Abstract:
A water resistant and electromagnetically shielded turret assembly, suitable for attachment to the undersurface of an unmanned surveillance aircraft. The turret, in its several variations, may contain one or more cameras, and may contain an internal positioning motor, which can be easily accessible for servicing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is related to U.S. patent application Ser. No. 13/220,619, entitled “Tilt-Ball Turret with Gimbal Lock Avoidance,” by Tom Szarek et al., filed currently herewith, the entire disclosure of which is hereby incorporated by reference. 
     TECHNICAL FIELD 
     This subject matter relates generally to heat transfer and electromagnetic shielding with application to a ball turret. 
     BACKGROUND 
     The way that the Vietnam War is now remembered as the helicopter war, the current conflicts in Iraq and Afghanistan may be remembered for the use of unpiloted aerial surveillance (UAV) craft or drones. Drones may facilitate remote intelligence gathering, alleviating the need for foot soldiers to enter into hostile areas “blind,” with little or no information about the location and strength of hostile forces. Drones may provide close combat support, such as identifying and eliminating targets of interest, alleviating the need to expose soldiers and/or airmen to potential small arms fire, mortars, rocket grenades, road-side bombs, anti-aircraft weaponry, missiles, and other dangers. 
     Although many presently used drones are roughly the same scale size as piloted aircraft, such aircraft are both relatively expensive and may be detected due to their size. Recently, smaller drones have been developed that may be deployed in greater numbers and are relatively less expensive resulting in greater use by individual units in the field. Smaller drones have certain tradeoffs as they cannot carry the amount of payload of a larger drone. Further, power for such smaller drones is limited due to the size of the aircraft and therefore operating periods are also limited. 
     Unpiloted drone aircraft typically mount a camera in a ball turret assembly which allows movement in three dimensions to allow the camera to track objects on the ground without altering the flight path of the aircraft. Data such as image data may be captured via a sensor such as a camera and transmitted back to a controller. 
     Because sensitive cameras and other equipment such as precise motors and gimbal systems are sensitive to weather, and must be kept from the elements, this equipment is generally enclosed in a casing or shell. Traditionally, turret shells have been made of glass or plastic. See, e.g., U.S. Patent App. No. 2009/0216394 A1(published Aug. 27, 2009). Polymer and glass shells have the disadvantage that they may allow electromagnetic radiation to enter the turret and interfere with the sensitive camera equipment. Polymers and glasses are also generally thermal insulators, so that heat may build up inside the turret, compromising the equipment. Solid metallic turret shells are possible, but are heavy and not ideal for aerial reconnaissance craft. 
     Thus, it would be desirable to have a ball turret that is both lightweight and waterproof, but also contains shielding from electromagnetic radiation, and comprises a heat sink to remove heat that builds up in the turret. 
     BRIEF SUMMARY 
     The present disclosure relates to a turret useful for, among other things, housing a surveillance camera on the underside of a surveillance aircraft. 
     Such a turret may comprise a front shell and a rear shell. Preferably, the rear shell may have an o-ring groove, into which an o-ring may be placed, although an o-ring groove may alternatively be placed on the front shell, or there may be multiple o-rings. The front shell can have one or more transparent windows for transmission of light, infrared, or other electromagnetic radiation. This radiation can be accepted and recorded by a camera attached to the interior of the turret and facing a transparent window. 
     The front shell may be constructed of a polymer material which can be coated in its interior with an electrically- and thermally-conductive coating such as metal, most preferably copper. At least a portion of the rear shell may also be conductive, particularly in its interior. This rear portion is preferably a metal-coated polymer, but may also for example be an anodized metal. The composition of the front and rear shell sections may be different. 
     Joining the front and rear shells may be an electrically- and thermally-conductive elastomeric o-ring situated in the o-ring groove and in contact with the conductive surface of both the front and rear shells. In some configurations, the conductive coating of the inner surface of the shell may wrap around and cover an outer part of the shell to maintain electrical contact between the o-ring groove and the internal surface of the shell. Any such exterior coating of metal is preferably covered by a portion of the other shell, so as to prevent exposure to the elements. 
     The o-ring may seal the connection between the front and rear shells so that the enclosure formed by the shells is water-resistant or waterproof under the design conditions of the aircraft with at least a margin or safety. Preferably, the o-ring may be electrically conductive and have enhanced thermal conductivity beyond typical elastomeric substances. For example, specialized elastomeric substances known in the art might have thermal conductivities at normal operating conditions greater than about 0.50 W/(m·K), or often significantly higher. Electrically, there is preferably an electrical connection between the interior front and rear shell surfaces through the o-ring so that as a whole, the turret acts as an electromagnetic shield. Thus, it is preferable to maximize the amount of interior surface that is electrically conductive, and to maintain electrical connection throughout the interior surface. 
     Various additional embodiments, including additions and modifications to the above embodiments, are described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated into this specification, illustrate one or more exemplary embodiments of the inventions disclosed herein and, together with the detailed description, serve to explain the principles and exemplary implementations of these inventions. One of skill in the art will understand that the drawings are illustrative only, and that what is depicted therein may be adapted, based on this disclosure, in view of the common knowledge within this field. 
       In the drawings: 
         FIGS. 1A and 1B  illustrate an unpiloted surveillance aircraft having an example ball turret assembly. 
         FIGS. 2A-E  are close up views of the example ball turret assembly mounted on the aircraft of  FIGS. 1A-B . Shown are a perspective view ( FIG. 2A ), a bottom view ( FIG. 2B ), a side view ( FIG. 2C ), a front view ( FIG. 2D ) and a rear view ( FIG. 2E ). 
         FIGS. 3A-C  illustrate views of the ball turret of  FIGS. 2A-E . In particular,  FIG. 3A  is a cross-section view,  FIG. 3B  is a cross-section top view taken along the line  460  in  FIG. 3A ;  FIG. 3C  is a cross-section top view of the example ball turret assembly of  FIG. 2A ; 
         FIGS. 4A-D  are views of an example front shell of a ball turret.  FIGS. 4A and 4C  are side views,  FIG. 4B  is a view from the rear, and  FIG. 4D  is a cross-section top view taken along the line  470 . 
         FIGS. 5A-B  are different perspective views of a front shell. 
         FIG. 6A  is a perspective view, and  FIG. 6B  is a perspective view of a rear shell. 
         FIG. 7A  is a back view, and  FIG. 7B  is a cross-section side view, of a rear shell. 
         FIG. 8  is a side and cross-sectional view of a front shell engaged with a back shell. 
     
    
    
     DETAILED DESCRIPTION 
     Various example embodiments of the present inventions are described herein in the context of providing a shell for a camera turret for attachment to a reconnaissance aircraft that may shield against electromagnetic radiation and may effectively dissipate heat that builds up in the system. The shell is also preferably lightweight and waterproof. 
     Those of ordinary skill in the art will understand that the following detailed description is illustrative only and is not intended to be in any way limiting. Other embodiments of the present inventions will readily suggest themselves to such skilled persons having the benefit of this disclosure, in light of what is known in the relevant arts, the provision and operation of information systems for such use, and other related areas. 
     Not all of the routine features of the exemplary implementations described herein are shown and described. In the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the specific goals of the developer, such as compliance with regulatory, military, safety, social, environmental, health, and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, such a developmental effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure. 
     Throughout the present disclosure, relevant terms are to be understood consistently with their typical meanings established in the relevant art. However, without limiting the scope of the present disclosure, exemplary clarifications and descriptions of certain terms are provided for relevant terms and concepts as set forth below: 
     As used herein, the term transparent includes transparency in any appropriate wavelength of electromagnetic (EM) radiation. It may include transparency in a very broad range of EM frequencies, or a very narrow set of frequencies. Most useful is transparency in the visible and/or infrared regions of the spectrum; however, other regions may also be useful for imaging purposes. 
     As used herein, the term water-resistant means that water does not penetrate under any expected operating conditions, including adverse weather. 
       FIGS. 1A and 1B  are perspective views of an unpiloted reconnaissance aircraft  100 . The example aircraft  100  may have a fuselage  102  mounting a left wing  104  and a right wing  106 . The aircraft  100  may be powered by an engine  108  which rotates a propeller  110 . The aircraft  100  may be stabilized with the assistance of elevators  114  and a tail  116  mounted on a boom  112 . Preferably, the aircraft  100  may be small enough to be carried by an individual soldier and have a top speed of preferably about 55 knots and a cruising speed of about 25 knots. However, the characteristics of the aircraft may vary widely in accordance with the inventions claimed herein. The ball turret assemblies described herein may be attached to any suitable aircraft. 
     The aircraft  100  may include a ball turret assembly  118  that may be suspended from an under-surface  120  of the fuselage  102 . The ball turret assembly  118  may include a ball turret  122  that may be mounted in a housing  124  on the under surface  120 . The ball turret  122  may be mounted in front of a fairing  126  that may also be part of the housing  124 . Preferably, the ball turret  122  may hold an infrared camera  130  and a color camera  132 . In one example, the infrared camera  130  may be a MicroTau 320 or 640 model camera available from FLIR and the color camera is a 5 megapixel Model MT9P031 EO sensor. However, the inventions described herein may also be used with any suitable camera devices. 
     If two cameras are used in accordance with this example, both of them are preferably configured for taking approximately 30 frames per second video stream of images but may also send still images at a different, preferably higher, resolution. Other types of cameras and/or sensors may also be mounted in the ball turret  122 , either in addition to or in place of those shown in the figures. The ball turret  122  may be rotated by a yoke which is mounted on the fairing  126 . In a preferably configuration, the fairing  126  in combination with the ball turret assembly  118  may reduce drag because the yoke is located behind the ball turret  122 . By actuators for tilting and rolling the ball turret  122 , the cameras  130  and  132  may be directed toward areas under the under surface  120  of the fuselage  102 . As shown in  FIG. 1A , the ball turret is rotated to point the cameras  130  and  132  to the left side of the aircraft  100 .  FIG. 1A  shows an approximate imaging area that may be viewed by the cameras  130  and  132  in this position.  FIG. 1B  shows an example of the ball turret  122  rotated to position the cameras  130  and  132  to view an area to the front of the aircraft  100 . 
       FIGS. 2A-2E  are close up views of the example ball turret assembly  118  in  FIG. 1 .  FIG. 2A  is close up perspective view of the example ball turret assembly  118 ,  FIG. 2B  is a bottom view of the example ball turret assembly  118 ,  FIG. 2C  is a side view of the example ball turret assembly  118 ,  FIG. 2D  is a front view of the example ball turret assembly  118  and  FIG. 2E  is a rear view of the example ball turret assembly  118 . The ball turret assembly  118  may include the ball turret  122  mounted on the fairing  126  on the under surface  120  of  FIG. 1  via a gimbal assembly  200 . A yoke  202  may extend from the fairing  126 . The yoke  202  may include a pair of forks  204  and  206  that have ends that hold the ball turret  122  via pins  208  and  210 . The forks  204  and  206  may have respective opposite ends from the pins  208  and  210  connected by a cross bar  212 . The cross bar  212  may be attached to a roll drive shaft  214  that supports the yoke  202  from the fairing  126 . The ball turret  122  may include an exterior surface  220  that is preferably waterproof and sealed to protect the mechanical and electrical components such as the cameras  130  and  132  stored therein. Because the yoke  202  preferably does not have any actuating or electronic components the number of parts requiring water-proofing may also be decreased. In this example, the exterior surface  220  may have an aperture  222  for infrared camera  130  and a mounting cylinder  224  for color camera  132 . 
     A roll axis is represented by a dashed line  240  which points forward relative to the aircraft  100 . The ball turret  122  may preferably be rotated around the roll axis  240  via the roll drive shaft  214  being rotated by a roll actuator in the fairing  126 . A tilt axis represented by a dashed line  250  is 90 degrees offset from the roll axis  240 . Preferably, the ball turret  122  may therefore be rotated on the forks  204  and  206  around the tilt axis  250  via a tilt actuator contained in the turret  122 . A wiring harness  260  containing wiring for power, data and communications may extend from the fairing  126  to the ball turret  122  through the interior of the drive shaft  214  and be attached to the yoke  202  and follow the fork  204  to the interior of the ball turret  122 . 
     Various means for positioning and directing the turret are known in the art. Certain such means are disclosed in 
       FIGS. 3A and 3B  show cross-section views of the example ball turret  122  and the related ball turret assembly  118  of  FIG. 2 . As shown in the example of  FIGS. 3A-3B , an interior surface  400  of the ball turret  122  may enclose various mechanical and electrical components. An infrared camera  130  may be mounted on, or wired to, a circuit board  410  while the color camera  132  may be mounted on or associated with a circuit board  420 . The circuit boards  410  and  420  may be fixed on the interior surface  400  in order to orient the infrared camera  130  through the aperture  222  and the color camera  132  through the mounting cylinder  224 . Circuit boards  410  and  420  may also be condensed into a single circuit board, and may be placed anywhere within the ball turret where there is space, or may in a less preferred embodiment be placed outside the ball turret. Various means of wiring may be used, depending on the contents of the turret, and the number, type, and placement of cameras. 
     The tilt actuator may include a tilt motor  430  that rotates a drive shaft  432 . The drive shaft  432  may drive the gears in a gear box  434 . The gear box  434  may down-shift the rotations from the motor  430  to rotate a drive shaft  436  that is mounted on the pin  208  rotatably coupled to the fork  204  of the yoke  202 . The other fork  206  of the yoke  202  may be rotatably mounted on the pin  210  on the exterior of the ball turret  122 . 
     The yoke  202  may be mounted on the drive shaft  214  connected to a fairing  126 . The fairing  126  may enclose the actuators for the roll or pan motion. The roll actuator thus may drive a drive shaft  214  and a yoke  202 . The fairing  126  may enclose a pan or roll motor  440  which rotates a drive shaft  442  which drives a gear box  444 . The gear box  444  in turn may drive the drive shaft  214  to rotate the yoke  202 .  FIG. 3C  is a top view of the mounting  124  which includes the fairing  126  and the ball turret  122 . The fairing  126  may in one embodiment enclose a circuit board  450  that hold the electronics for controlling the tilt and roll actuators. A vertical tab  452  may include an electronic connector  454  which provides connections to electronic components contained in the fuselage  102 . A set of cables  456  may extend from the connector  454  through an aperture  458  to provide control and data signals to and from the electronic components in the fairing  126  and the ball turret  122 . 
     As shown in  FIG. 2B , the wiring harness  260  containing wiring for power, data and communications may extend from the fairing  126  to the ball turret  122  through the interior of the drive shaft  214 . As shown in  FIGS. 2B and 2C , the wiring harness  260  may be attached to the yoke  202  and follow the fork  204  to the interior of the ball turret  122 . The controls for the roll and tilt actuators should preferably prevent the ball turret  122  from rotating the yoke  202  to tangle the wiring harness  260 . Because the data connections are hardwired from sensors such as the cameras  130  and  132 , maximum bandwidth may preferably be achieved from image data acquired by the cameras  130  and  132 . 
     This illustrative arrangement may allow the cameras  130  and  132  in the turret  122  maximum view of the area of interest and reduces the drag of the turret assembly  118 . As explained above, the pan or roll mechanics (actuators) driving the yoke  202  may be located behind the ball turret  122  in the fairing  126 . Because the actuators for the roll motion are preferably mounted in the fairing  126  and movement occurs preferably in the roll actuator in the fairing  126  to rotate the yoke  202  holding the ball turret  122 , the yoke  202  in a preferred embodiment has no moving parts or electronic components. This configuration may, in a particularly preferred embodiment, allow the ball turret  122  and fairing  126  alone to be water proofed to protect the electronic and mechanical components of the ball turret assembly  118  contained in the ball turret  122 . 
     The turret  122  preferably has a spherical or ball shape because of ease in maneuvering and thermodynamic properties. However, other shapes are possible, such as a teardrop shape, an oval or a rectangular prism. 
     Such a turret may comprise a front shell and a rear shell.  FIGS. 4A-D  and  FIGS. 5A-B  are various views of an example front shell.  FIGS. 4A and 4C  are side views,  FIG. 4B  is a view from the rear, and  FIG. 4D  is a cross-section top view taken along the line  470 . The front shell can have one or more transparent windows  471  for transmission of light, infrared, or other electromagnetic radiation. This radiation can be accepted and recorded by a camera attached to the interior of the turret and facing one of the transparent windows. In one embodiment, there can be two camera assemblies, one for detecting and recording infrared light, and another for detecting and recording visible light. Other combinations are also possible, and other camera types, such as detectors for ultraviolet light. There may also be multiple infrared cameras for multiple wavelength ranges of infrared light. In one embodiment, there may be two identical or similar cameras or camera lenses configured to record a stereoscopic view. Cameras may preferably be mounted to mounting points  472  to the inner surface  475  of the front shell by any means of attachment known in the art. Preferably, the cameras will be attached through conductive means, such as conductive bolts, clamps, or the equivalent. Thermal grease, thermal adhesives, thermal pads, or the equivalent may also be used to enhance the thermal connection between the cameras and the inner surface of the front shell. Alternatively, cameras may be attached to the rear shell by the same means. 
     The front shell may be constructed of a lightweight material. Preferably, this material will be a polymer, in one embodiment xenoy. Another suitable embodiment may be polycarbonate, or a mixture of polycarbonate and polybutylene terephthalate (PBT) and/or polyethylene terephthalate (PET). The polymer may in one embodiment be formed in a mold, or by numerous other means known in the art. 
     The interior surface of the front shell may be coated in its interior  475  with an electrically- and/or thermally-conductive coating such as metal. This coating can be applied by means known in the art, such as electroplating. Preferably, the coating will not be magnetic. The plating may have one or more layers, possibly of different metals. For example, in one embodiment, the conductive coating is a thin layer of nickel, followed by a thicker layer of copper, with a small layer of nickel on top for enhanced corrosion resistance. In this embodiment, the copper layer thickness may preferably be at least approximately 0.0635 mm (0.0025 inches) with the total coating thickness approximately 0.762 mm (0.003 inches). Other combinations of metal, or number of layers, or thickness of layers, are possible. For example, in one preferable embodiment, the total thickness of metal will be within the range of about 0.07 millimeters to about 0.13 millimeters. If copper is used in addition to another less-conductive metal, it is preferable to use as much copper as possible to enhance thermal and electrical conductivity. There are other highly conductive metals equivalent to copper, and there are other suitable metals that may take the place of Nickel in the above example. 
     The turret, in one embodiment, may comprise a motor ( 430  of  FIG. 3B ) or multiple motors for rotating a drive shaft ( 436  of  FIG. 3B ) or multiple drive shafts. The turret may also contain a gear box ( 434  of  FIG. 3B ) which may be attached to a region  473  of the inner surface of the front shell. A shaft may exit the turret through an aperture  474 . Preferably, this shaft is thermally conductive, and may act as a heat sink to transfer heat collected from the conductive inner surface of the turret to one or more locations exterior to the turret. In one embodiment, heat is ultimately dissipated by convection from wind as the aircraft travels through the air. Where the shaft leaves the turret will preferably be sealed to ensure that the turret is water resistant or waterproof. Such sealing may be accomplished with an o-ring or other means known in the art. 
     There may be several sources of heat within the turret. Each of the cameras may contribute heat, and the motor will also contribute heat. Other associated wiring and electronics may also generate heat. In one illustrative embodiment, an IR camera in the turret may generate 1 watt of heat, while a motor may generate 2 watts of heat. 
       FIGS. 6A-6B  and  FIG. 7A-7B  are views of an example rear shell. Preferably, at least a portion of the rear shell may also be conductive at least in its interior  601 . For example, the composition and plating of the rear shell may be substantially identical to that of the front shell; however, the composition of the front and rear shells can also be significantly different. It will preferably be a metal-coated polymer. 
     Alternatively, because the rear shell can in one embodiment be made smaller, or substantially smaller, than the front shell, the rear shell may be made of an anodized metal because weight concerns are not as significant as for the front shell. If the rear shell is composed of anodized metal, this means that there is an internal metallic layer, coated with an oxide of that metal or in one embodiment an oxide of a second metal that is coated on the base metal for the rear shell. The internal metallic layer is preferably conductive, and will serve to conduct heat and electricity, this aiding in electromagnetic shielding. If an anodized metallic rear shell is used, the region near the o-ring groove  602  (region  603  in the example of  FIG. 6B ) in contact with the o-ring should preferably have a conductive coating for engagement with the o-ring, in which the conductive coating is electrically connected to the bulk metal of the rear shell. Means of coating a region of an anodizable metal with another metal to prevent anodizing in that region are known in the art. Less preferably, if the anodic layer is sufficiently small, depending on the metal and other conditions, the electrical and thermal conductivity may be sufficient without such coating. 
     Preferably, the rear shell may have an o-ring groove  602 , into which an o-ring may be placed, although an o-ring groove may alternatively be placed on the front shell, or there may be multiple o-rings. 
     Joining the front and rear shells may be an electrically- and/or thermally-conductive elastomeric o-ring ( 801  in  FIG. 8 ) situated in the o-ring groove and in contact with the conductive surface of both the front and rear shells. In some configurations, the conductive coating of the inner surface of the shell may wrap around and cover an outer part of the shell to maintain electrical contact between the o-ring groove and the internal surface of the shell. Thus, region  603  of  FIG. 6B  and surface  604  of  FIG. 6A  may be coated, and preferably form a continuous coating across the o-ring groove  602  to the interior surface of the rear shell  601 . When the front shell and rear shell are engaged, as shown in  FIG. 8 , the front shell in this embodiment preferably covers the coated portion, so as to prevent exposure to the elements. 
     The o-ring may seal the connection between the front and rear shells so that the enclosure formed by the shells is water-resistant or waterproof under the design conditions of the aircraft with at least a margin or safety. Preferably, the o-ring  801  may be electrically conductive and have enhanced thermal conductivity beyond typical elastomeric substances. For example, in one embodiment the o-ring may be composed of a metal-filled elastomer such as silicone rubber. Examples of metal-filled and other types of relatively-conductive elastomers are known in the art. (See, e.g., U.S. Pat. No. 7,695,647, U.S. Application No. 2011/0103021 A1). Specialized, electrically conductive elastomeric substances known in the art might in one example have thermal conductivities at normal operating conditions greater than about 0.50 W/(m·K), or often higher, such as 3 W/(m·K), 7.5 W/(m·K), or higher. 
     Electrically, there is preferably an electrical connection between the interior front  475  and rear  601  shell surfaces through the o-ring  801  so that as a whole, the turret acts as an electromagnetic shield. Thus, it is preferable to maximize the amount of interior surface that is electrically conductive, and to maintain electrical connection throughout the interior surface. 
     There are many ways known in the art to mechanically connect a shell such as the front shell to rear shell. In addition, one of the shells may have a plurality of compliant members attached to it that may engage in corresponding cavities or holes  501  in the other shell, thus comprising a spring-loaded engagement mechanism. When engaged, the compliant springs or tags lock with cavities or holes and prevent the front and rear shells from coming apart. This arrangement has the advantage that it may be possible to disassemble the turret without loosening bolts, in order to service the cameras or other elements within the turret, or to replace the o-ring or other parts. The front and rear shell may, for example, be disengaged by bending or compressing the springs or tags to the point where they clear the locking mechanism. 
     Alternatively or in addition, one of the shells may be configured with a snap ring groove so that a portion of the other shell snaps into place to help hold the front and rear shells together. For example, a groove  605  may be provided in the rear shell (see  FIGS. 6B ,  7 B, and  8 ), and the edge of the front shell may comprise, in at least some locations along its perimeter, a small lip that engages with groove  605  and creates a locking mechanism. 
     Exemplary embodiments have been described with reference to specific configurations. The foregoing description of specific embodiments and examples of the invention have been presented for the purpose of illustration and description only, and although the invention has been illustrated by certain of the preceding examples, it is not to be construed as being limited thereby.