Abstract:
An unmanned vehicle including a body and a frame structure extending from the body and supporting a plurality of propeller assemblies, each propeller assembly including at least one propeller and a corresponding motor with the motor housed in a watertight housing or coated and made corrosion resistant. The propellers comprise a first subset of propellers of the propeller assemblies and a second subset of propellers of the propeller assemblies which rotate in a plane positioned below a plane in which the first subset of propellers rotate, wherein said first and second subset of propellers are configured for independent operation of one another as the vehicle transitions from an air medium to a water medium.

Description:
[0001]    This application claims the benefit of U.S. Provisional Appln. No. 62/001,244, filed on May 21, 2014, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Statement of the Technical Field 
         [0003]    The present disclosure relates to systems and methods for designing and operating a remote unmanned vehicle in multiple mediums. Specifically an unmanned vehicle is disclosed capable of operating in both air and underwater so that the transition between air and water is seamless. 
         [0004]    Description of the Related Art 
         [0005]    Unmanned aerial vehicles (UAVs) are well known in the art. UAVs can be fixed wing aircraft, resembling conventional human piloted airplanes, or may be rotorcraft using propellers similar to conventional human piloted helicopters. Typical UAVs are remotely controlled by humans, although some may be semi or fully autonomous. A presently popular UAV design involves a frame with a number of propellers, typically between four and eight. A UAV with four propellers is also referred to as a quadcopter. A UAV with six propellers is also referred to as a hexacopter. A UAV with eight propellers is also referred to as an octacopter. 
         [0006]    Unmanned underwater vehicles (UUVs) are also well known in the art. As with UAVs, UUVs are typically remotely operated by a human but can also be semi or fully autonomous. Conventional UUVs resemble a human operated submarine. 
       SUMMARY OF THE INVENTION 
       [0007]    In at least one embodiment, the present invention provides an unmanned vehicle including a body and a frame structure extending from the body and supporting a plurality of propeller assemblies, each propeller assembly including at least one propeller and a corresponding motor with the motor housed in a watertight housing or coated and made corrosion resistant. The propellers comprise a first subset of propellers of the propeller assemblies and a second subset of propellers of the propeller assemblies which rotate in a plane positioned below a plane in which the first subset of propellers rotate, wherein said first and second subset of propellers are configured for independent operation of one another as the vehicle transitions from an air medium to a water medium or from a water medium to an air medium. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0008]    The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate the presently preferred embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain the features of the invention. In the drawings: 
           [0009]      FIG. 1  is an isometric view of an exemplary unmanned vehicle in accordance with an embodiment of the invention. 
           [0010]      FIGS. 2A-2E  are schematic diagrams illustrating an exemplary transition sequence from air to water for one of the arms of the unmanned vehicle of  FIG. 1 . 
           [0011]      FIG. 3  is an isometric view of an exemplary motor housing in accordance with an embodiment of the invention. 
           [0012]      FIG. 4  is an isometric view of an exemplary heat sink in accordance with an embodiment of the invention. 
           [0013]      FIG. 5  is an isometric view of another exemplary unmanned vehicle in accordance with an embodiment of the invention. 
           [0014]      FIG. 6  is an isometric view of yet another exemplary unmanned vehicle in accordance with an embodiment of the invention. 
           [0015]      FIG. 7  is an isometric view of another exemplary unmanned vehicle in accordance with an embodiment of the invention. 
           [0016]      FIG. 8  is an isometric view of yet another exemplary unmanned vehicle in accordance with an embodiment of the invention. 
           [0017]      FIG. 9  is an isometric view of another exemplary unmanned vehicle in accordance with an embodiment of the invention. 
           [0018]      FIG. 10  is an isometric view of an exemplary unmanned vehicle kit in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    It will be readily understood that the components of the embodiments as generally described herein and illustrated in the appended figures could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of various embodiments, as represented in the figures, is not intended to limit the scope of the present disclosure, but is merely representative of various embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated. 
         [0020]    The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects as illustrative. The scope of the invention is, therefore, indicated by the appended claims. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. 
         [0021]    Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussions of the features and advantages, and similar language, throughout the specification may, but do not necessarily, refer to the same embodiment. 
         [0022]    Furthermore, the described features, advantages and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, in light of the description herein, that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention. 
         [0023]    Reference throughout this specification to “one embodiment”, “an embodiment”, or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the present invention. Thus, the phrases “in one embodiment”, “in an embodiment”, and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. 
         [0024]    As used in this document, the singular form “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. As used in this document, the term “comprising” means “including, but not limited to”. 
         [0025]    The need for unmanned vehicles has soared during recent years with many such vehicles being developed for countless applications in air and water. Current UUVs and UAVs can only operate in one medium; either water or air. This disclosure relates to a fully submersible unmanned aircraft which can operate in air and underwater and transition between both mediums seamlessly. Such a vehicle can have many military, industry, and consumer applications, for example, deployment of a payload in water (e.g., sensors, actuators), and applications in underwater recovery and inspection (e.g., ships, oil platforms, or other waterborne platforms). Additional applications may include surveillance and underwater stealth approach in unknown environments. Since underwater vehicles and air vehicles already exist, the challenge/discovery of this disclosure is finding a way to build a vehicle that can operate in both mediums and, more importantly, finding a way to transition smoothly and seamlessly between them. 
         [0026]    Referring to  FIGS. 1-4 , an unmanned vehicle  10  in accordance with an embodiment of the invention will be described. The unmanned vehicle  10  generally includes a body  20 , a frame structure  30  and a plurality of propeller assemblies  40 . The illustrated body  20  includes opposed housing members  22  and  24  with a sealing gasket  26  therebetween such that the body  20  defines a waterproof structure. The body  20  may house a controller, other instrumentation, sensors and the like. The controller (not shown) may be in the form of a microprocessor or the like and is preferably configured for wireless communication with a central station, a remote control and the like. The controller receives commands from the central station, the remote control, sensors or other inputs and controls the movement of the unmanned vehicle  10  in response thereto by controlling the rotation of each of the propellers  42 ,  46  to achieve the intended motion as will be described in more detail hereinafter. The controller may also control other instrumentation, for example, a camera or payload delivery system. 
         [0027]    The frame structure  30  extends from the body  20  and includes a plurality of arms  32  which support the propeller assemblies  40 . The current embodiment includes four arms  32  supporting four propeller assemblies  40  and therefore has a quadcopter configuration; however, the invention is not limited to such. In the present embodiment, support elements  34  depend from the arms  32  and are configured to further support the body  20 . Additionally, landing supports  38  extend downward from the arms  32  and are configured to provide a landing structure for the vehicle  10 . The arms  32  are preferably manufactured as hollow tubing which is in water tight communication with the interior of the body  20  and with the respective propeller assembly  40 , as described hereinafter. With the waterproof construction, batteries, speed controllers and the like may be stored in the arms  32 . Ideally, the body  20  and frame  30  are made of carbon fiber or other materials that are as light as possible and that can be waterproofed and also handle required immersion depth. 
         [0028]    In the illustrated embodiment, each propeller assembly  40  is a dual-propeller assembly with an upper propeller  42  co-axial with a lower propeller  46 , i.e. the propellers  42 ,  46  have a common thrust axis. The propellers  42  and  46  are supported for rotation by a bracket  45  which is sealingly connected to a respective arm  32 . The bracket  45  also supports a motor  44 ,  48  for each propeller  42 ,  46 . The motors  44 ,  48  are in communication with the controller and controlled thereby. Rotation of the motors  44 ,  48  is controlled to achieve desired movement of the vehicle  10  and also to assist with the transition between mediums as will be described in more detail hereinafter. 
         [0029]    Referring to  FIG. 3 , an exemplary housing  60  for waterproofing of the motors  44 ,  48  will be described. Advantageously, by using motors  44 ,  48  with copper windings  62  that are far more conductive than water, no shorts will occur and the motor does not need to be waterproof. Nevertheless, to improve the efficiency and more importantly, the endurance of the system, the motors  44 ,  48  may be sealed. In the illustrated embodiment, a sealed housing  60  extends about the windings  62  and a shaft  64  extends from the housing  60  and connects to the respective propeller  42 ,  46 . A sealing gasket  66  extends about the shaft  64  and prevents water from entering the housing  60  at the propeller drive shaft  64 . The housing  60  protects the motor  44 ,  48  from water and other environmental damage. 
         [0030]    However, the motors also need to breathe (dissipate heat) and sealing a shaft with such a high angular velocity as observed in multirotors will likely result in noticeable losses. Depending on the material of the case and the medium in which it operates, the motor could overheat. As such, a more viable approach is to coat the windings on the inside of the motor (which are stationary) and replace sensitive mechanical components such as bearings with their corrosion resistant counterparts such as ceramic or glass materials. The magnets on the motor should also be coated. 
         [0031]    An issue that arises as a result of waterproofing is heat transfer. The battery and especially the speed controllers are susceptible to overheating and an effective heat sink must be employed. As these are generally components that are used for model airplanes, the housing is air breathing and the convection of wind flow is enough to keep them cool. However, there is no airflow in the waterproof body  20 . An example solution is a heat sink  70  which includes, for example, an aluminum or copper plate with fins coming off the side and extending out through the body  20 . An example heat sink  70  is shown in  FIG. 4 . The heat sink  70  is large to compensate for being enclosed in a plastic case. In an alternative embodiment, the heat sink may be exposed to the fluid medium in which it operates, and a large heat sink would not be necessary. The internal heat sink would be sufficient, depending on its intended use. In another embodiment, the body  20  may be constructed out of aluminum or another material with high thermal conductivity, and the case itself could act as a heat sink, eliminating the need for an internal heat sink altogether. 
         [0032]    Referring to  FIGS. 2A-2E , an exemplary transition of the vehicle  10  from air  100  to water  110  will be described. As illustrated in  FIG. 2A , when the vehicle  10  is completely in the air  100 , both motors  44  and  48  are operated (as indicated by the curved arrows) so that both propellers  42 ,  46  create a downward thrust toward the water  110  (as indicated by the straight arrows). When the lower propellers  46  reach the water  110  as illustrated in  FIG. 2B , the lower propellers  46  slow down or stop rotating while the upper propellers  42  continue to rotate at regular speed and create downward thrust. Slowing or stopping of the lower propellers  46  as they enter the water  110  avoids disturbance and allows for a smooth transition of the lower propellers  46  into the water  110 . Meanwhile, the upper propellers  42  provide sufficient thrust to continue the downward motion of the vehicle  10 . 
         [0033]    Moving to  FIG. 2C , once the lower propellers  46  are submerged, they once again are rotated to provide a downward thrust which assists with the downward thrust generated by the upper propellers  42 . As the vehicle  10  continues to submerge and the upper propellers  42  reach the water  110  as illustrated in  FIG. 2D , the upper propellers  42  slow or stop rotating while the lower propellers  46  continue to rotate and create downward thrust. Again, slowing or stopping of the upper propellers  42  as they enter the water  110  avoids disturbance and allows for a smooth transition of the upper propellers  42  into the water  110 . Meanwhile, the lower propellers  46  provide sufficient thrust to continue the downward motion of the vehicle  10 . Once the propeller assembly  40  is completely submerged, as illustrated in  FIG. 2E , the upper and lower propellers  42 ,  46  each rotate and thereby create thrust to control motion of the vehicle within the water  110 . 
         [0034]    In the illustrated embodiment, sensors  50 ,  52  and  54  are supported on the landing supports  38  and brackets  45  to signal to the controller the position of the propeller assemblies  40  relative to the water  110  such that the controller may stop and start the motors  44  and  48  to achieve the propeller rotation described above. With this configuration, the sensors  50  on the landing supports  38  are positioned below the plane of the lower propellers  46  and signal to the controller when the lower propellers  46  are about to enter the water  110 . In response, the motors  48  may be stopped. The lower sensors  52  on the brackets  45  are positioned above the plane of the lower propellers  46  and thereby signal to the controller when the lower propellers  46  are submerged in the water  110  such that the motors  48  may be restarted. The upper sensors  54  on the brackets  45  are positioned below the plane of the upper propellers  42  and signal to the controller when the upper propellers  42  are about to enter the water  110  such that the motors  44  may be stopped or slowed. The controller may be programmed such that the motors  44  are slowed or stopped for a predetermined amount of time to allow the transition of the propellers  42  to a submerged condition. Alternatively, another sensor may be provided above the plane of the propellers  42  and operate similar to the sensors  52 . The sensors  50 ,  52 ,  54  may be, for example, float type sensors, however, any sensors configured to sense between an air atmosphere and a water atmosphere may be utilized. Additionally, more or fewer sensors may be utilized. 
         [0035]    It is further contemplated that no water sensors may be utilized. Instead, for example, the controller, or a sensor associated therewith, may be configured to sense a spike in resistance as the propeller  42 ,  46  moves from the less dense air  100  to the more dense water  110 . The controller may then stop or slow the respective motor  44 ,  48  for a predetermined amount of time to allow the smooth transition of the propeller  42 ,  46 . As a further alternative, the propeller  42 ,  46  entering the water  110  may naturally stop or slow due to the transition to the more dense water  110  and the respective motor  44 ,  48  is not stopped, but instead is controlled, after a predetermined amount of time, to provide greater torque such that the propeller  42 ,  46  will again rotate in the more dense medium. 
         [0036]    Transition of the vehicle  10  from water  110  to air  100  may occur in reverse of the process described above. However, it has been found that the propellers  42 ,  46  do not incur disturbance which affects the vehicle assent as they transition from the more dense water  110  to the less dense air  100 . Accordingly, stopping or slowing of the propellers  42 ,  46  during such transition may not be necessary. 
         [0037]    The controller is preferably further configured to control motor  44 ,  48  operation based on the medium in which the vehicle  10  is operating. For example, when the vehicle  10  is submerged in water, the motors  44 ,  48  will require larger torque to achieve the same speed achieved when operating in air. Additionally, it has been found that the more dense water medium requires greater vehicle tilting to achieve forward/reverse and side-to-side motion. For example, to move the vehicle  10  forward in an air medium, the various motors  44 ,  48  may be controlled such that the vehicle  10  tilts forward by approximately 5°, with such tilt generating forward propulsion. Similar tilt in a water medium generates little if any forward propulsion. It has been found that the motors  44 ,  48  have to be controlled to achieve a significant tilt, for example, 70°, to achieve the same forward propulsion. The specific variance will depend on the properties of the particular medium, however, the controller will be configured to adjust for such properties and to control the motors  44 ,  48  accordingly. The advantage of electric motors is that they respond within milliseconds to any input so that a proper control should be achievable for all configurations considered. 
         [0038]    Another factor in movement of the vehicle  10  between mediums and within each medium is the buoyancy of the vehicle  10 . Archimedes principle states that the buoyant force on a submerged object is equal to the weight of the water displaced. Applying this, if the density of the vehicle is higher than the density of water, the vehicle will sink, as gravity exerts a greater force. If the vehicle is less dense than water, it will float, as gravity exerts a lesser force on the vehicle. If the densities are exactly the same, the buoyant force and gravity cancel and the object will neither sink nor float. This presents three options for the vehicle: 1) make the density higher than water, and energy will be required to bring it to the surface; 2) make the density less than water and energy will be required to push the vehicle underwater; 3) make the vehicle neutrally buoyant and minimal energy is required to bring the vehicle under or to the surface. As it turns out, making the vehicle slightly lower density than water is beneficial as any failure in the vehicle would cause it to drift to the surface rather than sink. Nevertheless, the two prototypes built were slightly heavier than water as recovery was not an issue with all the testing being done in different size pools where it could be easily recovered in case of malfunction. 
         [0039]    For instance, for a vehicle  10  with a target weight of two kilograms, and a target density of water, we can calculate the maximum volume for the entire vehicle  10 . The buoyant force can be written as 
         [0000]      F B =ρgv  (Equation 1)
 
         [0040]    Here, ρ is the density of water, g is the gravitational constant, and v is the volume of water displaced, or the volume of the vehicle  10 . In order for the vehicle  10  to stay underwater, it needs to have a higher mass per volume than water. Since the prototype vehicle weighs two kilograms, the volume would need to be less than the volume of two kilograms of water. Two kilograms of water has a volume of 2000 cubic centimeters, or 122 cubic inches. If the vehicle volume was to exceed this volume, it would be less dense than water. Furthermore, the weight of the vehicle  10  is not limited to two kilograms and could be either more or less. In addition, the vehicle  10  may be scaled to either a larger or lesser size, depending on payload requirements. 
         [0041]    To further enhance the operation of the vehicle  10 , the configuration of the body  20  may be varied.  FIG. 5  illustrates a vehicle  10 ′ in accordance with an alternative embodiment of the invention. In this embodiment, the vehicle  10 ′ again includes a body  20 ′, a frame structure  30 ′ and a plurality of propeller assemblies  40 . The body  20 ′ has a spherical configuration which tends to provide a stronger pressure vessel and which also helps to minimize drag and to be less susceptible to side forces. The frame structure  30 ′ includes arms  32  which are sealingly connected to openings  25  in the body  20 ′. The frame supports and landing supports are removed. The sensors  52  and  54  are again provided on the brackets  45 . The sensor  50  (not shown) may be provided directly on a lower surface of the body  20 ′ or the bracket  45 . In other respects, the vehicle  10 ′ operates substantially the same as the embodiment described above. 
         [0042]    As explained above, the vehicle  10  is not limited to a quadcopter configuration with dual propellers on each arm. Various other exemplary, non-limiting configurations are illustrated in  FIGS. 6-9 .  FIG. 6  illustrates a vehicle  10 ″ comprising a spherical body  20 ″, a frame structure  30 ″ and a plurality of propeller assemblies  40 . The spherical body  20 ″ of the present embodiment includes three openings  25  to support the three arms  32  of the frame structure  30 ″. In other respects, the vehicle  10 ″ operates substantially the same as the embodiments described above. 
         [0043]    Referring to  FIG. 7 , the vehicle  10 ′″ includes a spherical body  20 ′″, a frame structure  30 ′″ and a plurality of propeller assemblies  40   a  and  40   b . The spherical body  20 ′″ of the present embodiment includes eight openings  25  to support the eight arms  32  of the frame structure  30 ′″. In the present embodiment, two different propeller assemblies  40   a ,  40   b  are utilized, with each propeller assembly  40   a ,  40   b  having a single propeller  42 ,  46  and motor  44 ,  48 . The propeller assemblies  40   a  are configured with upper propellers  42  with sensors  54 . The propeller assemblies  40   b  are configured with lower propeller  46  and sensors  52 . It is recognized that the propeller assemblies  40   a ,  40   b  may be the same component, just rotated 180° about the axis of the arm  32 . The propeller assemblies  40   a  and  40   b  alternate with each other about the body  20 ′″, however, other configurations may be utilized. In other respects, the vehicle  10 ′″ operates substantially the same as the embodiments described above. The vehicle  10   iv  illustrated in  FIG. 8  is substantially the same as the vehicle  10 ′″ in  FIG. 7  except that the body  20   iv  includes four openings  25  to support the four arms  32  of the frame structure  30   iv . 
         [0044]    Referring to  FIG. 9 , the vehicle  10   v  has a body  20   v  that includes four openings  25  to support the four arms  32  of the frame structure  30   iv  and a fifth opening on the bottom thereof. In the present embodiment, each of the propeller assemblies  40   a  supported by the arms  32  includes an upper propeller  42 , motor  44  and sensor  54 . The lower propeller  46  is provided by a propeller assembly  40   b  which is connected directly to the fifth opening  25  in the bottom of the body  20   v . Sensors may be associated with the propeller assembly  40   b . In other respects, the vehicle  10   v  operates substantially the same as the embodiments described above. 
         [0045]    It is recognized that different applications of the vehicle  10  may have different requirements and therefore different body, frame and propeller structures may be better suited for one application versus another. To provide flexibility,  FIG. 10  illustrates an unmanned vehicle kit  80  which allows the user to assemble a vehicle having preferred characteristics for a given application. In the illustrated embodiment, the kit  80  includes a body  20 ′ with a plurality of openings  25 , for example, eight openings  25 . The kit further includes a plurality of arms  32  with vary various propeller assemblies  40 ,  40   a ,  40   b , each of which may be secured to a respective opening  25 . In the event that all of the openings  25  are not utilized, the kit  80  further includes plugs  82  which may be utilized to seal the unused openings  25 . Once assembled, the vehicle would operate as described above. 
         [0046]    While various propeller assemblies are described herein, it is recognized that the propellers used as the lower propellers  46  do not need to be the same as those used as the upper propellers  42 . A preferable configuration would use water optimized propellers in the lower and air optimized propellers in the upper. Water optimized propellers tend to be shorter in length and have higher pitch angle when compared to air propellers. The dominant differences between water and air propellers have to do with the differences between water and air. Water is denser than air and is considered an incompressible fluid, unlike air. Air is capable of taking better advantage of the aerodynamic density and pressure changes associated with its blade&#39;s airfoil and velocity, which can be used toward propulsion; the same cannot be said for water, as density does not deviate by much. Additionally, rapid pressure changes in water are likely to result in cavitation, which is known to wear down and damage propellers. Thus, the pressure difference that could in fact be used toward aerodynamic lift/thrust is limited by the occurrence of cavitation. As such, when dealing with propellers intended for air, they should be: longer (so that the ends of the blade have a very high transverse velocity for a given angular velocity and desired since lift increases quadratically with stream velocity) and with a flatter pitch (so as to reduce drag on the blades and since airflow through means of high angular velocity/aerodynamics is desired and not by simply pushing the air out of the way). Alternatively, when dealing with propellers intended for water, they should be short (as to avoid high transverse velocities), have a higher pitch (to compensate for its shorter length) and have more blades (to compensate for its lower angular velocity and shorter length). For vehicles  10  intended to be used frequently in both mediums, it may be desirable to manufacture the propellers with a blended combination of features of both the air and water propellers. 
         [0047]    These and other advantages of the present invention will be apparent to those skilled in the art from the foregoing specification. Accordingly, it will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It should therefore be understood that this invention is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the invention as defined in the claims.