Motion simulator

Abstract

A motion simulator 100 comprising a base 102 and a platform 104, the platform being arranged to move relative to the base with six degrees of freedom. The base comprises three wedge pairs 110a-c, each

Description

Technical Field The present invention relates to motion simulators, particularly though not exclusively to motion simulators for automotive, motorsport, and / or aerospace applications. Background Art A motion simulator may provide for six degrees of freedom, allowing an occupant to be subjected to a range of motions that provide a realistic sensation of being in the environment under simulation. For example, a motion platform may provide an occupant with an accurate sensation of being in a motor racing car, e.g. a Formula One™ car. The six degrees of freedom correspond to linear movements in the surge, sway, and heave directions (i.e. along the x-, y-, and z-axes respectively), and rotational motions in the roll, pitch, and yaw directions (i.e. about the x-, y-, and z-axes respectively). A Stewart platform or hexapod uses a platform connected to a base unit by six telescopic struts or actuators. Such apparatus may be very large and heavy. Due to the large range of movement provided by the struts, the apparatus may also be very tall. Furthermore, there typically needs to be a large volume of dead space under the platform. With this type of configuration, the struts must be relatively powerful and as such it is difficult to provide a high bandwidth for horizontal and vertical motion. This type of simulator may be useful for aircraft of the type in which high horizontal forces and accelerations do not need to be simulated, however it is not universally adequate since some real vehicles such as motor racing cars can be subject to very high forces in both the horizontal (when braking, accelerating, or cornering) and vertical (ride handling). The Williams platform (WO 2014 / 087172 Al) helps to alleviate some of the limitations of a Stewart platform but has several limitations itself. The Williams platform uses a rod with spherical bearings at each end to connect the gimbal to the outer carriage. While the intention of this design is to accurately control the position of the gimbal along the wedge, there are several issues that makes accurate control of the gimbal position difficult to maintain. Firstly, the spherical bearings are always in compression or tension on the same spot causing wear and backlash to appear over time. Secondly, compliance on the outer carriage mount and the gimbal arm connecting to the rod causes the gimbal to be mis-positioned along the wedge, this causes resonances to appear in the system in the range of operation and therefore degrades performance. Thirdly, the force required to balance the payload is not equal on the inner and outer carriages. This causes instability issues within the control of the platform. Fourthly, the nature of the wedge arrangement on both the left and right sides of the platform with a higher payload with a higher centre of gravity causes a moment that reacts along the path of the linear bearing in the roll orientation. These issues reduce the overall performance of the Williams platform, particularly at higher frequencies. Systems that utilise a wedge to vary the height of the platform have an issue in which the centre of moment is relatively high and is not positioned on the bearing itself. Additionally, while wedges are advantageous for stiffness (which those skilled in the art will appreciate is important for high frequency operation), positioning of the pivot carriage that runs up and down the wedges relies on a device that lacks the stiffness characteristic of a wedge (typically a rod with spherical ends) - for example this is seen with the Williams platform. This lack of accurate pivot carriage positioning can mean that the platform suffers from 'crosstalk', in particular unwanted pitch movement when performing a surge movement, leading to a rocking motion when the platform moves in the surge direction. The Williams platform also requires a large footprint, i.e. it takes up a large amount of physical space. However, as driving simulator motion technology has matured, it has become apparent that a smaller footprint would be more than adequate for motorsport and some automotive simulation scenarios. Other examples of systems, known in the art perse, such as the Ansible Motion system show multi staged systems in which generally one stage will do sway and surge motions, another stage does yaw motions, while yet another stage does heave, pitch, and roll motions. Another multi-stage or 'stacked' system, known in the art perse, has been produced by Dynisma. In EP3739558A1, surge, sway, and yaw motions are completed using a large metallic flat base while roll, pitch and heave motion is achieved using rods with spherical bearings (similar to the Williams design) attached to the base and payload. Unlike using a wedge to generate heave, rods are suspectable to bending and the rod ends are subject to wear over time and therefore have compliance, particularly with a heavier payload. WO 2020 / 249262 describes an arrangement in which a circular disc shaped component (which provides the surge, sway and yaw stage) also uses motors mounted on the moving stage for generating yaw, whilst ironless linear motors could be used in this configuration for improved performance and no cogging. These magnets are said to be heavy and so the bottom stage will have reduced performance due to the increase in moving mass. The Applicant has appreciated that it would be advantageous to provide a low cost, single-stage, high-performance, dynamic motion platform. The Applicant has further appreciated that it would also be advantageous for such a motion platform to be capable of unlimited yaw motion whilst allowing for a heavier payload. Summary of the Invention When viewed from a first aspect, embodiments of the present invention provide a motion simulator comprising a base and a platform, said platform being arranged to move relative to the base with six degrees of freedom, wherein: a) the base comprises first, second, and third wedge pairs, wherein each wedge pair is moveable in-plane with respect to the other wedge pairs, wherein each wedge pair respectively comprises: i) a first wedge and a second wedge that are slidably moveable with respect to one another in-plane along a sliding path, said first and second wedges each comprising a sloped surface, wherein the sloped surface of the first wedge slopes upward in one direction along the sliding path while the second wedge slopes upward in the opposite direction along the sliding path; and ii) a wedge carriage arrangement coupled to both the first and second wedges, said wedge carriage arrangement being mechanically constrained to slide up and down the sloped surfaces of the first and second wedges as said wedges move with respect to one another such that a vertical position of the wedge carriage arrangement is dependent on the positions of the first and second wedges relative to one another; and b) the platform comprises: i) first, second, and third platform rails angled with respect to one another; and ii) first, second, and third platform carriage arrangements respectively coupled to and slidably moveable along the first, second, and third platform rails; c) the motion simulator further comprises first, second, and third pivotal coupling members respectively providing a pivotal coupling between the corresponding first, second, and third wedge carriage arrangements and the corresponding first, second, and third platform carriage arrangements. The first aspect of the invention extends to a base for a motion simulator, the base being arranged to provide a platform of said motion simulator with six degrees of freedom, wherein the base comprises: a) first, second, and third wedge pairs, wherein each wedge pair is moveable in-plane with respect to the other wedge pairs, wherein each wedge pair respectively comprises: i) a first wedge and a second wedge that are slidably moveable with respect to one another in-plane along a sliding path, said first and second wedges each comprising a sloped surface, wherein the sloped surface of the first wedge slopes upward in one direction along the sliding path while the second wedge slopes upward in the opposite direction along the sliding path; and ii) a wedge carriage arrangement coupled to both the first and second wedges, said wedge carriage arrangement being mechanically constrained to slide up and down the sloped surfaces of the first and second wedges as said wedges move with respect to one another such that a vertical position of the wedge carriage arrangement is dependent on the positions of the first and second wedges relative to one another; and b) first, second, and third pivotal coupling members for providing a pivotal coupling between the corresponding first, second, and third wedge carriage arrangement and the platform. Thus it will be appreciated by those skilled in the art that embodiments of the present invention provide an improved motion simulator in which a 'double wedge' arrangement is utilised to vary the height of the platform relative to the base. The three wedge pairs can move in-plane (i.e. within a 'base plane') and the wedges of a given wedge pair can also move relative to one another. As the wedges are sloped and the wedge carriage arrangement is coupled to and mechanically constrained to move up and down the wedge's slope, the sliding of the wedges together or apart causes the wedge carriage arrangement (and thus the platform held by that wedge carriage arrangement) to 'ride up' or 'ride down'. Motion with six degrees of freedom can thus be achieved through appropriate combinations of moving the wedge pairs and varying the Inter-wedge distance for each wedge pair, giving rise to translational (surge, sway, and heave) and rotational (pitch, roll, and yaw) movements of the platform as appropriate. The wedges and / or wedge pairs may be able to move out-of-plane with respect to one another (in addition to being able to move in-plane with respect to one another). Alternatively, the wedges and / or wedge pairs may be constrained such that they may only move in-plane with respect to one another. It will be appreciated that the term 'wedge' as used herein means a support that tapers from a thicker end to a thinner end. Typically, a wedge generally has a substantially triangular cross-section. A wedge provides a mechanical advantage provided by the ratio of its length to its height, also referred to as the 'motion ratio' of the wedge. In a particular set of embodiments, each wedge has a flared profile such that a bottom of the wedge has a thickness greater than a thickness of a top of the wedge. This flared profile helps to ensure that an applied moment does not act to 'tip over' the platform. The flared profile may extend the thickness of the bottom of the wedge in the direction opposite to the direction of the other wedge in the respective wedge pair. The 4 opposing faces of the wedges in a wedge pair may be substantially flat in profile (i.e. present a substantially vertical face to one another), whereas the faces of the wedges that do not oppose one another may provide the flared profile outlined above. This 'double-wedge' based approach provided by embodiments of the present invention may overcome a number of the technical problems exhibited by other simulator designs, such as those discussed previously. The wedge pair construction where two wedges are linked by a wedge carriage arrangement may exhibit greater stiffness in the vertical direction than with other designs known in the art perse which, in turn, improves the performance of the motion simulator. A wedge carriage arrangement may, at least in some embodiments, comprise a single wedge carriage which is directly coupled to both the first and second wedges in the associated wedge pair. However, in some alternative embodiments (for example with reference to a set of the 'unlimited yaw' embodiments that utilise circular base rails), the wedge carriage arrangement may comprise a pair of wedge carriages where the coupling to the two wedges is indirect and achieved via an intervening platform rail, as explained later. Additionally, the wedge pair structure employed by embodiments of the present invention may provide for greater control over where the pivotal coupling member (which, as outlined later, may be a gimbal or similar) is on that wedge. Embodiments of the present invention may provide for less compliance in the position of the pivotal coupling member and a reduced moment compliance. Furthermore, by employing a pair of wedges, the load at a given support (i.e. wedge pair) is split across two support structures, rather than one - with this split typically being equal. Where each wedge is driven by a respective motor as per certain embodiments detailed later below, this also means that the effort required to carry out a particular move is split (typically evenly) across two motors, rather than unevenly across two motors. This means that the control strategy across all motors is much easier to tune compared to prior art where the force to generate motion is not evenly split across the motors in that corner. This may also allow for the use of motors that, for example, are lower cost, smaller, lighter, more efficient, and / or have a lower energy consumption. It will be appreciated that 'six degrees of freedom' means that that the platform can move In the three translational and three rotational directions. In other words, the platform is arranged to perform movements relative to the base, said movements comprising translational movements in first, second, and third orthogonal axes and rotational movements about said first, second, and third axes. The 'first' and 'second' axes may be the 'in-plane' or 'horizontal' axes, referred to as the x-axis and y-axis respectively. The 'third' axis may be the 'out-of-plane' or 'vertical' axis, i.e. the direction along which the The first, second, and / or third platform rails may extend in a first plane defined by the first and second axes, and may all be substantially co-planar. The in-plane movement of the wedge pairs (and the individual wedges of those pairs) may be within a second plane defined by the first and second axes, which may be parallel to the first plane. The sloping 'upward' and 'downward' of the wedge's sloping surfaces should therefore be understood to be the relative height of the relevant part of the wedge with respect to the third axis. Similarly, the vertical position of the platform (or parts thereof) should be understood to be the relative position of the platform (or parts thereof) with respect to the third axis. As outlined above, as the wedges of a given pair slide relative to one another, the wedge carriage arrangement is forced to move up or down both slopes of the two wedges, leading to that portion of the platform raising or lowering in height, respectively. There are different mechanisms by which the coupling and mechanical constraint of the wedge carriage arrangement could be achieved. However, in some embodiments, each wedge pair further comprises: i) a first wedge rail extending along the sloped surface of the first wedge such that the first wedge rail slopes upward in one direction along the sliding path; and ii) a second wedge rail extending along the sloped surface of the second wedge such that second wedge rail slopes upward in the opposite direction along the sliding path; iii) wherein each wedge carriage arrangement is coupled to the respective first and second wedge rails of the wedge pair and is mechanically constrained to slide up and down the first and second wedge rails as said wedges of the wedge pair move with respect to one another. In a set of such embodiments, each wedge carriage arrangement comprises first and second bearing arrangements to couple the wedge carriage arrangement to the first and second wedge rails respectively. Each bearing arrangement may comprise a bearing or a plurality of bearings, where multiple bearings may be used if necessary for heavier payloads. In some embodiments, each bearing arrangement is arranged such that the centre of moment is located in the centre of the respective bearing arrangement. It will be appreciated by those skilled in the art that the term 'pivotal coupling member' is understood to be any suitable form of mechanical coupling that allows the platform to rotate relative to the base. In some embodiments, the first, second, and / or third pivotal coupling members comprise a gimbal, a spherical ball joint, or a universal joint. In some embodiments, the platform rails are arranged such that: the first platform rail is located at a central front portion of the platform; the second platform rail is located at a rear-left portion of the platform; and the third platform rail is located at a rear-right portion of the platform. Typically the first, second, and third platform rails are each positioned on an underside of the platform. In some embodiments, an angle between the first platform rail and each of the second and third platform rails is approximately 120 degrees. In some potentially overlapping embodiments, an angle between the second and third platform rails is approximately 120 degrees. In some embodiments, the base comprises first, second, and third linear base rails, wherein the first wedge pair is coupled to and mechanically constrained to move along the first linear base rail, the second wedge pair is coupled to and mechanically constrained to move along the second linear base rail, and the third wedge pair is coupled to and mechanically constrained to move along the third linear base rail. In some such embodiments, the motion simulator may be arranged such that when the platform is in a predetermined position: i) the first base rail is perpendicular to the first platform rail; ii) the second base rail is perpendicular to the second platform rail; and iii) the third base rail is perpendicular to the third platform rail. It will be appreciated that typically, the 'predetermined position' may be a 'rest position' of the platform (i.e. its default position when no motion is being applied). As the platform moves, the angles between the platform rails and base rails may change. It will be appreciated, therefore, that in such embodiments, the base rails may be in a triangular formation. In some such embodiments, the first wedge pair is a 'front' wedge pair that moves along the first linear base rail, while the second and third wedge pairs are 'rear' wedge pairs that both move along the second and third linear base rails respectively. The Applicant has appreciated that this 'triangular' configuration is particularly advantageous for motorsport simulation, owing to its range of motion in all six degrees of freedom. Additionally, this triangular configuration may allow for more travel within a compact space and may help to maximise stiffness which is of particular importance for high performance simulation such as motorsport applications. The angles between adjacent base rails may be selected as appropriate, however in some embodiments, an angle between the first base rail and each of the second and third base rails is approximately 60 degrees. In some potentially overlapping embodiments, an angle between the second and third base rails is approximately 60 degrees. Thus, in accordance with such embodiments, the base rails meet in such a way that their internal boundary is an equilateral triangle. In a particular set of embodiments, the angles between the platform rails is approximately 120 degrees, the angles between the base rails is approximately 60 degrees, and each platform rail is perpendicular to the corresponding base rail to which it is coupled via the wedge pair and associated carriage arrangement(s). In such an arrangement, the platform matches the base so that when the wedge pairs (e.g. driven via motors) are moved synchronously to generate surge (which may be achieved via a pair of 'rear' wedge pairs and rear motors), they are perpendicular to the platform rails for greater authority. In some embodiments, the first linear base rail is longer than each of the second and third linear base rails. This may allow for a greater yaw range, e.g. by allowing the front of the platform to turn through a greater range of motion. In some potentially overlapping embodiments, the first linear base rail has a length between approximately 2m and 3m, optionally between approximately 2.25 m and 2.75 m, and further optionally approximately 2.5 m. In some embodiments, the first linear base rail has a length of 2.5 m. In some potentially overlapping embodiments, the second and third base rails are approximately the same length, preferably wherein the second and third base rails are the same length. In some potentially overlapping embodiments, the second and / or third linear base rail has a length between approximately lm and 2m, optionally between approximately 1.4 m and 1.8 m, and further optionally approximately 1.6 m. In some embodiments, the second and / or third linear base rail has a length of 1.6 m. Other layouts of the base rails beyond the triangular layout set out above in respect of certain embodiments may be used. The Applicant has appreciated that other configurations are possible and may be advantageous for particular applications of the motion simulator. For example, in some alternative embodiments, the base comprises first and second linear base rails arranged such that: i) the first linear base rail is parallel to the second linear base rail; wherein the first wedge pair is coupled to and mechanically constrained to move along the first linear base rail, and the second and third wedge pairs are coupled to and mechanically constrained to move along the second linear base rail. It will be appreciated that, in such embodiments, the base has two parallel rails. The Applicant has appreciated that the 'parallel rails' configuration may be well-suited to non-motorsport automotive applications, where there is an unequal interest in the simulation of all degrees of motion, with a greater emphasis on the ability to simulate lateral or longitudinal cues at 1:1 scale, e.g. by allowing the motion simulator to simulate the accelerations experienced during a lane change or braking manoeuvres. In some such embodiments, the first wedge pair is a 'front' wedge pair that moves along the first linear base rail, while the second and third wedge pairs are 'rear' wedge pairs that both move along the second linear base rail. The Applicant has also appreciated that, for certain applications, it may be beneficial to have an 'unlimited yaw' system in which the platform can fully rotate, potentially continually. Thus, in some further alternative embodiments, the base comprises inner and outer circular base rails arranged such that: i) the inner and outer base rails are concentric and parallel to one another; wherein the first wedge of each wedge pair is coupled to and mechanically constrained to move along the outer base rail, and the second wedge of each wedge pair is coupled to and mechanically constrained to move along the inner base rail. Such an arrangement may advantageously not need to 'return to zero', i.e. it does not necessarily need to return to a 'default' or 'rest' position after a yaw movement is carried out, which may allow a 1:1 yaw cue to be imparted on the driver's vestibular and may simplify the controls and avoid needing to perform additional motions of the platform (commonly referred to as 'washout') which do not correspond to the simulated environment. Additionally, Returning the motion platform to centre can cue an incorrect sensation for the occupant. Conventionally in a platform that is yaw limited, the motion algorithm either has to scale the yaw cue or apply a 'washout' (continuous return the centre) to the platform. This is undesirable as the human vestibular is very sensitive to these cues. In a set of such embodiments, the wedge carriage arrangement of each wedge pair comprises a first wedge carriage and a second wedge carriage, arranged such that: the first wedge carriage is mechanically constrained to slide up and down the sloped surface of the first wedge as the first and second wedges move with respect to one another; the second wedge carriage is mechanically constrained to slide up and down the sloped surface of the second wedge as the first and second wedges move with respect to one another; and the first and second wedge carriages are mechanically coupled to one another via the respective platform carriage arrangement. The wedge pairs, and the wedges within those pairs, may be caused to move by any suitable means, and may be controlled via some means external to the motion simulator. In some embodiments, the motion simulator further comprises a controller configured to cause the wedge pairs and / or the wedges to move relative to one another. This controller may be a discrete hardware and / or software unit, or may be embodied within a computer or computer system. In a set of such embodiments, the controller is configured to generate a control signal for each wedge dependent on a planned motion input received by said controller. For example, simulation software may be used in conjunction with the motion simulator to provide a user on or in the platform to experience the simulated environment and perceive motions accordingly via the user's senses (e.g. visual and vestibular). The simulation software may generate motion inputs which are supplied to the controller, and the controller generates control signals for actuating the relevant wedge(s) so as to give rise to the desired motion of the platform. There are different means by which actuation of the wedges may be achieved, however typically the wedges may be motorised. In some embodiments, each wedge is coupled to a respective motor arranged to move said wedge in-plane, optionally wherein one or more of said motors comprises a linear motor, further optionally wherein each of said motors comprises a linear motor. Where circular base rails are provided, one or more of the linear motors may comprise a radial linear motor. Such linear motors may, in some such embodiments, comprise magnet-free linear motors, for example magnet-free track linear motors. The Applicant has appreciated that magnet-free linear motors are typically cheaper than ironless linear motors, providing a reduction in material costs of the platform for a trade-off in peak force output. While magnet free linear motors may have a lower peak force output than some other types of motors, the Applicant has appreciated such motors may nevertheless be sufficient for moving the platform (where the payload may be limited through advantageous choice of materials) for motorsport applications where accelerations may be approximately 10 ms2. The dual wedge mechanism provided in accordance with present invention advantageously allows multiple motors to contribute to sway and surge movements, and in certain embodiments all the motors may contribute to sway movements and all the rear motors may contribute to surge movements, meaning that the peak torque available at each corner is double that of a single motor. However, high specification motors could be used if higher accelerations are needed for a particular application. In other embodiments, the linear motors may comprise ironless linear motors (e.g. ironless linear motors or ironless radial linear motors). A combination of different types of motors may be used, if appropriate. The Applicant has appreciated that embodiments of the present invention may advantageously provide flexibility in the power supply the motion simulator requires. As the force may be supplied equally by two motors for each corner (i.e. one motor per wedge, in each wedge pair), the peak power requirements for a given motor are lower than in prior art arrangements in which all of the force in a given corner must be supplied by a single motor. The Applicant has appreciated that a motion simulator in accordance with certain embodiments of the present invention may be run using a single-phase electricity supply, rather than requiring three-phase power. This is highly advantageous because it enables the motion simulator to be installed in a wider variety of locations where three-phase power is not readily available. However, in some embodiments three-phase power may be used, e.g. where high power motors are required - for example a 40 A three-phase supply may be used. In a particular set of embodiments, the motion simulator is operable in a first power mode in which it receives a single-phase power supply, and is further operable in a second power mode in which it receives a three-phase power supply. In other words, a given motion simulator may be able to use either single-phase or three-phase power, as appropriate for a given installation. In some potentially overlapping embodiments, the motion simulator may comprise a capacitor arrangement configured to provide additional power during an excess load condition. Such a capacitor arrangement (which may be a single capacitor or multiple capacitors) may cover bursts of peak acceleration, which may be typical in motorsport simulation. This may be particularly advantageous when using a single-phase power supply, however this may also be advantageous even with the use of three-phase power. The gradient of the wedges provides for a trade-off between the amount of effort required to hold the static mass of the platform against the amount of vertical movement that the wedge can provide. In some embodiments, one or more of the wedges have a gradient of between approximately 1:2 and 7:2, preferably between approximately 1:1 and 3:1, more preferably approximately 2:1. In a particular set of embodiments, one or more of the wedges has a gradient of 2:1. It will be appreciated that these gradients are supplied in the accepted form used in the art where the first number of the ratio is the length and the second number of the ratio is the height, e.g. a ratio of 2:1 means that the slope extends 1 mm in height for every 2 mm extension in length. Equivalently, the gradient of the slope is also referred to as the 'motion ratio'. In some embodiments, both wedges of a given wedge pair have the same gradient. In a particular set of such embodiments, all the wedges have the same gradient. The wedges may, in some embodiments, have a constant gradient (i.e. the wedge angle is constant). As a wedge of a constant angle is used to generate vertical movement throughout the vertical range there is no change in motion ratio and therefore the vertical motion is always consistent. It will be appreciated that the wedge angle is typically equal to the inverse tangent of the length of the wedge divided by its height (i.e. the inverse of the motion ratio). With a motion ratio or gradient of 2:1, the wedge angle is given by tan-1(0.5) which is approximately 26.5°. A passive device may be used in some embodiments to help support the static mass of the platform. An example of such a passive device is a gas strut. However, in some embodiments, a bungee is provided on one or more of the wedges, said bungee comprising a resilient cord and a pulley arrangement, wherein one end of the cord is affixed to an fixed point on the wedge and the other end of the cord is affixed to the wedge carriage arrangement, and wherein the cord passes over the pulley arrangement. The pulley arrangement may, in some such embodiments, be positioned on a side wall of the wedge. The fixed point may be positioned on a side wall of the wedge, which may be the same side wall onto which the pulley arrangement is positioned. The pulley arrangement provides a path for the cord that enables the cord to be extended to a desired length, which enables the cord to be pre-tensioned. The Applicant has appreciated a particularly advantageous arrangement in which the bungee provides a passive device used to assist the motors such that the static mass of the platform and payload is significantly reduced. This is achieved by using a series of pulleys arranged to allow the bungee cord to extend while remaining in the cord's 'elongation rating', which reduces wear and damage to the bungee. Such a bungee arrangement may provide lower cost, reduced maintenance requirements, and / or enhanced energy savings when compared to other passive devices or having no such passive device. The cord may, in some such embodiments, be pre-tensioned at a predetermined position of the wedge carriage arrangement. The cord may, in a particular set of such embodiments, be pre-tensioned at a maximum heave position of the wedge carriage arrangement. This cord may be pre-tensioned at a multiple of its unstretched length where that multiple is selected to be less than the multiple required to break the cord. For example, with a cord where a break would be expected at 3 times its unstretched length, such a cord may be pre-tensioned at approximately twice its unstretched length, potentially up to approximately 2.5 times that unstretched length. The number and configuration of the pulleys may be selected so as to run the cord for the desired length along a particular path, making use of the space available. In a particular set of such embodiments, the bungee may comprise a plurality of cords, optionally wherein the bungee comprises two cords. The use of multiple cords may be advantageous with heavier payloads to hold the static mass. The bungee may be configured such that the spring rate is within a range that minimises the effort required by the motors to hold a position from the 'rest' position. The Applicant has found that, for example, an exemplary bungee may provide an assistive force of ±23% - for example, if holding the static mass for on a single wedge required 300 N of force, at maximum heave this bungee would give a 231 N force 'assist' (69 N below what is required to hold the static mass) and at minimum heave it would give 369 N force 'assist' (69 N above what is required to hold the static mass). In such an example, with a wedge angle of 26.5°, the motor for that wedge would need to have at least cos(26.5°)*69 N (approximately equal to 61.75 N) effort to hold the static mass at either end of the max / min height. Different bungees may provide a different assistive force, which may be at least ±10%, optionally at least ±15%, further optionally at least ±20%, potentially between ±20% and ±30%, for example between ±20% and ±25%, such as ±23%. Similarly, different wedge angles will impact the effort required. The Applicant has appreciated that the combination of a bungee arrangement and a 2:1 motion ratio (that is 1 mm of vertical motion for each 2 mm of horizontal motion) may allow the static mass of the platform to be held with little to no effort required at the motors. This allows for less electrical energy to be required and therefore lower powered (and cheaper) motors can be used. In some embodiments, one or more of the wedges comprises aluminium or a composite material. In particular, one or more of the wedges may comprise one or more of: carbon fibre, aluminium, and honeycomb / foam. These materials, or a combination of these materials, may be selected to form an extremely stiff lightweight component. In some potentially overlapping embodiments, the wedge may comprise aluminium, titanium and / or magnesium. Typically an advantageous material choice is one that is both light (to keep the moving mass down) and stiff (to improve the performance). In some embodiments, the or each wedge carriage arrangement comprises steel. In some embodiments, the or each platform carriage arrangement comprises aluminium or a composite material. In particular, one or more of the platform carriage arrangements may comprise one or more of: carbon fibre, aluminium, titanium, and honeycomb / foam. Again, an advantageous material choice is one that is both light (to keep the moving mass down) and stiff (to improve the performance). When viewed from a second aspect, embodiments of the present invention provide a motion simulator comprising a base and a platform, said platform being arranged to move relative to the base with six degrees of freedom, wherein the platform is pivotally coupled to the base via three wedge pairs, each wedge pair being arranged to move in-plane with respect to one another, wherein respective first and second wedges of each wedge pair can slide relative to one another to vary an out-of-plane height of at least a portion of the platform relative to the base. This second aspect of the invention extends to a base for a motion simulator, the base being arranged to provide a platform of said motion simulator with six degrees of freedom, wherein the base comprises three wedge pairs each comprising a pivotal coupling arrangement for pivotally coupling the respective wedge pair to the platform, each wedge pair being arranged to move in-plane with respect to one another, wherein respective first and second wedges of each wedge pair can slide relative to one another to vary an out-of-plane height of at least a portion of the platform relative to the base. Optional features set out in respect of certain embodiments of the first aspect of the invention are also applicable to the second aspect of the invention. In the context of this specification "comprising" is to be interpreted as "including". Approximately as employed herein is defined as ± 10%. Aspects of the invention comprising certain elements are also intended to extend to alternative embodiments "consisting" or "consisting essentially" of the relevant elements. Where technically appropriate, embodiments of the invention may be combined. Embodiments are described herein as comprising certain features / elements. The disclosure also extends to separate embodiments consisting or consisting essentially of said features / elements. Technical references such as patents and applications are incorporated herein by reference. Any embodiments specifically and explicitly recited herein may form the basis of a disclaimer either alone or in combination with one or more further embodiments. Brief Description of the Drawings Certain embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figs. 1A to ID shows a motion simulator in accordance with an embodiment of the present invention; Fig. 2 shows the base and platform rails of the motion simulator of Figs. 1A to ID in more detail; Fig. 3 shows a simplified model of the motion simulator of Figs. 1A to ID; Fig. 4 shows a motion simulator in accordance with a further embodiment of the present invention; Fig. 5 shows the base and platform rails of the motion simulator of Fig. 4 in more detail; Figs. 6A to 6E show a motion simulator in accordance with a yet further embodiment of the present invention; Figs. 7A to 7C shows a simplified model illustrating the relative sliding motion of two wedges within a wedge pair as used by embodiments of the invention; Fig. 8 shows a simplified model illustrating the rest position of a motion simulator in accordance with an embodiment of the present invention; Figs. 9A to 9K show simplified models illustrating yaw, sway, surge, heave, roll, and pitch motion of the simulator of Fig. 8; Figs. 10A to 10L show simplified models illustrating yaw, sway, surge, heave, roll, and pitch motion of the simulator of Figs. 1A to ID, 2, and 3; and Figs. 11A to 11C show simplified models of a bungee arrangement used by some embodiments of the invention. Detailed Description Figs. 1A to ID show a motion simulator 100 in accordance with an embodiment of the present invention, where Fig. 1A shows a perspective view, Fig. IB shows a front view, Fig. IC shows a top view, and Fig. ID shows a side view. Note that not all elements are labelled with reference numerals in all of Figs. 1A through ID for ease of illustration, as some elements are less visible in certain views, thus Figs. 1A through ID should be viewed collectively. Furthermore, Fig. 2 shows the base and platform rails of the motion simulator of Figs. 1A to ID in more detail. A simplified model of the motion simulator 100 can be seen in Fig. 3. The following description of the motion simulator 100 can be understood by reference to Figs. lAto ID, 2, and 3 together. The motion simulator 100 includes a base 102 and a platform 104, where the platform 104 is arranged to move relative to the base 102 with six degrees of freedom. The platform 104 carries a cockpit 106 shaped like the cockpit of a motorsport vehicle, where a user 108 can sit during operation of the motion simulator 100. The base 102 is constructed from three linear base rails 103a-c arranged in a triangular formation. In this case, the base rails 103a-c form an equilateral triangle, with the inner angles between adjacent base rails 103a-c each being 60°, as illustrated in Fig. 3. This 'triangular' configuration is particularly advantageous for motorsport simulation, owing to its range of motion in all six degrees of freedom. The triangular configuration may allow for more travel within a compact space and may help to maximise stiffness which is of particular importance for motorsport applications. The front 'first' base rail 103a is longer than the two rear 'second' and 'third' base rails 103b, 103c. This is to allow for a wider range of yaw motion. The base 102 includes three wedge pairs llOa-c, each wedge pair llOa-c being moveable in-plane with respect to the other wedge pairs llOa-c. The first wedge pair 110a is a 'front' wedge pair that moves along the first linear base rail. The second wedge pair 110b is a 'rear left' wedge pair that moves along the second linear base rail. In Fig. 1A, the second wedge pair 110b is obscured by the platform 104, however its position is indicated via the dashed lead line shown connected to the reference numeral '110b' in Fig. 1A. Each wedge pair llOa-c respectively comprises a first wedge Illa, 111b, 111c and a second wedge 112a, 112b, 112c that are slidably moveable with respect to one another in-plane along a sliding path. These wedges llla-c, 112a-c each comprise a sloped surface, but are 'opposites' or 'mirrors' of one another such that the sloped surface of the first wedge llla-c slopes upward in one direction along the sliding path while the second wedge 112a-c slopes upward in the opposite direction along the sliding path, as can be seen more readily in the cut-away view of Fig. 2. Each of these sloped surfaces carries a respective wedge rail 115, as explained below. The gradients of the wedges may be selected as appropriate, trading off the maximum height (for steeper gradients) against a reduction in effort required to move the static mass of the platform (for shallower gradients). In this case, the wedges llla-c, 112a-c each have a gradient (or 'motion ratio') of 2:1, i.e. they provide for 1 mm of vertical motion for every 2 mm of horizontal motion. The wedges llla-c, 112a-c are flared such that a bottom of the wedge has a thickness greater than a thickness of a top of the wedge. This flared profile helps to ensure that an applied moment does not act to 'tip over' the platform. The flared profile may extend the thickness of the bottom of the wedge in the direction opposite to the direction of the other wedge in the respective wedge pair. The opposing faces of the wedges in a wedge pair may be substantially flat in profile (i.e. present a substantially vertical face to one another), whereas the faces of the wedges that do not oppose one another may provide the flared profile outlined above. The wedge carriage 114a-c within each wedge pair llOa-c is coupled to both the first and second wedges llla-c, 112a-c within that wedge pair llOa-c. This wedge carriage 114a-c is mechanically constrained to slide up and down the wedge rails 115 of the first and second wedges llla-c, 112a-c as the wedges llla-c, 112a-c within that wedge pair llOa-c move with respect to one another. As a result, the vertical position of the wedge carriage 114a-c varies based on the relative positions of the first and second wedges llla-c, 112a-c in the corresponding wedge pair llOa-c. As can be seen in Figs. 2 and 3, the platform 104 comprises first, second, and third platform rails 113a-c angled with respect to one another. In this embodiment, these platform rails 113a-c are co-planar, nonparallel, and have an angle between adjacent platform rails of 120°, as shown in Fig. 3. A respective platform carriage 116a-c is coupled to and slidably moveable along each of the platform rails 113a-c. A respective gimbal 119 is provided as a coupling between the wedge carriage 114a-c and the corresponding platform carriage 116a-c for each wedge pair llOa-c (i.e. these gimbals 119 each act as a pivotal coupling member). The motion of the wedge pairs and wedges within the wedge pairs is effected via motors, with one motor assigned to each wedge. While there are different types of motor that can be employed, a particularly advantageous choice of motor is a magnet-free track linear motor or an ironless linear motor. The specific operation of the motion simulator 100, together with other motion simulators in accordance with embodiments of the present invention, will be described later. Fig. 4 shows a motion simulator 200 in accordance with a further embodiment of the present invention. Fig. 5 shows the base and platform rails of the motion simulator of Fig. 4 in more detail. Elements having reference numerals starting '2' in Figs. 4 and 5 are alike in form and function with those elements having reference numerals starting with '1' in Figs. 1A to ID, 1, and 3, unless technical context dictates otherwise. Similarly to the previous embodiment, in this embodiment the motion simulator 200 includes a base 202 and a platform 204, where the platform 204 carries a cockpit (or cabin) 206 for a user (not shown) to sit in. The base 202 is provided with three wedge pairs 210a-c which are again each constructed from a pair of wedges having opposite slopes, joined to one another via a wedge carriage that slides up and down wedge rails on those wedges' sloped surfaces dependent on the inter-wedge distance for that wedge pair. However, unlike the previous embodiment, the base 202 of this motion simulator 200 only has two linear base rails 203a, 203b, rather than three. Instead of the triangular configuration shown before, in this embodiment the base rails 203a, 203b are arranged as two parallel lines. The 'first' base rail 203a acts as the 'front' base rail and is arranged such that the first 'front' wedge pair 210a moves along the first base rail 203a. The 'rear' wedge pairs (i.e. the 'second' and 'third' wedge pairs 210b, 210c) are both arranged to move along the same base rail - the second 'rear' base rail 203b. In Figs. 4 and 5, the second wedge pair 110b is obscured by the platform 204, however its position is indicated via the dashed lead line shown connected to the reference numeral '210b' in Figs. 4 and 5. This 'parallel lines' configuration may be well-suited to non-motorsport automotive applications, where there is an unequal interest in the simulation of all degrees of motion, with a greater emphasis on the ability to simulate lane change or longitudinal (braking and accelerating) cueing. Figs. 6A to 6E shows a motion simulator in accordance with a yet further embodiment of the present invention. Elements having reference numerals starting '3' in Figs. 6Ato 6E are alike in form and function with those elements having reference numerals starting with '1' in Figs. lAto ID, 2, and 3 and / or with those elements having reference numerals starting with '2' in Figs. 4 and 5, unless technical context dictates otherwise. In this embodiment, the motion simulator 300 is arranged such the base 302 comprises an outer circular base rail 303a and an inner circular base rail 303b. These outer and inner base rails 303a, 303b are concentric and parallel to one another. The first wedge 311a-c of each wedge pair 310a-c is coupled to and mechanically constrained to move along the outer base rail 303a. The second wedge 312a-c of each wedge pair 310a-c is coupled to and mechanically constrained to move along the inner base rail 303b. As can be seen in Figs. 6B and 6C, in order to enable the wedges 311a-c, 312a-c within a given wedge pair 310a-c to move along their respective curved sliding paths, the wedge and platform carriage arrangements are different to those set out previously in respect of the embodiments that utilise straight line sliding paths. Specifically, in this embodiments, the first wedge carriage 314a-c is mechanically constrained to slide up and down the sloped surface of the first wedge 311a-c as the first 311a-c and second 312a-c wedges move with respect to one another. A second wedge carriage 317a-c is mechanically constrained to slide up and down the sloped surface of the second wedge 312a-c as the first 311a-c and second 312a-c wedges move with respect to one another. These first 314a-c and second 317a-c wedge carriages are mechanically coupled to one another via the respective platform carriage arrangement 316a-c, which is constructed from a pair of platform carriages each coupled to a respective one of the wedge carriages 314a-c, 317a-c via a gimbal 319 which acts as a pivotal coupling member (note that another type of pivotal coupling member such as a universal connector, universal joint, etc. could be used instead of a gimbal). It will be appreciated, therefore, that in this embodiment six wedge carriages and six platform carriages are connected via six pivotal coupling members, allowing for the wedges in each wedge pair to move along their respective curved sliding paths, accounting for the variable difference in radius between the respective paths followed by the first and second wedges. This embodiment provides an 'unlimited yaw' system in which the platform 304 can fully rotate, potentially continually as the wedge pairs 310a-c can continue around the circular base rails 303a, 303b as many times as needed, in either direction. With this 'circular' configuration, the platform 304 does not need to 'return to zero', i.e. it does not necessarily need to return to a 'default' or 'rest' position after a yaw movement is carried out. This simplifies the controls and avoids needing to perform additional motions of the platform 304 which do not correspond to the simulated environment. Figs. 6D and 6E respectively show the motion simulator 300 in its maximum and minimum heave positions, which will be explained later with reference to Figs. 7A to 7C, 8, and 9A to 9K. Figs. 7A-C shows a simplified model illustrating the relative sliding motion of two wedges within a wedge pair llOa-c, 210a-c, 310a-c as used by embodiments of the invention, including those embodiments described above. Depending on the position of the first wedge llla-c, 211a-c, 311a-c and the second wedge 112a-c, 212a-c, 312a-c relative to one another, the vertical position of the wedge carriage 114a-c, 214a-c, 314a-c is varied. This is because the wedge carriage 114a-c, 214a-c, 314a-c is coupled to and mechanically constrained to move along the wedge rails 115, 215, 315. As can be seen from the perspective shown in Fig. 7A, if the first wedge llla-c, 211a-c, 311a-c moves all the way to the left along the sliding path (i.e. along the direction the wedges can slide relative to one another) and if the second wedge 112a-c, 212a-c, 312a-c moves all the way to the right along the sliding path, the wedge carriage 114a-c, 214a-c, 314a-c is forced upwards. This is because the wedge carriage 114a-c, 214a-c, 314a-c is constrained by its connections to the wedge rails 115, 215, 315. Since the distance from one side to the other of the wedge carriage 114a-c, 214a-c, 314a-c is fixed, the wedge carriage 114a-c, 214a-c, 314a-c slides up the wedge rails 115, 215, 315 on its bearings. This is the maximum vertical position for the wedge carriage 114a-c, 214a-c, 314a-c. Fig. 7B shows the situation where the wedge carriage 114a-c, 214a-c, 314a-c is at the vertical mid-point, i.e. where the first wedge llla-c, 211a-c, 311a-c and the second wedge 112a-c, 212a-c, 312a-c are positioned in the middle of the sliding path. In this scenario, the wedge carriage 114a-c, 214a-c, 314a-c sits halfway up the wedge rails 115, 215, 315. Fig. 7C shows the other extreme, where the wedge carriage 114a-c, 214a-c, 314a-c is at its vertical minimum. As can be seen from the perspective shown in Fig. 7C, if the first wedge llla-c, 211a-c, 311a-c moves all the way to the right along the sliding path (i.e. along the direction the wedges can slide relative to one another) and if the second wedge 112a-c, 212a-c, 312a-c moves all the way to the left along the sliding path, the wedge carriage 114a-c, 214a-c, 314a-c is forced downwards because the wedge carriage 114a-c, 214a-c, 314a-c is constrained by its connections to the wedge rails 115, 215, 315. Since the distance from one side to the other of the wedge carriage 114a-c, 214a-c, 314a-c is fixed, the wedge carriage 114a-c, 214a-c, 314a-c slides down the wedge rails 115, 215, 315 on its bearings. This is the minimum vertical position for the wedge carriage 114a-c, 214a-c, 314a-c. It will readily be appreciated that other vertical positions of the wedge carriage 114a-c, 214a-c, 314a-c between the extremes can be achieved by positioning the first wedge llla-c, 211a-c, 311a-c and the second wedge 112a-c, 212a-c, 312a-c at a suitable relative distance along the sliding path with respect to one another. Fig. 8 shows a simplified model illustrating the rest position of a motion simulator in accordance with an embodiment of the present invention. For ease of illustration, the model is a simplified illustration of the 'circular' embodiment of the motion simulator 300 described previously with reference to Figs. 6A to 6E, however it will be readily appreciated that the same principles outlined here in respect of Fig. 8 and Figs. 9A to 9K are equally applicable to the other embodiments, with the wedges moving along the base rails in the triangular or parallel lines configurations (or any other suitable configuration) in substantially the same way. Fig. 8 shows the motion simulator 300 at its default or 'rest' position. In this state, all the wedge pairs 310a-c are equally spaced apart from one another, with the wedges 311a-c, 312a-c within those pairs sat at their midpoints. With this geometry, the wedges 311a-c, 312a-c are perpendicular to the respective platform rails 313a-c, and the wedge pairs 310a-c are angled at 120° relative to one another (the same angle as between the platform rails 313a-c). The platform (not shown) is therefore at the midpoint with respect to all six degrees of motion. Figs. 9A to 9K show simplified models illustrating yaw, sway, surge, heave, roll, and pitch motion of the simulator of Fig. 8. Fig. 9A shows yaw motion, in which all three wedge pairs 310a-c move clockwise or counter-clockwise around the base rails 303a, 303b. This causes the platform to rotate about the vertical axis, i.e. to yaw in the clockwise or counter-clockwise direction as appropriate. Figs. 9B and 9C respectively show right sway and left sway motion. To achieve right sway motion as shown in Fig. 9B, the front wedge pair 310a and rear left wedge pair 310c move toward one another, which pulls the platform 304 to the right such that the wedge and platform carriages in the rear right corner (from the perspective of looking at the front of the motion simulator 300) reach the extreme outer end of the travel afforded by the rear right platform rail 313b. Conversely, to achieve left sway motion as shown in Fig. 9C, the front wedge pair 310a and rear right wedge pair 310b move toward one another, which pulls the platform 304 to the left such that the wedge and platform carriages in the rear left corner (from the perspective of looking at the front of the motion simulator 300) reach the extreme outer end of the travel afforded by the rear left platform rail 313c. Figs. 9D and 9E respectively show forward surge and rearward surge motion. To achieve forward surge motion as shown in Fig. 9D, the rear right and rear left wedge pairs 310b, 310c move in equal amounts toward the front wedge pair 310a which remains at the default central position, which pulls the platform 304 forwards such that the wedge and platform carriages at the front (from the perspective of looking at the front of the motion simulator 300) reach the extreme inner end of the travel afforded by the front platform rail 313a. Conversely, to achieve rearward surge motion as shown in Fig. 9E, the rear right and rear left wedge pairs 310b, 310c move in equal amounts away from the front wedge pair 310a which remains at the default central position, which pulls the platform 304 rearwards such that the wedge and platform carriages at the front (from the perspective of looking at the front of the motion simulator 300) reach the extreme outer end of the travel afforded by the front platform rail 313a. Figs. 9F and 9G respectively show max heave and minimum heave motion. To achieve maximum heave motion as shown in Fig. 9F, the wedges within each of wedge pair slide relative to one another in the manner described previously with reference to Fig. 7A, which pushes the platform 304 upwards in all three corners. An example of the motion simulator 300 in the maximum heave position can be seen in Fig. 6D. Conversely, to achieve minimum heave motion as shown in Fig. 9G, the wedges within each of wedge pair slide relative to one another in the manner described previously with reference to Fig. 7C, which pushes the platform 304 downwards in all three corners. An example of the motion simulator 300 in the maximum heave position can be seen in Fig. 6E. Figs. 9H and 91 respectively show right and left roll motion. To achieve right roll motion as shown in Fig. 9H, the wedges in the front wedge pair 310a remain in the central position as shown in Fig. 7B. The wedges in the rear right wedge pair 310b slide toward one another into the position shown in Fig. 7A to raise the platform 304 in that corner. The wedges in the rear left wedge pair 310c slide apart from one another into the position shown in Fig. 7C to lower the platform 304 in that corner. This causes the platform 304 to roll toward the right (from the perspective of a user sat in the cockpit 306). Conversely, to achieve left roll motion as shown in Fig. 91, the wedges in the front wedge pair 310a remain in the central position as shown in Fig. 7B. The wedges in the rear left wedge pair 310c slide toward one another into the position shown in Fig. 7A to raise the platform 304 in that corner. The wedges in the rear right wedge pair 310b slide apart from one another into the position shown in Fig. 7C to lower the platform 304 in that corner. This causes the platform 304 to roll toward the left (from the perspective of a user sat in the cockpit 306). Figs. 9J and 9K respectively show downward and upward pitch motion. To achieve downward pitch motion as shown in Fig. 9J, the wedges in the front wedge pair 310a move apart from one another to the position shown in Fig. 7C, which lowers the front of the platform 304. The wedges in the rear right and left wedge pairs 310b, 310c slide toward one another into the position shown in Fig. 7A to raise the rear of the platform 304. This causes the platform 304 to pitch downwards, thus lowering the 'nose' of the cockpit 306 and raising the 'tail' of the cockpit 306. Conversely, to achieve upward pitch motion as shown in Fig. 9K, the wedges in the front wedge pair 310a move toward one another to the position shown in Fig. 7A, which raises the front of the platform 304. The wedges in the rear right and left wedge pairs 310b, 310c slide apart from one another into the position shown in Fig. 7C to lower the rear of the platform 304. This causes the platform 304 to pitch upwards, thus raising the 'nose' of the cockpit 306 and lowering the 'tail' of the cockpit 306. It will be appreciated that by combining these motions to various degrees, the platform 304 can be moved with full six degrees of freedom to carry out the full range of motions required during simulation. The above movements shown in Figs. 9A through 9K illustrate the 'maximum' move in yaw, sway, surge, heave, roll, and pitch - larger or smaller movements in these directions may be achieved by moving the wedges and / or wedge pairs to larger or smaller extents, as appropriate. Figs. 10A to 10L show simplified models illustrating yaw, sway, surge, heave, roll, and pitch motion of the simulator 100 of Figs. 1A to ID, 2, and 3, with the models of Figs. IDA to 10L using the simplified model previously shown in Fig. 3. Figs. 10A and 10B respectively show yaw motion to the right and left. This causes the platform to rotate about the vertical axis, i.e. to yaw. Figs. IOC and 10D respectively show right sway and left sway motion. To achieve right sway motion as shown in Fig. IOC, the front wedge pair 110a and rear left wedge pair 110c move toward one another, which pulls the platform 104 to the right such that the wedge and platform carriages in the rear right corner (from the perspective of looking at the front of the motion simulator 100) reach the extreme outer end of the travel afforded by the rear right platform rail 113b. Conversely, to achieve left sway motion as shown in Fig. 10D, the front wedge pair 110a and rear right wedge pair 110b move toward one another, which pulls the platform 104 to the left such that the wedge and platform carriages in the rear left corner (from the perspective of looking at the front of the motion simulator 100) reach the extreme outer end of the travel afforded by the rear left platform rail 113c. Figs. 10E and 10F respectively show forward surge and rearward surge motion. To achieve forward surge motion as shown in Fig. 10E, the rear right and rear left wedge pairs 110b, 110c move in equal amounts toward the front wedge pair 110a which remains at the default central position, which pulls the platform 104 forwards such that the wedge and platform carriages at the front (from the perspective of looking at the front of the motion simulator 100) reach the extreme inner end of the travel afforded by the front platform rail 113a. Conversely, to achieve rearward surge motion as shown in Fig. 10F, the rear right and rear left wedge pairs 110b, 110c move in equal amounts away from the front wedge pair 110a which remains at the default central position, which pulls the platform 104 rearwards such that the wedge and platform carriages at the front (from the perspective of looking at the front of the motion simulator 100) reach the extreme outer end of the travel afforded by the front platform rail 113a. Figs. 10G and 10H respectively show max heave and minimum heave motion. To achieve maximum heave motion as shown in Fig. 10G, the wedges within each of wedge pair slide relative to one another in the manner described previously with reference to Fig. 7A, which pushes the platform 104 upwards in all three corners. Conversely, to achieve minimum heave motion as shown in Fig. 10H, the wedges within each of wedge pair slide relative to one another in the manner described previously with reference to Fig. 7C, which pushes the platform 104 downwards in all three corners. Figs. 101 and 10J respectively show right and left roll motion. To achieve right roll motion as shown in Fig. 101, the wedges in the front wedge pair 110a remain in the central position as shown in Fig. 7B. The wedges in the rear right wedge pair 110b slide toward one another into the position shown in Fig. 7A to raise the platform 104 in that corner. The wedges in the rear left wedge pair 110c slide apart from one another into the position shown in Fig. 7C to lower the platform 104 in that corner. This causes the platform 104 to roll toward the right (from the perspective of a user sat in the cockpit 106). Conversely, to achieve left roll motion as shown in Fig. 10J, the wedges in the front wedge pair 110a remain in the central position as shown in Fig. 7B. The wedges in the rear left wedge pair 110c slide toward one another into the position shown in Fig. 7A to raise the platform 104 in that corner. The wedges in the rear right wedge pair 110b slide apart from one another into the position shown in Fig. 7C to lower the platform 104 in that corner. This causes the platform 104 to roll toward the left (from the perspective of a user sat in the cockpit 106). Figs. 10K and 10L respectively show downward and upward pitch motion. To achieve downward pitch motion as shown in Fig. 10K, the wedges in the front wedge pair 110a move apart from one another to the position shown in Fig. 7C, which lowers the front of the platform 104. The wedges in the rear right and left wedge pairs 110b, 110c slide toward one another into the position shown in Fig. 7A to raise the rear of the platform 104. This causes the platform 104 to pitch downwards, thus lowering the 'nose' of the cockpit 106 and raising the 'tail' of the cockpit 106. Conversely, to achieve upward pitch motion as shown in Fig. 10L, the wedges in the front wedge pair 110a move toward one another to the position shown in Fig. 7A, which raises the front of the platform 104. The wedges in the rear right and left wedge pairs 110b, 110c slide apart from one another into the position shown in Fig. 7C to lower the rear of the platform 104. This causes the platform 104 to pitch upwards, thus raising the 'nose' of the cockpit 106 and lowering the 'tail' of the cockpit 106. It will be appreciated that by combining these motions to various degrees, the platform 104 can be moved with full six degrees of freedom to carry out the full range of motions required during simulation. The above movements shown in Figs. 10A through 10L illustrate the 'maximum' move in yaw, sway, surge, heave, roll, and pitch - larger or smaller movements in these directions may be achieved by moving the wedges and / or wedge pairs to larger or smaller extents, as appropriate. Figs. 11A to 11C show simplified models of a bungee arrangement 401 used by some embodiments of the invention. This bungee arrangement 420 is a passive device that assists in supporting the static mass of the platform 104, 204, 304. A bungee 420 is provided on each of the wedges llla-c, 112a-c, 211a-c, 212a-c, 311a-c, 312a-c. For ease of illustration, only a single wedge is shown in Figs. 11A to 11C, rather than a full wedge pair. Each bungee 420 is constructed from a resilient cord 422 and a pulley arrangement 430, 432. One end of the cord 422 is affixed to a fixed point 426 of the wedge llla-c, 112a-c, 211a-c, 212a-c, 311a-c, 312a-c, and the other end of the cord 422 is affixed to the wedge carriage 114a-c, 214a-c, 314a-c. The cord 422 passes over the pulley arrangement 430, 432 which is positioned on a side wall 428 of the wedge llla-c, 112a-c, 211a-c, 212a-c, 311a-c, 312a-c between the fixed point 426 and the top of the sloped surface of the wedge llla-c, 112a-c, 211a-c, 212a-c, 311a-c, 312a-c. The bungee 420 acts as a passive device that assists the motors such that the static mass of the platform 104, 204, 304 and payload is significantly reduced. These pulleys 430, 432 allow the bungee cord to extend up to 250% of its original length (within the cord's 'elongation rating' of 300%, the expected breaking point for this specific cord) and reduce wear and damage to the bungee. Such a bungee arrangement may provide lower cost, reduced maintenance requirements, and / or enhanced energy savings when compared to other passive devices or having no such passive device. With a different cord having a different elongation rating, the amount of pre-tension to be applied may be selected differently, as appropriate. A first pulley 430 is arranged at a lower corner proximate to the bottom of the side wall 428 of the wedge llla-c, 112a-c, 211a-c, 212a-c, 311a-c, 312a-c. A second pulley 432 is arranged at an upper corner proximate to the top of the side wall 428 of the wedge llla-c, 112a-c, 211a-c, 212a-c, 311a-c, 312a-c. It will be appreciated, however, that a different number of pulleys and / or different positioning of the pulleys may be used - the principle is that the cord 422 is run along a path of a particular length to add the desired pretension to the bungee. The combination of a bungee arrangement 420 and a 2:1 motion ratio (that is 1 mm of vertical motion for each 2 mm of horizontal motion) may allow the static mass of the platform 104, 204, 304 to be held with little to no effort required at the motors. This allows for less electrical energy to be required and therefore lower powered (and cheaper) motors can be used. Thus it will be appreciated by those skilled in the art that embodiments of the present invention provide an improved motion simulator with six degrees of freedom, where all motions are imparted through in-plane movement of the wedge pairs and / or the wedges within those wedge pairs. As out-of-plane motions can be achieved only through in-plane movement of the wedges and wedge pairs, there is no need to stack layers of actuators, resulting in a lighter system that will typically exhibit an improved frequency response compared to conventional motion platforms. 5 The arrangement of wedge pairs linked by a wedge carriage may exhibit greater stiffness in the vertical direction than with other designs which may improve the performance of the motion simulator. This wedge pair structure may also provide for greater control over where the gimbal (or similar) is on that wedge. Embodiments of the present invention may also provide for less compliance in the position of the gimbal (or similar) and a reduced moment compliance. 10 By using a pair of wedges rather than singular wedges, the load is split across two support structures. This also means that the effort required to carry out a particular movement may be split equally across two motors, allowing for the use of motors that are lower cost, smaller, lighter, more efficient, and / or have a lower energy consumption. Embodiments of the present invention may also avoid issues with 'cross-talk', e.g. pitch-surge cross-talk. 15 While specific embodiments of the present invention have been described in detail, it will be appreciated by those skilled in the art that the embodiments described in detail are not limiting on the scope of the claimed invention.

Claims

1. A motion simulator comprising a base and a platform, said platform being arranged to move relative to the base with six degrees of freedom, wherein:a) the base comprises first, second, and third wedge pairs, wherein each wedge pair is moveable in-plane with respect to the other wedge pairs, wherein each wedge pair respectively comprises:i) a first wedge and a second wedge that are slidably moveable with respect to one another in-plane along a sliding path, said first and second wedges each comprising a sloped surface, wherein the sloped surface of the first wedge slopes upward in one direction along the sliding path while the second wedge slopes upward in the opposite direction along the sliding path; andii) a wedge carriage arrangement coupled to the first and second wedges, said wedge carriage arrangement being mechanically constrained to slide up and down the sloped surfaces of the first and second wedges as said wedges move with respect to one another such that a vertical position of the wedge carriage arrangement is dependent on the positions of the first and second wedges relative to one another; andb) the platform comprises:i) first, second, and third platform rails angled with respect to one another; andii) first, second, and third platform carriage arrangements respectively coupled to andslidably moveable along the first, second, and third platform rails;c) the motion simulator further comprises first, second, and third pivotal coupling members respectively providing a pivotal coupling between the corresponding first, second, and third wedge carriage arrangements and the corresponding first, second, and third platform carriage arrangements.

2. The motion simulator as claimed in claim 1, wherein each wedge pair further comprises:i) a first wedge rail extending along the sloped surface of the first wedge such that the first wedge rail slopes upward in one direction along the sliding path; andii) a second wedge rail extending along the sloped surface of the second wedge such that second wedge rail slopes upward in the opposite direction along the sliding path;iii) wherein each wedge carriage arrangement is coupled to the respective first and second wedge rails of the wedge pair and is mechanically constrained to slide up and down the first and second wedge rails as said wedges of the wedge pair move with respect to one another.

3. The motion simulator as claimed in claim 2, wherein each wedge carriage arrangement comprises first and second bearing arrangements to couple the wedge carriage arrangement to the first and second wedge rails respectively, optionally wherein each bearing arrangement is arranged such that the centre of moment is located in the centre of the respective bearing arrangement.

4. The motion simulator as claimed in any preceding claim, wherein the first, second, and / or third pivotal coupling members comprise a gimbal, a spherical ball joint, or a universal joint.

5. The motion simulator as claimed in any preceding claim, wherein the platform rails are arranged such that: the first platform rail is located at a central front portion of the platform; the second platform rail is located at a rear-left portion of the platform; and the third platform rail is located at a rear-right portion of the platform.

6. The motion simulator as claimed in any preceding claim, wherein an angle between the first platform rail and each of the second and third platform rails is approximately 120 degrees, and / or wherein an angle between the second and third platform rails is approximately 120 degrees.

7. The motion simulator as claimed in any preceding claim, wherein the base comprises first, second, and third linear base rails, wherein the first wedge pair is coupled to and mechanically constrained to move along the first linear base rail, the second wedge pair is coupled to and mechanically constrained to move along the second linear base rail, and the third wedge pair is coupled to and mechanically constrained to move along the third linear base rail.

8. The motion simulator as claimed in claim 7, arranged such that when the platform is in a predetermined position:i) the first base rail is perpendicular to the first platform rail;ii) the second base rail is perpendicular to the second platform rail; andiii) the third base rail is perpendicular to the third platform rail.

9. The motion simulator as claimed in claim 8, wherein the first linear base rail is longer than each of the second and third linear base rails.

10. The motion simulator as claimed in claim 8 or 9, wherein the second and third base rails are approximately the same length, preferably wherein the second and third base rails are the same length.

11. The motion simulator as claimed in any of claims 1 to 7, wherein the base comprises first and second linear base rails arranged such that:i) the first linear base rail is parallel to the second linear base rail;wherein the first wedge pair is coupled to and mechanically constrained to move along the first linear base rail, and the second and third wedge pairs are coupled to and mechanically constrained to move along the second linear base rail.

12. The motion simulator as claimed in any of claims 1 to 7, wherein the base comprises inner and outer circular base rails arranged such that:i) the inner and outer base rails are concentric and parallel to one another;wherein the first wedge of each wedge pair is coupled to and mechanically constrained to move along the outer base rail, and the second wedge of each wedge pair is coupled to and mechanically constrained to move along the inner base rail.

13. The motion simulator as claimed in claim 12, wherein the wedge carriage arrangement of each wedge pair comprises a first wedge carriage and a second wedge carriage, arranged such that:the first wedge carriage is mechanically constrained to slide up and down the sloped surface of the first wedge as the first and second wedges move with respect to one another;the second wedge carriage is mechanically constrained to slide up and down the sloped surface of the second wedge as the first and second wedges move with respect to one another; andthe first and second wedge carriages are mechanically coupled to one another via the respective platform carriage arrangement.

14. The motion simulator as claimed in any preceding claim, further comprising a controller configured to cause the wedge pairs and / or the wedges to move relative to one another, optionally wherein the controller is configured to generate a control signal for each wedge dependent on a planned motion input received by said controller15. The motion simulator as claimed in any preceding claim, wherein each wedge is coupled to a respective motor arranged to move said wedge in-plane, optionally wherein one or more of said motors comprises a linear motor, further optionally wherein each of said motors comprises a linear motor.

16. The motion simulator as claimed in claim 15 when dependent on claim 12, wherein one or more of the linear motors comprises a radial linear motor.

17. The motion simulator as claimed in any preceding claim, wherein one or more of the wedges have a gradient of between approximately 1:2 and 7:2, preferably between approximately 1:1 and 3:1, more preferably approximately 2:1, optionally wherein one or more of the wedges has a gradient of 2:1.

18. The motion simulator as claimed in any preceding claim, wherein both wedges of a wedge pair have the same gradient, optionally wherein all the wedges have the same gradient.

19. The motion simulator as claimed in any preceding claim, wherein a bungee is provided on one or more of the wedges, said bungee comprising a resilient cord and a pulley arrangement, wherein one end of the cord is affixed to a fixed point of the wedge and the other end of the cord is affixed to the wedge carriage arrangement, and wherein the cord passes over the pulley arrangement, optionally wherein said pulley arrangement being positioned on a side wall of the wedge.

20. The motion simulator as claimed in claim 19, wherein the or each bungee comprises a plurality of resilient cords, wherein each of said cords passes over the respective pulley arrangement.

21. The motion simulator as claimed in any preceding claim, wherein one or more of the wedges comprises one or more of: aluminium, titanium, and a composite material; and / or wherein the or each wedge carriage arrangement comprises steel.

22. A base for a motion simulator, the base being arranged to provide a platform of said motion simulator with six degrees of freedom, wherein the base comprises:a) first, second, and third wedge pairs, wherein each wedge pair is moveable in-plane with respect to the other wedge pairs, wherein each wedge pair respectively comprises:i) a first wedge and a second wedge that are slidably moveable with respect to one another in-plane along a sliding path, said first and second wedges each comprising a sloped surface, wherein the sloped surface of the first wedge slopes upward in one direction along the sliding path while the second wedge slopes upward in the opposite direction along the sliding path; andii) a wedge carriage arrangement coupled to both the first and second wedges, said wedge carriage arrangement being mechanically constrained to slide up and down the sloped surfaces of the first and second wedges as said wedges move with respect to one another such that a vertical position of the wedge carriage arrangement is dependent on the positions of the first and second wedges relative to one another; andb) first, second, and third pivotal coupling members for providing a pivotal coupling between the corresponding first, second, and third wedge carriage arrangement and the platform.5 23. The motion simulator as claimed in any preceding claim, wherein the motion simulator is operablein a first power mode in which it receives a single-phase power supply, and is further operable in a second power mode in which it receives a three-phase power supply.

24. A motion simulator comprising a base and a platform, said platform being arranged to move relative to the base with six degrees of freedom, wherein the platform is pivotally coupled to the base via three 10 wedge pairs, each wedge pair being arranged to move in-plane with respect to one another, wherein respective first and second wedges of each wedge pair can slide relative to one another to vary an out-of-plane height of at least a portion of the platform relative to the base.

25. A base for a motion simulator, the base being arranged to provide a platform of said motion simulator with six degrees of freedom, wherein the base comprises three wedge pairs each comprising a 15 pivotal coupling arrangement for pivotally coupling the respective wedge pair to the platform, each wedge pair being arranged to move in-plane with respect to one another, wherein respective first and second wedges of each wedge pair can slide relative to one another to vary an out-of-plane height of at least a portion of the platform relative to the base.

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