Patent Publication Number: US-2023159167-A1

Title: Package Loading Mechanism

Description:
An unmanned vehicle, which may also be referred to as an autonomous vehicle, is a vehicle capable of travel without a physically-present human operator. An unmanned vehicle may operate in a remote-control mode, in an autonomous mode, or in a partially autonomous mode. 
     When an unmanned vehicle operates in a remote-control mode, a pilot or driver that is at a remote location can control the unmanned vehicle via commands that are sent to the unmanned vehicle via a wireless link. When the unmanned vehicle operates in autonomous mode, the unmanned vehicle typically moves based on pre-programmed navigation waypoints, dynamic automation systems, or a combination of these. Further, some unmanned vehicles can operate in both a remote-control mode and an autonomous mode, and in some instances may do so simultaneously. For instance, a remote pilot or driver may wish to leave navigation to an autonomous system while manually performing another task, such as operating a mechanical system for picking up objects, as an example. 
     Various types of unmanned vehicles exist for various different environments. For instance, unmanned vehicles exist for operation in the air, on the ground, underwater, and in space. Examples include quad-copters and tail-sitter UAVs, among others. Unmanned vehicles also exist for hybrid operations in which multi-environment operation is possible. Examples of hybrid unmanned vehicles include an amphibious craft that is capable of operation on land as well as on water or a floatplane that is capable of landing on water as well as on land. Other examples are also possible. 
     UAVs may be used to deliver a payload to, or retrieve a payload from, an individual or business. In some operations, once the UAV arrives at a retrieval site, the UAV may land or remain in a hover position. At this point, a person at the retrieval site may secure the payload to the UAV at an end of a tether attached to a winch mechanism positioned with the UAV, or to the UAV itself. For example, the payload may have a handle that may be secured to a device at the end of the winch, or a handle that may be secured within the UAV. However, this scenario has a number of drawbacks. In particular, if the UAV is late for arrival at the retrieval site, the person designated for securing the payload to be retrieved by the UAV may have to wait a period of time before the UAV arrives, resulting in undesirable waiting time. Similarly, if the UAV arrives and the person designated to secure the payload to be retrieved to the UAV is delayed or fails to show up, the UAV may have to wait in a hover mode or on the ground until the designated person arrives to secure the payload to the UAV, resulting in undesirable delay and expenditure of energy by the UAV as the UAV waits for the designated person to arrive, and also resulting in undesirable delay in the subsequent delivery of the payload at a delivery site. 
     As a result, it would be desirable to provide for the automated pickup of a payload by the UAV, where the UAV may automatically pick up the payload without the need for a designated person to secure the payload to the UAV at the retrieval site. Such automated pickup of the payload by the UAV would advantageously eliminate the need for a designated person to secure the payload to the UAV and eliminate potential delays associated with the late arrival of the UAV or designated person at the retrieval site. 
     SUMMARY 
     The present embodiments provide a payload retrieval apparatus and method useful for automatic pickup of a payload at a payload retrieval site by a UAV having a payload retriever suspended from a tether attached to the UAV. The payload retrieval apparatus may be a non-permanent structure that includes an extending member that may be secured to a base or stand at a lower end of the extending member, and an angled extender may be attached at an upper end of the extending member. A channel may be attached to the angled extender, with a first end of the channel having one or more tether engagers extending therefrom. A payload holder secures a payload to a second end of the channel. 
     In operation, a UAV arrives at the payload retrieval site with a tether extending downwardly from the UAV and with the payload retriever suspended from the end of the tether. The UAV approaches the payload retrieval apparatus, and as it nears the payload retrieval apparatus, the tether comes into contact with a tether engager, and as the UAV moves forward, the tether slides inwardly along the tether engager where it is directed towards the first end of the channel. With further forward or upward movement of the UAV, or upward winching of the payload retriever, the tether moves into and through a tether slot in the channel and the payload retriever attached to the tether is pulled into the channel by the tether. The payload retriever is pulled through the channel where it engages, and secures, the payload positioned on a payload holder. The payload retriever then pulls the payload free from the payload holder. Once the payload is free from the payload holder, the payload may be winched upwardly into secure engagement with the UAV, and the UAV may continue on to a delivery site where the payload may be delivered by the UAV. In this manner, automatic pick up of a payload by a UAV is achieved without the need for a person to participate in the retrieval of the payload from a retrieval site. 
     In one aspect, a payload retrieval apparatus is provided including a stand having an upper end and a lower end, a channel having a first end and a second end, the channel coupled to the stand, a first extension that extends in a first direction from the first end of the channel, wherein the first extension is configured to direct a tether extending from a UAV and a payload retriever attached to an end of the tether_toward the first end of the channel, wherein the second end of the channel has a payload engaging member positioned near the second end of the channel that is adapted to secure a payload, and wherein the payload retrieval apparatus is configured to cause the UAV to pick up the payload with the payload retriever while maintaining flying. 
     In another aspect, system for payload retrieval is provided including a payload retrieval apparatus having a channel having a first end and a second end, the channel coupled to a stand, a first extension that extends in a first direction from the first end of the channel, wherein the first extension is configured to direct a tether extending from a UAV and a payload retriever attached to an end of the tether towards the first end of the channel, wherein the second end of the channel has a payload engaging member adapted to secure a payload, wherein the system is configured to cause the UAV to pick up the payload with the payload retriever while maintaining flying, and wherein the channel includes a tether slot that extends from the first end of the channel to the second end of the channel, the tether slot configured to guide passage of the tether coupled to the payload retriever when the payload retriever is passing within the channel. 
     In yet another aspect, a method of retrieving a payload is provided, including (i) positioning a payload having a handle with an aperture on a payload engaging member coupled to a channel on a payload retrieval apparatus; (ii) causing a UAV having a payload retriever attached to a tether suspended from the UAV to position the tether to come into contact with a first extension extending from an end of the channel; (iii) causing the UAV to advance the tether into a tether slot positioned on a top of the channel, wherein the tether slot has a width that is narrower than a width of the payload retriever; (iv) causing the UAV to advance the payload retriever into the channel; (v) causing the UAV to advance the payload retriever until the payload retriever engages the handle of the payload; and (vi) causing the UAV to pick up the payload by the payload retriever thereby disengaging the payload from the payload engaging member. 
     The present embodiments further provide means for automatically retrieving a payload from a payload retrieval apparatus with a UAV having a payload retriever attached to a tether that is suspended from the UAV. 
     These as well as other aspects, advantages, and alternatives will become apparent to those of ordinary skill in the art by reading the following detailed description with reference where appropriate to the accompanying drawings. Further, it should be understood that the description provided in this summary section and elsewhere in this document is intended to illustrate the claimed subject matter by way of example and not by way of limitation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is an isometric view of an example unmanned aerial vehicle  100 , according to an example embodiment. 
         FIG.  1 B  is a simplified illustration of an unmanned aerial vehicle, according to an example embodiment. 
         FIG.  1 C  is a simplified illustration of an unmanned aerial vehicle, according to an example embodiment. 
         FIG.  1 D  is a simplified illustration of an unmanned aerial vehicle, according to an example embodiment. 
         FIG.  1 E  is a simplified illustration of an unmanned aerial vehicle, according to an example embodiment. 
         FIG.  2    is a simplified block diagram illustrating components of an unmanned aerial vehicle, according to an example embodiment. 
         FIG.  3    is a simplified block diagram illustrating a UAV system, according to an example embodiment. 
         FIGS.  4 A,  4 B, and  4 C  show a payload delivery apparatus, according to example embodiments. 
         FIG.  5 A  shows a perspective view of a payload delivery apparatus  500  including payload  510 , according to an example embodiment. 
         FIG.  5 B  is a cross-sectional side view of payload delivery apparatus  500  and payload  510  shown in  FIG.  5 A . 
         FIG.  5 C  is a side view of payload delivery apparatus  500  and payload  510  shown in  FIGS.  5 A and  5 B . 
         FIG.  6 A  is a perspective view of payload coupling apparatus  800 , according to an example embodiment. 
         FIG.  6 B  is a side view of payload coupling apparatus  800  shown in  FIG.  6 A . 
         FIG.  6 C  is a front view of payload coupling apparatus  800  shown in  FIGS.  6 A and  6 B . 
         FIG.  7    is a perspective view of payload coupling apparatus  800  shown in  FIGS.  6 A- 6 C , prior to insertion into a payload coupling apparatus receptacle positioned in the fuselage of a UAV. 
         FIG.  8    is another perspective view of payload coupling apparatus  800  shown in  FIGS.  6 A- 6 C , prior to insertion into a payload coupling apparatus receptacle positioned in the fuselage of a UAV. 
         FIG.  9    shows a perspective view of a recessed restraint slot and payload coupling apparatus receptacle positioned in a fuselage of a UAV. 
         FIG.  10 A  shows a side view of a payload delivery apparatus  500  with a handle  511  of payload  510  secured within a payload coupling apparatus  800  as the payload  510  moves downwardly prior to touching down for delivery. 
         FIG.  10 B  shows a side view of payload delivery apparatus  500  after payload  510  has landed on the ground showing payload coupling apparatus  800  decoupled from handle  511  of payload  510 . 
         FIG.  10 C  shows a side view of payload delivery apparatus  500  with payload coupling apparatus  800  moving away from handle  511  of payload  510 . 
         FIG.  11 A  is a side view of handle  511  of payload  510  having openings  514  and  516  adapted to receive pins positioned on a payload holder, according to an example embodiment. 
         FIG.  11 B  is a side view of handle  511 ′ of a payload having magnets  514 ′ and  516 ′ positioned thereon for magnetic engagement with a payload holder, according to an example embodiment. 
         FIG.  12    shows a pair of locking pins  570 ,  572  extending through holes  514  and  516  in handle  511  of payload  510  to secure the handle  511  and top of payload  510  within the fuselage of a UAV, or to secure the handle  511  to a payload holder on a payload retrieval apparatus. 
         FIG.  13 A  is a side view of payload coupling apparatus  800 ′ with a slot  808  positioned above lip  806 ′, according to an example embodiment. 
         FIG.  13 B  is a side view of payload coupling apparatus  800 ′ after lip  806 ′ has been moved outwardly to facilitate engagement with a handle of a payload. 
         FIG.  13 C  is a side view of payload coupling apparatus  800 ″ having a plurality of magnets  830  positioned thereon, according to an example embodiment. 
         FIG.  13 D  is a side view of payload coupling apparatus  900  having a weighted side  840 , according to an example embodiment. 
         FIG.  14    is a perspective view of payload retrieval apparatus  1000  having a payload  510  positioned thereon, according to an example embodiment. 
         FIG.  15    is another perspective view of payload retrieval apparatus  1000  and payload  510  shown in  FIG.  14   . 
         FIG.  16    is a further perspective view of payload retrieval apparatus  1000  and payload  510  shown in  FIGS.  14  and  15   . 
         FIG.  17    shows a sequence of steps A-D performed in the retrieval of payload  510  from payload retrieval apparatus  1000  shown in  FIGS.  14 - 16   . 
         FIG.  18    is a perspective view of payload retrieval apparatus  1000  shown in  FIGS.  1 - 17    with a payload loading apparatus  1080  having a plurality of payloads positioned thereon, according to an example embodiment. 
         FIG.  19    is a perspective view of channel  1050  of the payload retrieval apparatus  1000  shown in  FIGS.  14 - 16    with a payload retriever  800  positioned therein. 
         FIG.  20    is a perspective view of channel  1050  of the payload retrieval apparatus  1000  shown in  FIGS.  14 - 16    with a payload retriever  800 ″ positioned therein. 
         FIG.  21 A  is a cross-sectional view of channel  1050 , according to an example embodiment. 
         FIG.  21 B  is a side view of channel  1050  having a spring  1059  biased against end  1057  thereof. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary methods and systems are described herein. It should be understood that the word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any implementation or feature described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other implementations or features. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. The example implementations described herein are not meant to be limiting. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are contemplated herein. 
     I. OVERVIEW 
     The present embodiments advantageously provide a payload retrieval apparatus used for the automatic pickup of a payload at a payload retrieval site. With the disclosed payload retrieval apparatus, a UAV may automatically pick up the payload without the need for a designated person to secure the payload to the UAV at the retrieval site. Such automated pickup of the payload by the UAV advantageously eliminates the need for a designated person to secure the payload to the UAV and eliminates potential delays associated with the late arrival of the UAV or designated person at the retrieval site. 
     The payload retrieval apparatus may be a non-permanent structure placed at a payload retrieval site. The apparatus includes an extending member that may be secured to a base or stand at a lower end of the extending member. An angled extender may be attached at an upper end of the extending member. The angled extender may have an upper end secured to a channel. A first end of the channel may have a first extension or tether engager that extends in a first direction from a lower end of the channel and a second extension or tether engager that extends in a second direction from the lower end of the channel. A second end of the channel may have a payload holder positioned near or thereon that is adapted to secure a payload to the second end of the channel. 
     The payload retrieval apparatus may be used to provide for automatic pickup of the payload by a UAV. In operation, a payload is positioned on the payload holder on the second end of the channel at the payload retrieval site. A UAV arrives at the payload retrieval site with a tether extending downwardly from the UAV and with a payload retriever positioned on the end of the tether. The UAV approaches the payload retrieval apparatus, and as it nears the payload retrieval apparatus, the tether comes into contact with the first or second extension (tether engager). As the UAV moves forward, the tether slides inwardly along the first or second extension where it is directed towards the first end of the channel. With further forward movement of the UAV, the tether moves through a tether slot in the channel and eventually the payload retriever attached to the tether is pulled into the channel by the tether. The payload retriever is pulled through the channel where it engages, and secures, the payload secured to the payload holder. The payload retriever then pulls the payload free from the payload holder. Once the payload is free from the payload holder, the payload may be winched upwardly into secure engagement with the UAV, and the UAV may continue on to a delivery site where the payload may be delivered by the UAV. As illustrated above, the payload may be a package having an upwardly extending handle with an aperture positioned within the handle. The handle may include a pair of openings through which pins positioned on the second end of the channel may be placed through to secure the payload to the payload retrieval payload retrieval apparatus prior to retrieval. In this manner, the payload is in a suspended position beneath the pins which secure the payload to the payload retrieval apparatus by the pins that extend through the openings in the handle of the payload, and the payload is ready to be retrieved. The payload retriever positioned on the end of the tether extending beneath the UAV may have a hook or other member that extends through the aperture in the handle as it moves through the second end of the channel to disengage the pins from the openings in the handle and thereby remove the payload from the payload holder on the channel of the payload retrieval apparatus. In other embodiments, rather than using pins that extend through openings in the handle, a magnet(s) could be placed on the handle that cooperates with a magnet(s), or a metal, on the channel that serves as the payload holder. Other ways of securing the payload to the payload retrieval apparatus are also contemplated. 
     The payload retriever may take the form of a capsule attached to an end of the tether, where the capsule has a slot with a hook or lip formed beneath the slot. The hook or lip is adapted to extend through the aperture in the handle of the payload during payload retrieval. The area above the aperture in the handle extends within the slot of the capsule and the payload is suspended beneath the handle by the hook or lip after retrieval. The capsule may also be provided with a movable hook or lip that may be extended outwardly from the capsule at the time of payload retrieval, and later retracted to prevent the hook from reengaging with the handle of the package after disengagement with the handle of the payload at the time of payload delivery, or engaging branches or wires following disengagement from the payload at the time of payload delivery. 
     During retrieval of the payload, the tether initially engages the first or second extension (tether engager) and is drawn towards the channel as the UAV moves forward. A shield may be positioned beneath the first end of the channel to prevent the tether or capsule from engaging the extending member or angled extender and becoming tangled therewith prior to entry of the capsule into the channel. The first and second extensions may also have extending shields, such as fabric layers that prevent the capsule and/or tether from wrapping around the first or second extensions as the tether engages the first or second extension. The channel includes a tether slot on its upper surface through which the tether passes as the capsule moves towards the payload positioned on the payload holder on the second end of the channel. The tether slot has a width that is less than the width of the capsule so that the capsule remains positioned within the channel as it moves towards the payload on the payload holder. 
     In order to ensure that the slot and hook of the capsule are in a proper orientation as the capsule exits the channel and engages the handle of the payload, the capsule may be provided with exterior cams or slots that correspond to cams or slots positioned on an interior surface of the channel. The interaction of the cams or slots on the capsule and cams or slots on the interior of the channel properly orient the capsule within the channel such that the hook or lip beneath the slot of the capsule is in proper position to extend through the aperture on the handle of the payload to remove the payload from the payload holder. The channel may also have an interior that tapers downwardly, or decreases in size, as the channel moves from the first end where the capsule enters to the second end where the capsule exits to further facilitate the proper orientation of the capsule within the channel. In addition, the second end of the channel could be spring loaded or operate as a leaf spring, to also facilitate the proper orientation of the capsule at the point of payload retrieval. 
     Alternately, the capsule may be equipped with one or more magnets that cooperate with one or more magnets, or a metal, positioned on an interior of the channel and magnetic interaction is used to properly orient the capsule within the channel during the process of payload retrieval. In addition, the capsule could be weighted to have an offset center of gravity such that the hook and slot of the capsule are positioned properly (with the “heavy” portion of the capsule on a lower side) to engage the handle of the payload and effect removal of the payload from the payload holder. 
     In addition, a payload loading apparatus or chute may be positioned adjacent the payload retrieval apparatus to allow for a plurality of payloads to be positioned for retrieval by a UAV. For example, the payload loading apparatus or chute may have a plurality of payloads positioned thereon, such that as soon as a payload is removed from the payload holder, a successive payload moves (or is moved) into position on the payload holder and is ready for retrieval by the next UAV that arrives at the payload retrieval site. 
     Not only does the payload retrieval apparatus disclosed herein provide for automatic payload retrieval without the need for human involvement, but the UAV advantageously is not required to land for the payload to be loaded onto the UAV at the payload retrieval site. Thus, the UAV may simply fly into position near the payload retrieval apparatus and maneuver itself to position the tether between the first and second extensions and then move forward to pull the capsule through the channel and into engagement with the handle of the payload and effect removal of the payload. In some payload retrieval sites, landing the UAV may be difficult or impractical, and also may engage with objects or personnel when landing. Accordingly, allowing for payload retrieval without requiring the UAV to land provides significant advantages over conventional payload retrieval methods. 
     Furthermore, the payload retrieval apparatus is advantageously a movable, non-permanent apparatus that may be easily set up, taken down, and removed, and may be easily moved from one payload retrieval site to another. The extending member may be removably positioned within a hole in the ground at the payload retrieval site, or may be positioned on a base. The payload retrieval apparatus preferably folds up, like an umbrella stand, to facilitate storage and transport of the payload retrieval apparatus. The non-permanent nature of the payload retrieval apparatus also may eliminate the need for a permit for the payload retrieval apparatus at the retrieval site. 
     II. ILLUSTRATIVE UNMANNED VEHICLES 
     Herein, the terms “unmanned aerial vehicle” and “UAV” refer to any autonomous or semi-autonomous vehicle that is capable of performing some functions without a physically present human pilot. 
     A UAV can take various forms. For example, a UAV may take the form of a fixed-wing aircraft, a glider aircraft, a tail-sitter aircraft, a jet aircraft, a ducted fan aircraft, a lighter-than-air dirigible such as a blimp or steerable balloon, a rotorcraft such as a helicopter or multicopter, and/or an ornithopter, among other possibilities. Further, the terms “drone,” “unmanned aerial vehicle system” (UAVS), or “unmanned aerial system” (UAS) may also be used to refer to a UAV. 
       FIG.  1 A  is an isometric view of an example UAV  100 . UAV  100  includes wing  102 , booms  104 , and a fuselage  106 . Wings  102  may be stationary and may generate lift based on the wing shape and the UAV&#39;s forward airspeed. For instance, the two wings  102  may have an airfoil-shaped cross section to produce an aerodynamic force on UAV  100 . In some embodiments, wing  102  may carry horizontal propulsion units  108 , and booms  104  may carry vertical propulsion units  110 . In operation, power for the propulsion units may be provided from a battery compartment  112  of fuselage  106 . In some embodiments, fuselage  106  also includes an avionics compartment  114 , an additional battery compartment (not shown) and/or a delivery unit (not shown, e.g., a winch system) for handling the payload. In some embodiments, fuselage  106  is modular, and two or more compartments (e.g., battery compartment  112 , avionics compartment  114 , other payload and delivery compartments) are detachable from each other and securable to each other (e.g., mechanically, magnetically, or otherwise) to contiguously form at least a portion of fuselage  106 . 
     In some embodiments, booms  104  terminate in rudders  116  for improved yaw control of UAV  100 . Further, wings  102  may terminate in wing tips  117  for improved control of lift of the UAV. 
     In the illustrated configuration, UAV  100  includes a structural frame. The structural frame may be referred to as a “structural H-frame” or an “H-frame” (not shown) of the UAV. The H-frame may include, within wings  102 , a wing spar (not shown) and, within booms  104 , boom carriers (not shown). In some embodiments the wing spar and the boom carriers may be made of carbon fiber, hard plastic, aluminum, light metal alloys, or other materials. The wing spar and the boom carriers may be connected with clamps. The wing spar may include pre-drilled holes for horizontal propulsion units  108 , and the boom carriers may include pre-drilled holes for vertical propulsion units  110 . 
     In some embodiments, fuselage  106  may be removably attached to the H-frame (e.g., attached to the wing spar by clamps, configured with grooves, protrusions or other features to mate with corresponding H-frame features, etc.). In other embodiments, fuselage  106  similarly may be removably attached to wings  102 . The removable attachment of fuselage  106  may improve quality and or modularity of UAV  100 . For example, electrical/mechanical components and/or subsystems of fuselage  106  may be tested separately from, and before being attached to, the H-frame. Similarly, printed circuit boards (PCBs)  118  may be tested separately from, and before being attached to, the boom carriers, therefore eliminating defective parts/subassemblies prior to completing the UAV. For example, components of fuselage  106  (e.g., avionics, battery unit, delivery units, an additional battery compartment, etc.) may be electrically tested before fuselage  106  is mounted to the H-frame. Furthermore, the motors and the electronics of PCBs  118  may also be electrically tested before the final assembly. Generally, the identification of the defective parts and subassemblies early in the assembly process lowers the overall cost and lead time of the UAV. Furthermore, different types/models of fuselage  106  may be attached to the H-frame, therefore improving the modularity of the design. Such modularity allows these various parts of UAV  100  to be upgraded without a substantial overhaul to the manufacturing process. 
     In some embodiments, a wing shell and boom shells may be attached to the H-frame by adhesive elements (e.g., adhesive tape, double-sided adhesive tape, glue, etc.). Therefore, multiple shells may be attached to the H-frame instead of having a monolithic body sprayed onto the H-frame. In some embodiments, the presence of the multiple shells reduces the stresses induced by the coefficient of thermal expansion of the structural frame of the UAV. As a result, the UAV may have better dimensional accuracy and/or improved reliability. 
     Moreover, in at least some embodiments, the same H-frame may be used with the wing shell and/or boom shells having different size and/or design, therefore improving the modularity and versatility of the UAV designs. The wing shell and/or the boom shells may be made of relatively light polymers (e.g., closed cell foam) covered by the harder, but relatively thin, plastic skins. 
     The power and/or control signals from fuselage  106  may be routed to PCBs  118  through cables running through fuselage  106 , wings  102 , and booms  104 . In the illustrated embodiment, UAV  100  has four PCBs, but other numbers of PCBs are also possible. For example, UAV  100  may include two PCBs, one per the boom. The PCBs carry electronic components  119  including, for example, power converters, controllers, memory, passive components, etc. In operation, propulsion units  108  and  110  of UAV  100  are electrically connected to the PCBs. 
     Many variations on the illustrated UAV are possible. For instance, fixed-wing UAVs may include more or fewer rotor units (vertical or horizontal), and/or may utilize a ducted fan or multiple ducted fans for propulsion. Further, UAVs with more wings (e.g., an “x-wing” configuration with four wings), are also possible. Although  FIG.  1    illustrates two wings  102 , two booms  104 , two horizontal propulsion units  108 , and six vertical propulsion units  110  per boom  104 , it should be appreciated that other variants of UAV  100  may be implemented with more or less of these components. For example, UAV  100  may include four wings  102 , four booms  104 , and more or less propulsion units (horizontal or vertical). 
     Similarly,  FIG.  1 B  shows another example of a fixed-wing UAV  120 . The fixed-wing UAV  120  includes a fuselage  122 , two wings  124  with an airfoil-shaped cross section to provide lift for the UAV  120 , a vertical stabilizer  126  (or fin) to stabilize the plane&#39;s yaw (turn left or right), a horizontal stabilizer  128  (also referred to as an elevator or tailplane) to stabilize pitch (tilt up or down), landing gear  130 , and a propulsion unit  132 , which can include a motor, shaft, and propeller. 
       FIG.  1 C  shows an example of a UAV  140  with a propeller in a pusher configuration. The term “pusher” refers to the fact that a propulsion unit  142  is mounted at the back of the UAV and “pushes” the vehicle forward, in contrast to the propulsion unit being mounted at the front of the UAV. Similar to the description provided for  FIGS.  1 A and  1 B ,  FIG.  1 C  depicts common structures used in a pusher plane, including a fuselage  144 , two wings  146 , vertical stabilizers  148 , and the propulsion unit  142 , which can include a motor, shaft, and propeller. 
       FIG.  1 D  shows an example of a tail-sitter UAV  160 . In the illustrated example, the tail-sitter UAV  160  has fixed wings  162  to provide lift and allow the UAV  160  to glide horizontally (e.g., along the x-axis, in a position that is approximately perpendicular to the position shown in  FIG.  1 D ). However, the fixed wings  162  also allow the tail-sitter UAV  160  to take off and land vertically on its own. 
     For example, at a launch site, the tail-sitter UAV  160  may be positioned vertically (as shown) with its fins  164  and/or wings  162  resting on the ground and stabilizing the UAV  160  in the vertical position. The tail-sitter UAV  160  may then take off by operating its propellers  166  to generate an upward thrust (e.g., a thrust that is generally along the y-axis). Once at a suitable altitude, the tail-sitter UAV  160  may use its flaps  168  to reorient itself in a horizontal position, such that its fuselage  170  is closer to being aligned with the x-axis than the y-axis. Positioned horizontally, the propellers  166  may provide forward thrust so that the tail-sitter UAV  160  can fly in a similar manner as a typical airplane. 
     Many variations on the illustrated fixed-wing UAVs are possible. For instance, fixed-wing UAVs may include more or fewer propellers, and/or may utilize a ducted fan or multiple ducted fans for propulsion. Further, UAVs with more wings (e.g., an “x-wing” configuration with four wings), with fewer wings, or even with no wings, are also possible. 
     As noted above, some embodiments may involve other types of UAVs, in addition to or in the alternative to fixed-wing UAVs. For instance,  FIG.  1 E  shows an example of a rotorcraft that is commonly referred to as a multicopter  180 . The multicopter  180  may also be referred to as a quadcopter, as it includes four rotors  182 . It should be understood that example embodiments may involve a rotorcraft with more or fewer rotors than the multicopter  180 . For example, a helicopter typically has two rotors. Other examples with three or more rotors are possible as well. Herein, the term “multicopter” refers to any rotorcraft having more than two rotors, and the term “helicopter” refers to rotorcraft having two rotors. 
     Referring to the multicopter  180  in greater detail, the four rotors  182  provide propulsion and maneuverability for the multicopter  180 . More specifically, each rotor  182  includes blades that are attached to a motor  184 . Configured as such, the rotors  182  may allow the multicopter  180  to take off and land vertically, to maneuver in any direction, and/or to hover. Further, the pitch of the blades may be adjusted as a group and/or differentially, and may allow the multicopter  180  to control its pitch, roll, yaw, and/or altitude. 
     It should be understood that references herein to an “unmanned” aerial vehicle or UAV can apply equally to autonomous and semi-autonomous aerial vehicles. In an autonomous implementation, all functionality of the aerial vehicle is automated; e.g., pre-programmed or controlled via real-time computer functionality that responds to input from various sensors and/or pre-determined information. In a semi-autonomous implementation, some functions of an aerial vehicle may be controlled by a human operator, while other functions are carried out autonomously. Further, in some embodiments, a UAV may be configured to allow a remote operator to take over functions that can otherwise be controlled autonomously by the UAV. Yet further, a given type of function may be controlled remotely at one level of abstraction and performed autonomously at another level of abstraction. For example, a remote operator could control high level navigation decisions for a UAV, such as by specifying that the UAV should travel from one location to another (e.g., from a warehouse in a suburban area to a delivery address in a nearby city), while the UAV&#39;s navigation system autonomously controls more fine-grained navigation decisions, such as the specific route to take between the two locations, specific flight controls to achieve the route and avoid obstacles while navigating the route, and so on. 
     More generally, it should be understood that the example UAVs described herein are not intended to be limiting. Example embodiments may relate to, be implemented within, or take the form of any type of unmanned aerial vehicle. 
     III. ILLUSTRATIVE UAV COMPONENTS 
       FIG.  2    is a simplified block diagram illustrating components of a UAV  200 , according to an example embodiment. UAV  200  may take the form of, or be similar in form to, one of the UAVs  100 ,  120 ,  140 ,  160 , and  180  described in reference to  FIGS.  1 A- 1 E . However, UAV  200  may also take other forms. 
     UAV  200  may include various types of sensors, and may include a computing system configured to provide the functionality described herein. In the illustrated embodiment, the sensors of UAV  200  include an inertial measurement unit (IMU)  202 , ultrasonic sensor(s)  204 , and a GPS  206 , among other possible sensors and sensing systems. 
     In the illustrated embodiment, UAV  200  also includes one or more processors  208 . A processor  208  may be a general-purpose processor or a special purpose processor (e.g., digital signal processors, application specific integrated circuits, etc.). The one or more processors  208  can be configured to execute computer-readable program instructions  212  that are stored in the data storage  210  and are executable to provide the functionality of a UAV described herein. 
     The data storage  210  may include or take the form of one or more computer-readable storage media that can be read or accessed by at least one processor  208 . The one or more computer-readable storage media can include volatile and/or non-volatile storage components, such as optical, magnetic, organic or other memory or disc storage, which can be integrated in whole or in part with at least one of the one or more processors  208 . In some embodiments, the data storage  210  can be implemented using a single physical device (e.g., one optical, magnetic, organic or other memory or disc storage unit), while in other embodiments, the data storage  210  can be implemented using two or more physical devices. 
     As noted, the data storage  210  can include computer-readable program instructions  212  and perhaps additional data, such as diagnostic data of the UAV  200 . As such, the data storage  210  may include program instructions  212  to perform or facilitate some or all of the UAV functionality described herein. For instance, in the illustrated embodiment, program instructions  212  include a navigation module  214  and a tether control module  216 . 
     A. Sensors 
     In an illustrative embodiment, IMU  202  may include both an accelerometer and a gyroscope, which may be used together to determine an orientation of the UAV  200 . In particular, the accelerometer can measure the orientation of the vehicle with respect to earth, while the gyroscope measures the rate of rotation around an axis. IMUs are commercially available in low-cost, low-power packages. For instance, an IMU  202  may take the form of or include a miniaturized MicroElectroMechanical System (MEMS) or a NanoElectroMechanical System (NEMS). Other types of IMUs may also be utilized. 
     An IMU  202  may include other sensors, in addition to accelerometers and gyroscopes, which may help to better determine position and/or help to increase autonomy of the UAV  200 . Two examples of such sensors are magnetometers and pressure sensors. In some embodiments, a UAV may include a low-power, digital 3-axis magnetometer, which can be used to realize an orientation independent electronic compass for accurate heading information. However, other types of magnetometers may be utilized as well. Other examples are also possible. Further, note that a UAV could include some or all of the above-described inertia sensors as separate components from an IMU. 
     UAV  200  may also include a pressure sensor or barometer, which can be used to determine the altitude of the UAV  200 . Alternatively, other sensors, such as sonic altimeters or radar altimeters, can be used to provide an indication of altitude, which may help to improve the accuracy of and/or prevent drift of an IMU. 
     In a further aspect, UAV  200  may include one or more sensors that allow the UAV to sense objects in the environment. For instance, in the illustrated embodiment, UAV  200  includes ultrasonic sensor(s)  204 . Ultrasonic sensor(s)  204  can determine the distance to an object by generating sound waves and determining the time interval between transmission of the wave and receiving the corresponding echo off an object. A typical application of an ultrasonic sensor for unmanned vehicles or IMUs is low-level altitude control and obstacle avoidance. An ultrasonic sensor can also be used for vehicles that need to hover at a certain height or need to be capable of detecting obstacles. Other systems can be used to determine, sense the presence of, and/or determine the distance to nearby objects, such as a light detection and ranging (LIDAR) system, laser detection and ranging (LADAR) system, and/or an infrared or forward-looking infrared (FLIR) system, among other possibilities. 
     In some embodiments, UAV  200  may also include one or more imaging system(s). For example, one or more still and/or video cameras may be utilized by UAV  200  to capture image data from the UAV&#39;s environment. As a specific example, charge-coupled device (CCD) cameras or complementary metal-oxide-semiconductor (CMOS) cameras can be used with unmanned vehicles. Such imaging sensor(s) have numerous possible applications, such as obstacle avoidance, localization techniques, ground tracking for more accurate navigation (e,g., by applying optical flow techniques to images), video feedback, and/or image recognition and processing, among other possibilities. 
     UAV  200  may also include a GPS receiver  206 . The GPS receiver  206  may be configured to provide data that is typical of well-known GPS systems, such as the GPS coordinates of the UAV  200 . Such GPS data may be utilized by the UAV  200  for various functions. As such, the UAV may use its GPS receiver  206  to help navigate to the caller&#39;s location, as indicated, at least in part, by the GPS coordinates provided by their mobile device. Other examples are also possible. 
     B. Navigation and Location Determination 
     The navigation module  214  may provide functionality that allows the UAV  200  to, e.g., move about its environment and reach a desired location. To do so, the navigation module  214  may control the altitude and/or direction of flight by controlling the mechanical features of the UAV that affect flight (e.g., its rudder(s), elevator(s), aileron(s), and/or the speed of its propeller(s)). 
     In order to navigate the UAV  200  to a target location, the navigation module  214  may implement various navigation techniques, such as map-based navigation and localization-based navigation, for instance. With map-based navigation, the UAV  200  may be provided with a map of its environment, which may then be used to navigate to a particular location on the map. With localization-based navigation, the UAV  200  may be capable of navigating in an unknown environment using localization. Localization-based navigation may involve the UAV  200  building its own map of its environment and calculating its position within the map and/or the position of objects in the environment. For example, as a UAV  200  moves throughout its environment, the UAV  200  may continuously use localization to update its map of the environment. This continuous mapping process may be referred to as simultaneous localization and mapping (SLAM). Other navigation techniques may also be utilized. 
     In some embodiments, the navigation module  214  may navigate using a technique that relies on waypoints. In particular, waypoints are sets of coordinates that identify points in physical space. For instance, an air-navigation waypoint may be defined by a certain latitude, longitude, and altitude. Accordingly, navigation module  214  may cause UAV  200  to move from waypoint to waypoint, in order to ultimately travel to a final destination (e.g., a final waypoint in a sequence of waypoints). 
     In a further aspect, the navigation module  214  and/or other components and systems of the UAV  200  may be configured for “localization” to more precisely navigate to the scene of a target location. More specifically, it may be desirable in certain situations for a UAV to be within a threshold distance of the target location where a payload  228  is being delivered by a UAV (e.g., within a few feet of the target destination). To this end, a UAV may use a two-tiered approach in which it uses a more-general location-determination technique to navigate to a general area that is associated with the target location, and then use a more-refined location-determination technique to identify and/or navigate to the target location within the general area. 
     For example, the UAV  200  may navigate to the general area of a target destination where a payload  228  is being delivered using waypoints and/or map-based navigation. The UAV may then switch to a mode in which it utilizes a localization process to locate and travel to a more specific location. For instance, if the UAV  200  is to deliver a payload to a user&#39;s home, the UAV  200  may need to be substantially close to the target location in order to avoid delivery of the payload to undesired areas (e.g., onto a roof, into a pool, onto a neighbor&#39;s property, etc.). However, a GPS signal may only get the UAV  200  so far (e.g., within a block of the user&#39;s home). A more precise location-determination technique may then be used to find the specific target location. 
     Various types of location-determination techniques may be used to accomplish localization of the target delivery location once the UAV  200  has navigated to the general area of the target delivery location. For instance, the UAV  200  may be equipped with one or more sensory systems, such as, for example, ultrasonic sensors  204 , infrared sensors (not shown), and/or other sensors, which may provide input that the navigation module  214  utilizes to navigate autonomously or semi-autonomously to the specific target location. 
     As another example, once the UAV  200  reaches the general area of the target delivery location (or of a moving subject such as a person or their mobile device), the UAV  200  may switch to a “fly-by-wire” mode where it is controlled, at least in part, by a remote operator, who can navigate the UAV  200  to the specific target location. To this end, sensory data from the UAV  200  may be sent to the remote operator to assist them in navigating the UAV  200  to the specific location. 
     As yet another example, the UAV  200  may include a module that is able to signal to a passer-by for assistance in either reaching the specific target delivery location; for example, the UAV  200  may display a visual message requesting such assistance in a graphic display, play an audio message or tone through speakers to indicate the need for such assistance, among other possibilities. Such a visual or audio message might indicate that assistance is needed in delivering the UAV  200  to a particular person or a particular location, and might provide information to assist the passer-by in delivering the UAV  200  to the person or location (e.g., a description or picture of the person or location, and/or the person or location&#39;s name), among other possibilities. Such a feature can be useful in a scenario in which the UAV is unable to use sensory functions or another location-determination technique to reach the specific target location. However, this feature is not limited to such scenarios. 
     In some embodiments, once the UAV  200  arrives at the general area of a target delivery location, the UAV  200  may utilize a beacon from a user&#39;s remote device (e.g., the user&#39;s mobile phone) to locate the person. Such a beacon may take various forms. As an example, consider the scenario where a remote device, such as the mobile phone of a person who requested a UAV delivery, is able to send out directional signals (e.g., via an RF signal, a light signal and/or an audio signal). In this scenario, the UAV  200  may be configured to navigate by “sourcing” such directional signals—in other words, by determining where the signal is strongest and navigating accordingly. As another example, a mobile device can emit a frequency, either in the human range or outside the human range, and the UAV  200  can listen for that frequency and navigate accordingly. As a related example, if the UAV  200  is listening for spoken commands, then the UAV  200  could utilize spoken statements, such as “I&#39;m over here!” to source the specific location of the person requesting delivery of a payload. 
     In an alternative arrangement, a navigation module may be implemented at a remote computing device, which communicates wirelessly with the UAV  200 . The remote computing device may receive data indicating the operational state of the UAV  200 , sensor data from the UAV  200  that allows it to assess the environmental conditions being experienced by the UAV  200 , and/or location information for the UAV  200 . Provided with such information, the remote computing device may determine altitudinal and/or directional adjustments that should be made by the UAV  200  and/or may determine how the UAV  200  should adjust its mechanical features (e.g., its rudder(s), elevator(s), aileron(s), and/or the speed of its propeller(s)) in order to effectuate such movements. The remote computing system may then communicate such adjustments to the UAV  200  so it can move in the determined manner. 
     C. Communication Systems 
     In a further aspect, the UAV  200  includes one or more communication systems  218 . The communications systems  218  may include one or more wireless interfaces and/or one or more wireline interfaces, which allow the UAV  200  to communicate via one or more networks. Such wireless interfaces may provide for communication under one or more wireless communication protocols, such as Bluetooth, WiFi (e.g., an IEEE 802.11 protocol), Long-Term Evolution (LTE), WiMAX (e.g., an IEEE 802.16 standard), a radio-frequency ID (RFID) protocol, near-field communication (NFC), and/or other wireless communication protocols. Such wireline interfaces may include an Ethernet interface, a Universal Serial Bus (USB) interface, or similar interface to communicate via a wire, a twisted pair of wires, a coaxial cable, an optical link, a fiber-optic link, or other physical connection to a wireline network. 
     In some embodiments, a UAV  200  may include communication systems  218  that allow for both short-range communication and long-range communication. For example, the UAV  200  may be configured for short-range communications using Bluetooth and for long-range communications under a CDMA protocol. In such an embodiment, the UAV  200  may be configured to function as a “hot spot;” or in other words, as a gateway or proxy between a remote support device and one or more data networks, such as a cellular network and/or the Internet. Configured as such, the UAV  200  may facilitate data communications that the remote support device would otherwise be unable to perform by itself. 
     For example, the UAV  200  may provide a WiFi connection to a remote device, and serve as a proxy or gateway to a cellular service provider&#39;s data network, which the UAV might connect to under an LTE or a 3G protocol, for instance. The UAV  200  could also serve as a proxy or gateway to a high-altitude balloon network, a satellite network, or a combination of these networks, among others, which a remote device might not be able to otherwise access. 
     D. Power Systems 
     In a further aspect, the UAV  200  may include power system(s)  220 . The power system  220  may include one or more batteries for providing power to the UAV  200 . In one example, the one or more batteries may be rechargeable and each battery may be recharged via a wired connection between the battery and a power supply and/or via a wireless charging system, such as an inductive charging system that applies an external time-varying magnetic field to an internal battery. 
     E. Payload Delivery 
     The UAV  200  may employ various systems and configurations in order to transport and deliver a payload  228 . In some implementations, the payload  228  of a given UAV  200  may include or take the form of a “package” designed to transport various goods to a target delivery location. For example, the UAV  200  can include a compartment, in which an item or items may be transported. Such a package may one or more food items, purchased goods, medical items, or any other object(s) having a size and weight suitable to be transported between two locations by the UAV. In other embodiments, a payload  228  may simply be the one or more items that are being delivered (e.g., without any package housing the items). 
     In some embodiments, the payload  228  may be attached to the UAV and located substantially outside of the UAV during some or all of a flight by the UAV. For example, the package may be tethered or otherwise releasably attached below the UAV during flight to a target location. In an embodiment where a package carries goods below the UAV, the package may include various features that protect its contents from the environment, reduce aerodynamic drag on the system, and prevent the contents of the package from shifting during UAV flight. 
     For instance, when the payload  228  takes the form of a package for transporting items, the package may include an outer shell constructed of water-resistant cardboard, plastic, or any other lightweight and water-resistant material. Further, in order to reduce drag, the package may feature smooth surfaces with a pointed front that reduces the frontal cross-sectional area. Further, the sides of the package may taper from a wide bottom to a narrow top, which allows the package to serve as a narrow pylon that reduces interference effects on the wing(s) of the UAV. This may move some of the frontal area and volume of the package away from the wing(s) of the UAV, thereby preventing the reduction of lift on the wing(s) cause by the package. Yet further, in some embodiments, the outer shell of the package may be constructed from a single sheet of material in order to reduce air gaps or extra material, both of which may increase drag on the system. Additionally or alternatively, the package may include a stabilizer to dampen package flutter. This reduction in flutter may allow the package to have a less rigid connection to the UAV and may cause the contents of the package to shift less during flight. 
     In order to deliver the payload, the UAV may include a winch system  221  controlled by the tether control module  216  in order to lower the payload  228  to the ground while the UAV hovers above. As shown in  FIG.  2   , the winch system  221  may include a tether  224 , and the tether  224  may be coupled to the payload  228  by a payload coupling apparatus  226 . The tether  224  may be wound on a spool that is coupled to a motor  222  of the UAV. The motor  222  may take the form of a DC motor (e.g., a servo motor) that can be actively controlled by a speed controller. The tether control module  216  can control the speed controller to cause the motor  222  to rotate the spool, thereby unwinding or retracting the tether  224  and lowering or raising the payload coupling apparatus  226 . In practice, the speed controller may output a desired operating rate (e.g., a desired RPM) for the spool, which may correspond to the speed at which the tether  224  and payload  228  should be lowered towards the ground. The motor  222  may then rotate the spool so that it maintains the desired operating rate. 
     In order to control the motor  222  via the speed controller, the tether control module  216  may receive data from a speed sensor (e.g., an encoder) configured to convert a mechanical position to a representative analog or digital signal. In particular, the speed sensor may include a rotary encoder that may provide information related to rotary position (and/or rotary movement) of a shaft of the motor or the spool coupled to the motor, among other possibilities. Moreover, the speed sensor may take the form of an absolute encoder and/or an incremental encoder, among others. So in an example implementation, as the motor  222  causes rotation of the spool, a rotary encoder may be used to measure this rotation. In doing so, the rotary encoder may be used to convert a rotary position to an analog or digital electronic signal used by the tether control module  216  to determine the amount of rotation of the spool from a fixed reference angle and/or to an analog or digital electronic signal that is representative of a new rotary position, among other options. Other examples are also possible. 
     Based on the data from the speed sensor, the tether control module  216  may determine a rotational speed of the motor  222  and/or the spool and responsively control the motor  222  (e.g., by increasing or decreasing an electrical current supplied to the motor  222 ) to cause the rotational speed of the motor  222  to match a desired speed. When adjusting the motor current, the magnitude of the current adjustment may be based on a proportional-integral-derivative (PID) calculation using the determined and desired speeds of the motor  222 . For instance, the magnitude of the current adjustment may be based on a present difference, a past difference (based on accumulated error over time), and a future difference (based on current rates of change) between the determined and desired speeds of the spool. 
     In some embodiments, the tether control module  216  may vary the rate at which the tether  224  and payload  228  are lowered to the ground. For example, the speed controller may change the desired operating rate according to a variable deployment-rate profile and/or in response to other factors in order to change the rate at which the payload  228  descends toward the ground. To do so, the tether control module  216  may adjust an amount of braking or an amount of friction that is applied to the tether  224 . For example, to vary the tether deployment rate, the UAV  200  may include friction pads that can apply a variable amount of pressure to the tether  224 . As another example, the UAV  200  can include a motorized braking system that varies the rate at which the spool lets out the tether  224 . Such a braking system may take the form of an electromechanical system in which the motor  222  operates to slow the rate at which the spool lets out the tether  224 . Further, the motor  222  may vary the amount by which it adjusts the speed (e.g., the RPM) of the spool, and thus may vary the deployment rate of the tether  224 . Other examples are also possible. 
     In some embodiments, the tether control module  216  may be configured to limit the motor current supplied to the motor  222  to a maximum value. With such a limit placed on the motor current, there may be situations where the motor  222  cannot operate at the desired operate specified by the speed controller. For instance, as discussed in more detail below, there may be situations where the speed controller specifies a desired operating rate at which the motor  222  should retract the tether  224  toward the UAV  200 , but the motor current may be limited such that a large enough downward force on the tether  224  would counteract the retracting force of the motor  222  and cause the tether  224  to unwind instead. And as further discussed below, a limit on the motor current may be imposed and/or altered depending on an operational state of the UAV  200 . 
     In some embodiments, the tether control module  216  may be configured to determine a status of the tether  224  and/or the payload  228  based on the amount of current supplied to the motor  222 . For instance, if a downward force is applied to the tether  224  (e.g., if the payload  228  is attached to the tether  224  or if the tether  224  gets snagged on an object when retracting toward the UAV  200 ), the tether control module  216  may need to increase the motor current in order to cause the determined rotational speed of the motor  222  and/or spool to match the desired speed. Similarly, when the downward force is removed from the tether  224  (e.g., upon delivery of the payload  228  or removal of a tether snag), the tether control module  216  may need to decrease the motor current in order to cause the determined rotational speed of the motor  222  and/or spool to match the desired speed. As such, the tether control module  216  may be configured to monitor the current supplied to the motor  222 . For instance, the tether control module  216  could determine the motor current based on sensor data received from a current sensor of the motor or a current sensor of the power system  220 . In any case, based on the current supplied to the motor  222 , determine if the payload  228  is attached to the tether  224 , if someone or something is pulling on the tether  224 , and/or if the payload coupling apparatus  226  is pressing against the UAV  200  after retracting the tether  224 . Other examples are possible as well. 
     During delivery of the payload  228 , the payload coupling apparatus  226  can be configured to secure the payload  228  while being lowered from the UAV by the tether  224 , and can be further configured to release the payload  228  upon reaching ground level. The payload coupling apparatus  226  can then be retracted to the UAV by reeling in the tether  224  using the motor  222 . 
     In some implementations, the payload  228  may be passively released once it is lowered to the ground. For example, a passive release mechanism may include one or more swing arms adapted to retract into and extend from a housing. An extended swing arm may form a hook on which the payload  228  may be attached. Upon lowering the release mechanism and the payload  228  to the ground via a tether, a gravitational force as well as a downward inertial force on the release mechanism may cause the payload  228  to detach from the hook allowing the release mechanism to be raised upwards toward the UAV. The release mechanism may further include a spring mechanism that biases the swing arm to retract into the housing when there are no other external forces on the swing arm. For instance, a spring may exert a force on the swing arm that pushes or pulls the swing arm toward the housing such that the swing arm retracts into the housing once the weight of the payload  228  no longer forces the swing arm to extend from the housing. Retracting the swing arm into the housing may reduce the likelihood of the release mechanism snagging the payload  228  or other nearby objects when raising the release mechanism toward the UAV upon delivery of the payload  228 . 
     Active payload release mechanisms are also possible. For example, sensors such as a barometric pressure based altimeter and/or accelerometers may help to detect the position of the release mechanism (and the payload) relative to the ground. Data from the sensors can be communicated back to the UAV and/or a control system over a wireless link and used to help in determining when the release mechanism has reached ground level (e.g., by detecting a measurement with the accelerometer that is characteristic of ground impact). In other examples, the UAV may determine that the payload has reached the ground based on a weight sensor detecting a threshold low downward force on the tether and/or based on a threshold low measurement of power drawn by the winch when lowering the payload. 
     Other systems and techniques for delivering a payload, in addition or in the alternative to a tethered delivery system are also possible. For example, a UAV  200  could include an air-bag drop system or a parachute drop system. Alternatively, a UAV  200  carrying a payload could simply land on the ground at a delivery location. Other examples are also possible. 
     IV. ILLUSTRATIVE UAV DEPLOYMENT SYSTEMS 
     UAV systems may be implemented in order to provide various UAV-related services. In particular, UAVs may be provided at a number of different launch sites that may be in communication with regional and/or central control systems. Such a distributed UAV system may allow UAVs to be quickly deployed to provide services across a large geographic area (e.g., that is much larger than the flight range of any single UAV). For example, UAVs capable of carrying payloads may be distributed at a number of launch sites across a large geographic area (possibly even throughout an entire country, or even worldwide), in order to provide on-demand transport of various items to locations throughout the geographic area.  FIG.  3    is a simplified block diagram illustrating a distributed UAV system  300 , according to an example embodiment. 
     In the illustrative UAV system  300 , an access system  302  may allow for interaction with, control of, and/or utilization of a network of UAVs  304 . In some embodiments, an access system  302  may be a computing system that allows for human-controlled dispatch of UAVs  304 . As such, the control system may include or otherwise provide a user interface through which a user can access and/or control the UAVs  304 . 
     In some embodiments, dispatch of the UAVs  304  may additionally or alternatively be accomplished via one or more automated processes. For instance, the access system  302  may dispatch one of the UAVs  304  to transport a payload to a target location, and the UAV may autonomously navigate to the target location by utilizing various on-board sensors, such as a GPS receiver and/or other various navigational sensors. 
     Further, the access system  302  may provide for remote operation of a UAV. For instance, the access system  302  may allow an operator to control the flight of a UAV via its user interface. As a specific example, an operator may use the access system  302  to dispatch a UAV  304  to a target location. The UAV  304  may then autonomously navigate to the general area of the target location. At this point, the operator may use the access system  302  to take control of the UAV  304  and navigate the UAV to the target location (e.g., to a particular person to whom a payload is being transported). Other examples of remote operation of a UAV are also possible. 
     In an illustrative embodiment, the UAVs  304  may take various forms. For example, each of the UAVs  304  may be a UAV such as those illustrated in  FIGS.  1 A- 1 E . However, UAV system  300  may also utilize other types of UAVs without departing from the scope of the invention. In some implementations, all of the UAVs  304  may be of the same or a similar configuration. However, in other implementations, the UAVs  304  may include a number of different types of UAVs. For instance, the UAVs  304  may include a number of types of UAVs, with each type of UAV being configured for a different type or types of payload delivery capabilities. 
     The UAV system  300  may further include a remote device  306 , which may take various forms. Generally, the remote device  306  may be any device through which a direct or indirect request to dispatch a UAV can be made. (Note that an indirect request may involve any communication that may be responded to by dispatching a UAV, such as requesting a package delivery). In an example embodiment, the remote device  306  may be a mobile phone, tablet computer, laptop computer, personal computer, or any network-connected computing device. Further, in some instances, the remote device  306  may not be a computing device. As an example, a standard telephone, which allows for communication via plain old telephone service (POTS), may serve as the remote device  306 . Other types of remote devices are also possible. 
     Further, the remote device  306  may be configured to communicate with access system  302  via one or more types of communication network(s)  308 . For example, the remote device  306  may communicate with the access system  302  (or a human operator of the access system  302 ) by communicating over a POTS network, a cellular network, and/or a data network such as the Internet. Other types of networks may also be utilized. 
     In some embodiments, the remote device  306  may be configured to allow a user to request delivery of one or more items to a desired location. For example, a user could request UAV delivery of a package to their home via their mobile phone, tablet, or laptop. As another example, a user could request dynamic delivery to wherever they are located at the time of delivery. To provide such dynamic delivery, the UAV system  300  may receive location information (e.g., GPS coordinates, etc.) from the user&#39;s mobile phone, or any other device on the user&#39;s person, such that a UAV can navigate to the user&#39;s location (as indicated by their mobile phone). 
     In an illustrative arrangement, the central dispatch system  310  may be a server or group of servers, which is configured to receive dispatch messages requests and/or dispatch instructions from the access system  302 . Such dispatch messages may request or instruct the central dispatch system  310  to coordinate the deployment of UAVs to various target locations. The central dispatch system  310  may be further configured to route such requests or instructions to one or more local dispatch systems  312 . To provide such functionality, the central dispatch system  310  may communicate with the access system  302  via a data network, such as the Internet or a private network that is established for communications between access systems and automated dispatch systems. 
     In the illustrated configuration, the central dispatch system  310  may be configured to coordinate the dispatch of UAVs  304  from a number of different local dispatch systems  312 . As such, the central dispatch system  310  may keep track of which UAVs  304  are located at which local dispatch systems  312 , which UAVs  304  are currently available for deployment, and/or which services or operations each of the UAVs  304  is configured for (in the event that a UAV fleet includes multiple types of UAVs configured for different services and/or operations). Additionally or alternatively, each local dispatch system  312  may be configured to track which of its associated UAVs  304  are currently available for deployment and/or are currently in the midst of item transport. 
     In some cases, when the central dispatch system  310  receives a request for UAV-related service (e.g., transport of an item) from the access system  302 , the central dispatch system  310  may select a specific UAV  304  to dispatch. The central dispatch system  310  may accordingly instruct the local dispatch system  312  that is associated with the selected UAV to dispatch the selected UAV. The local dispatch system  312  may then operate its associated deployment system  314  to launch the selected UAV. In other cases, the central dispatch system  310  may forward a request for a UAV-related service to a local dispatch system  312  that is near the location where the support is requested and leave the selection of a particular UAV  304  to the local dispatch system  312 . 
     In an example configuration, the local dispatch system  312  may be implemented as a computing system at the same location as the deployment system(s)  314  that it controls. For example, the local dispatch system  312  may be implemented by a computing system installed at a building, such as a warehouse, where the deployment system(s)  314  and UAV(s)  304  that are associated with the particular local dispatch system  312  are also located. In other embodiments, the local dispatch system  312  may be implemented at a location that is remote to its associated deployment system(s)  314  and UAV(s)  304 . 
     Numerous variations on and alternatives to the illustrated configuration of the UAV system  300  are possible. For example, in some embodiments, a user of the remote device  306  could request delivery of a package directly from the central dispatch system  310 . To do so, an application may be implemented on the remote device  306  that allows the user to provide information regarding a requested delivery, and generate and send a data message to request that the UAV system  300  provide the delivery. In such an embodiment, the central dispatch system  310  may include automated functionality to handle requests that are generated by such an application, evaluate such requests, and, if appropriate, coordinate with an appropriate local dispatch system  312  to deploy a UAV. 
     Further, some or all of the functionality that is attributed herein to the central dispatch system  310 , the local dispatch system(s)  312 , the access system  302 , and/or the deployment system(s)  314  may be combined in a single system, implemented in a more complex system, and/or redistributed among the central dispatch system  310 , the local dispatch system(s)  312 , the access system  302 , and/or the deployment system(s)  314  in various ways. 
     Yet further, while each local dispatch system  312  is shown as having two associated deployment systems  314 , a given local dispatch system  312  may alternatively have more or fewer associated deployment systems  314 . Similarly, while the central dispatch system  310  is shown as being in communication with two local dispatch systems  312 , the central dispatch system  310  may alternatively be in communication with more or fewer local dispatch systems  312 . 
     In a further aspect, the deployment systems  314  may take various forms. In general, the deployment systems  314  may take the form of or include systems for physically launching one or more of the UAVs  304 . Such launch systems may include features that provide for an automated UAV launch and/or features that allow for a human-assisted UAV launch. Further, the deployment systems  314  may each be configured to launch one particular UAV  304 , or to launch multiple UAVs  304 . 
     The deployment systems  314  may further be configured to provide additional functions, including for example, diagnostic-related functions such as verifying system functionality of the UAV, verifying functionality of devices that are housed within a UAV (e.g., a payload delivery apparatus), and/or maintaining devices or other items that are housed in the UAV (e.g., by monitoring a status of a payload such as its temperature, weight, etc.). 
     In some embodiments, the deployment systems  314  and their corresponding UAVs  304  (and possibly associated local dispatch systems  312 ) may be strategically distributed throughout an area such as a city. For example, the deployment systems  314  may be strategically distributed such that each deployment system  314  is proximate to one or more payload pickup locations (e.g., near a restaurant, store, or warehouse). However, the deployment systems  314  (and possibly the local dispatch systems  312 ) may be distributed in other ways, depending upon the particular implementation. As an additional example, kiosks that allow users to transport packages via UAVs may be installed in various locations. Such kiosks may include UAV launch systems, and may allow a user to provide their package for loading onto a UAV and pay for UAV shipping services, among other possibilities. Other examples are also possible. 
     In a further aspect, the UAV system  300  may include or have access to a user-account database  316 . The user-account database  316  may include data for a number of user accounts, and which are each associated with one or more person. For a given user account, the user-account database  316  may include data related to or useful in providing UAV-related services. Typically, the user data associated with each user account is optionally provided by an associated user and/or is collected with the associated user&#39;s permission. 
     Further, in some embodiments, a person may be required to register for a user account with the UAV system  300 , if they wish to be provided with UAV-related services by the UAVs  304  from UAV system  300 . As such, the user-account database  316  may include authorization information for a given user account (e.g., a user name and password), and/or other information that may be used to authorize access to a user account. 
     In some embodiments, a person may associate one or more of their devices with their user account, such that they can access the services of UAV system  300 . For example, when a person uses an associated mobile phone, e.g., to place a call to an operator of the access system  302  or send a message requesting a UAV-related service to a dispatch system, the phone may be identified via a unique device identification number, and the call or message may then be attributed to the associated user account. Other examples are also possible. 
     V. EXAMPLE SYSTEM AND APPARATUS FOR PAYLOAD DELIVERY 
       FIGS.  4 A,  4 B, and  4 C  show a UAV  400  that includes a payload delivery system  410  (could also be referred to as a payload delivery apparatus), according to an example embodiment. As shown, payload delivery system  410  for UAV  400  includes a tether  402  coupled to a spool  404 , a payload latch  406 , and a payload  408  coupled to the tether  402  via a payload coupling apparatus  412 . The payload latch  406  can function to alternately secure payload  408  and release the payload  408  upon delivery. For instance, as shown, the payload latch  406  may take the form of one or more pins that can engage the payload coupling apparatus  412  (e.g., by sliding into one or more receiving slots in the payload coupling apparatus  412 ). Inserting the pins of the payload latch  406  into the payload coupling apparatus  412  may secure the payload coupling apparatus  412  within a receptacle  414  on the underside of the UAV  400 , thereby preventing the payload  408  from being lowered from the UAV  400 . In some embodiments, the payload latch  406  may be arranged to engage the spool  404  or the payload  408  rather than the payload coupling apparatus  412  in order to prevent the payload  408  from lowering. In other embodiments, the UAV  400  may not include the payload latch  406 , and the payload delivery apparatus may be coupled directly to the UAV  400 . 
     In some embodiments, the spool  404  can function to unwind the tether  402  such that the payload  408  can be lowered to the ground with the tether  402  and the payload coupling apparatus  412  from UAV  400 . The payload  408  may itself be an item for delivery, and may be housed within (or otherwise incorporate) a parcel, container, or other structure that is configured to interface with the payload latch  406 . In practice, the payload delivery system  410  of UAV  400  may function to autonomously lower payload  408  to the ground in a controlled manner to facilitate delivery of the payload  408  on the ground while the UAV  400  hovers above. 
     As shown in  FIG.  4 A , the payload latch  406  may be in a closed position (e.g., pins engaging the payload coupling apparatus  412 ) to hold the payload  408  against or close to the bottom of the UAV  400 , or even partially or completely inside the UAV  400 , during flight from a launch site to a target location  420 . The target location  420  may be a point in space directly above a desired delivery location. Then, when the UAV  400  reaches the target location  420 , the UAV&#39;s control system (e.g., the tether control module  216  of  FIG.  2   ) may toggle the payload latch  406  to an open position (e.g., disengaging the pins from the payload coupling apparatus  412 ), thereby allowing the payload  408  to be lowered from the UAV  400 . The control system may further operate the spool  404  (e.g., by controlling the motor  222  of  FIG.  2   ) such that the payload  408 , secured to the tether  402  by a payload coupling apparatus  412 , is lowered to the ground, as shown in  FIG.  4 B . 
     Once the payload  408  reaches the ground, the control system may continue operating the spool  404  to lower the tether  402 , causing over-run of the tether  402 . During over-run of the tether  402 , the payload coupling apparatus  412  may continue to lower as the payload  408  remains stationary on the ground. The downward momentum and/or gravitational forces on the payload coupling apparatus  412  may cause the payload  408  to detach from the payload coupling apparatus  412  (e.g., by sliding off a hook of the payload coupling apparatus  412 ). After releasing payload  408 , the control system may operate the spool  404  to retract the tether  402  and the payload coupling apparatus  412  toward the UAV  400 . Once the payload coupling apparatus reaches or nears the UAV  400 , the control system may operate the spool  404  to pull the payload coupling apparatus  412  into the receptacle  414 , and the control system may toggle the payload latch  406  to the closed position, as shown in  FIG.  4 C . 
     In some embodiments, when lowering the payload  408  from the UAV  400 , the control system may detect when the payload  408  and/or the payload coupling apparatus  412  has been lowered to be at or near the ground based on an unwound length of the tether  402  from the spool  404 . Similar techniques may be used to determine when the payload coupling apparatus  412  is at or near the UAV  400  when retracting the tether  402 . As noted above, the UAV  400  may include an encoder for providing data indicative of the rotation of the spool  404 . Based on data from the encoder, the control system may determine how many rotations the spool  404  has undergone and, based on the number of rotations, determine a length of the tether  402  that is unwound from the spool  404 . For instance, the control system may determine an unwound length of the tether  402  by multiplying the number of rotations of the spool  404  by the circumference of the tether  402  wrapped around the spool  404 . In some embodiments, such as when the spool  404  is narrow or when the tether  402  has a large diameter, the circumference of the tether  402  on the spool  404  may vary as the tether  402  winds or unwinds from the tether, and so the control system may be configured to account for these variations when determining the unwound tether length. 
     In other embodiments, the control system may use various types of data, and various techniques, to determine when the payload  408  and/or payload coupling apparatus  412  have lowered to be at or near the ground. Further, the data that is used to determine when the payload  408  is at or near the ground may be provided by sensors on UAV  400 , sensors on the payload coupling apparatus  412 , and/or other data sources that provide data to the control system. 
     In some embodiments, the control system itself may be situated on the payload coupling apparatus  412  and/or on the UAV  400 . For example, the payload coupling apparatus  412  may include logic module(s) implemented via hardware, software, and/or firmware that cause the UAV  400  to function as described herein, and the UAV  400  may include logic module(s) that communicate with the payload coupling apparatus  412  to cause the UAV  400  to perform functions described herein. 
       FIG.  5 A  shows a perspective view of a payload delivery apparatus  500  including payload  510 , according to an example embodiment. The payload delivery apparatus  500  is positioned within a fuselage of a UAV (not shown) and includes a winch  514  powered by motor  512 , and a tether  502  spooled onto winch  514 . The tether  502  is attached to a payload coupling apparatus or payload retriever  800  positioned within a payload coupling apparatus receptacle  516  positioned within the fuselage of the UAV (not shown). A payload  510  is secured to the payload coupling apparatus  800 . In this embodiment a top portion  517  of payload  510  is secured within the fuselage of the UAV. A locking pin  570  is shown extending through handle  511  attached to payload  510  to positively secure the payload beneath the UAV during high speed flight. 
       FIG.  5 B  is a cross-sectional side view of payload delivery apparatus  500  and payload  510  shown in  FIG.  5 A . In this view, the payload coupling apparatus is shown tightly positioned with the payload coupling apparatus receptacle  516 . Tether  502  extends from winch  514  and is attached to the top of payload coupling apparatus  800 . Top portion  517  of payload  510  is shown positioned within the fuselage of the UAV (not shown) along with handle  511 . 
       FIG.  5 C  is a side view of payload delivery apparatus  500  and payload  510  shown in  FIGS.  5 A and  5 B . The top portion  517  of payload  510  is shown positioned within the fuselage of the UAV. Winch  514  has been used to wind in tether  502  to position the payload coupling apparatus within payload coupling apparatus receptacle  516 .  FIGS.  5 A-C  disclose payload  510  taking the shape of an aerodynamic hexagonally-shaped tote, where the base and side walls are six-sided hexagons and the tote includes generally pointed front and rear surfaces formed at the intersections of the side walls and base of the tote providing an aerodynamic shape. 
     VI. EXAMPLE PAYLOAD RETRIEVAL APPARATUS AND PAYLOAD RETRIEVERS 
       FIG.  6 A  is a perspective view of payload coupling apparatus  800 , according to an example embodiment. Payload coupling apparatus  800  includes tether mounting point  802 , and a slot  808  to position a handle of a payload handle in. Lower lip, or hook,  806  is positioned beneath slot  808 . Also included is an outer protrusion  804  having helical cam surfaces  804   a  and  804   b  that are adapted to mate with corresponding cam mating surfaces within a payload coupling apparatus receptacle positioned with a fuselage of a UAV. 
       FIG.  6 B  is a side view of payload coupling apparatus  800  shown in  FIG.  6 A . Slot  808  is shown positioned above lower lip, or hook,  806 . As shown lower lip or hook  806  has an outer surface  806   a  that is undercut such that it does not extend as far outwardly as an outer surface above slot  805  so that the lower lip or hook  806  will not reengage with the handle of the payload after it has been decoupled, or will not get engaged with power lines or tree branches during retrieval to the UAV. 
       FIG.  6 C  is a front view of payload coupling apparatus  800  shown in  FIGS.  6 A and  6 B . Lower lip or hook  806  is shown positioned beneath slot  808  that is adapted for securing a handle of a payload. 
       FIG.  7    is a perspective view of payload coupling apparatus  800  shown in  FIGS.  6 A- 6 C , prior to insertion into a payload coupling apparatus receptacle  516  positioned in the fuselage  550  of a UAV. As noted previously payload coupling apparatus  800  includes a slot  808  positioned above lower lip or hook  806 , adapted to receive a handle of a payload. The fuselage  550  of the payload delivery system  500  includes a payload coupling apparatus receptacle  516  positioned within the fuselage  550  of the UAV. The payload coupling apparatus  800  includes an outer protrusion  810  have helical cammed surfaces  810   a  and  810   b  that meet in a rounded apex. The helical cammed surfaces  810   a  and  810   b  are adapted to mate with surfaces  530   a  and  530   b  of an inward protrusion  530  positioned within the payload coupling apparatus receptacle  516  positioned within fuselage  550  of the UAV. Also included is a longitudinal recessed restraint slot  540  positioned within the fuselage  550  of the UAV that is adapted to receive and restrain a top portion of a payload (not shown). As the payload coupling apparatus  800  is pulled into to the payload coupling apparatus receptacle  516 , the cammed surfaces  810   a  and  810   b  of outer protrusion  810  engage with the cammed surfaces  530   a  and  530   b  within the payload coupling apparatus receptacle  516  and the payload coupling apparatus  800  is rotated into a desired alignment within the fuselage  550  of the UAV. 
       FIG.  8    is another perspective view of an opposite side of payload coupling apparatus  800  shown in  FIGS.  6 A- 6 C , prior to insertion into a payload coupling apparatus receptacle  516  positioned in the fuselage  550  of a UAV. As shown, payload coupling apparatus  800  include a lower lip or hook  806 . An outer protrusion  804  is shown extending outwardly from the payload coupling apparatus having helical cammed surfaces  804   a  and  804   b  adapted to engage and mate with cammed surfaces  530   a  and  530   b  of inner protrusion  530  positioned within payload coupling apparatus receptacle  516  positioned within fuselage  550  of payload delivery system  500 . It should be noted that the cammed surfaces  804   a  and  804   b  meet at a sharp apex, which is asymmetrical with the rounded or blunt apex of cammed surfaces  810   a  and  810   b  shown in  FIG.  7   . In this manner, the rounded or blunt apex of cammed surfaces  810   a  and  810   b  prevent possible jamming of the payload coupling apparatus  800  as the cammed surfaces engage the cammed surfaces  530   a  and  530   b  positioned within the payload coupling apparatus receptacle  516  positioned within fuselage  550  of the UAV. In particular, cammed surfaces  804   a  and  804   b  are positioned slightly higher than the rounded or blunt apex of cammed surfaces  810   a  and  810   b . As a result, the sharper tip of cammed surfaces  804   a  and  804   b  engages the cammed surfaces  530   a  and  530   b  within the payload coupling apparatus receptacle  516  positioned within the fuselage  550  of payload delivery system  500 , thereby initiating rotation of the payload coupling apparatus  800  slightly before the rounded or blunt apex of cammed surfaces  810   a  and  810   b  engage the corresponding cammed surfaces within the payload coupling apparatus receptacle  516 . In this manner, the case where both apexes (or tips) of the cammed surfaces on the payload coupling apparatus end up on the same side of the receiving cams within the payload coupling apparatus receptacle is prevented. This scenario results in a prevention of the jamming of the payload coupling apparatus within the receptacle. 
       FIG.  9    shows a perspective view of a recessed restraint slot and payload coupling apparatus receptacle positioned in a fuselage of a UAV. In particular, payload delivery system  500  includes a fuselage  550  having a payload coupling apparatus receptacle  516  therein that includes inward protrusion  530  having cammed surfaces  530   a  and  530   b  that are adapted to mate with corresponding cammed surfaces on a payload coupling apparatus (not shown). Also included is a longitudinally extending recessed restrained slot  540  into which a top portion of a payload is adapted to be positioned and secured within the fuselage  550 . 
       FIG.  10 A  shows a side view of a payload delivery apparatus  500  with a handle  511  of payload  510  secured within a payload coupling apparatus  800  as the payload  510  moves downwardly prior to touching down for delivery. Prior to payload touchdown, the handle  511  of payload  510  includes a hole  513  through which a lower lip or hook of payload coupling apparatus  800  extends. The handle sits within a slot of the payload coupling apparatus  800  that is suspended from tether  502  of payload delivery system  500  during descent of the payload  510  to a landing site. 
       FIG.  10 B  shows a side view of payload delivery apparatus  500  after payload  510  has landed on the ground showing payload coupling apparatus  800  decoupled from handle  511  of payload  510 . Once the payload  510  touches the ground, the payload coupling apparatus  800  continues to move downwardly (as the winch further unwinds) through inertia or gravity and decouples the lower lip or hook  808  of the payload coupling apparatus  800  from handle  511  of payload  510 . The payload coupling apparatus  800  remains suspended from tether  502 , and can be winched back up to the payload coupling receptacle of the UAV. 
       FIG.  10 C  shows a side view of payload delivery apparatus  500  with payload coupling apparatus  800  moving away from handle  511  of payload  510 . Here the payload coupling apparatus  800  is completely separated from the hole  513  of handle  511  of payload  510 . Tether  502  may be used to winch the payload coupling apparatus back to the payload coupling apparatus receptacle positioned in the fuselage of the UAV. 
       FIG.  11 A  is a side view of handle  511  of payload  510 . The handle  511  includes an aperture  513  through which the lower lip or hook of a payload coupling apparatus extends through to suspend the payload during delivery, or for retrieval. The handle  511  includes a lower portion  515  that is secured to the top portion of a payload. Also included are holes  524  and  526  through which locking pins positioned within the fuselage of a UAV, may extend to secure the handle and payload in a secure position during high speed forward flight to a delivery location. In addition, holes  524  and  526  are also designed for pins of a payload holder to extend therethrough to hold the payload in position for retrieval on a payload retrieval apparatus. The handle may be comprised of a thin, flexible plastic material that is flexible and provides sufficient strength to suspend the payload beneath a UAV during forward flight to a delivery site, and during delivery and/or retrieval of a payload. In practice, the handle may be bent to position the handle within a slot of a payload coupling apparatus. The handle  511  also has sufficient strength to withstand the torque during rotation of the payload coupling apparatus into the desired orientation within the payload coupling apparatus receptacle, and rotation of the top portion of the payload into position with the recessed restraint slot. 
       FIG.  11 B  is a side view of handle  511 ′ of payload  510 . The handle  511 ′ includes an aperture  513  through which the lower lip or hook of a payload coupling apparatus extends through to suspend the payload during delivery, or for retrieval. The handle  511 ′ includes a lower portion  515  that is secured to the top portion of a payload. Also included are magnets  524 ′ and  526 ′ adapted for magnetic engagement with corresponding magnets (or a metal) of a payload holder to secure the payload to the payload holder in position for retrieval on a payload retrieval apparatus. In some examples, magnets  524 ′ and  526 ′ are provided on a handle (e.g., handle  511  or  511 ′) in place of holes  524  and  526 . In other examples, magnets  524 ′ and  526 ′ are provided in addition to holes  524  and  526 . 
       FIG.  12    shows a pair of pins  570 ,  572  extending through holes  524  and  526  in handle  511  of payload  510  to secure the handle  511  and top portion of payload  510  within the fuselage of a UAV, or to secure payload  510  to a payload holder of a payload retrieval apparatus. In this manner, the handle  511  and payload  510  may be secured within the fuselage of a UAV, or to a payload holder of a payload retrieval apparatus. In this embodiment, the pins  570  and  572  have a conical shape so that they pull the package up slightly or at least remove any downward slack present. In some embodiments the pins  570  and  572  may completely plug the holes  524  and  526  of the handle  511  of payload  510 , to provide a secure attachment of the handle and top portion of the payload within the fuselage of the UAV, or to secure the payload to a payload retrieval apparatus. Although the pins are shown as conical, in other applications they may have other geometries, such as a cylindrical geometry. 
       FIGS.  13 A and  13 B  show various views of payload coupling apparatus or payload retriever  800 ′ which is a variation of payload coupling apparatus  800  described above. Payload coupling apparatus  800 ′ includes the same exterior features as payload coupling apparatus  800 . However, in payload coupling apparatus  800 ′, lower lip or hook  806 ′ is extendable and retractable. As shown in  FIG.  13 A , payload coupling  800 ′ is in a retracted state where end  806   a ′ of lip or hook  806 ′ is positioned inwardly from outer wall  807  of capsule housing  805 . In  FIG.  13 B , payload coupling apparatus  800 ′ is in an extended state where end  806   a ′ of lip or hook  806 ′ has been moved outwardly from capsule housing  805  such that the end  806   a  of the lip or hook  806 ′ is positioned outwardly from outer wall  807  of capsule housing  805 . Lip of hook  806 ′ may be moved outwardly via cams or protrusions within channel  1050 , or by a spring-loaded portion of channel  1050 , or other mechanisms. In the extended state shown in  FIG.  13 B , the hook or lip  806 ′ is in position to easily extend through the aperture  513  in handle  511  of payload  510 , such that the handle  511  is positioned within slot  808  of payload coupling apparatus  800 ′ and retrieval of the payload and removal from the payload holder of the payload retrieval apparatus can be achieved. Once the payload  510  is removed from the payload holder the hook or lip  806 ′ may be moved back to its retracted sate as shown in  FIG.  13 A . 
       FIG.  13 C  is a side view of payload coupling apparatus  800 ″ which in this illustrative embodiment is the similar to payload coupling apparatus  800  shown in  FIGS.  6 A- 6 C , but instead includes a plurality of magnets  830  positioned thereon. The plurality of magnets  830  are adapted to magnetically engage a plurality of magnets  1060  (or a metal) positioned within the channel  1050  of a payload retrieval apparatus  1000  as shown in  FIG.  20    below to orient the payload coupling apparatus  800 ″ within the channel  1050  of payload retrieval apparatus  1000  so that the hook or lip  806   a  is in proper position to extend through aperture  513  of handle  511  of payload  510  to effect removal of payload  510  from the payload holder of payload retrieval apparatus  1000 . 
       FIG.  13 D  is a side view of payload coupling apparatus  900  which in this illustrative embodiment is similar to payload coupling apparatus  800 ″ shown in  FIG.  6 C , but instead includes a weighted side  840 . The weighted side  840  serves to orient the payload coupling apparatus  900  within the channel  1050  of payload retrieval apparatus  1000  so that the hook or lip  806   a  is in proper position to extend through aperture  513  of handle  511  of payload  510  to effect removal of payload  510  from the payload holder of payload retrieval apparatus  1000 . 
     In each of the payload coupling apparatuses  800 ,  800 ′,  800 ″, and  900  described above, the upper and lower ends are rounded, or hemispherically shaped, to prevent the payload coupling apparatus from snagging during descent from, or retrieval to, the fuselage of a UAV. Furthermore, each of payload coupling apparatuses  800 ,  800 ″, and  900  may have a retractable and extendable hook or lip as is shown in  FIGS.  13 A and  13 B  with regard to payload coupling apparatus  800 ′. 
     In addition, as illustrated in  FIG.  9   , the payload delivery system may automatically align the top portion of the payload during winch up, orienting it for minimum drag along the aircraft&#39;s longitudinal axis. This alignment enables high speed forward flight after pick up. The alignment is accomplished through the shape of the payload hook and receptacle. In the payload coupling apparatus  800 , the lower lip or hook  806  has cam features around its perimeter which always orient it in a defined direction when it engages into the cam features inside the receptacle of the fuselage of the UAV. The tips of the cam shapes on both sides of the capsule are asymmetric to prevent jamming in the 90 degree orientation. In this regard, helical cam surfaces may meet at an apex on one side of the payload coupling mechanism, and helical cam surfaces may meet at a rounded apex on the other side of the payload coupling mechanism. The hook is specifically designed so that the package hangs in the centerline of the hook, enabling alignment in both directions from 90 degrees. 
     Payload coupling apparatuses  800 ,  800 ′,  800 ″, and  900  include a hook  806  (or  806 ′) formed beneath a slot  808  such that the hook also releases the payload passively and automatically when the payload touches the ground upon delivery. This is accomplished through the shape and angle of the hook slot and the corresponding handle on the payload. The hook slides off the handle easily when the payload touches down due to the mass of the capsule and also the inertia wanting to continue moving the capsule downward past the payload. The end of the hook is designed to be recessed slightly from the body of the capsule, which prevents the hook from accidentally re-attaching to the handle. After successful release, the hook gets winched back up into the aircraft. 
       FIGS.  14 - 16    are perspective views of payload retrieval apparatus  1000  having a payload  510  positioned thereon, according to an example embodiment. The payload retrieval apparatus  1000  may be a non-permanent structure placed at a payload retrieval site. The apparatus includes an extending member  1010  that may be secured to a base or stand  1012  at a lower end of the extending member  1010 . Alternately, the extending member  1010  may have a lower end that may be positioned within a corresponding hole in the ground or hole in an apparatus positioned on the ground. The payload retrieval apparatus  1000  may be readily folded up, like an umbrella stand, to provide for ease of transport. In addition, because of its non-permanent configuration, payload retrieval apparatus  1000  may not require any type permitting, which may not be the case for a permanent device used for UAV loading and unloading. 
     An angled extender  1020  may be attached at an upper end of the extending member  1010 , and adapter  1016  may be used to adjust the height or angle of the angled extender  1020 , and having a threaded set screw with knob  1018  to set the angled extender  1020  into a desired position. The angled extender  1020  is shown with an upper end secured to a channel  1050 . A first end of the channel may have a first extension or tether engager  1040  that extends in a first direction from a lower end of the channel  1050  and a second extension or tether engager  1030  that extends in a second direction from the lower end of the channel  1050 . A second end of the channel  1050  may have a payload holder  570 ,  572  positioned near or thereon that is adapted to secure a payload  510  to the second end of the channel  1050 . 
     A shield  1042  is shown extending from the first tether engager  1040 , and another shield  1032  is shown extending from the second tether engager  1030 . Shield  1042  and  1032  may be made of a fabric material, or other material such as rubber or plastic. A shield  1052  is also shown extending from the first end of channel  1050 . Shields  1042 ,  1032 , and  1052  serve to prevent a payload retriever  800  extending from an end of a tether  1200  attached to a UAV from wrapping around the tether engagers  1040  and  1032  or other components of payload retrieval apparatus  1000  when the payload retriever comes into contact with tether engagers  1040  or  1030  during a payload retrieval operation. 
     Channel  1050  includes a tether slot  1054  extending from a first end to a second end of the channel  1050 , and the tether slot  1054  allows for a payload retriever to be positioned within the channel  1050  attached to a tether which extends through the tether slot  1054 . A payload holder is shown that is a pair of pins  570 ,  572  that extend through openings in handle  511  of payload  510  to suspend payload  510  in position adjacent the second end of the channel  1050  ready to be retrieved by a payload retriever attached to a tether suspended from a UAV. 
     To provide for automatic retrieval of payload  510  with a payload retriever suspended from a UAV with a tether, payload  510  is secured to the payload holder  570 ,  572  on the second end of the channel  1050  at the payload retrieval site. A UAV arrives at the payload retrieval site with a tether  1200  extending downwardly from the UAV and with the payload retriever  800  positioned on the end of the tether, as shown in  FIGS.  14  and  17   . The UAV approaches the payload retrieval apparatus  1000 , and as it nears the payload retrieval apparatus  1000 , the tether  1200  comes into contact with the first or second extension (tether engager)  1040 ,  1030 . As the UAV moves forward, or the UAV is moved upwardly, or the payload retriever is winched upwardly to the UAV while the UAV is hovering in place (or any combination thereof), the tether slides inwardly along the first or second extension  1040 ,  1030  where it is directed towards the first end of the channel  1050 . With further forward or upward movement of the UAV, or upward winching of the payload retriever, the tether  1200  moves through the tether slot  1054  of channel  1050  and eventually the payload retriever  800  attached to the tether  1200  is pulled into the channel  1050  by the tether. The payload retriever  800  is pulled through the channel  1050  where it engages, and secures, the payload  510  secured to the payload holder  570 ,  572 . The payload retriever  800  then pulls the payload  510  free from the payload holder  570 ,  572 . Once the payload  510  is free from the payload holder  570 ,  572 , the payload  510  may be winched upwardly into secure engagement with the UAV, and the UAV may continue on to a delivery site where the payload  510  may be delivered by the UAV. 
       FIG.  17    shows a sequence of steps A-D performed in the retrieval of payload  510  from payload retrieval apparatus  1000 , shown in  FIGS.  14 - 16   . A payload retriever, shown in  FIG.  17    as payload coupling apparatus  800  having a hook or lip  806  positioned beneath slot  808 , is attached to an end of tether  1200  which is in turn to attached to a UAV. At point A in the sequence of steps shown from right to left, payload retriever  800  is shown suspended at the end of tether  1200  at a position below the height of tether engagers  1040  and  1030 . Payload retriever  800  and tether  1200  move towards the payload retrieval apparatus  1000 , where tether  1200  contacts tether engager  1040  or tether engager  1030 , and tether  1200  and payload retriever  800  move towards channel  1050  until payload retriever  800  is positioned just outside of channel  1050  shown at point B in the sequence. With further forward or upward movement of the UAV, or upward winching of payload retriever  800  (or any combination thereof), tether  1200  extends through tether slot  1054  of channel  1050  and payload retriever  800  is positioned within channel  1050  as shown at point C of the sequence. With further forward or upward movement of the UAV, or upward winching of the payload retriever  800  (or any combination thereof), payload retriever  800  exits channel  1050  and hook or lip  806  of payload retriever  800  engages handle  511  of payload  510  and removes payload  510  from payload holder  570 ,  572  positioned on the end of the channel  1050 . After removal of payload  510  from payload holder  570 ,  572  of payload retrieval apparatus  1000 , at point D of the sequence, payload  510  is suspended from tether  1200  with handle  511  of payload  510  positioned in slot  808  above hook or lip  806  of payload retriever  800 , where payload  510  may be winched up to the UAV and flown for subsequent delivery at a payload delivery site. 
       FIG.  18    is a perspective view of payload retrieval apparatus  1000  shown in  FIGS.  14 - 17    with a payload loading apparatus  1080  having a plurality of payloads  510 - 2  and  510 - 3  positioned thereon, according to an example embodiment. Payload loading apparatus  1080  includes a platform  1082  positioned on platform base  1086  having an upper surface  1084  that downwardly slopes towards payload retrieval apparatus  1000 . Payload loading apparatus  1080  allows for automatic loading of a subsequent payload positioned on upper surface  1084  of payload loading apparatus  1080  onto payload retrieval apparatus  1000  after a payload positioned on the payload holder has been retrieved. In particular, once payload  510 - 1  has been removed from payload holder  570 ,  572  of payload retrieval apparatus  1000 , subsequent payload  510 - 2  slides down the upper surface  1084  of the payload loading apparatus  1080  and is secured to payload holder  570 ,  572  of payload retrieval apparatus  1000 . Payload loading apparatus  1080  may include one or more rollers  1088  that provide for the downward movement of upper surface  1084 , like a conveyor belt. 
     As shown in  FIG.  18   , the handle  511  of payload  510 - 1  has openings  524  and  526  (see  FIG.  11 A ) through which pins  570 ,  572  extend to hold payload  510 - 1  in position for retrieval. However, handle  511  may also include magnets  524 ′ and  526 ′ (see  FIG.  11 B ) that are adapted to magnetically engage corresponding magnets or a metal positioned on the payload holder of the payload retrieval apparatus  1000 . With a magnetic handle, the magnets  524 ′ and  526 ′ on the handle  511  move into engagement with the payload holder to hold subsequent payload  510 - 2  into position for subsequent retrieval as illustrated in the sequence of steps at points A-D shown in  FIG.  17   . In addition, payloads  510 - 1  through  510 - 3  may include fiducials  585  that may take the form of an RFID tag or bar code to identify the contents of the payload and delivery site information and/or delivery instructions. As a result, using payload loading apparatus  1080  in conjunction with payload retrieval apparatus  1000 , a plurality of payloads may be retrieved from payload apparatus  1000  without the need for a person to reload subsequent payloads for retrieval, providing for further automated payload retrieval. 
     In order for the hook or lip  806  of the payload retriever  800  (shown in  FIGS.  6 A-C ) to engage the handle  511  of payload  510  to effect removal and retrieval of the payload  510  from the payload retrieval apparatus  1000 , the hook or lip  806  should be positioned downwardly when it exits the channel  1050  in the embodiment shown (different orientations are possible in alternate embodiments). As illustrated in  FIG.  19   , to ensure that the slot hook or lip  806  of the payload retriever  800  is in a proper orientation as the payload retriever  800  exits the channel  1050  and engages the handle  511  of the payload  510 , the payload retriever  800  may be provided with exterior cams  804  or slots that correspond to cams or slots  1058 ,  1059  positioned on an interior surface of the channel  1050 . The interaction of the cams  804  or slots on the payload retriever  800  and cams or slots  1058 ,  1059  on the interior of the channel  1050  properly orient the payload retriever  800  within the channel  1050  such that hook or lip  806  beneath the slot  808  of the payload retriever  800  is in proper position to extend through the aperture  513  on the handle  511  of the payload  510  to remove the payload  510  from the payload holder  570 ,  572 . 
       FIG.  19    is a perspective view of channel  1050  of the payload retrieval apparatus  1000  shown in  FIGS.  14 - 16    with a payload retriever  800  positioned therein. Channel  1050  includes a tether slot  1054  through which tether  1200  extends when tether  1200  draws payload retriever  800  into the interior of channel  1050 . The interior of channel  1050  includes cams or slots  1058 ,  1059  which cooperate with cams  804  or slots on the payload retriever  800  to properly orient the hook or lip  806  and slot  808  in a downward facing position within the channel  1050 . Thus, the interaction of cams or slots  1058 ,  1059  on the interior of channel  1050  with cams  804  or slots on the payload retriever  800  provides a desired orientation of the payload retriever  800  at the point that payload retriever  800  exits the channel  1050  and engages handle  511  of payload  510  to remove the payload  510  from the payload holder  570 ,  572 . 
     Alternately, or in addition to cams  804 , the payload retriever  800 ″ may have one or more magnets  830  positioned thereon as shown in  FIG.  13 C and  20    that cooperate with one or more magnets  1060 , or a metal, positioned on an interior of the channel  1050  and magnetic interaction is used to properly orient the payload retriever  800 ″ within the channel  1050  during the process of payload retrieval. 
       FIG.  20    is a perspective view of channel  1050  of the payload retrieval apparatus  1000  shown in  FIGS.  14 - 16    with a payload retriever  800 ″ positioned therein. Channel  1050  includes a tether slot  1054  through which tether  1200  extends when tether  1200  draws payload retriever  800 ″ into the interior  1056  of channel  1050 . The interior  1056  of channel  1050  includes a plurality of magnets  1060  which magnetically engage with magnets  830 , or a metal, on the payload retriever  800 ″ to properly orient the hook or lip  806  and slot  808  in a downward facing position within the channel  1050 . Thus, the interaction of magnets  1060  on the interior  1056  of channel  1050  with magnets  830  or simply a metal on the payload retriever  800 ″ provides a desired orientation of the payload retriever  800 ″ at the point that payload retriever  800 ″ exits the channel  1050  and engages handle  511  of payload  510  to remove the payload  510  from the payload holder  570 ,  572 . Alternatively, or in addition, a metal strip or plurality of metal pieces could be positioned within the channel  1050  to provide for magnetic engagement with the magnets  830  on the payload retriever  800 ″. Similarly, one or more magnets may be positioned on the interior of channel  1050  that magnetically engage a metal positioned on a payload retriever. 
     In addition, the payload retriever could be weighted to have an offset center of gravity (see payload retriever  900  shown in  FIG.  13 D ) such that the hook  806  and slot  808  of the payload retriever  900  are positioned properly (with the “heavy” portion of the capsule on a lower side) to engage the handle  511  of the payload  510  and effect removal of the payload  510  from the payload holder  570 ,  572 . The weighted side  840  of payload retriever  900  helps to insure that the hook or lip  806  and slot  808  are positioned downwardly within the channel  1050  so as to be in position for the hook or lip  806  to extend through aperture  513  in handle  511  of payload  510  during the retrieval process. It will be appreciated that the use of cams, magnets, and a weighted side could all be used separately, or used in combination in whole or in part, to provide for a desired orientation of the payload retriever within the channel to effect removal of the payload from the payload retrieval apparatus  1000 . 
     As shown in  FIG.  21 A , the channel  1050  may also have an interior that tapers downwardly, or decreases in size, as the channel  1050  extends from the first end where the payload retriever enters the interior  1056  of channel  1050  to the second end where the payload retriever exits the channel  1050  to further facilitate the proper orientation of the payload retriever within the channel. In addition, as shown in  FIG.  21 B , the second end of the channel  1050  could be spring loaded with a spring  1061  exerting a force against outer surface  1057  of channel  1050 , or operate as a leaf spring, to also facilitate the proper orientation of the payload retriever (or extension or the hook or lip of the payload retriever) at the point of payload retrieval. 
     Not only does the payload retrieval apparatus  1000  described above provide for automatic payload retrieval without the need for human involvement, but the UAV advantageously is not required to land for the payload  510  to be loaded onto the UAV at the payload retrieval site. Thus, the UAV may simply fly into position near the payload retrieval apparatus  1000  and maneuver itself to position the tether  1200  between the first and second tether engagers  1040 ,  1030 , which may be aided by the use of fiducials (which could take the form of an RFID tag or bar code) positioned on or near the payload retrieval apparatus  1000  and/or an onboard camera system positioned on the UAV. Once in position, the UAV may then move forward or upward, or the payload retriever may be winched up towards the UAV (or any combination thereof) to pull the payload retriever through the channel  1050  and into engagement with the handle  511  of the payload  510  and effect removal of the payload  510 . In some payload retrieval sites, landing the UAV may be difficult or impractical, and also may engage with objects or personnel when landing. Accordingly, allowing for payload retrieval without requiring the UAV to land provides significant advantages over conventional payload retrieval methods. 
     Furthermore, the payload retrieval apparatus  1000  is advantageously a movable, non-permanent apparatus that may be easily set up, taken down, and removed, and may be easily moved from one payload retrieval site to another. The payload retrieval apparatus  1000  preferably folds up, like an umbrella stand, to facilitate storage and transport of the payload retrieval apparatus  1000 . The non-permanent nature of the payload retrieval apparatus  1000  also may eliminate the need for a permit for the payload retrieval apparatus  1000  at the retrieval site. 
     VII. CONCLUSION 
     The particular arrangements shown in the Figures should not be viewed as limiting. It should be understood that other implementations may include more or less of each element shown in a given Figure. Further, some of the illustrated elements may be combined or omitted. Yet further, an exemplary implementation may include elements that are not illustrated in the Figures. 
     Additionally, while various aspects and implementations have been disclosed herein, other aspects and implementations will be apparent to those skilled in the art. The various aspects and implementations disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. Other implementations may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are contemplated herein.