WO2023012714A1

WO2023012714A1 - Method of and control system for increasing the efficiency of an aerial vehicle

Info

Publication number: WO2023012714A1
Application number: PCT/IB2022/057245
Authority: WO
Inventors: Jacques Venter
Original assignee: Iarc Cc
Priority date: 2021-08-05
Filing date: 2022-08-04
Publication date: 2023-02-09

Abstract

A method of increasing the efficiency of rotor propelled aerial vehicle which includes a body having a roll axis, and at least two rotors secured relative to the body. The method includes the step of orientating the aerial vehicle in order for the roll axis to be substantially aligned with a vector sum of the airspeed and the wind speed of the aerial vehicle.

Description

METHOD OF AND CONTROL SYSTEM FOR INCREASING THE EFFICIENCY OF AN AERIAL VEHICLE

BACKGROUND TO THE INVENTION

THIS invention relates to a method of increasing the efficiency of an aerial vehicle, and more particularly but not exclusively to a method of controlling the flight of an aerial vehicle in a way in which the efficiency of the vehicle is increased in order to reduce energy consumption.

An aircraft is a vehicle or machine that is able to fly by counteracting gravity using the dynamic lift of an airfoil. Some examples of aircraft include fixed wing airplanes and helicopters utilizing rotating rotors. Crewed aircraft are flown by an onboard pilot, whereas unmanned aerial vehicles may be remotely controlled or self-controlled by onboard computers.

Multi rotor aerial vehicles are well known in the art, in particular insofar as unmanned aerial vehicles (UAV’s - commonly referred to as drones) are concerned. These vehicles typically have two or more rotors, and most commonly have four rotors, although aerial vehicles with more than four rotors are also known. In the case of aerial vehicles with four rotors, two of the rotors typically rotates clockwise, and two rotate counter clockwise in order to balance the system. These kind of aerial vehicles yaws (turns left and right by rotating about a yaw axis - typically the vertical axis in normal flight) by increasing the speed of one set of the rotors (e.g. the set of clockwise rotating rotors) while decreasing the speed of the other set of the rotors (e.g. the set of anti-clockwise rotating rotors), in so doing utilizing the dynamic imbalance between the two sets of motors to turn the vehicle left or right. When the speed of one set is increased proportionally to the decrease of the other set, the vehicle will maintain the same height while yawing against the torque of the faster set of rotors.

These multi-rotor aerial vehicles can also pitch and roll by adjusting the speed of the various rotors. In this case this is not achieved by changing the rotational speed of the rotors that rotate in the same direction, but rather by changing the speed of a set of rotors on the same side of an axis about which the vehicle is intended to roll (longitudinal axis - the axis that would run from nose to tail in a fixed wing aircraft) or pitch (cross axis - the axis that would run through the wings in the case of a fixed wing aircraft) so as to increase or reduce the lift on the opposing sides of the axis about which the vehicle is intended to rotate.

Movement of these aerial vehicles is likewise achieved by providing more power to some rotors, while the power of other rotors is decreased, thus resulting in pitching of the vehicle in a direction of required travel. This in turn results in movement of the direction of the lower rotors due to the thrust vector of the rotors being moved away from a vertical axis.

With the addition of a flight controller the vehicle can stabilize itself by utilizing a number of sensors including a tilt sensor, for example a gravitometer, to sense the direction of gravity and hence the tilt of the vehicle, multiple accelerometers to sense movement, a compass to sense direction, a barometer to sense altitude and change in altitude, a GPS to sense location and pressure sensors to measure pressure differentials across the vehicle. When combining all these sensors such an aerial vehicle can be flown totally autonomously and can complete set out missions on its own, or when piloted make the skill level required to fly the vehicle very low, so much so that anyone can learn to fly one in a matter of minutes, as the vehicle does all the stability control automatically - for example maintaining height and even compensating for wind effects.

Several flight modes has been developed to make flying of these aerial vehicles even easier. For example, “Home lock” is a flight mode where the directional movement of the aerial vehicle is controlled relative to the remote pilot’s position and orientation as opposed to that of the aerial vehicle. This means that if the pilot gives the aerial vehicle the command to move to the pilot’s right, the aerial vehicle will move to the right irrespective of the direction that the aerial vehicle is actually facing. Likewise, if the pilot pushes the control stick away from him the aerial vehicle will move away from the pilot even if the front of the aerial vehicle is in fact facing the pilot. This is a very useful feature if the aerial vehicle is far away from the pilot and it is accordingly hard to see visually which way the aerial vehicle is facing.

Another such mode is “course lock”, where the directional control remains relative to a current heading, which is for example useful for videographers filming a subject that is not in front of the aerial vehicle.

Most aerial vehicles in the nature of UAV’s and Quad/hexa/octa copters are relatively symmetrical as they are meant to operate as multi directional camera platforms able to fly in any direction with the same ease. However, more and more of these aerial vehicles have started to transform to be elongated from the front to back in order to be more aerodynamic whilst flying forward, similar to helicopters. This design migration introduces inefficiency when the aerial vehicle is exposed to cross-winds, as the most aerodynamic axis of the vehicle (the longitudinal axis of the body about with the vehicle will roll) will not always be aligned with the effective airflow vector, being the vector sum of the airspeed and wind speed. In addition, one pair of diametrically opposed rotors will also be aligned or at least partially aligned with the effective airflow vector, which means that the rear of the two diametrically opposed but aligned rotors will be exposed to the turbulence created by the forward of the two rotors, thus further decreasing the efficiency of the vehicle due to the rear rotor having to work harder.

Current flight modes are designed with ease of operability in mind, and are not focused on using the aerial vehicles in the most effective flight orientations.

It is accordingly an object of the invention to provide a method of increasing the efficiency of an aerial vehicle that will, at least partially, alleviate the above shortcomings.

It is also an object of the invention to provide a method of controlling an aerial vehicle in such a way that the energy consumption of the aerial vehicle is reduced.

It is a further object of this invention to provide a control system for facilitate the method, and a drone including such control system.

SUMMARY OF THE INVENTION

According to the invention there is provided a method of increasing the efficiency of a rotor propelled aerial vehicle, the aerial vehicle including a body having a roll axis and at least two rotors secured relative to the body, the method including the step of orientating the aerial vehicle in order for the roll axis to be substantially aligned with a vector sum of the airspeed and the wind speed of the aerial vehicle. Preferably, there is provided for the roll axis to be substantially aligned with a horizontal component of the vector sum of the airspeed and the wind speed of the aerial vehicle.

In one embodiment there is provided for the method to include the step of controlling the aerial vehicle in order for the roll of the aerial vehicle to be substantially zero during forward movement, irrespective of the yaw or pitch of the aerial vehicle.

There is provided for the aerial vehicle to include a tilt sensor, and for the roll to be controlled by controlling the power of the rotors in response to feedback from the tilt sensor.

There is also provided for the aerial vehicle to include pressure sensors on opposite sides of the body, and for the roll to be controlled by controlling the yaw of the drone until the pressure on opposite sides of the body are substantially equalized.

There is provided for the method to include the steps of measuring the sum of the current draw or power usage of the rotors on the one side of the roll, measuring the sum of the current draw or power usage of the rotors on the opposite side of the roll axis, and balancing the sum of the current draw or power usage about the roll axis so that the current draw or power usage is equal on either side of the roll axis.

In a preferred embodiment the aerial vehicle includes four rotors.

According to a further aspect of the invention there is provided a control system for an aerial vehicle including a body having a roll axis and at least two rotors secured relative to the body, the control system including a controller that is configured to orientate the aerial vehicle in order for the roll axis of the drone to be substantially aligned with a vector sum of the airspeed and the wind speed of the aerial vehicle.

There is provided for the control system to include a tilt sensor, and for the controller to control the power of the rotors in response to feedback from the tilt sensor until the tilt sensor indicates that the drone experiences no roll.

There is provided for the control system to include pressure sensors on opposite sides of the body, and for the controller to control the yaw of the drone until the pressure on opposite sides of the body are substantially equalized.

There is provided for the control system to measure the sum of the current draw or power usage of the rotors on the one side of the roll, to measure the sum of the current draw or power usage of the rotors on the opposite side of the roll axis, and to balance the sum of the current draw or power usage about the roll axis so that the current draw or power usage is equal on either side of the roll axis.

According to a further aspect of the invention there is provided a drone including a control system as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention is described by way of a nonlimiting example, and with reference to the accompanying drawings in which:

Figure 1 is a perspective view of an aerial vehicle illustrating the various axes of rotation; Figure 2 is a front view of an aerial vehicle in a hovering mode in the presence of a cross-wind, without any forward movement, with the vehicle rolling;

Figure 3 is a front view of an aerial vehicle in forward flight mode, in the absence of a cross-wind, with the vehicle pitching;

Figure 4 is a front view of a prior art aerial vehicle utilizing conventional control methodology, in which the aerial vehicle is now moving in a forward direction while exposed to a cross-wind, with the vehicle rolling and pitching, but not yawing, thus essentially showing the combination of Figures 2 and 3;

Figure 5 is a perspective view of the aerial vehicle controlled to face into the vector sum of the airspeed and wind speed using the method in accordance with the present invention, with the vehicle pitching and yawing, but not rolling;

Figure 6 is a control diagram of a first control system that can be used in order to implement the method;

Figure 7 is a control diagram of a second control system that can be used in order to implement the invention.

DETAILED DESCRIPTION OF INVENTION Referring to the drawings, in which like numerals indicate like features, a non-limiting and simplified example of an aerial vehicle controlled using the methodology in accordance with the invention is generally indicated by reference numeral 10.

The invention can be applied to various forms of aerial vehicles, including drones with four, six or eight rotors. In this example, reference is made to an aerial vehicle or drone with four rotors, also known as a quadcopter.

The aerial vehicle 10 described in this example comprises a body 11 which houses a number of components not shown in the drawings, including for example a battery, control circuitry, an accelerometer, a tilt sensor (for example a gravitometer), a compass, a barometer, a GPS and pressure sensors. All of these components are well known in the art, and requires no detailed explanation. The invention does not relate to the introduction of new sensors or actuators, but rather to a new way of controlling an aerial vehicle using existing sensors and actuators.

Four arms extend sideways outwardly from the body 11. In the case of the aerial vehicle described in this embodiment the arms can be described as two front arms 12 and two rear arms 13. Each arm terminates in a motor and rotor assembly 14. In order to achieve stability in flight and control, two of the diametrically opposed rotors are clockwise rotating rotors 14.1 , while the other two are anti-clockwise rotating rotors 14.2.

The movements of an aerial vehicle 10 of this nature can be described with reference to three axis. In this example, a first axis R-R is an axis that extends longitudinally along the center of the body 11 and which is called the roll axis, and which in essence the longitudinal axis of the body. Rotation about this axis is called ‘roll’. Roll is achieved by increasing the rotational speed of two rotors on one side of the roll axis, and decreasing the rotational speed of two rotors on the opposing side of the roll axis. When this happens, the aerial vehicle will roll, but will remain at the same altitude. If the vehicle rolls in the absence of a cross-wind, the vehicle will move sideways. Prior art control methodologies rely heavily on roll to counteract the influences of cross-winds.

A second axis P-P is an axis that extends sideways through the body of the aerial vehicle, and is called the pitch axis. Rotation about this axis is called ‘pitch’. Pitch is achieved by increasing the rotational speed of the two rotors on the rear (or on the front) end of the body 11 (depending on the direction of pitch required) and simultaneously decreasing the rotational speed of the two rotors on the front (or on the rear) end of the aerial vehicle. Prior art control methodologies rely on pitch to induce forward or backward movement.

A third axis Y-Y is an axis that extends vertically through a center point of the body 11 , and is called the yaw axis. Rotation about this axis is called ‘yaw’. Yaw is achieved by increasing the rotational speed of two diametrically opposed rotors (i.e. two rotors rotating in the same direction) and/or decreasing the rotational speed of the other two diametrically opposed rotors (i.e. two rotors rotating in the opposite direction to the first set of rotors). Prior art control methodologies rely on yaw to facilitate a sideways directional change, but not to counter the influences of crosswinds when flying straight.

Modern aerial vehicles are equipped with the necessary sensors to enable the control system to control the movement and stability of the aerial vehicle. As mentioned above, these include, but are not limited to an accelerometer, a tilt sensor (for example a gravitometer), a compass, a barometer, a GPS and pressure sensors.

Figure 2 shows a stationary aerial vehicle that is exposed to a cross-wind Vw. The aerial vehicle controller will identify that the aerial vehicle is being displaced sideways by the wind, and will control the aerial vehicle to roll to counter the effect of the wind. The force vectors induced by the rotors now include horizontal components that counteract the force induced due to the impact of the cross-wind Vw on the drone 10. This rolling action is the conventional mechanism used to counteract the effects of cross-winds.

Figure 3 shows a forward moving aerial vehicle, which is moving in the direction of arrow F. In Figure 3, the aerial vehicle is not exposed to a cross wind, and therefore only encounters the airspeed V_A. In this case, the airspeed is only a result of the forward movement of the aerial vehicle, and the forward movement is in turn achieved by pitching the aerial vehicle so that the front end of the aerial vehicle is operatively lower than the rear end of the aerial vehicle, thus resulting in a net forward thrust vector due to all four rotors being inclined and each rotor therefore having a forward thrust vector.

Figure 4 shows the situation where the aerial vehicle is moving forward (in the direction of arrow F) whilst now also being exposed to a crosswind V_w. This aerial vehicle accordingly represents the combination of the aerial vehicles shown in Figures 2 and 3, thus being exposed to Vw and V_A. This results in the aerial vehicle now being exposed to a relative wind speed vector V_R. It will be appreciated that the relative direction of the relative wind speed vector V_R will be a function of the magnitude and directions of the cross wind and the forward velocity. In an example where the cross wind comes directly from a side of the aerial vehicle while the aerial vehicle is moving forward at a velocity which is the same as the speed of the cross wind, the relative wind vector will be at a 45 degree angle to the aerial vehicle. In conventional control methodology, the aerial vehicle will pitch to move forward, and will also roll to counter the cross wind. The front end of the aerial vehicle will still face the direction of travel, and will not face into the direction of the relative wind speed vector V . All of the above is known in the art. Some modern aerial vehicles, such as the one shown in the drawings, have elongated aerodynamic bodies, and it would be ideal from an efficiency perspective for the longitudinal axis of the aerial vehicle always to point in the direction of the relative wind vector V_R. If this does not happen, such an aerial vehicle will be less efficient compared to a configuration where the longitudinal axis (and hence the smallest frontal area) were to face into the relative wind vector V_R.

The gist of the present invention is accordingly a new control methodology, in which the aerial vehicle is orientated in order for the longitudinal axis (or then the roll axis as defined) to point in the direction of the vector sum of the airspeed and the wind speed of the aerial vehicle, as opposed to the direction of movement of the aerial vehicle. This means that the most aerodynamic profile will at all times be pointed into the direction of the relative wind vector V_R in order to minimize drag.

This mode of flight is shown in Figure 5, as opposed to the conventional mode of flight shown in Figure 4. In Figure 4, the aerial vehicle is aligned with the direction of movement, thus resulting in the smallest area not being exposed to the relative wind vector. In Figure 5, the aerial vehicle is aligned with the vector sum of the airspeed and the wind speed of the aerial vehicle, thus resulting in the smallest area being exposed to the relative wind vector.

Another shortcoming of the conventional control methodology is that, in addition to increased drag, the combination of the pitch and roll shown in Figure 4 also results in the rear left of the aerial vehicle lifting high and the front right dipping low. The other set of rotors remain in approximately the same plane relative to one another. Due to the direction of the relative wind vector, the higher rear rotor is now exposed to the turbulent air caused by the diametrically opposed front rotor. All of the rotors will in use cause turbulence, but in this case the thrust of the rear left rotor is exerted into the turbulent air caused by the front right rotor, which waste significant energy and reduced the efficiency of the rear rotors. In addition, in the embodiment shown in Figure 4, the rear left rotor (defined in the direction of travel) is the highest rotor which already has to work harder than the other rotors because it has to contribute towards pitch and roll, and this rotor is therefore now even more affected by the turbulence it experiences. All references to direction would of course change depending on the direction of the cross-wind.

In accordance with the present invention (which is the flight mode shown in Figure 5), the most efficient approach would be to have the aerial vehicle point its nose exactly into the direction of the relative wind vector which is the actual true wind vector in this scenario, in which case the back motors (left and right) would be at the same height, while doing the same work. The same goes for the front motors being lower but at the same relative height to one another needing the same power. This also puts the smallest total frontal area directly into the relative wind.

In this orientation, the rotors on the same side of the roll axis will also not be aligned in the direction of movement of the drone (i.e. they are offset from one another when seen from the direction of movement), and the effect of the turbulence caused by the leading rotors on the diametrically opposing trialing rotors will be reduced, because the rotors will not move through exactly the same airspace.

If the aerial vehicle is fitted with a camera, the camera could be controlled in order automatically to still face into the direction in which the aerial vehicle is travelling, in order to show the pilot where the aerial vehicle is heading.

There are several ways of achieving the above flight mode in practice. In a first example, shown in Figure 6, the drone includes a control system 100 having a controller 101 and a tilt sensor 103 (such as for example a gravitometer). In this case the control methodology will simply entail ensuring that the tilt sensor 103 always has the left and right side of the aerial vehicle level relative to one another (i.e. so that there is no roll) and for the effect of a cross-wind then being counteracted by a combination of pitch and yaw. This will be achieved by equalizing the power of the motors 102 on the two opposing sides of the roll axis in response to a control signal from the controller 101 .

In another embodiment, shown in Figure 7 the drone also includes a control system 100 including a controller 101 , but in this case pressure sensors 104 are used to determine a pressure differential across the drone, and these pressure differentials can be used as control input to the motors 102. When measuring the pressure differential from the left and right sides of the elongated body, the high pressure side would be facing the wind and the low pressure would be down wind. Yawing in the direction of the high pressure (i.e. turning the nose of the aerial vehicle into the wind) until there is no pressure differential, will result in the roll axis being substantially aligned with a vector sum of the airspeed and the wind speed of the aerial vehicle. Once there is no pressure differential between the two sides, it will be clear that the roll axis is aligned with the relative wind velocity experienced by the aerial vehicle.

The above control methodologies are only two examples, and various other closed loop control systems may be utilized. In one further example, an optical sensor (e.g. a camera) could be used to verify the relative orientation of the vehicle relative to the horizon, and the power supplied to the rotors can then be adjusted until the horizon is horizontal from the vehicles perspective while allowing the vehicle to roll and yaw. This will then result in the vehicle stabilizing in a position where the vehicle is pitching and yawing, but not rolling, with the roll axis pointing into the relative wind direction. In another example, the sum of the current draw or power usage of the rotors on the one side of the roll axis can be balanced with the sum of the current draw or power usage of the rotors on the opposite side of the roll axis. Again, if the vehicle is then allowed to yaw and roll while the current / power is balanced, it will stabilize in the required position where the vehicle pitches and yaws, but does not roll. In this example, the control system will include the capability of measuring the current draw or power output of all the motors of the drone.

It will be appreciated that the control calculation require to achieve the above control methodology happens in real time, and multiple fast calculations must therefore be done in real time. In order to achieve this, the processor housing and executing the control algorithm has to be located on-board the aerial vehicle in order to facilitate fast reaction times for best results. It will, however, not always be convenient for the enabling / disabling of the control methodology to have to be done manually when the aerial vehicle is physically accessible by the user, and it is accordingly also an feature of the present invention for the control mode to be enabled and disabled remotely via a remote while the aerial vehicle is in use.

This switch can be software application based or control transmitter based, giving the user the option as to when the user would like the feature enabled or disabled whilst in flight or whilst preparing for a flight. In one embodiment an easily accessible, physical toggle switch (not shown) will accordingly be provided on the remote (not shown), and in another embodiment the switch will take the form of a button accessible on the flight software application.

Whilst the above is demonstrated using a multi-rotor it would also be effective on VTOL and other aircraft, especially aircraft that operate at airspeeds that is heavily influenced by the environmental wind airspeed. Always ensuring that the left and right sides of the craft is level without using trim or rudder ensures balanced energy usage and thus result in the most efficient flight. It will even find application with helicopters that would use the least power on the tail rotor.

It will be appreciated that the above is only one embodiment of the invention and that there may be many variations without departing from the spirit and/or the scope of the invention. It is easily understood from the present application that the particular features of the present invention, as generally described and illustrated in the figures, can be arranged and designed according to a wide variety of different configurations. In this way, the description of the present invention and the related figures are not provided to limit the scope of the invention but simply represent selected embodiments.

The skilled person will understand that the technical characteristics of a given embodiment can in fact be combined with characteristics of another embodiment, unless otherwise expressed or it is evident that these characteristics are incompatible. Also, the technical characteristics described in a given embodiment can be isolated from the other characteristics of this embodiment unless otherwise expressed.

Claims

CLAIMS:

1. A method of increasing the efficiency of a rotor propelled aerial vehicle, the aerial vehicle including a body having a roll axis and at least two rotors secured relative to the body, the method including the step of orientating the aerial vehicle in order for the roll axis to be substantially aligned with a vector sum of the airspeed and the wind speed of the aerial vehicle.

2. The method according to claim 1 including the step of controlling the aerial vehicle in order for the roll of the aerial vehicle to be substantially zero during forward movement, irrespective of the yaw or pitch of the aerial vehicle.

3. The method according to claim 2 wherein the aerial vehicle includes a tilt sensor, the method including the step of controlling the roll by controlling the power of the rotors in response to feedback from the tilt sensor until the tilt sensor indicates that no roll is present.

4. The method according to claim 2 wherein the aerial vehicle includes pressure sensors on opposite sides of the body, the method including the step of controlling the yaw of the drone until the pressure on opposite sides of the body are substantially equalized.

5. The method according to claim 1 including the steps of measuring the sum of the current draw or power usage of the rotors on the one side of the roll, measuring the sum of the current draw or power usage of the rotors on the opposite side of the roll axis, and balancing the sum of the current draw or power usage about the roll axis so that the current draw or power usage is equal on either side of the roll axis. The method according to claim 1 wherein the vehicle is a quad, hexa or octocopter. A control system for an aerial vehicle including a body having a roll axis and at least two rotors secured relative to the body, the control system including a controller that is configured to orientate the aerial vehicle in order for the roll axis of the drone to be substantially aligned with a vector sum of the airspeed and the wind speed of the aerial vehicle. The control system according to claim 7 including a tilt sensor, wherein the controller controls the power of the rotors in response to feedback from the tilt sensor until the tilt sensor indicates that no roll is present. The control system according to claim 7 including pressure sensors on opposite sides of the body, wherein the controller controls the yaw of the drone until the pressure on opposite sides of the body are substantially equalized. The control system of claim 7 being configured to measure the sum of the current draw or power usage of the rotors on the one side of the roll, to measure the sum of the current draw or power usage of the rotors on the opposite side of the roll axis, and to balance the sum of the current draw or power usage about the roll axis so that the current draw or power usage is equal on either side of the roll axis. A drone including the control system according to any one of claims 7 to 10. The drone according to claim 11 , including four, six or eight rotors.