WO2004041381A2

WO2004041381A2 - Control systems for use with flying craft and other remote elements

Info

Publication number: WO2004041381A2
Application number: PCT/GB2003/004742
Authority: WO
Inventors: Phil Jermyn
Original assignee: Levitation Technologies Limited
Priority date: 2002-11-04
Filing date: 2003-11-04
Publication date: 2004-05-21
Also published as: GB0225661D0; WO2004041381A3; AU2003276441A8; AU2003276441A1

Abstract

A method and apparatus for controlling a powered craft in flight by an unsupported hand held control element. The position and attitude of the craft are controlled by the position and attitude of the control element. The position and attitude of the craft is determined with respect to a straight line between the controller and the craft, for example a beam of radiation. The controller and the craft are both provided with transducers comprising emitter and/or detector arrays in communication with one another.

Description

CONTROL SYSTEMS FOR USE WITH FLYING CRAFT AND OTHER REMOTE ELEMENTS

This invention relates generally to the sensing and control of objects relative to a remote location. In an important example the invention relates to the control and stabilisation of aircraft in flight, and still more specifically, but not exclusively, to the control of miniature aircraft by remote means.

Methods of control and stabilisation of aircraft are well known and numerous different systems exist for this purpose. The vast majority of prior art systems however rely on expensive components such as gyrocompasses and require a large amount of computational complexity. In the area of hobby or toy flying craft the skills required to control the craft restrict application to enthusiasts.

It is an object of the present invention therefore to provide an improved method of aircraft control. A further object of the present invention is to provide a simple, economical method of aircraft control suitable for use in say, remote controlled miniature aircraft.

The invention is defined by the accompanying claims. There will be described a suite of systems and arrangements providing an efficient and economic stabilisation and remote control regime for a flying craft, with optional user interfaces that permit operation by non-experts.

Most of these systems, arrangements and interfaces will find independent and separate application; many will find utility in the control or monitoring of objects other than miniature aircraft.

An important concept in this context is the control of a powered craft in flight by a remote operator, wherein light or other radiation extends between a control element and the craft to enable determination of the angular orientation of the craft and of the control element with respect toa straight line extending between the craft and the control element. Typically, each of the craft and the control element has a light emitting or a light sensing arrangement; it is possible for both light emitting and light sensing to take place at both the craft and the control element, but there are advantages in having light passing in only one sense. In much of the following description, the term "light" will be used as a non-limiting example of radiation. Various portions of the electromagnetic spectrum may of course be employed and there are often advantages in operating in the non-visible regions, it being then simpler to discriminate from ambient light. In certain applications, it will be appropriate to utilise, for example, ultrasonic radiation.

Light passing between the control element and the craft (or other object) defines a straight line and the emitting and sensing arrangements cooperate to determine angles of inclination with respect to this line. Thus, angles determined at the craft may measure roll, pitch and yaw inclinations. Angles determined at the control element may determine the direction of the craft with respect to the control element. A separate determination may be made of range, conveniently using part or all of the same emitting and sensing arrangements.

Angles may be determined through polarisation characteristics. A rotation angle about the axis of a polarised beam can be determined in a straightforward manner; further techniques will be described, some of which provide angle determinations about axes orthogonal to the beam axis.

An alternative or complementary set of techniques employ light emitting and sensing arrangements made up from numbers (typically two, three or four) of discrete elements, having polar distributions of emission or sensitivity which vary as between one element and the next. Differential measurements then provide angular information.

The approach of defining position and attitude with respect to a line extending between the craft and a control element, rather with respect to any absolute frame of reference, has a number of important advantages. Key amongst these is that changes in the attitude or position of the craft may be effected through changes in the attitude or position of the control element. Simply, a freely movable control element may be held in the hand of the operator, with movement of the hand (and therefore of the control element) effecting changes in the attitude or position of the craft. It is important to note here that there is no requirement for the position of the control element to separately sensed or measured. There need be no sensing or actuation linkage between the control element and a support structure; the control element is un-supported.

Various aspects of the invention will now be described by way of example with reference to the following Figures in which: Figure 1 shows a light emitting arrangement. Figure 2 shows a light sensing arrangement. Figure 3 illustrates possible outputs of a light sensing arrangement. Figure 4 illustrates a light emitting and receiving system.

Figure 5 shows possible outputs of a light sensing arrangement. Figures 6 & 7 show light emitting and receiving systems. Figure 8 illustrates a light emitting arrangement. Figure 9 schematically depicts an arrangement for controlling an aircraft. Figures 10 & 11 illustrate optical transducer arrangements.

Figure 12 schematically depicts a set of flight parameters for an aircraft. Figures 13 & 14 schematically depict methods of controlling an aircraft. Figure 15 schematically depicts an arrangement for controlling an aircraft. Figure 16 & 17 illustrate optical transducer arrangements. Figure 18 illustrates a control system block diagram for an arrangement for controlling an aircraft.

Figure 19 illustrates an example of an aircraft which can be used with the present invention.

Figure 20 shows two possible embodiments of a control element.

Figure 1a shows a light emitting arrangement adapted to allow a remote sensor to determine the rotation of the emitting arrangement about a generally horizontal axis X-X relative to the direction of a beam of light from the emitter to the sensor. The arrangement (generally designated by numeral 101) comprises a light source (not shown) and a housing 102. The light source might typically comprise an LED, but could equally comprise an alternative light source such as a tungsten bulb. The housing 102 has disposed on a front side two polarising filters 102 & 104. The front side is defined as the side which generally faces the remote sensor during normal operation. The direction of the sensor is shown schematically by arrow 'S'. The polarising filters 102 & 104 share a common edge which is substantially vertical, and are angled away from one another so as to form a ridge shape, sloping away from the central common edge to the left and right when viewed from the front. The direction of polarisation of the filters is perpendicular to the common edge.

Figures 1b, 1c and 1d show the light emitting arrangement at different angles of rotation about axis X-X, as viewed from the sensor. Figure 1b shows the arrangement at a reference 'level' position. It can be seen that at this position, the polarising filters 102 & 104 have the same direction of polarisation as viewed by the sensor. In other words, light arriving at the sensor has uniform polarisation. Figure 1c shows the arrangement rotated slightly about the (fixed position) sensor. Because of the ridge shaped arrangement of the polarising filters, the direction of polarisation of each filter now appears different as viewed by the sensor. Light arriving at the sensor emitted from the right hand side of the arrangement has a different angle of polarisation than light emitted from the left hand side of the arrangement. Figure 1d shows the arrangement rotated still further (in the same sense). The directions of polarisation of the two filters as seen in projection by the sensor are now at a greater angle to one another, and are approximately perpendicular.

By sensing a measure of the difference in angle of polarisation of light arriving at the sensor it is possible to determine the relative angle of rotation of the light emitting arrangement about the generally horizontal axis X-X.

In one embodiment of this method only a single polarising filter is used at the emitter, and the absolute angle of rotation of polarisation of light emitted is determined, as seen by the sensor, relative to a fixed reference angle. This could be achieved by using a sensor arrangement as shown in Figure 2. The arrangement comprises a photodiode 202, and a rotating polarising filter 204 mounted to a drive spindle 206, such that incident light (shown schematically by arrow 208) arriving at the photodiode passes through the filter. An alternative light sensing component such as a photoresistor could be used instead of photodiode 202. A shaft encoder is included on the spindle driving the rotating filter at the sensor, in this arrangement, the signal produced at the sensor in response to incident light from the emitter would have a substantially constant frequency but, in response to a change in orientation of the emitter, would vary in phase with respect to a reference position of the rotating filter, as measured by the shaft encoder. Figure 3 shows sensor outputs for such an emitter-sensor arrangement for two different angles of orientation of the emitter as viewed by the sensor.

This embodiment can provide a measure of angle of rotation from a relatively simple phase determination. This embodiment however suffers the limitation that only the degree of rotation, and not the direction of rotation can be determined

A more advantageous embodiment of this method uses the ridge shaped structure of polarising filters shown in Figure 1 not as an emitter arrangement, but as a sensor arrangement. Conversely, this embodiment uses an emitter arrangement resembling that shown in Figure 2, but with the light sensing component replaced with a light emitting component. This embodiment is illustrated in Figure 4.

Sensor arrangement 502 comprises a housing 504 having two polarising filters 506 & 508 disposed on a front side. The front side is defined as the side which faces the emitter during normal operation. The polarising filters 506 & 508 share a common edge which is substantially vertical, and are angled away from one another so as to form a ridge shape, sloping away from the central common edge to the left and right when viewed from the front. The direction of polarisation of the filters is perpendicular to the common edge. The sensor arrangement further comprises two light sensing components within the housing, arranged such that each sensor receives light through just one of the polarising filters 506 & 508. Preferably the light sensing components comprise photodiodes.

Emitter arrangement 510 comprises an LED 512, and a rotating polarising filter 514 mounted to a drive spindle 516, such that light emitted from the LED (indicated by arrow 518) passes through the filter. An alternative light emitting component such as a tungsten element could be used instead of LED 512.

This embodiment uses the same novel concept of angle determination as illustrated in Figure 1. The angle of the housing about a generally horizontal axis X'-X' relative to a beam of light passing from the emitter to the sensor is determined by detecting the angle of polarisation of filters 506 & 508 as projected onto a plane normal to the direction of light travelling from the emitter to the sensor. It should be noted though, that in this embodiment the information of angle is determined at the housing.

A benefit of this arrangement is that light passing through filter 506 can be distinguished from light passing through filter 508. Figure 5 shows the output signals of the two sensors for different angles of the sensor arrangement relative to the emitter arrangement. Although two sensor components are used in this embodiment, it should be appreciated that a number of alternative methods of distinguishing between light passing through the different filters are possible. This is true both of embodiments using the ridge/filter structure as an emitter arrangement, and embodiments which use the same structure as a sensor arrangement. Examples of methods of discriminating the two sides include using colour or frequency filters, or by using a sequencing method.

Figure 5a shows the sensors arranged 'level' with the emitter. Consequently the two sensors have the same angle of polarisation, and the output in response to the incident (rotating polarised) light of the two sensors are in phase. In Figure 5b the sensor arrangement is tilted downwards slightly. The two sensors are now detecting the incident light through different angles of polarisation, and their output signals are therefore out of phase. Sensor 1 illustrated by trace 602 leads sensor 2 illustrated by trace 604 by phase angle 606. In Figure 5c the sensor arrangement is again tilted, but this time it is tilted upwards. The output signals from the two sensors are again out of phase, but this time sensor 1 (trace 602) lags sensor 2 (trace 604) rather than leading it. In this way the degree of rotation of the housing can be determined from the phase angle of the two sensor signals, and the direction of rotation can be ascertained by determining whether sensor 1 leads or lags sensor 2. A further advantage of this particular embodiment is that a reference signal (such as that provided by a shaft encoder) is not required.

Figure 6 illustrates an arrangement for determining the relative angle of rotation of a sensor arrangement 702 about an axis Y-Y, relative to an emitter arrangement 704.

Emitter arrangement 704 comprises an LED 706, and a rotating polarising filter 708 mounted to a drive spindle 710, such that light emitted from the LED (indicated by arrow 712) passes through the filter. An alternative light emitting component such as a tungsten element could be used instead of LED 712.

Sensor arrangement 702 simply comprises a light sensing component 714, with a fixed polarising filter 716 through which incident light arriving at the component 714 passes.

The output from the sensor in response to the incident (rotating polarised) light will be periodic with peaks substantially every 180 degrees, corresponding to the direction of polarisation of the two filters aligning every half rotation of the emitter filter. In order to determine the relative angle of rotation of the sensor arrangement, this output signal can be compared in phase to a reference signal representative of the degree of rotation of the rotating filter, produced at the emitter arrangement. The reference signal could be obtained by, for example, providing a further sensor having a fixed polarising filter on the emitter arrangement , located opposite the rotating filter to the emitter (718). Alternatively a shaft encoder 720 could be used in conjunction with the spindle to provide a reference signal. The difference in phase of the two signals will provide a measure of the angle of rotation, and whether the sensor signal leads or lags the reference signal will determine the direction of rotation. It can be seen that in this arrangement it is necessary to compare a signal obtained at the sensor arrangement with a signal obtained at the emitter arrangement. In order to overcome this limitation, the arrangement of Figure 7 can be used to provide a similar function. An emitter arrangement 802 simply comprises a light emitting component 804 with a fixed polarising filter 806. A sensor arrangement 808 comprises two light sensing components 810, each having a fixed polarising filter 812, 814, the directions of polarisation of the two filters 812 & 814 being at different angles as shown in the Figure. Since filters 812 & 814 have different directions of polarisation, the sensors 810 will detect different intensities of light depending on the orientation of the emitter arrangement about generally horizontal axis Y'-Y'. When the direction of polarisation of filter 806 lies midway between the directions of polarisation of filters 812 & 814, the sensors will detect equal intensities of light. If the emitter arrangement rotates from this position about axis Y'-Y' then one of sensors 810 will detect an increase in intensity, while the other sensor will detect a decrease in intensity. By determining the ratio of sensed intensities of the two sensors 810 therefore, a measure of rotation of the emitter arrangement about axis Y'-Y' can be determined.

Referring now to Figure 8a, there is shown an emitter arrangement generally designated by numeral 902This emitter arrangement is used in conjunction with simple light sensor 903, whose output varies with detected light intensity. The emitter arrangement 902 comprises four light emitting components 904, 906, 908, 910, inclined to a base surface 912, and arranged in a diamond formation, pointing away from each other. The light emitting components are adapted to have an output intensity characteristic that varies with angle of dispersion. A typical intensity characteristic is shown in Figure 8b. Preferably the tops of the emitting components are ground to a suitable shape to provide an advantageous intensity characteristic. In a particular embodiment the tops of the emitters may be ground substantially flat. Although one possible arrangement of emitters is shown in Figure 8a it should be recognised that alternative emitter arrangements could be used which produce a directional variation in intensity with viewing angle.

The emitters 904, 906, 908, 910 are driven in a sequence recognizable to sensor 903 (either implicitly, or by means of a clocking signal) so that the intensity of each emitter can be detected in turn and compared. Since the emitters are arranged in a divergent fashion, the relative intensities of the light detected from each emitter provide a measure of the orientation of the emitter arrangement 902 about axes P-P and Q-Q, with respect to the axis C-C passing through the centre of the emitter arrangement and the sensor 903. For example, if the intensities of emitters 904 and 908 are detected as being equal, then the emitter arrangement is oriented perpendicular to axis C-C about axis P-P (ie not facing to the left or to the right). If the intensity of emitter 906 is detected as being greater than the intensity of emitter 910, then the emitter arrangement is oriented to face upwards to a degree, as seen along axis C-C.

Figure 8c shows a sensor arrangement capable of determining the direction with respect to a reference base plane of an incident beam of light. Four sensors 952, 954, 956 & 958 are arranged on a base 960, one pair of sensors 952 & 956 spaced apart in an X direction, and another pair of sensors 954 & 958 spaced apart in a Y direction, orthogonal to the X direction. A determination of angle of incident light from a remote light source in two orthogonal component planes can be made by comparing the intensity of light sensed at respective receivers. In an alternative embodiment, only three individual sensors are required to detect the angle of incidence of a light beam in two orthogonal component planes

In certain embodiments of emitter and sensor arrangements described above, it may be advantageous to tailor the angular response of the emitter means to approximately match that of the sensor means. It may also be advantageous to adapt the emitter and sensor arrangements to have a wide field of view. Preferably the operational field of view is greater than 40 degrees from the reference 'central' position in any direction.

It should be appreciated that the methods and arrangements described above can be used in a number of different orientations, and that a combination of these methods and arrangements can provide a number of simultaneous angular measurements.

Figures 9 to 12 show a first embodiment of an arrangement for controlling an aircraft relative to a hand held control element, using a combination of the methods described above. Figure 9 is a schematic illustration of the main components of the arrangement. A control element 1002 and an aircraft 1004 are linked via wire means 1005 to a processor unit 1006. The control element and the aircraft each have an optical transducer arrangement 1008 and 1010 comprising both emitter means and sensor means, as will be described in detail below. Thus a light path 012 between the aircraft and the control element is established with light travelling in both directions as indicated schematically in the diagram.

Referring now to Figure 10, there is shown in greater detail transducer arrangement 1008 located on the control element. Transducer arrangement 1008 comprises a light emitter such as an LED and a rotating polarising filter in an arrangement (designated generally by numeral 1102) substantially identical to the emitter arrangement described above with reference to Figures 4 and 6, and a sensor array 1104 capable of detecting the direction of an incident beam of light. Typically sensor array 1104 comprises three photodiodes angled away from each other and spaced at 120 degrees from each other. By comparing the intensity detected by the three sensors, a measure of the direction of incident light can be obtained. Emitter arrangement 1102 also includes means for producing a reference signal representative of the orientation of the rotating filter, for example by the use of a shaft encoder 1106.

Transducer arrangement 1010, located on the aircraft and shown in detail in Figure 11 , comprises a pair of sensor arrangements 1206 & 1208, each substantially identical to the sensor arrangement described above with reference to Figure 4. Sensor 1208 is arranged orthogonal to sensor 1206 however. Transducer 1010 further comprises a simple light source 1210 which comprises an LED in this embodiment.

Figure 13 illustrates schematically a set of flight parameters which can be derived by the system and method of an embodiment of the invention. The aircraft , represented by block 1052, has a position relative to a front face of the control element 1054. This position is defined by an angle of pan 1056 and an angle of elevation 1058. This position is also determined by a measure of range of the aircraft from the control element.

The attitude of the aircraft is defined by rotation about three orthogonal axes shown, for a given position of the aircraft, labelled pitch, roll and yaw, as shown in the Figure.

Information from the two transducer arrangements passed to processor 1006 can be used to determine the attitude and position of the aircraft relative to the control element 1002. The flight parameters of the aircraft (attitude determined relative to the light path from the control element transducer to the aircraft transducer, and position determined relative to the control element) are derived as summarised in the following table:

Since the flight parameters are derived relative to control element and aforementioned light path, processor 1006 can be advantageously configured (by the use of feedback circuits well known to one skilled in the art) to provide control signals to the aircraft (via wire means 1005) such that the attitude and position of the aircraft can be controlled by changes in the attitude or position of the controller. It should be noted that this novel arrangement allows for the absolute motion of the control element to control the aircraft, and thus the control element is preferably freely movable and unsupported. Preferably a separate height control is additionally provided in this arrangement, which can be implemented for example, by a dial or wheel on the control element. The height control may be made linear, but may advantageously be made non linear on or around the take off position, to compensate for ground effects. In embodiments where the aircraft is powered and/or controlled via an umbilical wire, the wire will act to provide proportional feedback of the height of the craft. At a greater height, a greater length of wire and hence weight of wire is supported by the craft. Therefore the increase in height of the craft resulting from an increase in lift thrust is to some extent cancelled by the increased weight of wire acting downwards on the craft. This effect can advantageously be used to create a more stable response to the height control, and it can be arranged that the vertical position of the aircraft itself to be substantially representative of the absolute value of the height control input.

Figures 13a - 13c demonstrate how the processor unit can control height and pitch of the aircraft in response to the position of the control element, and the height input control.

In Figures 13a and 13b the aircraft 1302 is set, by the height input control, at a height approximately level with the control element 1304. The processor unit is adapted to control the aircraft such that the pitch of the control element relative to the light path 1306 is equal and opposite to the pitch of the aircraft relative to the light path. In Figure 13a this results in steady hovering of the aircraft. In Figure 13b the pitch of the control element is varied resulting in a measured elevation angle1308. The processor unit controls the aircraft to pitch relative to the light path by an equal and opposite angle 1309. This results in the aircraft pitch corresponding to the control element pitch (this will cause the aircraft to approach the control element at a steady height).

In Figures 13c and 13d, the aircraft is set, by the height input control at a height above the level of the control element. It can be seen from Figure 13c that the action of the processor unit has the effect of subtracting the elevation angle of the aircraft 1310 from the pitch attitude of the aircraft relative to the light path. This results in the steady hovering of the aircraft at a height above the level of the control element. Figure 13d illustrates that the pitch angle of the aircraft can still be controlled at this height by varying the pitch angle of the control element, angles 1312 and 1313 being made substantially equal. Figure 14 illustrates how the aircraft can be controlled in response to changes in roll and yaw angle of the control element.

In one embodiment, as represented in Figure 14a, the processing unit controls the aircraft 1402 so as to maintain the yaw angle of the aircraft with respect to the light path 1406, whilst at the same time maintaining the pan angle of the aircraft at a 'twelve o'clock' position with respect to the control element 1404. This has the effect that the aircraft automatically faces away from the control element at the twelve o'clock position. In this way a yawing motion of the control element (as viewed from above in Figure 14a) results in substantially lateral motion of the aircraft along an arc.

Figure 14b shows a view of the aircraft 1402 and control element 1404 as seen from behind the control element, facing outwards, and with the aircraft at a height above the level of the control element for simplified viewing. The roll attitude of the aircraft 1402 can be controlled in a similar manner to the control of the pitch attitude described above. The processing unit controls the aircraft so as to maintain the alignment of the aircraft 1402 with respect to the control element 1404 about the roll axis. This has the effect that a variation of roll angle of the control element causes a corresponding variation of the roll angle of the aircraft. (It should be noted that this in turn causes lateral movement away from the twelve o'clock position reference above, and is therefore an alternative method of controlling lateral movement). The novel methods of control described here are advantageous in providing an intuitive and easy to use system for controlling an aircraft in flight. One of the key aspects of these methods is that the response of the aircraft is not to integrate the various control signals, as is commonly the case in most prior art methods of controlling aircraft (and other moving objects). Instead the aircraft 'mimics' to an extent the movements of the control element, and can therefore be maintained in a stable flight more easily, even by an inexperienced user.

The methods of determining the flight parameters provided in the table above represent one embodiment of an arrangement for controlling an aircraft relative to a hand held control element, using a combination of the control methods and apparatus described above. An alternative embodiment will now be described with reference to Figures 15 to 17.

Figure 15 is a schematic illustration of the main components of the embodiment. A control element 1502 and an aircraft 1504 are linked via wire means to a processor unit 1506. The control element and the aircraft each have an optical transducer arrangement 1508 and 1510, transducer arrangement 1510 on the aircraft comprising only an emitter arrangement, and transducer 1508 on the control element comprising only a sensor arrangement . Thus a light path 1512 between the aircraft and the control element is established with light travelling in only one direction (from the aircraft to the control element) as indicated schematically in the diagram.

Referring now to Figure 16, there is shown in greater detail transducer arrangement 1508 located on the control element. Transducer arrangement 1508 comprises a first sensor array 1610 capable of detecting the direction of an incident beam of light and a sensor array 1612 substantially identical to the arrangement 808 as described above and with reference to Figure 8.

Preferably sensor array 1610 comprises three photodiodes angled away from each other, and spaced at 120 degrees from each other. By comparing the intensity detected by the three sensors, a measure of the direction of incident light can be obtained. Preferably the directions of polarisation of the two filters in sensor array 1612 are at an angle of 60 degrees to one another.

Transducer arrangement 1510, located on the aircraft and shown in detail in Figure 17, comprises a an array of emitters 1702 substantially identical in arrangement to array 902 shown in Figure 9a and described above. In array 1702 however the individual emitters 1704, 1708 lying in the vertical plane (ie. angled upwards and downwards) have polarising filters mounted thereon, with the direction of polarisation lying in the vertical plane (ie. being substantially vertical when viewed normal to base of the array). The emitters in array 1702 are driven one at a time in sequence (1704, 1706,

1708, 1710) and then finally emitters 1704 and 1708 are driven together. This cycle is repeated. The emitters are typically pulsed at a first frequency, and the sequence can be controlled by drive electronics, and cycled at a second frequency. Preferably said first frequency is significantly higher than said second frequency. Signals produced by transducer arrangement 1508 can be multiplexed and passed to the processing unit, which is in communication with transducer 1510.

The flight parameters of the aircraft (attitude determined relative to the light path from the control element transducer to the aircraft transducer, and position determined relative to the control element) are derived as summarised in the following table:

of range of emitter array 1702 on the aircraft from an average measure of intensity of light detected from any of the emitters of the emitter array.

In determining the range of the aircraft from the controller, although any of the emitters of array 1702 can be used, it is advantageous to use a 'brightest light prevails' method. This is preferably achieved by basing the measurement of range on the average intensity reading from the emitter which is oriented to point most nearly towards the sensor array 1610. This method reduces the variation with angular sensitivity of range determination. This in turn is important for controlling the pitch of the aircraft both in flight and for take off. In determining the elevation and pan angles of the aircraft it is preferable to take readings based on polarised emitters 1704 and 1708, since this method provides greater discrimination against reflections, which might otherwise distort readings.

Figure 18 shows a control system block diagram for the embodiment described immediately above.

Since the same flight parameters can be derived in this alternative embodiment, the attitude and position of the aircraft can be controlled by changes in the attitude or position of the controller exactly as described above and with reference to Figures 13 and 14. This embodiment has the added advantage however, that only light emitting components are required on the aircraft, and all of the flight parameters are derived from information received at the control element. Thus only power and control signals need to be provided to the aircraft from the processing unit. Although in the two embodiments described the aircraft is tethered by wire means (1012 and 1512) further embodiments of the present invention could be used to control an aircraft wirelessly. The embodiment described above, in which only power and control signals need to be provided to the aircraft from the processing unit, would be of great benefit in an embodiment for controlling an aircraft wirelessly since remote communication is only required in one direction, from the processing unit to the aircraft. In a wireless embodiment, power could be provided to the aircraft by an on board battery. Many different types of aircraft could be used within the embodiments described above. In a preferred embodiment however, an aircraft having an airframe and a number of propellers arranged to provide substantially vertical thrust is used. An example of such an aircraft is illustrated in Figure 19. The airframe 1902 has mounted on it four motors 1904, each of which drives a propeller 1906 oriented generally vertically. Although such an aircraft may be inherently unstable, the feedback and control of the present invention are such that no separate stabilisation need be provided.

A large number of designs of control element are possible. Figures 20a and 20b show two possible examples. Figure 20a shows a 'console' style control element, while Figure 20b illustrates a 'pistol grip' type arrangement. Each control element includes a thumb wheel 2002 for height control, and an optical transducer 2004.

The present invention is described mostly with respect to control of an aircraft, however it is not limited to such an application. The methods and arrangements described will find application in a wide range of situations where it is desired to determine the position and attitude of an object in space, accurately and at a low cost.

In a still further embodiment of the invention the control element and the processing unit could be integrated into a single unit, to control the flight of the aircraft.

Claims

1. A method of controlling a powered craft in flight by a remote operator employing a freely movable and un-supported control element held in the hand or hands of the operator, wherein changes in attitude of the hand or hands of the operator and therefore of the held control element are caused to effect changes in the attitude or position of the remote craft.

2. A method according to Claim 1 , comprising the step of determining the angular orientation of the craft and of the control element with respect to a straight line extending between the craft and the control element.

3. A method according to Claim 1 or Claim 2, in which there is a monotonic relationship between the craft in at least one degree of freedom and the attitude of the control element.

4. A method according to any one of the preceding claims, wherein radiation extends between the control element and the craft, to enable determination of the angular orientation of the craft or of the control element with respect to a straight line extending between the craft and the control element.

5. A method according to Claim 4, wherein the radiation is provided by at least two emitters, the radiation from the respective emitters being capable of being discriminated.

6. A method according to Claim 5, wherein the polar distribution of radiation differs as between the emitters.

7. A method according to Claim 5 or Claim 6, wherein the respective emitters are each mutually inclined.

8. A method according to any one of Claims 5 to 7, wherein four emitters are provided.

9. A method according to any one of Claims 5 to 8, in which attitude with respect to said straight line of that of the craft or the control element which carries the emitters, is sensed through determination of a differential in radiation received from respective emitters at the other of the craft or control element.

10. A method according to any one of Claims 4 to 7, wherein the radiation is sensed by at least two receivers.

11. A method according to Claim 10, wherein the polar distribution of sensitivity differs as between the receivers.

12. A method according to Claim 10 or Claim 11 , wherein the receivers comprise a pair of receivers spaced apart in an X direction and a pair of receivers spaced apart in an orthogonal Y direction.

13. A method according to any one of Claims 10 to 12, in which attitude with respect to said straight line of that of the craft or the control element which carries the receivers, is sensed through determination of a differential in radiation received at respective receivers.

14. A method of controlling a powered craft in flight by a remote operator, wherein radiation extends between a control element and the craft to enable determination of the angular orientation of the craft and of the control element with respect to a straight line extending between the craft and the control element.

15. A method according to Claim 14, wherein radiation extends in one sense only between the control element and the craft.

16. A method according to Claim 14 or Claim 15, wherein the radiation is provided by at least two emitters, the radiation from the respective emitters being capable of being discriminated.

17. A method according to Claim 16, wherein the polar distribution of radiation differs as between the emitters.

18. A method according to Claim 16 or Claim 17, wherein the respective emitters are each mutually inclined.

19. A method according to any one of Claims 16 to 18, wherein four emitters are provided.

20. A method according to any one of Claims 16 to 19, in which attitude with respect to said straight line of that of the craft or the control element which carries the emitters, is sensed through determination of a differential in radiation received from respective emitters at the other of the craft or control element.

21. A method according to any one of Claims 14 to 20, wherein the radiation is sensed by at least two receivers.

22. A method according to Claim 21 , wherein the polar distribution of sensitivity differs as between the receivers.

23. A method according to Claim 21 or Claim 22, wherein the receivers comprise a pair of receivers spaced apart in an X direction and a pair of receivers spaced apart in an orthogonal Y direction.

24. A method according to any one of Claims 21 to 23, in which attitude with respect to said straight line of that of the craft or the control element which carries the receivers, is sensed through determination of a differential in radiation received at respective receivers.

25. A method for detecting the rotation about an object rotation axis of an object located at a direction from a remote location; comprising the step of establishing between the object and the remote location a beam of radiation that is plane polarised in the plane orthogonal to said direction and detecting said radiation with a polarisation sensitive detector.

26. A method according to Claim 25, wherein two polarisation sensitive detectors are provided to produce a differential detection signal which represents the degree of rotation of the object about the object rotation axis.

27. A method according to Claim 25 or Claim 26, wherein the angle of the beam polarisation or of the polarisation sensitivity of the detector, rotates about said direction to produce a detection signal the phase of which represents the degree of rotation of the object about the object rotation axis.

28. A method according to Claim 27, wherein the angle of the beam polarisation rotates about said direction and wherein a reference polarisation sensitive detector serves to produce a reference signal the phase of which is independent of the degree of rotation of the object about the object rotation axis

29. A method according to any one of Claims 25 to 28, in which the object rotation axis is orthogonal to said direction and wherein the polarisation sensitive detector is inclined with respect to the object rotation axis and with respect to said direction such as to produce a detection signal which represents the degree of rotation of the object about the object rotation axis.

30. A method according to Claim 29, wherein there are provided two polarisation sensitive detectors inclined at different angles with respect to the object rotation axis and with respect to said direction to produce a differential detection signal which represents the degree of rotation of the object about the object rotation axis.

31. A method according to any one of Claims 25 to 28, in which the object rotation axis is orthogonal to said direction and wherein a polarisation filter serving to produce said polarised beam is inclined with respect to the object rotation axis and with respect to said direction such as to produce a detection signal which represents the degree of rotation of the object about the object rotation axis.

32. A method according to Claim 31 , wherein there are provided two polarisation filters inclined at different angles with respect to the object rotation axis and with respect to said direction to produce a differential detection signal which represents the degree of rotation of the object about the object rotation axis.

33. A method according to any one of Claims 25 to 32, wherein the object is a flying craft.

34. A method of determining at a remote location the attitude of an object relative to a line of sight between said object and said remote location, said method comprising arranging an array of light emitters on the object, said emitters angled away from each other; arranging a light detector at said reference location; activating said array of light emitters in a sequence, and detecting the relative intensities of light from each emitter at said detector.

35. Remotely controlled flight apparatus comprising a powered flying craft; a control element; means establishing radiation extending between the control element and the craft; and means for determining with reference to said radiation the angular orientation of the craft or of the control element with respect to a straight line extending between the craft and the control element.

36. Apparatus according to Claim 35, wherein the radiation is provided by at least two emitters, the radiation from the respective emitters being capable of being discriminated.

37. Apparatus according to Claim 36, wherein the polar distribution of radiation differs as between the emitters.

38. Apparatus according to Claim 36 or Claim 37, wherein the respective emitters are each mutually inclined.

39. Apparatus according to any one of Claims 36 to 38, wherein four emitters are provided.

40. Apparatus according to any one of Claims 35 to 39, in which attitude with respect to said straight line of that of the craft or the control element which carries the emitters, is sensed through determination of a differential in radiation received from respective emitters at the other of the craft or control element.

41. Apparatus according to any one of Claims 35 to 40, wherein the radiation is sensed by at least two receivers.

42. Apparatus according to Claim 41 , wherein the polar distribution of sensitivity differs as between the receivers.

43. Apparatus according to Claim 41 or Claim 42, wherein the receivers comprise a pair of receivers spaced apart in an X direction and a pair of receivers spaced apart in an orthogonal Y direction.

44. Apparatus according to any one of Claims 41 to 43, in which attitude with respect to said straight line of that of the craft or the control element which carries the receivers, is sensed through determination of a differential in radiation received at respective receivers.

45. Apparatus according to any one of Claims 35 to 44, wherein radiation extends in one sense only between the control element and the craft.

46. Apparatus for detecting the rotation about an object rotation axis of an object located at a direction from a remote location; comprising means for establishing between the object and the remote location a beam of radiation that is plane polarised in the plane orthogonal to said direction and means for detecting said radiation with a polarisation sensitive detector.

47. Apparatus according to Claim 46, wherein two polarisation sensitive detectors are provided to produce a differential detection signal which represents the degree of rotation of the object about the object rotation axis.

48. Apparatus according to Claim 46 or Claim 47, wherein the angle of the beam polarisation or of the polarisation sensitivity of the detector, rotates about said direction to produce a detection signal the phase of which represents the degree of rotation of the object about the object rotation axis.

49. Apparatus according to Claim 48, wherein the angle of the beam polarisation rotates about said direction and wherein a reference polarisation sensitive detector serves to produce a reference signal the phase of which is independent of the degree of rotation of the object about the object rotation axis

50. Apparatus according to any one of Claims 46 to 49, in which the object rotation axis is orthogonal to said direction and wherein the polarisation sensitive detector is inclined with respect to the object rotation axis and with respect to said direction such as to produce a detection signal which represents the degree of rotation of the object about the object rotation axis.

51. Apparatus according to Claim 50, wherein there are provided two polarisation sensitive detectors inclined at different angles with respect to the object rotation axis and with respect to said direction to produce a differential detection signal which represents the degree of rotation of the object about the object rotation axis.

52. Apparatus according to any one of Claims 48 to 51 , in which the object rotation axis is orthogonal to said direction and wherein a polarisation filter serving to produce said polarised beam is inclined with respect to the object rotation axis and with respect to said direction such as to produce a detection signal which represents the degree of rotation of the object about the object rotation axis.

53. Apparatus according to Claim 52, wherein there are provided two polarisation filters inclined at different angles with respect to the object rotation axis and with respect to said direction to produce a differential detection signal which represents the degree of rotation of the object about the object rotation axis.

54. Apparatus according to any one of Claims 46 to 53, wherein the object is a flying craft.

5. Apparatus for determining at a remote location the attitude of an object relative to a line of sight between said object and said remote location, comprising an array of light emitters on the object, said emitters angled away from each other; a light detector at said reference location; means for activating said array of light emitters in a sequence, and means for detecting the relative intensities of light from each emitter at said detector.