Patent Description:
<CIT> relates to an aerial robot including at least one pair of counter-rotating blades or propellers.

<CIT> relates to an aircraft cabin noise control apparatus.

<CIT> relates to a repetitive noise cancellation system for multiple noise sources. <CIT> relates to a propeller for an aircraft with an odd number of unequally circumferentially spaced blades.

This invention is directed to an automated aerial vehicle ("AAV") and systems, methods, and techniques pertaining to canceling noise generated by the AAV as defined in claim <NUM> and claim <NUM>. This disclosure also shows exemplary systems, methods, and techniques for generating audible and visible signals/communications/announcements via the AAV. While various aspects are described with reference to AAVs, it should be understood that examples may include any type of vehicle suitable for use with the systems, methods, and techniques described herein. For example, any other type of aircraft (e.g., a passenger airplane), any type of land craft (e.g., an automobile), or any type of watercraft (e.g., a motor boat), may be used with the systems, methods, and techniques described in this disclosure.

The AAV includes multiple propellers (also called rotors). The AAV includes a first propeller configured to rotate in a first rotational direction to cause lift and thrust of the AAV. The AAV also includes a second propeller configured to rotate in a second rotational direction that is opposite the first rotational direction. That is, in some cases the first propeller may rotate counter-clockwise and the second propeller may rotate clockwise. In other cases, the first propeller may rotate clockwise and the second propeller may rotate counter-clockwise. In yet other cases, an AAV controller or an operator of the AAV may be capable of selectively changing the rotational direction of both the first propeller and the second propeller.

While the second propeller causes lift of the AAV, the second propeller is configured to produce sound that cancels noise generated by the first propeller. An audio sensor (e.g., a microphone) located near the first propeller detects the noise generated by the first propeller. A controller may be in direct or indirect communication with the audio sensor. The controller is configured to receive a signal representing the noise detected by the audio sensor. The controller is also in direct or indirect communication with the second propeller, and causes the second propeller to produce anti-noise sound that cancels the noise generated by the first propeller.

In a particular embodiment, the first propeller and the second propeller may be arranged in a vertically stacked configuration. For example, the second propeller may be located above the first propeller. The second propeller may also be coaxial with the first propeller. A microphone may be located below the first propeller to detect the noise generated by the first propeller while the first propeller is rotating in a first rotational direction. A controller may be in direct or indirect communication with at least the microphone and a motor that drives rotation of the second rotor. The controller may receive an input signal from the microphone representing the noise generated by the first propeller. The controller may output an anti-noise signal (e.g., a signal based at least in part on phase shifting the received input signal) to the motor that causes the motor to modulate rotational speed of the second propeller. While rotating at the modulated rotational speed, the second propeller may generate anti-noise that cancels the noise generated by the first propeller.

In some implementations, the AAV may utilize one or multiple propellers for generating audible communications. For example, a controller of the AAV may receive various parameters as input. Based at least partly on a received input parameter, the controller may determine that a flight condition is satisfied. The flight condition may, for example, correspond to an audible communication that is to be communicated.

Suppose, for instance, that the AAV were delivering an inventory item to a location. Upon approaching the location, the AAV determines (e.g., based on a video signal fed as an input parameter to the controller via a camera) that a person is situated at or near an intended or a suitable landing area corresponding to the delivery location. Such an input parameter may satisfy a flight condition corresponding to an audible communication, such as a "Watch out!" warning message. Accordingly, the controller may determine and cause to implement modulations of the rotational speed of a propeller, thereby causing the propeller to produce a series of sounds that are audibly perceptible as "Watch out!".

In some implementations, the AAV may utilize one or multiple propellers for generating visible communications. For example, a controller of the AAV may receive various parameters as input. Based at least partly on a received input parameter, the controller may determine that a flight condition is satisfied. The flight condition may, for example, correspond to a visible communication that is to be communicated.

Suppose now that the controller of the AA V were to receive an input parameter satisfying a flight condition corresponding to a visible communication, such as a "HELLO" greeting message to be communicated to a person situated at or near the delivery location. To generate the visible communication, light sources [e.g., light-emitting diodes (LEDs)] coupled to one or multiple propellers may be caused to intermittently emit light in a synchronized manner while the propellers are rotating to generate patterns that are visibly perceptible as "HELLO.

In some cases, the visible communications may include multiple words that together form phrases or sentences. Individual propellers may generate one or more of: a single letter or symbol of the visible communication, multiple letters of the visible communication, multiple symbols of the visible communication, etc. Multiple propellers may cooperatively generate one or more of: a single letter or symbol of the visible communication, multiple letters of the visible communication, multiple symbols of the visible communication, etc. It <NUM> should be understood, however, that the propellers in conjunction with the light sources coupled thereto may be caused to generate a visible communication in any suitable manner.

The AAV may be implemented as virtually any type of aircraft. In some embodiments, the AAV may be a multi-rotor vertical takeoff and landing vehicle, such as a quadcopter, octocopter, or other multi-rotor aerial vehicle. In various embodiments, the AAV may include at least one fixed wing to provide at least some upward lift during forward flight of the AAV. The AAV may be configured to transition from rotor flight to a fixed-wing flight during operation, such as by redirecting rotors/propellers from a lift configuration to a forward propulsion configuration when the AAV includes at least one wing that provides upward lift.

<FIG> is an illustrative diagram of an example automated aerial vehicle (AAV) <NUM> that includes components used to implement noise cancellation. The AAV <NUM> may include a first set of propellers <NUM> and a second set of propellers <NUM>. The propellers <NUM> and <NUM> may be any form of propeller (e.g., graphite, carbon fiber) and of a size sufficient to lift the AAV <NUM> and any inventory/payload engaged by the AAV <NUM> so that the AAV <NUM> can navigate through the air, for example, to deliver an inventory item to a location/destination. While <FIG> shows eight propellers visible from a side of the AAV <NUM>, in other implementations, more or fewer propellers may be utilized.

Likewise, in some implementations, the propellers may be positioned at different locations on the AAV <NUM>. In other examples, alternative methods of upward or forward propulsion may be utilized. For example, fans, jets, turbojets, turbo fans, jet engines, and the like may be used to propel the AAV <NUM>.

The first set of propellers <NUM> may include a lower propeller <NUM>, and the second set of propellers <NUM> may include an upper propeller <NUM>. For clarity, the following discussion with respect to <FIG> refers primarily to the lower propeller <NUM> and the upper propeller <NUM>, but it should be understood that the corresponding description may similarly be implemented with respect to one or various combinations of multiple propellers of the AAV <NUM>. In some <NUM> instances, the lower propeller <NUM> and the upper propeller <NUM> may be arranged in a vertically stacked configuration. For example, the upper propeller <NUM> may be disposed above the lower propeller <NUM>. Additionally, the upper propeller <NUM> may be oriented substantially coaxial with the lower propeller <NUM>. That is, the central axis about which the upper propeller <NUM> rotates may be aligned with or approximately aligned with the central axis about which the lower propeller <NUM> rotates, as indicated in <FIG> by the dotted line A.

In various implementations, the AAV <NUM> may include a lower motor <NUM>. The lower motor <NUM> may drive rotation of the lower propeller <NUM>. Likewise, the AA V <NUM> may include an upper motor <NUM> that drives rotation of the upper propeller <NUM>. Although <FIG> shows the lower propeller <NUM> and the upper propeller <NUM> each being coupled to an individual motor, it should be understood that in some implementations a same motor may drive multiple propellers ( e.g., via a transmission system). In other implementations, multiple motors may drive an individual propeller.

The lower propeller <NUM> and the upper propeller <NUM> rotate at independently varying rotational speeds. For example, during various stages of flight of the AA V <NUM>, the lower motor <NUM> and the upper motor <NUM> may cause the lower propeller <NUM> and the upper propeller <NUM>, respectively, to rotate at rotational speeds ranging from approximately <NUM> RPM to approximately <NUM> RPM to provide the AA V <NUM> with lift and thrust suitable for conditions (e.g., weather conditions) under which the AAV <NUM> is flying.

While rotating, the propellers of the AAV <NUM> generate noise. One or multiple propellers of the AAV <NUM> may be operable to produce sound that cancels noise generated at least partly by one or multiple other propellers of the AAV <NUM>. In some instances, the lower propeller <NUM> may be operable to rotate in a first rotational direction <NUM>, and the upper propeller <NUM> may be operable to rotate in a second rotational direction <NUM> that is opposite the first rotational direction <NUM>. As depicted in <FIG>, the lower propeller <NUM> rotates in a first rotational direction <NUM> corresponding to a clockwise direction and the upper propeller <NUM> rotates in a second rotational direction <NUM> corresponding to a counter-clockwise direction. However, it should be understood that in various implementations the lower propeller <NUM> may rotate in a counter-clockwise direction and the upper propeller <NUM> may rotate in a clockwise direction. In some cases, a controller of the AAV <NUM> or an operator of the AAV <NUM> may be capable of selectively changing the rotational direction of both the lower propeller <NUM> and the upper propeller <NUM>.

A sensor <NUM> is disposed proximate the lower propeller <NUM>. In some implementations, the sensor <NUM> may be located below the lower propeller <NUM>. In examples, the sensor <NUM> may be disposed in any other suitable location.

The sensor <NUM> is configured to sense/detect/measure the noise <NUM> generated by the lower propeller <NUM>. For example, the sensor <NUM> may be an audio sensor such as a microphone. However, the sensor <NUM> may be any type of sensor suitable for directly or indirectly sensing/detecting/measuring an operational characteristic or parameter associated with the lower propeller <NUM> that may be interpreted as a representation of the noise <NUM> generated by the lower propeller <NUM>. For example, the sensor <NUM> may be configured to detect rotational speed of the lower propeller <NUM>, rotational speed of the lower motor <NUM>, etc. Although <FIG> shows an individual sensor <NUM>, multiple sensors may be used to detect n01se generated by an individual propeller, by multiple propellers, in the ambient environment, etc..

The AAV <NUM> includes one or multiple control systems <NUM> in direct or indirect communication with the sensor <NUM>. For example, the control systems <NUM> may include a noise controller <NUM> in direct or indirect communication with the sensor <NUM>. The noise controller <NUM> may be configured to control the perceptible noise level of one or multiple types of noise-generating mechanisms of the AAV <NUM>. In some arrangements, the noise controller <NUM> is dedicated to controlling the cancellation of noise generated by one or multiple propellers.

Implementations (e.g., as illustrated in <FIG>) involve the noise controller <NUM> controlling the cancellation of noise <NUM> generated by the lower propeller <NUM>. The noise controller <NUM> receives from the sensor <NUM> an input signal representing the noise <NUM> generated by the lower propeller <NUM>. The noise controller <NUM> may interpret the received input signal and, based at least in part on the interpretation, send to the upper motor <NUM> an output signal that causes the upper propeller <NUM> to produce sound <NUM> that destructively interferes with the noise <NUM> generated by the lower propeller <NUM>, resulting in canceled noise <NUM>. The output signal causes the upper motor <NUM> to modulate rotational speed of the upper propeller <NUM> such that the upper propeller <NUM>, while rotating at the modulated rotational speed, produces anti-noise <NUM> that destructively interferes with and cancels or substantially cancels the noise <NUM> generated by the lower propeller <NUM>.

In various implementations, the anti-noise <NUM> generated by the upper propeller <NUM> may be anti-noise sound waves <NUM> having approximately the same frequency and amplitude as the noise sound waves <NUM> generated by the lower propeller <NUM>. However, the anti-noise sound waves <NUM> may be in antiphase with the noise sound waves <NUM>. That is, in some implementations, the anti-noise sound waves <NUM> and the noise sound waves <NUM> may have a phase difference of approximately <NUM> degrees. Additionally or alternatively, some implementations may involve the noise controller <NUM> causing the upper propeller <NUM> to generate sound waves that have a phase difference other than approximately <NUM> degrees to, for example, reinforce or weaken the sound waves generated by the lower propeller <NUM>.

The noise controller <NUM> is configured to receive as an input signal a representation of rotational speed of the upper propeller <NUM>. In some instances, the noise controller <NUM> may determine an output signal based at least in part on the received input signals representing each of the noise <NUM> generated by the lower propeller <NUM> and the rotational speed of the upper propeller <NUM>. The noise controller <NUM> determines the rotational speed of the upper propeller <NUM> and, based on prior modeling, utilizes the determined rotational speed to determine various characteristics (e.g., frequency, amplitude, phase, etc.) of the sound waves being produced by the upper propeller <NUM>. The noise controller <NUM> compares the determined characteristics corresponding to the sound waves of the upper propeller <NUM> to the respective characteristics of the noise sound waves <NUM> corresponding to the lower propeller <NUM> as determined based on the received input signal representing the noise <NUM> generated by the lower propeller <NUM>. The noise controller <NUM> determines how the rotational speed of the upper propeller <NUM> is to be modulated to cause the upper propeller <NUM> to produce anti-noise <NUM> that will substantially cancel the noise <NUM> generated by the lower propeller <NUM>.

In some implementations, the rotational speed of the upper propeller <NUM> may be modulated at a rate ranging from about <NUM> to about <NUM>. For instance, in some implementations, the rate of modulation of the rotational speed of the upper propeller <NUM> may be approximately <NUM>. In some cases, the lower propeller <NUM> may be the primary thrust generator with respect to the thrust generated by the upper propeller <NUM>. The upper propeller <NUM>, also capable of generating thrust, may modulate its thrust at a high frequency that corresponds to the rate of modulation of the rotational speed of the upper propeller <NUM>.

In a non-limiting example scenario, at a first time the upper propeller <NUM> rotates at a rotational speed of about <NUM> RPM. The rotational speed of the upper propeller <NUM> may be modulated or adjusted at a rate of about <NUM>. That is, the rotational speed of the upper propeller <NUM> may be modulated or adjusted at a rate of about <NUM> times per second to cancel the noise <NUM> generated by the lower propeller <NUM>. In this example, the rotational speed of the upper propeller <NUM> may be modulated at a second time to about <NUM> RPM, then modulated at a third time to about <NUM> RPM, then modulated at a fourth time to about <NUM> RPM, and so on, where the second, third, and fourth times are three of about <NUM> modulations that occur within the span of a second, i.e., a rate of modulation of about <NUM>. In this manner, the rotational speed of the upper propeller <NUM> may be incrementally modulated at a high frequency in some implementations.

<FIG> is a top view of another example automated aerial vehicle (AAV) <NUM> that includes components used to implement noise cancellation, in accordance with some implementations. As illustrated, the AAV <NUM> includes eight lower propellers <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> that are respectively located below eight upper propellers <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>. The propellers <NUM> and <NUM> may be spaced about a frame <NUM> of the AAV <NUM>. The propellers <NUM> and <NUM> may be any form of propeller (e.g., graphite, carbon fiber) and of a size sufficient to lift the AAV <NUM> and any inventory/payload engaged by the AAV <NUM> so that the AAV <NUM> can navigate through the air, for example, to deliver an inventory item to a location/destination. While this example includes eight pairs of propellers, in other implementations, more or fewer propellers may be utilized. Likewise, in some implementations, the propellers may be positioned at different locations on the AAV <NUM>. In addition, alternative methods of upward and/or forward propulsion may be utilized. For example, fans, jets, turbojets, turbo fans, jet engines, and the like may be used to propel the AAV <NUM>.

The frame <NUM> or body of the AAV <NUM> may likewise be of any suitable material, such as graphite, carbon fiber, plastic, composite, and/or aluminum. In this example, the frame <NUM> of the AAV <NUM> includes four structures (or spars) <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> arranged in a hash pattern with the structures intersecting and joined at approximately perpendicular angles. However, more or fewer structures may be included in the AAV <NUM>. The structures may be rigid or substantially rigid to allow minimal flex during operation of the AAV <NUM>. The structures may include a circular, oval, square, or polynomial cross section in some implementations. However, the structures <NUM> may be formed as open structures such as U-beams, I-beams, and fins. In this example, structures <NUM>-<NUM> and <NUM>-<NUM> are arranged parallel to one another and are approximately the same length. In some implementations, the structures <NUM>-<NUM> and <NUM>-<NUM> may be arranged parallel to one another, yet substantially perpendicular to structures <NUM>-<NUM> and <NUM>-<NUM>. Some of the structures <NUM>-<NUM> and <NUM>-<NUM> may be approximately the same length or may be different lengths. In some implementations, all of the structures <NUM> may be of approximately the same length, while in other implementations, some or all of the structures <NUM> may be of different lengths. Likewise, the spacing between the two sets of structures may be approximately the same or different.

While the implementation illustrated in <FIG> includes four structures <NUM> that are joined to form the frame <NUM>, in other implementations, there may be fewer or more components to the frame <NUM>. For example, rather than four structures, in other implementations, the frame <NUM> of the AAV <NUM> may be configured to include six structures.

Although the structures <NUM> are shown as being straight or linear structures, the structures may include some curvature in some embodiments. The structures may be coupled to one another at other angles besides <NUM> degrees to position and/or support the propellers <NUM>, <NUM> as discussed herein.

In some implementations, the AAV <NUM> may be configured for aerodynamics. For example, an aerodynamic housing may be included on the AAV <NUM> that encloses the AAV control system <NUM>, one or more of the structures <NUM>, the frame <NUM> and/or other components of the AAV <NUM>. The housing may be made of any suitable material(s) such as graphite, carbon fiber, plastic, composite, aluminum, etc. Likewise, in some implementations, the location and/or the shape of the inventory (e.g., item or container) may be aerodynamically designed. For example, in some implementations, the inventory engagement mechanism may be configured such that, when the inventory is engaged, it is enclosed within the frame <NUM> and/or housing of the AAV <NUM> so that no additional drag is created during transport of the inventory by the AAV <NUM>. In other implementations, the inventory may be shaped to reduce drag and provide a more aerodynamic design of the AAV <NUM> and the inventory. For example, if the inventory is a container and a portion of the container extends below the AAV <NUM> when engaged, the exposed portion of the container may have a curved shape.

The propellers <NUM>, <NUM> and corresponding propeller motors are positioned at both ends of each structure <NUM>. For inventory transport purposes, the propeller motors may be any form of motor capable of generating enough speed with the propellers to lift the AAV <NUM> and any engaged inventory thereby enabling aerial transport of the inventory. For example, the propeller motors may each be a FX-<NUM>-<NUM>740kv multi rotor motor. The propeller motors may be any form of motor (e.g., permanent magnet, brushless, etc.).

Extending outward from each structure is a support arm <NUM> that is connected to a barrier <NUM>. In this example, each barrier <NUM> is positioned around and attached to each propeller of the AAV <NUM> in such a manner that the motors and propellers <NUM>, <NUM> are within the perimeter of the barrier <NUM>. The barriers <NUM> may protect the propellers <NUM>, <NUM> from damage and/or protect other objects from damage by preventing the propellers <NUM>, <NUM> from engaging other objects. The barriers <NUM> may be plastic, rubber, etc., and may be round, oval, or any other shape.

Mounted to the frame <NUM> is the AAV control system <NUM>. In this example, the AAV control system <NUM> is mounted centrally and on top of the frame <NUM>. The AAV control system <NUM>, as discussed in further detail below with respect to <FIG>, controls the operation, routing, navigation, noise cancellation, communication, and the inventory engagement mechanism of the AAV <NUM>.

Likewise, the AAV <NUM> includes one or more power modules <NUM>. In this example, the AAV <NUM> includes two power modules <NUM> that are removably mounted to the frame <NUM>. The power modules <NUM> for the AAV <NUM> may be in the form of battery power, solar power, gas power, super capacitor, fuel cell, alternative power generation source, or a combination thereof. For example, the power modules <NUM> may each be a 6000mAh lithium-ion polymer battery (Li-poly, Li-Pol, LiPo, LIP, PLI or Lip) battery. The power module(s) <NUM> are coupled to and provide power for the AAV control system <NUM> and the propeller motors <NUM>, <NUM>.

As mentioned above, the AAV <NUM> may also include an inventory engagement mechanism <NUM>. The inventory engagement mechanism <NUM> may be configured to engage and disengage items and/or containers that hold items. In this example, the inventory engagement mechanism <NUM> is positioned within a cavity of the frame <NUM> that is formed by the intersections of the structures <NUM>. The inventory engagement mechanism <NUM> may be positioned beneath the AAV control system <NUM>. In implementations with additional structures, the AAV <NUM> may include additional inventory engagement mechanisms and/or the inventory engagement mechanism <NUM> may be positioned in a different cavity within the frame <NUM>. The inventory engagement mechanism <NUM> may be of any size sufficient to securely engage and disengage containers that contain inventory. In other implementations, the inventory engagement mechanism may operate as the container, containing the inventory item(s) to be delivered. The inventory engagement mechanism communicates with (via wired or wireless communication) and is controlled by the AAV control system <NUM>.

While the implementations of the AAV <NUM> discussed herein utilize propellers <NUM>, <NUM> to achieve and maintain flight, in other implementations, the AAV <NUM> may be configured in other manners. For example, the AAV <NUM> may include fixed wings and/or a combination of both propellers and fixed wings. For example, the AAV <NUM> may utilize one or more propellers to enable takeoff and landing and a fixed wing configuration or a combination wing and propeller configuration to sustain forward flight while the AAV <NUM> is airborne.

<FIG> is a block diagram illustrating example components <NUM> of a vehicle that includes a noise controller <NUM>, in accordance with some implementations. The vehicle components <NUM> are components of an AAV. In examples, the vehicle components may be components of any other type of vehicle. For example, the vehicle components <NUM> can be included in any other type of aircraft (e.g., a passenger airplane), any type of land craft (e.g., an automobile), or any type of watercraft (e.g., a motor boat).

The vehicle components <NUM> include a propulsion device or mechanism <NUM> operable to cause propulsion of the vehicle. The propulsion device <NUM> generates noise. A sensor <NUM> is located near the propulsion device <NUM> to detect the noise generated by the propulsion device <NUM>. The sensor <NUM> may be in direct or indirect communication with the noise controller <NUM>. The noise controller <NUM> receives from the sensor <NUM> a signal representing the noise detected by the sensor <NUM> (i.e., the noise generated by the propulsion device <NUM>).

The noise controller <NUM> may also be in direct or indirect communication with a sound generator <NUM>. In implementations, the sound generator <NUM> is a propeller (e.g., the upper propeller <NUM> of <FIG>). In examples, the sound generator <NUM> may be another mechanical device or system or an electrical or an electromechanical device or system ( e.g., an audio speaker). The noise controller <NUM> is configured to cause the sound generator <NUM> to substantially cancel the noise generated by the propulsion device <NUM>. For example, the noise controller <NUM> may transmit a signal to the sound generator <NUM> that causes the sound generator <NUM> to produce anti-noise that destructively interferes with the noise generated by the propulsion device <NUM>.

<FIG> is a block diagram illustrating example components <NUM> of an AAV with a control system <NUM>. The AAV includes a noise controller <NUM>. In examples, the AAV includes an audible communication controller <NUM>, or a visible communication controller <NUM>.

The AAV components <NUM> may include a first lower rotor <NUM> that is driven by a first lower motor <NUM>. A first audio sensor <NUM> may be located near the first lower rotor <NUM> and configured to detect noise substantially generated by the first lower rotor <NUM>. In some cases, the first audio sensor <NUM> may additionally or alternatively detect ambient noise from a noise source that is not the first lower rotor <NUM>. The noise controller <NUM> may be in direct or indirect communication with the first audio sensor <NUM> and a first upper motor <NUM> that drives rotation of the first upper rotor <NUM>. In various implementations, the noise controller <NUM> may receive from the first audio sensor <NUM> a signal representing the noise detected by the first audio sensor <NUM>. Based at least in part on the signal received from the first audio sensor <NUM>, the noise controller <NUM> may determine how to modulate the rotational speed of the first upper rotor <NUM> such that the first upper rotor <NUM> produces sound that substantially cancels the noise generated by at least the first lower rotor <NUM>.

In some implementations, the noise controller <NUM> may receive a signal representing the rotational speed of the first lower rotor <NUM>. In such cases, the noise controller <NUM> may interpret or translate the rotational speed of the first lower rotor <NUM> into a representation of noise generated by the first lower rotor <NUM>. Accordingly, the noise controller <NUM> may determine how to modulate rotational speed of the first upper rotor <NUM> based at least in part on the received signal representing the rotational speed of the first lower rotor <NUM>.

In various implementations, the AAV components <NUM> may also include a second lower rotor <NUM>, a second lower motor <NUM>, a second audio sensor <NUM>, a second upper motor <NUM>, and a second upper rotor <NUM> that, in some cases, are functionally similar to the first lower rotor <NUM>, the first lower motor <NUM>, the first audio sensor <NUM>, the first upper motor <NUM>, and the first upper rotor <NUM>, respectively. It should be understood that the AAV components <NUM> may include additional rotors, motors, sensors, other components, or any combination thereof, which may or may not be functionally similar to one or more of the AAV components <NUM> depicted in <FIG>.

In some cases, the noise controller <NUM> may receive a plurality of signals representing noise generated by different rotors. For instance, the noise controller <NUM> may receive a first signal from the first audio sensor <NUM> that represents first noise generated by the first lower rotor <NUM>. The noise controller <NUM> may also receive a second signal from the second audio sensor <NUM> that represents second noise generated by the second lower rotor <NUM>. The noise controller <NUM> may determine a global ambient noise based at least in part on noise detected by multiple sensors, such as the first noise and the second noise detected by the first audio sensor <NUM> and the second audio sensor <NUM>, respectively. In some cases, one or more of the first noise, the second noise, or the determined ambient noise may include noise detected in the ambient environment from one or more noise sources other than propellers of the AAV (e.g., noise from weather, other aircraft, birds, construction, etc.).

In some implementations, the AAV control system <NUM> may include an audible communication controller <NUM> that causes one or multiple propellers to generate audible communications. In some cases, the audible communication controller <NUM> may receive various input parameters, such as parameters received from one or more of the first audio sensor <NUM>, the second audio sensor <NUM>, or input/output devices <NUM>.

Input/output devices <NUM> may, in some implementations, include one or more audio sensors, image capture devices, thermal sensors, infrared sensors, time of flight sensors, accelerometers, pressure sensors, weather sensors, airflow sensors, etc. Multiple input/output devices <NUM> may be present and controlled by the AAV control system <NUM>. One or more of these or other sensors may be utilized to assist in landings as well as avoiding obstacles during flight. Additionally or alternatively, one or more of these or other sensors may be utilized to detect a presence and/or a location (relative or absolute) of living beings, such as humans or animals.

The audible communication controller <NUM> may determine that one or more of the received input parameters satisfy a condition that corresponds to an audible communication that is to be communicated. For example, the audible communication controller <NUM> may receive one or more input parameters (e.g., a video signal from a camera) that indicate a location of a person. The audible communication controller <NUM> may determine that the location of the person indicated by the received one or more input parameters satisfies a flight condition, e.g., a flight condition associated with the person being dangerously near the landing path of the AAV. In this example, satisfaction of the flight condition may correspond to a warning message audible communication, such as a "Watch out!" type of warning message.

In some implementations, the audible communication controller <NUM> may determine how to modulate rotational speed of one or multiple rotors to cause the rotor(s) to produce a series of sounds that are audibly perceptible as the audible communication (e.g., "Hello!", "Watch out!", "Incoming!", "Get out of the way!", etc.). In some implementations, the series of sounds produced by the rotor(s) while rotating at the modulated rotational speeds may be synthesized speech.

Additionally or alternatively, the series of sounds produced by the rotor(s) may be at audio frequencies corresponding to pitches intended to annoy or scare away animals. For example, the audible communication controller <NUM> may determine that the location of an animal (e.g., a bird) indicated by the received one or more input parameters satisfies a flight condition associated with the animal being dangerously near the flight path of the AAV. In this example, satisfaction of the flight condition may correspond to an audible communication perceptible as one or more sounds predetermined to scare away the animal. The sounds may, in some instances, be tailored to particular types of animals. That is, sounds produced as an audible communication directed to one type of animal may be different than sounds produced as an audible communication direct to another type of animal.

In some implementations, a history of received input parameters provided by the input/output devices <NUM> and/or data provided by any other source may be utilized by the audible communication controller <NUM> to infer that a flight condition is satisfied. For example, the audible communication controller <NUM> may, based on a history of received input parameters, infer that a portion of a flight path of the AAV is associated with a high traffic of birds. For that portion of the flight path, the audible communication controller <NUM> may cause the rotor(s) to generate an audible communication based at least in part on the history of received input parameters/data.

In various cases, rotational speed(s) of the rotor(s) may be modulated at a rate ranging from about <NUM> to about <NUM> to generate an audible communication. For instance, in some implementations, the rate of modulation of the rotational speed of a rotor may be approximately <NUM>.

In some cases, one or more components of the control system <NUM> may include a software-defined radio (SDR) component or the like capable of generating signals at audio frequencies of approximately <NUM> or higher. The SDR component (or the like) may be utilized, for example, by the audible communication controller <NUM> or the noise controller <NUM> to generate an output signal that modulates the speed of the rotor(s). That is, instead of audio speakers being connected to a SDR, the rotor(s) may act as audio speakers connected to the SDR component (or the like).

Additionally or alternatively, the AAV control system <NUM> may include a visible communication controller <NUM> that causes one or multiple rotors to generate visible communications. For example, the visible communication controller <NUM> may receive various input parameters, such as parameters received from one or more of the first audio sensor <NUM>, the second audio sensor <NUM>, or input/output devices <NUM>.

The visible communication controller <NUM> may determine that one or more of the received input parameters satisfy a condition that corresponds to a visible communication that is to be communicated. For example, the visible communication controller <NUM> may receive one or more input parameters (e.g., a video signal from a camera) that indicate a location of a person. The visible communication controller <NUM> may determine that the location of the person indicated by the received one or more input parameters satisfies a flight condition, e.g., a flight condition associated with the person being near, but not dangerously near, the landing path of the AAV. In this example, satisfaction of the flight condition may correspond to a greeting message visible communication, such as the "HI" greeting message illustrated in <FIG> and described below.

In various implementations, to generate the visible communication, light sources [e.g., light-emitting diodes (LEDs)] may be coupled to one or multiple rotor(s). The light sources may be intermittently illuminated in a synchronized manner while the rotor(s) are rotating to generate patterns that are visibly perceptible as the visible communication.

In some cases, the visible communications may include multiple words that together form phrases or sentences. Individual rotors may generate one or more of: a single letter or symbol of the visible communication, multiple letters of the visible communication, multiple symbols of the visible communication, etc. Multiple rotors may cooperatively generate one or more of: a single letter or symbol of the visible communication, multiple letters of the visible communication, multiple symbols of the visible communication, etc. It should be understood, however, that the rotors in conjunction with the light sources coupled thereto may be caused to generate a visible communication in any suitable manner.

<FIG> is an illustrative diagram of example AAV propellers <NUM> with light sources <NUM> that are illuminated to generate a visible communication, in accordance with some implementations. Light sources <NUM> may be coupled to the propellers <NUM>. In some implementations, the light sources <NUM> may be light-emitting diodes (LEDs). However, in other implementations, the light sources <NUM> may be any other type of light source or any combination of different types of light sources.

In the illustrated implementation, movement of the propellers <NUM> and illumination activity of the light sources <NUM> are depicted at three different snapshots taken at times t0, t1, t2. At time t0, the propellers <NUM> are indicated as standing still and the light sources <NUM> are indicated as not being illuminated. At time t1, the propellers <NUM> are indicated as rotating, and some of the light sources <NUM> are indicated as a pattern of illuminated light sources <NUM> that are visibly perceptible as "HI" <NUM>, with each letter of the visible communication being implemented by light sources <NUM> coupled to an individual propeller. That is, in this example, light sources <NUM> coupled to the first propeller <NUM>-<NUM> are illuminated to implement the "H" of a first instance of the "HI" visible communication, and light sources <NUM> coupled to the second propeller <NUM>-<NUM> are illuminated to implement the "I" of the first instance of the "HI" visible communication.

None of the light sources <NUM> coupled to the third propeller <NUM>-<NUM> are indicated as illuminated at time t1. In some instances, such an absence of illumination may indicate a space between words, phrases, and/or sentences of a visible communication. Light sources <NUM> coupled to the fourth propeller <NUM>-<NUM> implement an "H" of a second instance of the "HI" visible communication. At time t1, the "I" of the second instance of the "HI" visible communication is yet to be generated.

At time t2, the propellers <NUM> are indicated as rotating, and some of the light sources <NUM> are indicated as a pattern of illuminated light sources <NUM> that are visibly perceptible as "HI" <NUM>. As compared to time t1, the characters representing the "HI" visible communication are indicated as having shifted or scrolled one position ( e.g., one propeller) to the left. That is, at time t2 of this example, light sources <NUM> coupled to the first propeller <NUM>-<NUM> are now illuminated to implement the "I" of a first instance of the "HI" visible communication (the "H" of the first instance of the "HI" visible communication is no longer visible). None of the light sources <NUM> coupled to the second propeller <NUM>-<NUM> are indicated as illuminated at time t2. Light sources <NUM> coupled to the third and fourth propellers <NUM>-<NUM>, <NUM>-<NUM> are illuminated to implement the "H" and the "I", respectively, of the second instance of the "HI" visible communication. It should be understood that the example illustrated in <FIG> is just one non-limiting example according to some implementations. Numerous other implementations, variations, and configurations will be apparent to those of skill in the art in view of the disclosure herein.

<FIG> are example flow diagrams illustrating example processes <NUM>, <NUM>, and <NUM>. These processes <NUM>, <NUM>, and <NUM> are illustrated as logical flow diagrams, each operation of which represents a sequence of operations that can be implemented in hardware, software, or a combination thereof. In the context of software, the operations represent computer-executable instructions that, when executed by one or more processors, perform the recited operations. Generally, computer-executable instructions include routines, programs, objects, components, data structures, and the like that perform particular functions or implement particular abstract data types. The order in which the operations are described is not intended to be construed as a limitation, and any number of the described operations can be combined in any order and/or in parallel to implement the process, and not all of the operations are necessarily required.

<FIG> is an example flow diagram illustrating an example noise cancelling process <NUM>. At block <NUM>, the process <NUM> includes detecting noise generated by a first propeller. For example, an AAV may include one or more audio sensors disposed proximate the first propeller to detect the noise generated by the first propeller. The AAV may also include a control system that receives from the one or more audio sensors a representation of the noise generated by the first propeller.

At block <NUM>, the process <NUM> includes determining rotational speed modulation of a second propeller. The control system of the AAV determines one or more modulations of rotational speed of the second propeller that cause the second propeller to produce a sound that cancels the noise generated by the first propeller.

At block <NUM>, the process <NUM> includes modulating rotational speed of the second propeller to cancel noise generated by the first propeller. For example, the control system of the AA V may cause a motor that drives rotation of the second propeller to modulate the rotational speed of the second propeller. While rotating at the modulated rotational speed, the second propeller may produce anti-noise that cancels the noise generated by the first propeller.

<FIG> is an example flow diagram illustrating an example process <NUM> for generating an audible communication, in accordance with some implementations. At block <NUM>, the process <NUM> includes determining that a flight condition is satisfied. For instance, the control system of the AAV may determine that one or more received input parameters satisfy a condition that corresponds to generating an audible communication.

At block <NUM>, the process <NUM> includes determining a plurality of rotational speed modulations for one or multiple propellers. In some instances, for example, the control system of the AAV may determine a plurality of rotational speed modulations that cause the propeller(s) to generate a series of sounds that correspond to an audible communication.

At block <NUM>, the process <NUM> includes modulating rotational speed of the propeller(s) to generate an audible communication. For example, the control system of the AAV may cause the propeller(s) to generate a series of sounds that are audibly perceptible as an audible communication, such as a warning message (e.g., "Watch out!").

<FIG> is an example flow diagram illustrating an example process <NUM> for generating a visible communication, in accordance with some implementations. At <NUM>, the process <NUM> includes determining that a flight condition is satisfied. For instance, the control system of the AAV may determine that one or more received input parameters satisfy a condition that corresponds to generating a visible communication.

At block <NUM>, the process <NUM> includes determining a series of illuminations of at least a portion of one or multiple propellers. For example, light sources may be coupled to the propeller(s), and the control system of the AAV may determine a series of illuminations of the light sources that cooperatively produce a visible communication. In some cases, the light sources may be light-emitting diodes (LEDs). Determining a series of illuminations that implement a visible communication may include, for example, determining a first LED of a plurality of LEDs to illuminate at a first time, and determining a second LED of the plurality of LEDs to illuminate at a second time that is different than the first time.

At block <NUM>, the process <NUM> includes illuminating at least a portion of one or multiple propellers to generate a visible communication. In some implementations, this may include illuminating at least a portion of a first propeller at a first time, and illuminating at least a portion of a second propeller at a second time that is different than the first time. Additionally or alternatively, in some cases, illuminating at least a portion of one or multiple propellers to generate a visible communication may include illuminating a first LED that is coupled to a first propeller of the multiple propellers at a first time, and illuminating a second LED that is coupled to a second propeller of the multiple propellers at a second time that is different than the first time.

<FIG> is a block diagram of an illustrative computing architecture of the AAV <NUM>, <NUM>. In various examples, the block diagram may be illustrative of one or more aspects of the AAV control system <NUM> that may be used to implement the various systems, devices, and techniques discussed above. In the illustrated implementation, the AAV control system <NUM> includes one or more processors <NUM>, coupled to a non-transitory computer readable storage medium <NUM> via an input/output (I/O) interface <NUM>. The AAV control system <NUM> may also include a propeller motor controller <NUM>, power supply module <NUM> and/or a navigation system <NUM>. The AAV control system <NUM> further includes a noise controller <NUM>, an audible communication controller <NUM>, a visible communication controller <NUM>, an inventory engagement mechanism controller <NUM>, a network interface <NUM>, and one or more input/output devices <NUM>.

In various implementations, the AAV control system <NUM> may be a uniprocessor system including one processor <NUM>, or a multiprocessor system including several processors <NUM> (e.g., two, four, eight, or another suitable number). The processor(s) <NUM> may be any suitable processor capable of executing instructions. For example, in various implementations, the processor(s) <NUM> may be general-purpose or embedded processors implementing any of a variety of instruction set architectures (ISAs), such as the x86, PowerPC, SPARC, or MIPS ISAs, or any other suitable ISA. In multiprocessor systems, each processor(s) <NUM> may commonly, but not necessarily, implement the same ISA.

The non-transitory computer readable storage medium <NUM> may be configured to store executable instructions, data, flight paths and/or data items accessible by the processor(s) <NUM>. In various implementations, the non-transitory computer readable storage medium <NUM> may be implemented using any suitable memory technology, such as static random access memory (SRAM), synchronous dynamic RAM (SDRAM), nonvolatile/Flash-type memory, or any other type of memory. In the illustrated implementation, program instructions and data implementing desired functions, such as those described above, are shown stored within the non-transitory computer readable storage medium <NUM> as program instructions <NUM>, data storage <NUM>, and flight path data <NUM>, respectively. In other implementations, program instructions, data and/or flight paths may be received, sent or stored upon different types of computer-accessible media, such as non-transitory media, or on similar media separate from the non-transitory computer readable storage medium <NUM> or the AAV control system <NUM>. Generally, a non-transitory, computer readable storage medium may include storage media or memory media such as flash memory (e.g., solid state memory), magnetic or optical media (e.g., disk) coupled to the AAV control system <NUM> via the I/O interface <NUM>. Program instructions and data stored via a non-transitory computer readable medium may be transmitted by transmission media or signals such as electrical, electromagnetic, or digital signals, which may be conveyed via a communication medium such as a network and/or a wireless link, such as may be implemented via the network interface <NUM>.

The propeller motor(s) controller <NUM> communicates with the navigation system <NUM> and adjusts the power of each propeller motor to guide the AAV along a determined flight path. The power supply module <NUM> may control the charging and any switching functions associated with one or more power modules (e.g., batteries) of the AAV, such as the power sources <NUM>. The navigation system <NUM> may include a GPS or other similar system that can be used to navigate the AAV to and/or from a location.

The noise controller <NUM> operates to cause noise cancellation as described herein. The noise controller <NUM> causes one or more propellers of the AAV to produce anti-noise that cancels noise generated by one or more other propellers. The audible communication controller <NUM> may operate to cause generation of audible communications as described herein. For example, the audible communication controller <NUM> may cause modulation of rotational frequency of one or more propellers to cause the propeller(s) to generate a series of sounds that are audibly perceptible as an audible communication.

The visible communication controller <NUM> may operate to cause generation of visible communications as described herein. For example, the visible communication controller <NUM> may cause intermittent illumination of light sources that are coupled to one or more propellers to generate a pattern that is visibly perceptible as a visible communication.

The inventory engagement mechanism controller <NUM> communicates with the motor(s) (e.g., a servo motor) used to engage and/or disengage inventory. For example, when the AAV is positioned over a level surface at a delivery location, the inventory engagement mechanism controller <NUM> may provide an instruction to a motor that controls the inventory engagement mechanism to release the inventory.

The network interface <NUM> may be configured to allow data to be exchanged between the AAV control system <NUM>, other devices attached to a network, such as other computer systems, and/or with AAV control systems of other AAVs. For example, the network interface <NUM> may enable wireless communication between numerous AAVs. In various implementations, the network interface <NUM> may support communication via wireless general data networks, such as a Wi-Fi network. For example, the network interface <NUM> may support communication via telecommunications networks such as cellular communication networks, satellite networks, and the like.

Input/output devices <NUM> may, in some implementations, include one or more displays, audio sensors, image capture devices, thermal sensors, infrared sensors, time of flight sensors, accelerometers, pressure sensors, weather sensors, airflow sensors, etc. Multiple input/output devices <NUM> may be present and controlled by the AAV control system <NUM>. One or more of these or other sensors may be utilized to assist in landings as well as avoiding obstacles during flight. Additionally or alternatively, one or more of these or other sensors may be utilized to detect a presence and/or a location (relative or absolute) of living beings, such as humans or animals.

As shown in <FIG>, the memory <NUM> may include program instructions <NUM> which may be configured to implement the example processes and/or sub-processes described above. The data storage <NUM> may include various data stores for maintaining data items that may be provided for determining flight paths, causing noise cancellation, causing generation of audible communications, causing generation of visible communications, retrieving inventory, landing, identifying a level surface for disengaging inventory, etc..

In various implementations, the parameter values and other data illustrated herein as being included in one or more data stores may be combined with other information not described or may be partitioned differently into more, fewer, or different data structures. In some implementations, data stores may be physically located in one memory or may be distributed among two or more memories.

In selected embodiments, an automated aerial vehicle (AAV) may include one or more of a plurality of propellers that include a first propeller operable to rotate in a first rotational direction to cause lift of the AAV, the first propeller generating noise sound waves while rotating and a second propeller operable to rotate in a second rotational direction that is opposite the first rotational direction, the second propeller being substantially coaxial with the first propeller. The AAV may also include one or more of a microphone to detect the noise sound waves generated by the first propeller, a propeller motor that drives rotation of the second propeller, and a control system in communication with at least the microphone and the propeller motor. The control system may be configured to receive a signal representing the detected noise sound waves, and cause the propeller motor to modulate rotational speed of the second propeller such that the second propeller generates anti noise sound waves that are in antiphase with the noise sound waves generated by the first propeller and that have a same amplitude as the noise sound waves, the anti noise sound waves substantially canceling the noise sound waves.

Optionally, the AAV above may further be configured to determine that an object is in a flight path of the AAV, determine a plurality of rotational speed modulations that cause at least one propeller of the plurality of propellers to generate a series of sounds that correspond to an audible communication, and/or modulate rotational speed of the at least one propeller based on the determined plurality of rotational speed modulations to communicate the audible communication. The AAV may further comprise a plurality of light emitting diodes (LEDs), where individual LEDs of the plurality of LEDs may be coupled to a propeller of the plurality of propellers, wherein the control system may further be configured to one or more of determine that a person is in a flight path of the AAV, and/or determine a series of LED illuminations that correspond to a visible communication. Optionally, determining the series of LED illuminations may include one or more of determining a first LED of the plurality of LEDs to illuminate at a first time, determining a second LED of the plurality of LEDs to illuminate at a second time, the second time being different than the first time; and causing illumination of the plurality of LEDs based on the determined series of LED illuminations to communicate the visible communication.

Alternatively, embodiments disclosed herein may include a vehicle including one or more of a rotor operable to rotate and cause propulsion of the vehicle, the rotor generating noise while rotating, a sound generator, and a control system. The control system may be configured to receive a signal representing one or more operational characteristics of the rotor, and/or cause modulation of the sound generator such that the sound generator produces sound that substantially cancels the noise generated by the rotor, the modulation being determined based at least in part on the received signal.

Optionally, the rotor is a first rotor operable to rotate in a first rotational direction, and the sound generator is a second rotor operable to rotate in a second rotational direction that is opposite the first rotational direction. Optionally, the vehicle above may include an audio sensor that is configured to detect the noise generated by the rotor, and wherein the control system is configured to receive a signal representing one or more operational characteristics of the rotor comprises the control system being configured to receive, from the audio sensor, a signal representing the detected noise. Optionally, the rotor is a first rotor that is operable to rotate in a first rotational direction, the sound generator is a second rotor operable to rotate in a second rotational direction that is opposite the first rotational direction, and the control system being configured to cause modulation of the sound generator comprises the control system being configured to cause modulation of rotational speed of the second rotor to modulate the sound produced by the second rotor. Optionally, the vehicle may include an audio sensor that is configured to detect the noise generated by the rotor, wherein the second rotor is substantially coaxial with the first rotor, the second rotor is disposed proximate a first side of the first rotor, the audio sensor is disposed proximate a second side of the first rotor, the second side being opposite the first side, and/or the control system being configured to receive a signal representing one or more operational characteristics of the rotor comprises the control system being configured to receive, from the audio sensor, a signal representing the detected noise. Optionally, the control system may be configured to cause modulation of the sound generator comprises the control system being configured to cause modulation of the sound generator at a rate of modulation of approximately <NUM> or higher. Optionally, the vehicle may include an automated aerial vehicle (AAV). Optionally, the one or more operational characteristics of the rotor includes rotational speed of the rotor and the sound generator may include an audio speaker. Optionally, the vehicle may further include a plurality of audio sensors configured to detect ambient sound outside the vehicle, wherein: the rotor is one of a plurality of rotors, a first audio sensor of the plurality of audio sensors is disposed proximate a first rotor of the plurality of rotors, a second audio sensor of the plurality of audio sensors is disposed proximate a second rotor of the plurality of rotors, the control system is further configured to receive a first signal from the first audio sensor, the first signal representing first detected ambient noise that includes noise generated by the first rotor, receive a second signal from the second audio sensor, the second signal representing second detected ambient noise that includes noise generated by the second rotor, determine a global ambient noise based at least in part on the first received signal and the second received signal, determine a plurality of modulations of rotational speed of one or more rotors of the plurality of rotors, the plurality of modulations corresponding to an audible communication, and/or cause modulation of rotational speed of the one or more rotors of the plurality of rotors based on the determined plurality of modulations such that the one or more rotors produce a series of sounds that provide the audible communication, the audible communication being perceptible from outside the vehicle.

Alternatively, additional embodiments disclosed herein may relate to a method including one or more of detecting noise generated by a first propeller of a plurality of propellers of an aerial vehicle and modulating, based at least in part on the detected noise, rotational speed of a second propeller of the plurality of propellers of the aerial vehicle such that the second propeller produces sound that substantially cancels the noise generated by the first propeller.

Optionally, the method above may include detecting, via a first audio sensor, first noise that is generated by the first propeller of the plurality of propellers, the method may further include detecting, via a second audio sensor, second noise that is generated by a third propeller of the plurality of propellers. The method may further include determining a global ambient noise based at least in part on the detected first noise and the detected second noise, and/or modulating rotational speed of one or more propellers of the plurality of propellers based at least in part on the determined global ambient noise. The method may further include modulating rotational speed of one or more propellers of the plurality of propellers to cause the one or more propellers to produce a series of sounds corresponding to an audible communication. The method may further include at least partly illuminating one or more propellers of the plurality of propellers in a series of illuminations that cooperatively produce a visible communication, optionally wherein the at least partly illuminating one or more propellers of the aerial vehicle comprises illuminating at least a portion of the first propeller at a first time, and/or illuminating at least a portion of the second propeller at a second time, the second time being different than the first time. Furthermore, multiple light emitting diodes (LEDs) may be optionally coupled to individual propellers of the plurality of propellers, the at least partly illuminating the one or more propellers comprising illuminating a first LED that is coupled to the first propeller of the plurality of propellers at a first time, and/or illuminating a second LED that is coupled to the second propeller of the plurality of propellers at a second time, the second time being different than the first time.

Those skilled in the art will appreciate that the AAV control system <NUM> is merely illustrative and is not intended to limit the scope of the present disclosure, which is defined by the appended claims. In particular, the computing system and devices may include any combination of hardware or software that can perform the indicated functions, including computers, network devices, internet appliances, PDAs, wireless phones, pagers, etc. The AAV control system <NUM> may also be connected to other devices that are not illustrated, or instead may operate as a stand-alone system. In addition, the functionality provided by the illustrated components may in some
implementations be combined in fewer components or distributed in additional components. Similarly, in some implementations, the functionality of some of the illustrated components may not be provided and/or other additional functionality may be available.

Claim 1:
An unmanned aerial vehicle (<NUM>, <NUM>) comprising:
a first propeller operable to rotate and cause propulsion of the unmanned aerial vehicle, the first propeller generating noise while rotating;
a first sensor (<NUM>) disposed proximate to the first propeller and configured to detect the noise generated by the first propeller (<NUM>);
a second propeller (<NUM>) operable to rotate and cause propulsion of the unmanned aerial vehicle (<NUM>, <NUM>), the second propeller generating noise while rotating;
wherein in use, the first propeller (<NUM>) and the second propeller (<NUM>) are configured to rotate at independently varying rotational speeds and in a first rotational direction and a second rotational direction opposite to the first rotational direction respectively;
and a control system (<NUM>) configured to:
receive a signal from the first sensor (<NUM>) representing the detected noise generated by the first propeller (<NUM>) and a signal representing a rotational speed of the second propeller (<NUM>);
determine, based on prior modelling and the rotational speed of the second propeller (<NUM>), characteristics of sound waves produced by the second propeller (<NUM>);
compare the determined characteristics of the sound waves produced by the second propeller (<NUM>) to the respective characteristics of the detected noise generated by the first propeller (<NUM>); and
based on the comparison, modulate the rotational speed of the second propeller (<NUM>), such that the second propeller (<NUM>) produces sound that destructively interferes with the noise generated by the first propeller (<NUM>) and substantially cancels the noise generated by the first propeller.