configured to land the UAV on the ferromagnetic cylindrical surface and to magnetically perch the UAV on the ferromagnetic cylindrical surface after landing, each magnetic leg having a fixed portion coupled to the body portion and a pivot portion pivotally coupled to the fixed portion at a pivot axis; Including, the pivot portion has a center of gravity relative to the pivot axis; The pivot portion is a flat bottom contact surface that contacts the surface of the cylindrical shape during the landing and maintains contact with the cylindrical shape during the perch; a switchable magnet, the magnetism of which is switched on to magnetically attach the UAV to the ferromagnetic cylindrical surface at the end of the landing and throughout the perch, and switched off to magnetically detach the UAV from the ferromagnetic cylindrical surface at the beginning of the takeoff; a single articulation joint configured to provide the pivot portion and the center of gravity with a single degree of freedom about the pivot axis, the articulation joint being configured to passively orient the flat bottom contact surface inwardly and tangent to the cylindrical surface and (2) outwardly of the pivot axis in response to the flat bottom contact surface contacting the cylindrical surface during landing, and to passively maintain the inward orientation of the flat bottom contact surface and the outward orientation of the center of gravity during takeoff; Including, each of the plurality of magnetic legs includes an angular rotation sensor that measures an amount of pivoting of the pivot portion about the pivot axis after the pivot portion contacts the cylindrical surface; The UAV further includes a control circuit configured to use the measured pivot amount of the pivot portion of the magnetic leg to determine: (1) a diameter of a cylinder corresponding to the cylindrical shape; or (2) a distance from the body portion to a surface of the cylindrical shape. Unmanned aerial vehicle (UAV).

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

3. the UAV is further configured to land on and take off from a flat landing surface, the articulated joint of each magnetic leg being further configured to provide the pivot portion and the center of gravity with the single degree of freedom about the pivot axis, to passively orient the flat bottom contact surface parallel to the flat landing surface and inwardly of the pivot axis in response to the flat bottom contact surface contacting the flat landing surface during the landing on the flat landing surface, and to passively maintain the flat orientation of the flat bottom contact surface and the inward orientation of the center of gravity during the takeoff from the flat landing surface. The UAV of claim 1.

4. the fixed portion of each magnetic leg includes an outward rotation limiter for limiting outward rotation of the flat bottom contact surface to a nearly flat orientation and for limiting inward rotation of the center of gravity during the landing on and the takeoff from the flat landing surface. The UAV of claim 3.

5. the pivot portion of each magnetic leg further includes a switch actuator on top of the switchable magnet and configured to actuate the magnet to switch the magnet between on and off, the center of gravity of the switch actuator being outer than the pivot axis during the takeoff from the cylindrical surface and inner than the pivot axis during the takeoff from the flat landing surface. The UAV of claim 3.

6. An unmanned aerial vehicle (UAV) configured to land, take off, and magnetically perch on a ferromagnetic cylindrical surface, the UAV comprising: A main body portion, a plurality of articulating magnetic legs configured to land the UAV on the ferromagnetic cylindrical surface and to magnetically perch the UAV on the ferromagnetic cylindrical surface after landing, each magnetic leg having a fixed portion coupled to the body portion and a pivot portion pivotally coupled to the fixed portion at a pivot axis; Including, the pivot portion has a center of gravity relative to the pivot axis; The pivot portion is a flat bottom contact surface that contacts the surface of the cylindrical shape during the landing and maintains contact with the cylindrical shape during the perch; a switchable magnet, the magnetism of which is switched on to magnetically attach the UAV to the ferromagnetic cylindrical surface at the end of the landing and throughout the perch, and switched off to magnetically detach the UAV from the ferromagnetic cylindrical surface at the beginning of the takeoff; a single articulation joint configured to provide the pivot portion and the center of gravity with a single degree of freedom about the pivot axis, the articulation joint being configured to passively orient the flat bottom contact surface inwardly and tangent to the cylindrical surface and (2) outwardly of the pivot axis in response to the flat bottom contact surface contacting the cylindrical surface during landing, and to passively maintain the inward orientation of the flat bottom contact surface and the outward orientation of the center of gravity during takeoff; Including, each magnetic leg includes an angular rotation sensor configured to measure an amount of pivoting of the pivot portion about the pivot axis after the flat bottom contact surface contacts the cylindrical surface; The UAV further includes a control circuit configured to use the measured pivot amount of the pivot portion of the magnetic leg to determine when to switch on the magnets of the magnetic leg at the end of the landing. Unmanned aerial vehicle (UAV).

7. For each magnetic leg, the pivoting portion includes a switch actuator, the switch actuator coupled to a top of the magnet and configured to actuate the magnet to switch the magnet between on and off, and the control circuitry is further configured to control the switch actuator to switch on the magnet when the measured pivoting amount of the pivoting portion of the magnetic leg is at the same inward angle. The UAV described in claim 6.

8. The ferromagnetic cylindrical surface is a portion of a carbon steel pipe or vessel. The UAV of claim 1.

9. 1. A method of landing, taking off, and magnetically perching an unmanned aerial vehicle (UAV) on a ferromagnetic cylindrical surface, the UAV including a body portion and a plurality of articulating magnetic legs, each of the plurality of articulating magnetic legs having a fixed portion coupled to the body portion and a pivot portion pivotally coupled to the fixed portion at a pivot axis, the pivot portion having a center of gravity relative to the pivot axis, the pivot portion including a flat bottom contact surface, a switchable magnet, and a single articulated joint having a single degree of freedom about the pivot axis, the method comprising: landing the UAV on the ferromagnetic cylindrical surface using the magnetic legs; for each magnetic leg using the single articulated joint having the single degree of freedom about the pivot axis, in response to the flat bottom contact surface contacting the cylindrical surface during landing, (1) passively orienting the flat bottom contact surface inwardly and tangent to the cylindrical surface, and (2) the center of gravity outwardly from the pivot axis; magnetically attaching the UAV to the ferromagnetic cylindrical surface upon completion of the landing by switching on the switchable magnets in each of the magnetic legs; using the magnetic legs with each switchable magnet of the magnetic legs remaining switched on to magnetically perch the UAV on the ferromagnetic cylindrical surface after the landing; magnetically detaching the UAV from the ferromagnetic cylindrical surface at the start of the takeoff by switching off the switchable magnets in each of the magnetic legs; taking off the UAV from the cylindrical surface after the perching step; for each magnetic leg using said articulation joint, passively maintaining an inward orientation of said flat bottom contact surface and an outward orientation of said center of gravity during said takeoff, with said center of gravity of said pivot portion outboard of said pivot axis; A method comprising:

10. and limiting the inward rotation of the flat bottom contact surface and the outward rotation of the center of gravity during the landing and the takeoff for each magnetic leg using an inward rotation limiter of the fixed portion of the magnetic leg.

10. The method of claim 9.

11. landing the UAV on a flat landing surface using the magnetic legs; for each of the magnetic legs using the single articulation joint having the single degree of freedom about the pivot axis, in response to the flat bottom contact surface contacting the flat landing surface during the landing on the flat landing surface, passively orienting (1) the flat bottom contact surface parallel to the flat surface and (2) the center of gravity inboard of the pivot axis; taking off the UAV from the flat landing surface; for each of the magnetic legs using the articulated joint, passively maintaining a planar orientation of the flat bottom contact surface and an inward orientation of the center of gravity during the takeoff from the flat landing surface with the center of gravity of the pivot portion on an inboard side of the pivot axis; Further comprising:

10. The method of claim 9.

12. and (2) limiting the outward rotation of the center of gravity for each magnetic leg using an outward rotation limiter of the fixed portion of the magnetic leg during the landing on and the takeoff from the flat landing surface. The method of claim 11.

13. further comprising, for each of the magnetic legs, measuring an amount of pivoting of the pivot portion about the pivot axis after the flat bottom contact surface contacts the cylindrical surface using an angular rotation sensor of the magnetic leg.

10. The method of claim 9.

14. and using the measured amount of pivoting of the pivoting portion of the magnetic leg by a control circuit of the UAV to determine when to switch on the magnets of the magnetic leg at the end of the landing. The method of claim 13.

15. For each of the magnetic legs, the method further includes the steps of activating the magnet using a switch actuator of the pivot part coupled to a top of the magnet to switch the magnet between on and off, and controlling, by the control circuit, the switch actuator to switch on the magnet when the measured pivot amounts of the pivot parts of the magnetic legs are at the same inward angle. The method of claim 14.

16. and determining, by a control circuit of the UAV, a diameter of a cylinder corresponding to the cylindrical surface using the measured pivot amount of the pivot portion of the magnetic leg. The method of claim 13.

17. and determining, by a control circuit of the UAV, a distance from the body to the cylindrical surface using the measured pivot amount of the pivot portion of the magnetic leg. The method of claim 13.

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

19. The UAV is further configured to land on and take off from a flat landing surface, and the articulated joint of each magnetic leg is further configured to provide the pivot portion and the center of gravity with the 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, to passively orient (1) the flat bottom contact surface parallel to the flat landing surface and (2) the center of gravity inwardly of the pivot axis, and to passively maintain the flat orientation of the flat bottom contact surface and the inward orientation of the center of gravity during the takeoff from the flat landing surface. The UAV described in claim 6.

20. The fixed portion of each magnetic leg includes an outward rotation limiter for limiting outward rotation of the flat bottom contact surface to a nearly flat orientation and for limiting inward rotation of the center of gravity during the landing on and the takeoff from the flat landing surface. The UAV of claim 19.