Abstract:
A system and method for efficiently maneuvering a multirotor drone having a control system, an electrical power source, a plurality of rotor assemblies each having a rotor boom, a rotor mast, at least one rotor blade, a rotor assembly adjustment apparatus, a plurality of electric motors, wherein each electric motor is connected to a rotor boom positioned in a substantially horizontal direction and drives a rotor mast positioned in a substantially vertical direction and connected to at least one rotor blade, with the position of said rotor boom automatically adjustable in a substantially horizontal direction by the adjustment apparatus and the control system.

Description:
GRANT OF NON-EXCLUSIVE RIGHT 
       [0001]    This application was prepared with financial support from the Saudi Arabian Cultural Mission, and in consideration therefore the present inventor(s) has granted The Kingdom of Saudi Arabia a non-exclusive right to practice the present invention. 
       BACKGROUND 
       [0002]    Field of the Disclosure 
         [0003]    The present disclosure is directed toward a multirotor drone with a variable center of lift and variable center of mass for dynamic stability over a range of operating conditions. 
         [0004]    Description of the Related Art 
         [0005]    Autonomous or remotely controlled multirotor drone aircraft with vertical takeoff and landing (VTOL) abilities have become more widely available. These craft are available in various sizes and have many uses including military and surveillance applications, aerial photography and videography, mapping, and package delivery. They take off and fly much like helicopters, though generally without the aid of a tail rotor. 
         [0006]    As drone use proliferates and the range of applications expand, a number of shortcomings in the state of the art have appeared, namely limited flight time between refueling or recharging, and dynamic maneuverability and stability, an acute problem for smaller drones operating in windy conditions. 
       SUMMARY 
       [0007]    The present disclosure is directed toward a multirotor drone with a variable center of lift and variable center of mass for dynamic stability over a range of operating conditions. 
         [0008]    Multirotor drone roll and pitch is controlled, for example, by having half the rotors turn one direction while the other half rotate the opposite direction to cancel out gyroscopic effects. Yaw is produced by increasing the relative rotational speed of a diagonal set of rotors with respect to the opposite pair of rotors, while roll and pitch are produced by increasing the relative rotational speed of adjacent rotors on one side of the drone. Increasing relative speed of rotors can also include reducing the rotational speed of other rotors, or some combination of rotational speed adjustment among a plurality of rotors. In general, the greater the angle a drone tilts toward the direction of travel, the faster it will fly. 
         [0009]    The center of mass is the instantaneous position about which the resultant force of the mass of the drone acts, and changes with the drone&#39;s position, fuel use, and movement of any applicable payload. The center of lift is the resultant force of the instantaneous sum of the lift generated by all the rotors. 
         [0010]    Payload and fuel load, for drones powered by a liquid fuel, can shift dynamically due to, for example, fuel use and movement of the payload in flight. 
         [0011]    Further, the speed at which an engine or electric motor operates affects the flight time of the drone. For either propulsion type there is generally some finite amount of energy that is carried on-board. The ability to operate an engine or motor at or near its most efficient speed can extend flight time. Adjusting the length of one or more of the rotor booms, and therefore the torque created by the rotors&#39; lift about the drone, in combination with altering motor and rotor speeds can enhance stability, maneuverability, and energy efficiency and flight time. 
         [0012]    The foregoing general description of the illustrative implementations and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure, and are not restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
           [0014]      FIG. 1A  is a plan view of a multirotor drone. 
           [0015]      FIG. 1B  is a plan view of a multirotor drone with some of the rotor assembly in the horizontally extended position. 
           [0016]      FIG. 1C  is a side view of a multirotor drone. 
           [0017]      FIGS. 2A and 2B  are plan and side views, respectively, of a main frame. 
           [0018]      FIGS. 3A, 3B, and 3C  are plan, side, and front views, respectively, of a rotor assembly. 
           [0019]      FIGS. 4A and 4B  are plan and side views, respectively, of a mounting plate. 
           [0020]      FIG. 5  is a diagram representing a hybrid power unit. 
           [0021]      FIG. 6 . is a diagram of a pneumatic circuit and air supply system. 
           [0022]      FIG. 7  is a diagram of a control module. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0023]    In the drawings, like reference numerals designate identical or corresponding parts throughout the several views. Further, as used herein, the words “a”, “an” and the like generally carry a meaning of “one or more”, unless stated otherwise. The drawings are generally drawn to scale unless specified otherwise or illustrating schematic structures or flowcharts. 
         [0024]    Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views. 
         [0025]      FIG. 1A  is a plan view of an embodiment of a multirotor drone  1 , a multirotor drone capable of vertical takeoff and landing (VTOL), and externally controlled by wireless communication or by autonomous function, and having multiple instances of a rotor assembly  5  arranged about the center of a main frame  2 . 
         [0026]    The position of each of the rotor assemblies  5  is adjustable along a horizontal axis in the X-Y plane relative to the main frame  2 , shown with each in the fully retracted position and of equal length to all of the other rotor assemblies  5 , the multirotor drone  1  generally possessing at least three rotor assemblies  5 . In one embodiment there are eight, each with a rotor boom  4  having a single degree of freedom of motion. 
         [0027]      FIG. 1B  is a plan view of an embodiment of a multirotor drone  1  similar to that of  FIG. 1A  with some of the rotor assemblies  5  in the horizontally extended position. Any one or more of the rotor assemblies  5  can be extended some length between a fully retracted position and a fully extended position. The use of variable position rotor assemblies  5  provides adjustment of the distance between the electric motor  10 , allowing for changes to the center of lift of the multirotor drone  1 , center of lift defined as the resultant sum of the lift produced by each individual rotor assembly  5 , which enhances stability when payload shifts or changes, and provides greater transient responsiveness compared to a case where the rotor assemblies  5  all remain in fixed positions for the duration of a flight. 
         [0028]      FIG. 1C  is a side view of an embodiment of a multirotor drone  1  having a main frame  2  connected to a plurality of landing gears  3 , a power unit  12 , a mounting plate  22 , a servo motor  24 , and a plurality of rotor assemblies  5 , each having a rotor boom  4 , a rotor mast  6 , an electric motor  10 , and rotor blades  8 . In this embodiment the rotor assemblies  5  are shown in the fully retracted position. The landing gears  3  support the main frame  2  to which all other components are connected. 
         [0029]    Each electric motor  10  operates at variable speeds to drive the rotor mast  6  which is connected to the pair of rotor blades  8  to generate lift. Each embodiment of this disclosure has at least one electric motor  10 , and each rotor assembly  5  is connected to the main frame  2  by its rotor boom  4 . 
         [0030]    Other embodiments possess one piece or multi-piece assemblies of three or more rotor blade  8 . 
         [0031]    The power unit  12  is eccentrically connected to a mounting plate  22 , which is connected to the main frame  2  and the servo motor  24 . The horizontal position of the power unit  12  is adjusted by rotation of the mounting plate  22 , which is controlled by movement of the servo motor  24 , as described by  FIG. 4A and 4B . 
         [0032]    Multirotor drones equipped with eight equally spaced rotors have a number of advantages over drones with fewer rotors, namely much greater payload capacity and the ability to operate with certain rotors deactivated, whether to conserve energy or due to failure of some of the rotors or motors. In addition to being dynamically balanced across two orthogonal horizontal axes, as is the case with a four rotor drone with rotors spaced 90 degrees apart, having an additional four equally spaced rotors provides the eight rotor drone with greater precision in yaw and roll control, for example if the additional rotors are positioned in between the 90 degree intervals, such as every 45 degrees. 
         [0033]    However, multirotor drones with adjustable rotor booms do not necessarily need to have rotors equally spaced apart, and can function with varying combinations of rotor boom positions and speeds to achieve the desired resultant lift and thrust. 
         [0034]    Further, an eight rotor drone can be formed by combining two drones, whether on the ground or in mid-flight, each having four rotors. With fixed rotor booms and rotor lengths an ideal arrangement for dynamic balance results from combining two four rotor drones at a 45 degree angle relative to each other in the plan view, the relationship of the rotor length to the boom length a key constraint for rotor clearance purposes. 
         [0035]    With two substantially similar four rotor drones with telescoping rotor booms, there is additional flexibility as more space can be made available between the rotors for in-flight combination if one drone has its rotor booms fully extended while the second drone has its rotor booms fully retracted. Merging such drones can allow combining and sharing of energy stored aboard the drones, increasing payload capacity, extending flight time and providing redundancy. 
         [0036]      FIGS. 2A and 2B  are plan and side views, respectively, of an embodiment of an assembly having a main frame  2 , a servo motor  24 , a plurality of landing gears  3 , a plurality of pneumatic circuits  25 , an air supply system  27 , and a control module  38 . 
         [0037]    The main frame  2  serves as a mounting platform for the servo motor  24 , the pneumatic circuit  25  ( FIG. 6 ), the air supply system  27 , and the control module  38  ( FIG. 7 ). 
         [0038]    In the embodiment shown the servo motor  24  is disposed inside of the main frame  2  and the mountings for each rotor assembly  5  are arranged symmetrically about the center of the main frame  2  in the plan view. Each mounting position for a rotor assembly  5  has one pneumatic circuit  25  positioned at the inboard end where the rod end of a piston  33  is connected to a rotor boom  4  ( FIG. 3 ). The pneumatic circuit  25  controls the position of the rotor boom  4  relative to the main frame  2 . As air pressure increases in the pneumatic circuit  25 , its corresponding rotor boom  4  can extend radially from the center of main frame  2  ( FIG. 2A ), increasing the distance from the center of the electric motor  10  to the center of the servo motor  24  due to displacement of the piston  33  ( FIG. 6 ) connected to the rotor boom  4 . 
         [0039]    As air pressure decreases in the pneumatic circuit  25 , its corresponding rotor boom  4  can retract due to a return spring  34  ( FIG. 6 ) overcoming the force of the pressure in the single acting cylinder  32 . 
         [0040]    The control module  38  controls all electronic functions of the multirotor drone  1 , while the air supply system  27  provides pressurized air to an at least one pneumatic circuit  25 , and each pneumatic circuit  25  controls horizontal movement of a rotor assembly  5  by its connection to a rotor boom  4 . The main frame  2  is supported by a plurality of landing gear  3 . 
         [0041]      FIGS. 3A, 3B, and 3C  are plan, side, and front views, respectively, of an embodiment of a rotor assembly  5  having a rotor boom  4 , a rotor mast  6 , an electric motor  10 , and two rotor blades  8 . 
         [0042]    The electric motor  10  operates at variable speed, is controlled individually by the control module  38  ( FIG. 7 ), turns a rotor mast  6  connected to at least one rotor blade  8 , which produces upward lift centered about that electric motor  10  and the rotor blades  8 . 
         [0043]    The rotor boom  4  connects to the main frame  2  and a piston  33 , and its position is controlled by the pneumatic circuit  25  ( FIG. 2A ). The piston  33  connects to the pneumatic circuit  25  at its opposite end away from the electric motor  10  ( FIG. 2A ). 
         [0044]      FIGS. 4A and 4B  are plan and side views, respectively, of an embodiment of a mounting plate  22 . The mounting plate  22  connects to the main frame  2 , has a plurality of mounting holes  23  within for attachment to a power unit  12  ( FIG. 5 ) and a servo motor  24  ( FIG. 1C ), and can be rotated about a mounting hole  23 . The mounting hole  23  can be eccentric, allowing repositioning of the power unit  12  to move about both the X and Y axes simultaneously during rotation of the mounting plate  22 . The position of the power unit  12  is adjustable in flight by the control module  38  ( FIG. 7 ) through rotation of the mounting plate  22 , which can simultaneously and independently vary with extension and retraction of any or all of the rotor assemblies  5 , allowing flexible control of the center of mass for the case that dynamic conditions change asymmetrically, for example, as fuel load decreases or the payload and cargo shifts or changes, climatic conditions change, a rotor assembly  5  fails, speed changes of various electric motors  10 , air speed changes, or to enhance stability and responsiveness during transient maneuvers. 
         [0045]    In another embodiment a mounting plate  22  is equipped with at least one position sensor  21 , and through which the control module  38  detects the position of the mounting plate  22  relative to the multirotor drone  1 . 
         [0046]      FIG. 5  is a diagram representing an embodiment of a hybrid power unit  12 , the power unit  12  having an engine  14 , a generator  16 , a fuel line  17 , a fuel tank  18 , an energy storage unit  20 , and a fuel level sensor  52 . 
         [0047]    In the embodiment shown, fuel from the fuel tank  18  is supplied to the engine  14  through the fuel line  17  by the force of gravity. The operation of the engine  14  drives the generator  16  to produce electricity. The engine  14  and the generator  16  convert relatively high energy density fuel sources, for example gasoline, into electricity for flexibility of use among the plurality of electric motors  10  and other electrical loads. The fuel tank  18  has a fuel level sensor  52  that provides data to the control module  38  ( FIG. 7 ), for example, to monitor remaining available fuel, to calculate center of mass, and to calculate remaining range or flight time. 
         [0048]    The generator  16  generates electricity and transmits it to the energy storage unit  20  for use as an energy buffer, providing constant electrical power to the various electric motors  10 , the servo motor  24 , the compressor  26 , and the control module  38 . The energy storage unit  20  is an energy storage unit, for example, including batteries, capacitors, mechanical flywheels, or any combination thereof. 
         [0049]    The use of electrical energy allows for flexibility and simplicity in the powertrain, for example to quickly vary the speed of any of the electric motors  10 , or to operate any number of the electric motors  10  at any time, and to maintain or quickly change the overall resultant center of lift of the multirotor drone  1 . The connections involved are limited to a few wires per electric motor  10  rather than that which would be required if, for example, the rotor mast  6  were each operated by gasoline-powered engines, while the use of high energy density fuel extends flight time for a given mass. 
         [0050]    The use of an integrated power unit  12  attached to a mounting plate  22  allows the power unit  12  to be quickly and easily replaced as a unit. 
         [0051]      FIG. 6  is a diagram of an embodiment of a pneumatic circuit  25  and an air supply system  27 . Each multirotor drone  1  can have at least one air supply system  27  and at least one pneumatic circuit  25 , the air supply system  27  having a compressor  26 , an air tank  28 , a pressure sensor  44 , and at least one air line  30 . The air supply system  27  supplies pressurized air to the at least one pneumatic circuit  25 . The compressor  26  takes in air, generally at atmospheric pressure, and compresses it into the air tank  28  for storage. The air tank  28  has a pressure sensor  44  to measure internal pressure with the ability to supply the data to a control module  38 , and at least one air line  30  for supplying pressurized air to the at least one pneumatic circuit  25 . 
         [0052]    Each pneumatic circuit  25  has a control valve  36 , a single acting cylinder  32 , a piston  33 , a return spring  34 , and at least one linear position sensor  50 . The control valve  36  is connected to the pressurized side of the single acting cylinder  32 . The piston  33  is positioned within, and shares its longitudinal axis with the single acting cylinder  32 . The return spring  34 , disposed between the rod side of the piston  33  and an internal wall of the single acting cylinder  32 , resists linear movement of the piston  33  such that when air pressure increases inside the pressurized side of the single acting cylinder  32 , the return spring  34  is compressed by the piston  33 . The rod end of the piston  33  is connected to a rotor assembly  5 , at the inboard end of the rotor boom  4  opposite of the electric motor  10 , and movement of the piston  33  is proportional to the horizontal movement of the rotor assembly  5  it is connected to. 
         [0053]    The control valve  36  has three distinct positions. In position A it is closed such that air cannot enter nor exit the single acting cylinder  32 , and maintains a substantially constant internal pressure within the single acting cylinder  32 , and thus maintains the horizontal position of the rotor assembly  5  to which it is connected. 
         [0054]    In position B, air from inside the single acting cylinder  32  is allowed to escape out to the atmosphere until the internal pressure of single acting cylinder  32  reaches equilibrium. The force of the return spring  34  pushes the piston  33 , and the rotor assembly  5  to which it is connected, to retract horizontally as air pressure is reduced in the single acting cylinder  32 . 
         [0055]    In position C pressurized air from the air tank  28  flows through the air line  30  and control valve  36 , and into the single acting cylinder  32 , increasing pressure on the piston  33 , compressing the return spring  34 , and extending the effective length of the rotor assembly  5  as the piston  33  moves. 
         [0056]    The purpose of the single acting cylinder  32  is to effect the horizontal movement of the rotor assembly  5 . A plurality of linear position sensors  50  are positioned along the body of the single acting cylinder  32  to monitor the position of the piston  33 , and to relay those readings to the control module  38  ( FIG. 7 ). 
         [0057]    In another embodiment the multirotor drone  1  has one pneumatic circuit  25  for all of the rotor assembly  5 . Any horizontal movement of the rotor assembly  5  is equal and simultaneous. 
         [0058]    In another embodiment the multirotor drone  1  has one pneumatic circuit  25  for each pair of opposite rotor assembly  5 . Any horizontal movement of a corresponding pair of rotor assembly  5  is equal and simultaneous. 
         [0059]    In another embodiment the multirotor drone  1  has one pneumatic circuit  25  for each rotor assembly  5 . Horizontal movement of each rotor assembly  5  is independent of that of any other rotor assembly  5 . 
         [0060]      FIG. 7  is a diagram of an embodiment of a control module  38  having a wireless circuitry  40 , an altitude sensor  46 , a plurality of yaw sensors  48 , and a wire harness  42 . The wireless circuitry  40  is circuitry for communicating wirelessly with external devices, including circuitry to send and receive signals and data, for example through smart phones and other wireless devices, using a variety of communication protocols, such as Radio Frequency (RF), satellite, or cellular. 
         [0061]    The wire harness  42  electrically connects the various systems, assemblies, components, and power sources of the multirotor drone  1 , for example the electric motors  10 , the generator  16 , the energy storage unit  20 , the servo motor  24 , the compressor  26 , the control valves  36 , the pressure sensor  44 , the yaw sensors  48 , the linear position sensors  50 , and the fuel level sensor  52 . 
         [0062]    The altitude sensor  46  measures the altitude of the multirotor drone  1 . Each yaw sensor  48  measures rotation about a particular axis of the multirotor drone  1 . A control module  38  having three yaw sensors  48  allows for simultaneous measurement of, for example, yaw, pitch, and roll of the multirotor drone  1  about multiple axes. 
         [0063]    In this embodiment the control module  38  controls all functions of and is connected to the multirotor drone  1  at the main frame  2 . 
         [0064]    Thus, the foregoing discussion discloses and describes merely exemplary embodiments of the present invention. As will be understood by those skilled in the art, the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting of the scope of the invention, as well as other claims. The disclosure, including any readily discernable variants of the teachings herein, define, in part, the scope of the foregoing claim terminology such that no inventive subject matter is dedicated to the public.