A VEHICLE

FIELD

The invention relates to vehicles.

BACKGROUND The vast majority of land vehicles are either wheeled or tracked. Tracked vehicles are often better adapted to rougher terrain but nonetheless have their limitations.

Technabob (Strauss, P. "1960s Walking Truck: The First AT-AT?" Technabob.com (26 May 2011) <https://technabob.com/blog/2011/05/26/ge-walking-truck/& gt; (retrieved 17 April 2020)) discloses a four-legged "walking truck" and suggests that the truck was developed in the late 1960's as an experimental vehicle for rough terrain. The embedded video shows the operator's cabin rocking as the machine takes a few awkward steps during which the vehicle is tethered to an overhead gantry. The video explains that "the strain of thinking about which leg to move next exhausted the operator in about 15 minutes". More recently, unmanned quadrupeds, such as Boston Dynamics' Big Dog™, have been developed. "The Evolution of Boston Dynamics' Robot Dogs" (YouTube, uploaded by Vocativ (18 November 2017) <https://www.youtube. com/watch ?v=RYzn _gmFs5w> (retrieved 17 April 2020)) shows autonomous quadrupeds that are deft of foot. With the foregoing in mind, the present invention aims to provide improvements in and for vehicles, or at least to provide alternatives in and for vehicles.

It is not admitted that any of the information in this patent specification is common general knowledge, or that the person skilled in the art could be reasonably expected to ascertain or understand it, regard it as relevant or combine it in any way before the priority date. SUMMARY

One aspect of the invention provides a bipedal vehicle comprising two extendible output legs to support the vehicle; two foot holds to accept input movement from an operator; and a control system comprising powered actuators to move the output legs in relation to the input movement to produce output movement.

Preferably, the control system comprises a respective knee sub-system for each respective output leg of the two output legs. The output legs may have pivotal knee joints controlled by the knee sub-systems. Alternatively, the output legs may comprise other means of extension controlled by the knee sub-systems. By way of example, the output legs might be telescopically extendable.

Each respective knee sub-system may comprise a respective position-feedback Flexible Pulling System (FPS) routed to be tensioned by a respective knee input movement and relaxed by a respective knee output movement corresponding to the respective knee input movement. A respective position-feedback FPS relative-length being a respective position-feedback FPS length relative to a respective position- feedback FPS path length. Preferably, the respective knee output movement is extension of the respective output leg.

Preferably, each respective knee sub-system comprises a respective knee actuator arranged to effect the respective knee output movement and controlled in response to a respective tension in the respective position-feedback FPS. Preferably, each respective knee actuator comprises a respective output fluid actuator. Optionally, each respective knee sub-system comprises a respective force-feedback fluid actuator, e.g. plumbed to operate in parallel to the respective knee output fluid actuator.

Optionally, each respective knee sub-system comprises a respective actuator-drive comprising a respective drive input movable to vary a respective drive to the respective knee actuator. Each respective knee sub-system may comprise a respective bias against which the respective drive input is moved by the respective tension. Each respective knee sub-system preferably comprises a respective preload adjustor for adjusting a respective preload on the respective bias.

The vehicle may comprise a preload user-interface by which the operator, whilst operatively engaged with the foot holds, can provide a single user-input to simultaneously adjust each respective preload adjustor.

Optionally, each respective drive input is movable to reconfigure the respective actuator-drive to each of a respective advance configuration for advancing the respective knee actuator; a respective neutral configuration for stopping the respective knee actuator; and a respective reversal configuration for reversing the respective knee actuator.

Preferably, the respective actuator drive is configured to provide a respective continuously-variable drive; the respective advance configuration and respective reversal configuration may each be a range of driving amounts in respective directions each side of a respective neutral point. Preferably, the amount of drive is related to the amount of drive input movement. The actuator drive might take the form of a proportional spool valve, although non-linear input/output relationships across the actuator drive are possible.

Each respective knee actuator may be a respective fluid actuator, e.g. a respective ram. Each respective actuator-drive may be a respective valve system.

Preferably, each respective knee sub-system comprises a respective force-feedback system to vary the respective bias in relation to a respective output load. Each respective force-feedback system may comprise a respective anchor against which the respective bias acts; a respective resilient portion arranged to be resiliently deformed by the respective output load by a respective amount-of-deformation; and a respective force-feedback mechanical transmission by which the respective amount-of-deformation moves the respective anchor a respective corresponding anchor-movement-amount.

Optionally, each respective force-feedback mechanical transmission comprises a respective force-feedback FPS, in which case each respective force-feedback system may be configured to lengthen, by a respective lengthening-amount related to the respective amount-of-deformation, the respective position-feedback FPS relative length.

Preferably, each respective knee sub-system comprises a respective force-feedback system to vary the respective bias in relation to a respective output load. Optionally, each respective force-feedback system comprises a respective anchor, against which the respective bias acts, and a respective force-feedback fluid actuator driven by the respective valve system to move the respective anchor.

Preferably, each respective force-feedback system comprises a respective magnitude-adjustor to adjust a respective magnitude of a respective variation of the respective bias in relation to the respective load. The vehicle may comprise a magnitude user-interface by which the operator, whilst operatively engaged with the foot holds, can provide a single user-input to simultaneously adjust each respective magnitude-adjustor.

Each respective output leg is preferably mounted to swing fore and aft about a respective output hip. Preferably, each respective output leg has a respective ride smoothing mechanical transmission by which the respective position-feedback FPS relative-length is varied in relation to a respective magnitude-of-departure of the respective output hip from a respective mid-stance position. Each respective output leg may comprise a respective adjustor to adjust a respective extent to which the respective position-feedback FPS relative-length is varied in relation to the respective magnitude-of-departure. The control system may comprise a respective hip sub-system for each hip. Each respective hip sub-system may comprise a respective hip actuator arranged to effect a respective hip output movement corresponding to a respective hip input movement; a respective hip actuator-drive comprising a respective hip drive input movable to vary a respective drive to the respective hip actuator; a respective hip command mechanical transmission by which the respective hip input movement moves the respective hip drive input in a respective direction; and a respective hip position-feedback mechanical transmission by which the respective hip output movement moves the respective hip drive input a respective opposite direction opposite to the respective direction.

The respective hip output movement may be one of forward movement of the respective output leg about the respective hip; and rearward movement of the respective output leg about the respective hip.

Preferably, each respective hip sub-system comprises a respective see-saw link connected to each of the respective hip command mechanical transmission; the respective hip drive input; and the respective hip position-feedback mechanical transmission.

Optionally, each respective hip drive input is movable to reconfigure the respective hip actuator-drive to each of a respective advance configuration for advancing the respective hip actuator; a respective neutral configuration for stopping the respective hip actuator; and a respective reversal configuration for reversing the respective hip actuator.

Preferably, each respective hip actuator is a respective fluid actuator and each respective actuator-drive is a respective valve system.

Each respective hip sub-system may comprise a respective hip force-feedback system; each respective hip force-feedback system comprising a respective hip resilient portion arranged to be resiliently deformed by the hip actuator by a respective hip amount-of-deformation; a respective hip force-feedback mechanical transmission by which the respective hip amount-of-deformation urges the respective hip drive input to move.

Preferably, each respective output leg has a respective walk-assist mechanical transmission via which load borne by the respective output leg urges the respective hip drive input towards rearwardly moving the respective output leg.

The vehicle may comprise a vehicle-lowering member. Preferably, each respective hip command mechanical transmission comprises a respective hip control member mounted to move, relative to the vehicle-lowering member and in response to a respective user-input via a respective foot hold, to transmit movement to the respective hip drive input; and the vehicle-lowering member is movable simultaneously to move each respective hip control member; and vary each respective position-feedback FPS relative-length; and thereby lower the vehicle whilst legs of the operator remain extended. Preferably, the control system is configured to extend each respective output leg by an amount, more than proportionate to a respective input extension, positively related to a respective magnitude-of-departure of the respective output hip from a respective mid-stance position to smooth a ride of the vehicle.

The vehicle may have a mode user-selectable to lower the vehicle whilst the legs of the operator remain extended.

Preferably, each respective output leg comprises a respective knee. Most preferably, each respective knee is rearwardly directed. Optionally, each respective output leg comprises a respective ankle driven by a respective one of the powered actuators in relation to the input movement. Preferably, each respective output leg is movable in abduction and adduction. Preferably, each respective output leg is movable toe-in and toe-out. Preferred variants of the control system may be configured to provide force-feedback to the operator via the foot holds. The control system may be configured to produce an output gait at least 20%, or preferably at least 100%, longer than an input gait. The vehicle may comprise a cabin to house the operator.

Preferably, the control system is configured to rearwardly bias each output leg in positive relation to weight borne by that leg. Most preferably, the relationship is so as to forwardly bias each output leg at least when it is fully relieved of weight.

The vehicle preferably comprises a restraint for restraining at least a portion of torso of the operator. The restraint may be arranged with respect to the foot holds to enable an operator to stand, on the foot holds, with a neutral posture. The vehicle may be configured to stand with a neutral stance in response to the operator standing with a neutral stance. Preferably, the restraint is configured to constrain the torso to about pivot about a lateral axis coincident with a centre of mass of the operator.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a perspective view of one example of a vehicle; Figures 2 to 21 and 23 to 30 show selected components of the vehicle of Figure 1 ; Figures 2 and 3 are perspective views showing selected major components;

Figure 4 is a side perspective view of an output hip;

Figure 5 is a rear perspective view of an operator restraint; Figure 6 is a side view of a flex mount;

Figure 7 is a side perspective view of a leg;

Figure 8 is a perspective view of an ankle;

Figure 9 is a front view of a groin;

Figure 10 is a side view of a hip; Figure 11 is a front perspective view of a pair of input legs;

Figure 12 is a rear perspective view of an input hip;

Figure 13 is a front perspective view of an input hip;

Figure 14 is a front-left perspective view of a knee control unit;

Figure 15 is a front-right perspective view of the knee control unit; Figure 16 is a rear-left perspective view of the knee control unit;

Figure 17 is an enlargement of a right-rear portion of the knee control unit;

Figure 18 schematically illustrates an ankle control system;

Figure 19 schematically illustrates a hip-flexor control system;

Figure 20 is a perspective view of a hip-flexor control unit; Figure 21 schematically illustrates a hip-abduction control system;

Figure 22 illustrates a human gait cycle;

Figure 23 illustrates vehicle legs at the start of a swing phase;

Figure 24 illustrates a ride-smoothing system at mid-stance; Figure 25 illustrates the ride-smoothing system at toes-off;

Figure 26 illustrates the ride-smoothing system at toes-off and adjusted to 0% effect; Figure 27 is a side view of a vehicle leg at full squat;

Figure 28 is a perspective view of a vehicle-lowering system configured for lowering;

Figure 29 is a perspective view of an end portion of the vehicle-lowering system of Figure 28;

Figure 30 is a perspective view of the vehicle-lowering system in its operative configuration;

Figure 31 is a front-right perspective view of an alternative knee control unit;

Figure 32 is a rear-left perspective view of the alternative knee control unit; Figure 33 is the perspective view of selected components of an ankle control system; Figure 34 is a side view of the linkage system of the ankle control system of Figure 3; and Figure 35 is a perspective view of the rotaries of the ankle control system of Figure 33. DETAILED DESCRIPTION

The vehicle 1 comprises a body 3 supported by legs 5L, 5R controlled by control system 7. The body 3 comprises a cabin 9 for housing an operator. Preferably, the cabin 9 is fully enclosed to shield the operator from the elements, etc. The cabin may comprise a windscreen. For military applications, the cabin might be armoured.

The vehicle comprises a chassis 11 carrying a combustion engine 13 and a fuel tank 15. The engine drives a hydraulic pump 17. In other variants of the vehicle 1 , components 13, 15 might be replaced by batteries and an electric motor, and hybrid systems are also possible. Variants of the vehicle 1 capable of operating in electric- only (or other emission-free) mode may be preferable for operation in confined spaces, such as in the context of mining applications.

Preferably, the cabin is forward-mounted to counterbalance other rearward components and to give the operator a better view of what lies ahead. For this purpose, the cabin may have low-mounted windows akin to the low-mounted windows in the vicinity of a helicopter's pedals.

A restraint 19 is mounted in the cabin to restrain an operator's torso. In this example, the restraint comprises a back rest 21 , shoulder straps 25, and a waist band 27. There are other options. By way of example, an operator might be strapped into a harness akin to a parachute harness. Indeed, a means of locating, such as a seat akin to a bicycle or unicycle seat, might be employed to locate the operator's body in conjunction with, or as an alternative to, a restraint.

The restraint comprises a fixed piece 29 fixed relative to the chassis 11 and carrying three pairs of rollers 31. The rollers 31 sit within arcuate slots 33 formed in fore-aft vertical flanges 35 fixed to a rear of the back rest 21. The arcuate slots 33 are concentric to point 37 oriented to be about coincident with a centre of mass of the operator. In this way, when the operator is strapped in, the operator's torso is about restrained to about pivot about their centre of mass about a lateral axis. The left leg 5L comprises femur 39L, knee 41 L, tibia 43L, ankle 45L and foot 47L. The right leg 5R comprises corresponding components 39R, 43R, 43R, 45R, 47R.

Left input leg 49L and right input leg 49R are also mounted within the cabin 9. The left input leg 49L comprises an input femur 51 L, and input knee 53L, an input tibia 55L, an input ankle 57L and an input foot hold 59L. The right input leg 49R comprises corresponding components 51 R, 53R, 55R, 57R, 59R. The foot holds 59L, 59R may comprise foot straps or other securements.

Preferably, the input legs are of corresponding configuration to the output legs (e.g. comprise 90° posterior knees in this case), and are designed and sized to ergonomically capture the gait cycle of the operator for transference, via the control system 7, to the output legs 5L, 5R.

Whilst other input arrangements are possible, preferably each output joint has a corresponding input joint. Preferably, there is position-feedback connecting each corresponding two of the joints. Most preferably, there is also force-feedback between each corresponding two of the joints.

The output legs 5L, 5R are connected to the chassis 11 via output hips 61 L, 61 R. The chassis 11 comprises chassis rails 63, upright 65 and cross member 67 (Figure 9). The cross member 67 runs laterally across the vehicle 1 and has an upright journal 69L, 69R at each end. Each journal 69L, 69R pivotally carries a respective inverted T pieces 71 L, 71 R.

The horizontal arms of the T pieces 71 L, 71 R are journaled to rotate within pillow blocks 73L, 73R which blocks are in turn fixed to webs 75L, 75R. Each web 75L, 75R mutually connects a respective pair of pelvis plates 77L, 77R. The two pelvis plates 77L are mutually parallel and fixed in mutually spaced relation by the web 75L and spacers 79L. The web 75L, pelvis plates 77L and spacers 79L thus together constitute a pelvis unit 81 L gimballed to rotate about the horizontal and vertical axes of the T piece 71 L. The right-hand pelvis unit 81 R has a corresponding construction. Other forms of pelvis unit are possible. The femur 39L is mounted to rotate about a generally lateral axis with respect to the pelvis unit 81 L. In this case, the pelvis unit 81 defines arcuate bearing tracks 83L whilst a femur head 85L of the femur 39L carries an arcuate array of rollers 87L to roll along the bearing tracks 83L. An actuator 89L acts between the femur 39L and the pelvis unit 81 L. More specifically, the actuator acts between an upper portion of the femur head 85L and the pelvis unit 81 L. The femur head 85L comprises a pair of parallel plates mutually spaced in a lateral direction to accommodate the actuator 89L therebetween. The actuator 89i_ is trunnion-mounted to pivot about a transverse pivot axis at the front of its main body from which front its actuator rod 91 L extends. The actuator 89L is actuatable to drive the leg 5L fore and aft about a generally lateral axis.

In this case, the vertical and horizontal axes of the T piece 71 L and the generally lateral axis (concentric to the bearing track 83L) about which the femur 39L rotates substantially intersect at the junction of the inverted T piece 71 L.

Turning to Figure 7, the left knee 41 L mutually connects the femur 39L to the tibia 43L. The knee 41 L is a simple single-pivot joint. This construction is preferred because it is simple and robust, although other options (such as a polycentric gear joint) are possible. In this example, the knee 41 L is rearwardly directed (unlike a human knee which is forwardly directed) and is configured to work through a range of motion ai_ of 0° to about 120°.

Actuator 93L acts between components 39L, 43L to open and close the knee 41 L. In this example, the actuator 93L is inverted and trunnion-mounted. Preferably, the knee 41 L is extended to about 90° (say 90° ± 10°) when the vehicle is standing with a neutral stance and when the leg is mid-stance as the vehicle is walking. Beyond 90°, the effectiveness of the self-aligning actuator 93L may be diminished by the changing geometry about the knee.

A lower end of the actuator is received within the tibia 43L and is equipped with a flex mount 95L. The flex mount 95L comprises a body 97L pivotally connected to the rod end of the actuator 93L. The body is also pivotally connected via pins 99L to the tibia 43L. The axes of these two pivotal connections are offset whereby load from the actuator 93L produces a corresponding bending moment about the pin 99L. A resilient arm 101 L projects from the body 97L, along the tibia 43L to a mounting point 103L fixed to the tibia 43L. The resilient arm 101 L is a cantilevered leaf spring to resist the bending moment about the pin 99L. The resilient arm 101 L may be formed of spring steel. A push-pull cable is connected between the tibia 43L and the body 97L to be driven in relation (e.g. proportion) to the angle of the body 97L relative to the tibia 43L and thereby to provide force-feedback indicative of the force supplied by the actuator 93L. In this way, the force applied by the actuator 93L, the deformation of the resilient arm 101 L, the rotation of the pin 99L and the displacement of the push-pull cable are related quantities. In this case, a sheath of the push-pull cable is fixed relative to the tibia 43L and a core of the push-pull cable and movable relative to the sheath is fixed to the body 97L.

As shown in Figure 8, the ankle 45L is another simple pivotal connection and comprises an actuator 105L to act between the tibia 43L and the foot 47L via a flex mount 107L. The foot 47L comprises a horizontal plate which, in this example, is rectangular. A variety of aspect ratios, e.g. square, is possible, although preferably the foot 47L is about twice as long as it is wide. In this example, the plate 47L has upturned leading and trailing edges akin to ski tips. Advantageously, the foot 47L is dimensioned with respect to a dry, unladen weight of the vehicle so as to present not more than 70 kPa to the ground when the foot 47L is bearing an entire weight of the vehicle 1.

More elaborate ankle configurations are possible. By way of example, the foot plate 47L might be mounted to rotate (with respect to the tibia 43L) about a longitudinal axis as well as a lateral axis. On the other hand, simpler variants are also possible. The actuator 105L might be replaced by a gas spring (or the foot 47L might be otherwise resiliently connected to the tibia 43L) to simply deform to match the ground contours. Indeed, some variants of the vehicle 1 may do without ankles, e.g. the foot 47L might take the form of a resilient sphere fixed at the lower end of the tibia 43L.

The input legs 49L, 49R are suspended from input hip gimbals 109L, 109R (Figure 11 ). The gimbal 109L comprises a fixed portion 111 L fixed with respect to the chassis 11. Yoke 113L sits atop the fixed portion 111 L and is pivotally connected to pivot about an upright axis. The arms of the yoke 113L project upwardly to accommodate pelvis unit 115L. The pelvis unit 115L is mounted between the arms of the yoke 113 L to pivot horizontally about a generally fore-aft axis. A rotary 117L sits on an outside face of one arm of the yoke 113L to drive push-pull cables in relation to the orientation of the pelvis unit 115L about this horizontal pivot axis. The femur 51 L is mounted on the inside of the pelvis unit 115L and pivotally connected thereto to pivot about a generally horizontal, generally lateral, axis. A rotary 119L drives a push-pull cable in relation to an angular orientation of the femur 51 L about this horizontal, generally lateral, axis. On its outboard side, the pelvis unit 115 carries a pair of attachment points 121 mutually spaced in the fore-aft direction. Preferably, the pelvis units 115L,

1 15R (or more specifically, the generally fore-aft pivot axes of those units in this case) are spaced in the range of 600 mm ± 100 mm, preferably 600 mm ± 50 mm, or more preferably 600 mm ± 25 mm.

The input knee 53R is a rearwardly-directed knee comprising a simple pivotal connection. Preferably, the input knees are limited to a maximum extension in the range of 90° ± 10°. Preferably, a maximum extension of each input leg corresponds to a maximum distance between the generally transverse pivot axes of the hip and the ankle in the range of 830 mm ± 100 mm, more preferably in the range of 830 mm ± 50 mm.

A take-up arrangement 123R is associated with the knee 53R. The arrangement 123R comprises an arc 125R fixed to the tibia 55R and concentric to the knee 53R, and a pulley 127R radially adjacent the arc 125R. A portion of a control cable 129R is fixed with respect to the tibia 55R wherefrom free portions of the cable wrap about the exterior of the arc 125R and then turn about the pulley 127R. In this way, the take-up arrangement 123R takes up (in this case pulls about pulley 127R) a length of the cable 129R proportional to an opening of the knee 53R.

The foot hold 59L comprises a cradle support 131 L that includes a portion 133L running in the fore-aft direction and pivotally connected to the tibia 55L at ankle 57L. A projection 135L projects inwardly from each end of the fore-aft portion 133L. A cradle 137L comprising a generally planar floor is suspended between the projections 135L and pivotally connected thereto so as to pivot, with respect to the cradle support 131 L, about a fore-aft axis. The cradle support 131 L carries a rotary 139L connected to rotary 117L by push-pull cables to hold the cradle 137L (as characterised by its generally planar floor) substantially lateral with respect to the chassis 11. The planar floor of the cradle 137L carries a foot plate 141 L. The foot plate is mounted to slide on the floor of the cradle so that it has a small degree of freedom to move laterally and twist (about a generally upright axis) with respect to the cradle 137L.

Preferably, the foot hold 49L, as characterised by the top foot-receiving surface of the foot plate 141 L, is in the range of 120 mm ± 70 mm (or more preferably 120 mm ±

25 mm) below the generally transverse pivot axis of the input ankle 57L.

The foot holds 59L, 59R are mounted inboard of their corresponding tibias and femurs so that the operator can fit between the tibias and femurs and, when the operator stands with their feet shoulder-width apart, so the operator's legs are about straight up and down, the tibias and femurs of the input legs are also about straight up and down.

Rotaries 143L, 145L are mounted along the cradle 137L and co-operate with feelers in contact with the foot plate 141 L to drive push-pull cables in response to the foot plate 141 L moving relative to the cradle 137L. The output knee 41 R internally carries a take- up arrangement (not shown) akin to the take-up arrangement 123R but configured to take up the cable 129R as the output knee 41 R closes. The actuator 93R is driven to open the knee 41 R SO as to maintain a tension in the cable 129R.

Each output leg 5L, 5R is associated with a respective knee control unit. In this example, the knee control units are carried by the femurs. The knee control unit 147L can be seen attached to the femur 39L in Figure 2 and is illustrated in more detail in Figures 14 to 16. The knee control unit 147L comprises an actuator drive in the form of a hydraulic spool valve 149L. The valve 149L comprises a valve body 151 L and an input shaft 153L projecting from the valve body.

The valve 149L is, in this example, a proportional spool valve for driving the actuator 93L in relation to a position of the input shaft 153L. The valve 149L has a neutral position at which the actuator 93L is not driven one way or the other. The further that the input shaft 153L is moved from its neutral position, the harder the actuator 93L is driven. The knee control unit further comprises an input link 155L, a null link 157L and a support structure 158L fixed relative to the valve body 151 L. The support structure 158L runs parallel to a stroke of the input shaft 153L to mutually space pivotal connections 159L, 161 L by which the links 155L, 157L are mounted to pivot with respect to each of the valve body 151 L and the superstructure 158L. Each of the links 155L, 157L carries a pair of pulleys.

The pulleys of the input link 155L are spaced along that link (with respect to the pivotal connection 159L). Cable 129L (akin to the cable 129R) is routed in an S-shaped path about these two pulleys so that tension in the cable 129L urges the link 155L to rotate clockwise as drawn in Figure 14. As the link 155L moves in this way, the length of the path about which the cable 129L is routed is reduced. A tension spring 163L is connected to the input link to counteract this movement (i.e. to urge the link 155L to rotate counterclockwise as drawn).

The input shaft 153L is arranged to be moved in relation to the outcome of the tension in the cable 129L working against the spring 163L. In this case, the input shaft 153L and a yoke-like extension of the spring 163L are both dowelled to an axle of the lower pulley of the link 155L.

The valve 149L is a spool valve that takes power from the hydraulic pump 17 and forcibly drives the actuator 93L in either direction, dependent on the position of the input shaft 153L. The valve 149L also has an intermediate, neutral, position at which fluid flow to and from the actuator 93L is blocked off, whereby the actuator holds the knee 41 L at a select position without consuming power.

The valve 149L is oriented so that, when a user depresses the foot hold 59L and thereby opens the input knee 53L and causes the take-up arrangement 123L to take up cable 129L, tension in the cable is increased, the link 155L moves (clockwise as drawn in Figure 14) to cause the valve 149L to drive the actuator 93L to open the knee 41 L until the take-up arrangement (not shown) on the knee 41 L releases sufficient cable to restore steady-state tension in the cable, whereupon the link 155L and in turn the valve 149L returns to its neutral position. The null link 157L also carries a pair of pulleys about which the cable 129L is routed in a manner akin to the routing about the pulleys of the link 155L. The link 157L is restrained from pivoting in response to tension in the cable 129L by a multiplier assembly 165L. The multiplier assembly 165L comprises a multiplier link 167L and con rod 169L.

The multiplier link 167L comprises a crank shaft portion (horizontal as drawn) mounted to pivot relative to the valve body 149L about a pivot axis parallel to the pivot axes of the pivotal connections 159L, 161 L. A slotted crank portion projects from the shaft portion. The con rod 169L mutually connects this crank portion to the null link 157L to ensure components 157L, 167L move in unison.

A trim adjuster 171 L connects the spring 163L to the multiplier link 167L or more specifically to the crank portion of that link in this case. The flex mount 95L is connected to the crank shaft portion of the multiplier link 167i_via a push-pull cable (not shown) so that the link 167L is driven to rotate and thereby extend the spring 163L in response to the load applied by the actuator 93L.

The crank portion of the multiplier link 167L is an anchor against which the spring 163L acts. Other forms of anchor are possible. By way of example, the trim adjuster may be directly connected to the null link 157L to anchor the spring 163L thereto. In this case, the force-feedback from the flex mount 95L may be applied directly to the null link 157L. The push-pull cable connecting the flex mount 95L to the multiplier link 167L is an example of a mechanical transmission. Other forms of mechanical transmission are possible. Indeed, other feedback systems more generally are possible. By way of example, an encoder on the flex mount 95L may relay control signals to a relatively small actuator on the multiplier link 167L. However the multiplier link 167L is rotated, as a result of the spring 163L being extended, the input link 155L is retracted to extend the cable path which increases tension in the cable and tends to lift the foot hold 59L. To counteract this, the operator must push harder down on the foot hold 59L to hold the actuator 93L in its neutral position, whereby the user experiences force-feedback related to the force applied by the actuator 93L.

When load is applied to the output leg 5L, force-feedback is provided via the flex mount 95L that tends to increase the tension within the control cable 129L. This feedback is associated with some deformation within the flex mount, which deformation also tends towards increasing the cable tension by the cable take-up arrangement on the knee 41 L taking up some more cable as a result of the "uncommanded" closure of the knee. This tension could cause the actuator 93L to drive harder, whereby there is the potential for an undesirable runaway effect. Preferred variants of the null link 157L prevent this potential runaway effect by shortening the cable path by an amount corresponding to the amount of cable taken up by the take-up arrangement of the knee as a result of the movement associated with the flexing of the flex mount.

The knee control unit 147L enables two distinct force-feedback adjustments. Firstly, the trim adjuster 171 L is length-adjustable to adjust a preload on the spring 163L. Typically, this adjustment would be configured when an operator first takes to the machine. Preferably, the preload is initially relaxed. An operator then stands on the foot holds 59L, 59R SO that, without adequate preload, the input legs 49L, 49R reach a base of their range of movement. The input knees 53L, 53R are restricted to 90° ranges of movement in this example. From a user interface in the cabin, and whilst standing on the foot holds, the operator shortens trim adjusters 171 L, 171 R until they can feel upward force- feedback through the foot holds as the cable 129L is tightened to take the user's weight away from the stop by which the range of input knee movement is limited. In this way, the force-feedback can be adjusted to suit operators of different weights.

Secondly, the trim adjuster is adjustable along the crank portion of the multiplier link 167L to vary the extent to which the feedback force varies in response to variations in the load applied by the actuator 93L. Through these two mechanisms, the operator can adjust the baseline feedback force to suit their weight and can adjust the magnitude of the variation in that force to suit their preferences. Preferably, the con rod 169L is also relocatable along the con rod of the multiplier link 167L to give operators further scope to tune the response of the control system. Other modes of adjustment are possible. By way of example, the spring 163L may be a gas spring, the initial pressure and/or internal volume of which may be adjustable to vary a response of the knee control unit 147L.

The cable 129L and the pulleys of the knee control unit 147L together constitute a flexible pulling system. In principle, other flexible pulling elements (such as rope and/or chain) could be used instead of a cable. Preferably, the flexible pulling element is substantially unstretchable. In this example, the FPS mutually connects the input knee to the output knee (or more specifically, mutually connects the take-up arrangements of those knees). In other implementations of the concept, other mechanical transmissions might connect portions of the cable emerging from the links 155L, 157L to the knees.

In this particular example, the take-up arrangements each comprise constant radii arcuate take-up members concentric to the pivot axes of the corresponding knees and the input take-up members have substantially the same radii as the output take- up members. In other variants, one or both of the input and output arcuate members might have an alternate form and/or be eccentrically mounted to vary the transfer function between the input and output systems. Indeed, entirely different take-up arrangements might be employed. By way of example, a straight run of cable might run from a point of fixation in the vicinity of one of the foot holds up and about a pulley in the vicinity of the corresponding input hip, whereby the length of that straight run is relatable to the desired leg extension. Likewise, instead of rotary 1 19L, a straight run of a cable might connect the foot hold 59L to a pulley at about foot level behind the operator.

Preferred variants of the described mechanical systems are simple and robust and provide quality tactile feedback to the operator, although other options are possible. By way of example, encoders may be associated with each of the input joints and the actuators may be electronically controlled in response to the encoders. Indeed, variants without the input legs are also contemplated. By way of example, control cable and/or encoders may be associated with input foot holds that are supported from below. The cable 129L operates in tension, tending to lift the input foot hold 59L. Other arrangements are possible. By way of example, the cable might operate in tension to counteract a spring tending to lift the input foot hold 59L.

As noted, the knee actuator 93L is controlled in response to tension in the cable 129L. This is preferably implemented using an actuator drive (in the form of hydraulic valve 149L) having a neutral position at which the position of the actuator is substantially fixed without drawing power. Of course, other forms of actuator are possible and there are other forms of actuator capable of holding position without drawing power. By way of example, a pneumatic actuator or a worm drive might be employed.

In this example, the actuator 93L takes the form of a single hydraulic ram. Other arrangements are possible. By way of example, the actuator might take the form of a pair of rams arranged in parallel or otherwise teamed to effect a desired movement. As the wording is used herein, hydraulic rams, pneumatic rams, ball screws and teams of these things are all examples of powered actuators, and a simple spring is not an example of a powered actuator.

The flex mount 95L is a convenient means for providing force-feedback. The flex mount 95L and the other flex mounts of the vehicle 1 are examples of mechanical force-feedback sensors. There are other options. By way of example, the sheath and the core of a push-pull cable may be connected to opposite ends of a helical compression spring mounted in series with an actuator. Wholly electronic control systems that do without cables or other forms of mechanical transmission can be configured to provide force-feedback. By way of example, a strain gauge mounted at any convenient point on the tibia may provide output relatable to the load borne by the leg and/or the output of the actuator on the knee of that leg. There are also intermediate electromechanical options. Byway of example, a respective load cell might be mounted in series with each of the actuator 93L and the cable 129L and a logic system may drive the actuator 93L so as to maintain a relativity between the outputs of these load cells.

In the knee control unit 147L, the valve 149L is essentially mounted in parallel to the combination of the spring 163L and multiplier assembly 165L, etc. A rudimentary knee control unit might take the form of a tension spring interrupting the cable 129L and a valve (or other actuator drive) mounted in parallel to that spring. A trinary output valve 149L (as opposed to a proportional valve) is another option.

An ankle control unit 173L is carried on the tibia 43i_ (Figures 2 and 18). The ankle control unit 173L comprises an actuator drive in the form of a valve 175L akin to the valve 149L. A see-saw link 177L is connected to the input shaft 179L. The see-saw link 177L projects transversely either side of the input shaft 179L. On one side, the see-saw link is connected to a push-pull cable 181 L that is driven by the rotary on the input ankle 57L. On the other side of the input shaft 179L, the see-saw link 177L is connected to push-pull cable 183L, which cable connects to the output foot 47L to provide feedback on the angular position of the ankle 45L. Via the see-saw link 177L, the difference between an angle of the input ankle 57L and an angle of the output ankle 45L is applied to the valve 175L. The valve 175L in turn drives the actuator 105L whereby the output ankle 45L tracks the movement of the input ankle 57L.

A spring unit 185L comprises a yoke bracketing the see-saw link 177L to connect to the input shaft 179L in parallel to that link. The spring unit 185L defines a resilient buffer between the input shaft 179L and a push-pull cable 187L connected to the flex mount 107L. In this way, the push-pull cable 187L conveys translation related to the load applied by the actuator 105L and the spring unit 185L converts this translation to a force applied to the input shaft 179L. The spring unit 185L provides a feedback force against which an operator must work to hold the input ankle 57L at a desired position whereby, through the foot hold 59L, the operator can feel angular forces being applied through the ankle 45L.

Figures 33 to 35 illustrate an alternative ankle control system 173i_'. The ankle control unit 173L' is configured to provide force feedback without resilient elements akin to the resilient arm of the flex mount 107L or to the spring unit 185L. In this way, preferred variants of the ankle control unit 173L' may provide more accurate force feedback. Tibia portions 43AL' and 43BL' are portions of a tubular tibia member which houses much of the control unit 173i_'. Much of the tubular tibia is omitted from Figure 33 to reveal the details of the ankle control system 173L'.

A hydraulic cylinder 105 _L ' acts between the foot 47 _L ' and the tibia portion 43A _L '. The cylinder 105 _L ' connects to the tibia portion 43A _L ' via an eccentric mounting 107 _L ' whereby the actuator force leads to a corresponding torque about the axis of the mounting.

A set of linkages 176 _L ' connects the hydraulic cylinder 105 _L ' to a proportional valve 175 _L '. The set of linkages 176A _L ' comprises an arm of the eccentric mounting 107 _L ' that extends generally parallel to the tibia, upwards therealong. A short link connects the free end of that arm to a bell crank 176B _L ', which in turn connects to link 176C _L ' which in turn connects to link 176D _L '.

The link 176D _L ' is mounted to pivot with respect to the tibia portion 43A _L ' at one of its ends. At its other end, the link 176D _L ' is connected to seesaw link 177 _L ' and to input link 179Ai_'. The input link 179A _L ' in turn connects to input arm 179 _L ' of the valve 175i_'.

The linkage system 176 _L ' defines a leverage ratio by which the force at the actuator 105 _L ' is reduced and applied to the centre of the seesaw link 177 _L '. In this case, the force is reduced by a factor of 48. Preferably each link of the linkage system 176 _L ' is rigid. Optionally components 174 _L \ 175 _L \ 176 _L ' may be assembled with respect to the tibia portion 47A _L ' and then slid into a tubular housing portion of the tibia.

The control unit 173 _L ' may be adjustable to vary the force feedback to the user. In this example, the link 176C _L ' is pivotally connectable to any one of a plurality of mounting holes spaced along the length of the link 176B _L ' whereby the force-reduction ratio can be adjusted to suit user preferences. Other modes of adjustment, such as the various options discussed in respect of the multiplier link 167L, may be incorporated in the ankle control unit 173 _L '. Input rotary 181 _L ' connects the ankle control unit 173 _L ' to the input ankle. Arm 181 A _L ' of that rotary is connected to one end of the seesaw link 177 _L ' via link 181 B _L \

In analogous fashion, output rotary 183 _L ' (Figure 35) connects the ankle control unit 173 _L ' to the output ankle to take feedback therefrom. The arm 183A _L ' of that rotary is connected to the other end of the seesaw link 177 _L ' via link 183B _L '. The output rotary 183 _L ' is a feedback rotary from the output ankle. It responds, replicates and transmits the output ankle rotation to the seesaw link 177 _L '.

The bodies of the rotaries 181 _L ', 183 _L ' are fixed on a common shaft fixed with respect to the tibia portion 43A _L ' whilst the arms 181 A _L ', 183A _L ' are mounted to pivot independently about that shaft in direct relation to the corresponding cable movements.

Figure 19 illustrates the actuator 89L trunnion-mounted to the femur head 85L and a flex mount 189L by which the actuator 89L is connected to the pelvis unit 81 L (not shown in Figure 19). A hip control unit 191 L is of analogous construction to the ankle control unit 173L (Figure 20). It comprises a valve 193L, a see-saw link 195L, a push- pull cable 197L, a push-pull cable 199L, and a spring unit 201 L.

The push-pull cable 197L applies a translational signal from the rotary 119L of the input hip to the see-saw link. The push-pull cable 199L is connected between the pelvis unit 81 L and the femur head 85L and serves to apply a translational signal indicative of an angle of the femur 39L with respect to the pelvis unit 81 L and to apply that signal to the valve 193L via the see-saw link 195L.

The spring unit 201 L sits between the input shaft of the valve 193L and a see-saw link 203L. On one side of the spring unit, a force-feedback push-pull cable is connected to the see-saw link 203L. On the other side of the spring unit 201 L, a walk-assist push- pull cable 207L is connected to the see-saw link 203L.

The other end of the walk-assist push-pull cable 207L is connected to the multiplier link 167L (Figure 17) via amplitude link 209L. When the vehicle 1 is walking, the left leg 5L takes weight during its stance phase, and in turn the left multiplier link 167L deflects (anti-clockwise as drawn in Figure 17) as load is taken by the left leg before returning to its "leg unladen" position as the load is released from the left leg.

One end of the amplitude link 209L is connected to the push-pull cable 207L whilst the other end is connected at the end of another crank of the multiplier link 167L. This other crank is the same length as the amplitude link 209L. An adjuster 211 L is arranged to adjust an angle of the amplitude link with respect to the crank of the multiplier link, whereby a radius of the end of the push-pull cable 207L with respect to the pivot axis of the multiplier link 167L is adjustable upwards from 0 mm. Other radial adjustment mechanisms are possible.

Components 207L, 209L, 211 L constitute a walk-assist mechanism that provides a mode of the vehicle 1 user-selectable to reduce the operator effort necessary for walking.

For some tasks, the end of the cable 207L can be positioned coincident with the pivot axis of the multiplier link 167L whereby the push-pull cable 207L is essentially fixed in position, and in turn the hip control unit 191 L operates in a manner closely analogous to the ankle control unit 173L.

To adopt walk-assist mode, via a suitable user interface within the cabin, the operator triggers the adjuster 211 L to move the point of connection (between components 207L, 209L) to a radius from the pivot axis of the multiplier link 167L, whereby the push-pull cable 207L is periodically pushed back and forth in response to the periodic motion of the multiplier link 167L as the vehicle is walking. This period movement is applied to the see-saw link 203L. Walk-assist serves to bias the actuator 89L towards rearwardly driving the leg 5L (so as to forwardly propel the vehicle 1 ) in positive relation to the weight borne by the leg 5L.

Without walk-assist, when the vehicle is standing stationary with a neutral stance, the fore-aft feedback on the operator's left leg (delivered via the rotary 1 19L in this case) is also neutral. The radial adjustment mechanism illustrated in Figure 17 is configured so that, when walk-assist is engaged, not only is the cable 207 periodically driven, but a mid-point of that periodic motion is displaced from a non-walk-assist position of the cable. This shift tends to urge the hip actuator 89L towards forward movement. The net effect of these two changes is that the rearward urging of the leg 5L is positively related to an amount of weight borne by the leg 5L and a neutral point at which no fore-aft feedback is delivered to the operator via the rotary 119L is shifted so as to occur when the leg 5L is bearing a proportion of a weight of the vehicle 1.

In this way, when walk-assist is activated and the leg 5L is bearing the entire weight of the vehicle, the leg 5L is rearwardly urged without, or more than, corresponding rearward urging from the operator (i.e. the leg 5L is rearwardly biased). Towards the end of the stance phase of the leg 5L, as load is being relieved from that leg, the amount of weight passes a predetermined proportion of the vehicle's weight corresponding to neutral feedback, and walk-assist then urges the right leg to move forward without, or more than, corresponding forward urging from the operator (i.e. the leg 5L is forwardly biased, or to put it another way, negatively rearwardly biased). Walk-assist may be usefully employed in the context of vehicles with no analog of the cable 129L.

Turning to Figures 9 and 21 , actuators 213i_, 215L are mutually spaced in the fore-aft direction, in this case respectively fore and aft of the cross member 67, and act between the chassis 11 and the pelvis unit 81 L to control the leg 5L in abduction/adduction and toe-in/toe-out. Each of the actuators comprises a respective flex mount 217L, 219L. In this case, the actuators are inverted and the flex mounts sit atop the tail ends of the actuator bodies, whilst the actuator rods project downwardly to the lower reaches of the pelvis unit 81 L.

A lateral control unit 221 L takes translational feedback from the rotary 143L (Figure 11 ) and force-feedback from the flex mount 217L, and drives the actuator 213L. Instead of positional feedback being routed to the control unit 221 , a push-pull cable 223 connects the pelvis unit 81 L to a corresponding attachment point 121 L of the input hip. Thus, the rotary 143L, lateral control unit 221 L, actuator 213L, flex mount 217L and the forwardmost attachment point 121 L comprise a feedback loop via which the position of a front lower portion of the pelvis unit 81 L is controlled. The rotary 145L, lateral control unit 225L, actuator 215L, flex mount 219L and the rearward point of attachment 121 L together form a feedback loop for controlling a lateral position of a rearward lower portion of the pelvis unit 81 L.

Outwardly pushing on the foot plate 141 L to cause it to move with respect to the cradle 137L triggers the rotaries 143L, 145L, which in turn triggers the actuators 213L, 215L to move in unison to outwardly drive the lower reaches of the pelvis unit 81 L, whereby the leg 5L outwardly pivots about the T piece 71 L (abduction), and in turn, via the attachment points 121 L, the input leg 49L is driven to move outwardly until the neutral position of the foot plate 141 L with respect to the cradle 137L is resumed. The foot plate 141 L is mounted to twist with respect to the cradle 137L to differentially drive the actuators 213L, 215L to effect toe-in and toe-out movement (i.e. to pivot the leg 5L about the upright axis of the T piece 71 L).

Figure 22 illustrates a typical human gait in which the hips bob up and down with local maxima at mid-stance. The present inventor has recognised that if the output hips 61 L, 61 R were to bob up and down in a corresponding manner, this would be most uncomfortable for the operator, would consume power, and would stress and fatigue components of the vehicle. Preferred variants of the vehicle define a transfer function between the input and the output legs, such that the output legs do not simply mimic the movement of the input legs but, rather, serve to provide a smoother ride whilst the operator moves the foot holds 59L, 59R in a manner approximating the relative movement of the feet with respect to the hips during a typical human gait. This enables the operator to comfortably walk on the foot holds on the one hand, and on the other hand enables smoother forward conveyance. A preferred approach to this variation is to extend the output legs by an amount disproportional to the extension of the input legs and positively related (e.g. proportionate) to a magnitude of a departure of the output hips from their mid-stance position (e.g. a departure of the femur 39L with respect to the pelvis unit 81 L).

A preferred implementation of the concept comprises ride-smoothing units 227L, 227R (Figures 4 and 24 to 26) intercepting the cables 129L, 129R behind the operator.

The unit 227L comprises two pairs 229L, 231 L of rollers fixed with respect to each other and a further movable pair 233L of rollers. When the leg 5L is at mid-stance, the roller pairs 229L, 231 L, 233L sit in register to guide the cable 129L along a straight course (Figure 24). When the ride-smoothing mechanism 227L is in its operative configuration (Figures 24 and 25), the movable roller pair 233L rises and falls with respect to the fixed roller pairs 229L, 231 L to extend the cable path, thereby shortening the length of the cable relative to the cable path. This has similar effect to pressing down on the foot hold 59L whereby the actuator 93L is driven to open the knee 41 L as that knee departs from the mid-stance position.

Preferably, the movable rollers are carried by a rocker 235L driven to rotate by push- pull cable 237L connected (in a manner akin to the push-pull cable 199L) between the femur 39L and the pelvis unit 81 L to take a translational feedback signal related to the angular orientation of the femur with respect to the pelvis unit.

Preferably, the one or more of the movable pair 233L and the point of attachment of the cable 237L to the rocker 235L is movable with respect to a pivot axis of the rocker to enable the extent of ride-smoothing to be adjusted. In this example, an adjuster 238L is connected to a suitable user interface within the cabin to enable the operator to slide the movable pair 233L along the rocker 235L from the 100% position illustrated in Figure 25 to the 0% ride-smoothing illustrated in Figure 26. In the 0% position, the movable pair of rollers 233 (or more precisely, the cable-guiding gap therebetween) is moved into register with the pivot axis of the rocker 235 whereby the cable 129L remains undeflected from its straight path (from the roller pair 231 to the roller pair 233) as the rocker oscillates back and forth.

In the described example of the vehicle 1 , without ride-smoothing a user input akin to a typical human gait results in the output hips bobbing by about 155 mm (peak to trough). Preferred variants of the ride-smoothing mechanism enable operators to adjust the adjuster 238 to substantially eliminate this bobbing.

The legs 5L, 5R are preferably more than twice as long as a typical human's legs. Preferably, when the output leg 5L is at mid-stance (when the knee 41 L is at 90° in this case), the axis of the hips (i.e. the key point at the juncture of the T pieces 71 ) is more than 2 m above the ground, preferably more than 2 m above the ankles 45L, 45R. In this case, the positions of the ankles 45L, 45R are characterised by the position of their generally transverse pivot axes. Preferably, the ankle to hip measurement is in the range of 2,400 mm ± 500 mm, or more preferably 2,400 mm ± 150 mm.

A width of the output hips is characterised by the separation of the horizontal axes of the T pieces 71 L, 71 R. Preferably, a ratio of (a) an output hip-to-ankle length to (b) the output hip width is within 20%, more preferably within 10%, of a corresponding ratio for the input legs. The corresponding ratio for the input legs is the hip-to-ankle measurement (about 830 mm in this case) to an adjusted input hip width. The adjusted input hip width is the spacing of the input hips (about 600 mm in this case) less the inboard offsets of the foot holds 59L, 59R (i.e. less about 2 x 150 mm in this case). In this example, the output hip width is about 870 mm. In another variant having an output hip-to-ankle measurement of about 3 m, a hip width in the vicinity of 1 ,080 mm would be desirable.

Applying these geometric relationships:

A. when an operator stands so that their feet (corresponding to the foot holds) directly underlie their hips, the output feet directly underlie the output hips; and

B. when one of the extended input legs is abducted to move one of the foot holds into the operator's sagittal plane, the corresponding output foot is moved into the sagittal plane of the vehicle 1. These two correspondences contribute to the intuitive feel of the vehicle, and it is preferred that even variants of the vehicle 1 that do not comprise input legs are configured to provide A or B, or more preferably A and B, e.g. are configured so that when the foot of an extended operator's leg is moved into the operator's sagittal plane, the corresponding foot of the vehicle is moved substantially into the sagittal plane of the vehicle.

Preferred variants of the vehicle 1 are configured so that input movements relative to the operator's centre of mass produce output movements, relative to a centre of mass of the vehicle, that are about proportional. This also contributes to intuitive operation of the vehicle. The constraint 19 configured to enable an operator's body to pivot about at least one axis about coincident with the operator's centre of mass also helps in this regard. In a more elaborate implementation, the operator might be restrained to spherically pivot about their centre of mass whilst that centre point is fixed with respect to the chassis 11 (or more relevantly, with respect to the vehicle's centre of mass).

Preferred variants of the vehicle have long legs enabling them to traverse significant distances and step on and over obstacles that would impede the movement of other land vehicles. This however presents the challenge that, when the vehicle is standing, the cabin is high in the air. Whilst the operator might squat so as to draw the foot holds 59L, 59R as high as possible, and thereby lower the cabin, it would then be awkward for the operator to exit the vehicle from this position. Accordingly, preferred variants of the vehicle 1 comprise a vehicle-lowering mode user-selectable to lower the vehicle whilst the input legs 49L, 49R remain extended. Most preferably, the vehicle-lowering mode lowers the knees 41 L, 41 R to 0° (see Figure 27) and the vehicle is configured to stably retain this position. A body of the vehicle may be equipped with landing gear (or other stabilising ground-contacting portions) that is arranged to contact the ground when the body is lowered in this way and/or a centre of mass of the vehicle 1 may be positioned so as to remain within the footprint of the feet 47 without user input.

Preferred variants of the vehicle 1 lower to the ground and rest stably to enable the operator to climb in and out without the need for elevated docking facilities (e.g. without the need for elevated docking facilities akin to those required by large passenger jets). Variants of the vehicle 1 may be equipped with boarding ladders (e.g. akin to the ladders carried by large mining trucks) although preferred variants do not require ladders.

Preferably the vehicle is equipped to rest stably in its lowered position whilst one, or preferably both, of the plurality of ankle actuators and the plurality of knee actuators are relaxed. Most preferably, this is achieved whilst substantially all of the weight of the vehicle is borne by the feet of the vehicle. In a preferred implementation the knees are configured to fully close (e.g. wherein the included angle at the front of each knee is reduced to zero) and a permanent or selectively engageable stop limits the ankle movement so that as the vehicle is lowered to the ground it cants forward with respect to its upright walking position. In this way the mass of the high mounted components move forward to offset the rearward movement of the mass of the legs. This arrangement allows the vehicle to advantageously be stored on stable level ground without any power supply to maintain pressure in the actuators. It also enables the actuators to be conveniently serviced.

A vehicle-lowering system 239 intercepts the cables 129L, 129R behind the ride smoothing units 227L, 227R (see Figures 4 and 28 to 30).

The vehicle-lowering unit 239 comprises a single member 241 mounted to pivot so as to simultaneously manipulate the respective control sub-systems for the left and right output legs 5L, 5R. The member 241 is preferably a compound member comprising separate integral bodies fastened to each other. Alternatively, it may itself be a single integral body of material, e.g. it may be machined from billet. "Integral" and similar terminology is used herein in its conventional sense to refer to a single contiguous body of material. As such, two bodies may be integrated by welding, but not by conventional mechanical fastening.

Each end of the member 241 is essentially the same as the other. The left-hand end of the member 241 carries a movable roller 243L carried by the member 241 at a radius to a lateral axis about which the member 241 pivots. The movable roller 243L sits between a pair of fixed rollers 245L, 247L and the cable 129L follows a serpentine path about these three rollers. As best shown in Figure 29, rotaries 249L, 251 L each are fixed to the member 241 and each carry a respective crank 253L, 255L.

Rotary 249L is connected to the input ankle 57L via a push-pull cable (not shown). The rotary 249L takes the translational control signal from the rotary of the ankle 57L and drives the cable 181 L via the crank 253L with respect to the body of the rotary 249L. Components 251 L, 255L likewise connect the hip-position push-pull cable 197i_to the rotary 119L via push-pull cable 197'L (Figure 12). Figure 30 illustrates the vehicle- lowering system 239 in its operative configuration. To lower the vehicle, whilst the input legs 49L, 49R remain extended, the member 241 is pivoted to simultaneously turn cranks 253L, 255L and move roller 243L (with respect to rollers 245L, 247L so as to shorten the cable path). In this way, the vehicle-lowering system 239 co-ordinates the operation of the hips, knees and ankles to lower the vehicle.

In variants of the vehicle 1 comprising only an electrical connection between the input system and the output system, the vehicle-lowering member 241 might be replaced by a software element.

This example of the vehicle 1 comprises an interlock between the vehicle-lowering and ride-smoothing systems. Preferably, a user interface by which a user triggers rotation of the vehicle-lowering member 241 is also connected to the adjuster 238L (and the corresponding adjuster of the right leg) to deactivate the ride-smoothing system before lowering the vehicle.

The combination of a forward-mounted cabin and rearwardly-bending knees is preferred in that it enables the cabin to be brought lower to the ground when the vehicle squats. The low-mounted cabin also keeps the operator closer to a centre of mass of the machine which improves the feel of the machine. It helps the operator to feel as if they are a part of the machine rather than sitting atop it. Ideally, operating the vehicle quickly becomes instinctive, thereby reducing operator fatigue and freeing cognitive capacity for other tasks.

Many variants of the concepts disclosed herein are possible. By way of example, whilst mechanical transmissions in the form of push-pull cables are described for a variety of purposes, various of those cables might be replaced by cables acting only in tension (e.g. acting in tension against a suitable spring). Hydraulic circuits are another example of mechanical transmissions. By way of example, some of the push-pull cables described herein might be replaced by hydraulic lines akin to automotive brake lines. In some places, this might further improve the fidelity of the feedback. Whilst hydraulic servo systems have been described, other control systems are possible. Figures 31 and 32 illustrate an alternative knee control unit 147L' and correspond to Figures 15 and 16. The knee control unit 147L' does without the flex mount 95L and instead relies upon a hydraulic force-feedback system. Without the flex mount 95L, there is no need to compensate for the uncommanded knee closure associated with flexing within the flex mount, and in turn there is no need for the null link 157L.

Instead of the flex mount and cable based force-feedback system, the knee control unit 147L' incorporates a fluid actuator 253L. In this case, the actuator is mounted to a short crank portion 255L opposite the crank portion 257L to which the trim adjuster 171 L' is attached.

The valve 149L' comprises outlet ports 259L that are connected towards corresponding ports towards each end of the body of the actuator on the output knee. The ports 259L are also directly connected to a corresponding pair of ports 261 along the body of the actuator 253L. In this way, the actuator 253L is plumbed in parallel to the actuator on the output knee. As such, the pressure differential across the two ports 261 substantially corresponds to the pressure differential across the two ports of the actuator on the output knee, which also substantially corresponds to the pressure differential across the ports 259L.

A bleed-down orifice 263 mutually connects the ports 261 to cause the valve 149L' to deliver a small volume of fluid to maintain constant force-feedback. This small flow rate entails a negligible loss of efficiency but aims to provide improved force-feedback by ameliorating lags and transients (e.g. shuddering) that might occur if the pressure between the output actuator and feedback actuator pressures were simply allowed to equalise "under their own steam", particularly in the context of a change in the load on the output leg without commanded movement of the output actuator, e.g. in the context of ground-subsidence and/or movement of the other output leg.

In this example, the actuator 253L and the corresponding actuator on the output knee are configured to simultaneously expand in response to the same pressure signal. It would also be possible for one of the actuators to be driven to expand whilst the other actuator is driven to retract, whilst the two actuators are plumbed in parallel to each other as the wording "parallel" is used herein. Likewise, in some potentially practical plumbing configurations, the output actuator and the feedback actuator might be mutually connected when the valve is driving the output actuator in one way or the other, but not when the valve is in its neutral position. Such arrangements are "parallel" as that word is used herein.

In this way, as the actuator on the output knee is urged to open the knee, the actuator 253 urges the multiplier link 167L' to rotate so as to shift the anchor point against which the spring 163L' acts, and thereby urges the input link 155L towards extending the cable path (that is, shortening the relative length of the cable 129L'), thereby providing force- feedback to the user.

Typically, the actuator 253L will have a much smaller effective area (e.g. piston diameter) than the actuator on the output knee whereby, whilst exposed to the same fluid pressure differential, a smaller force is applied to the multiplier link 167i_'. The effective length of the crank 255L relative to the effective length of the crank 257L also influences a magnitude of the force-feedback. A hydraulic intensifier mutually connecting the feedback and output actuator is another possibility. Typically, it is convenient for the effective length of the crank 255L to be relatively shorter. One or both of the effective lengths might be adjustable. In this case, the effective length of the crank 257L is adjustable and, at a midpoint of a range of that adjustment, the effective length of the crank 257L is about three times the effective length of the crank 255L.

Many variations on the concept are possible. By way of example, the actuator 253 L and the spring 163L' essentially work in parallel whereby these two components might be swapped. Indeed, in a simple knee control system without the walk-assist function, the multiplier link 167L' and the spring 163L' might be eliminated and the actuator 253L might simply act directly on the input link 155L'.

Fundamentally, the illustrated force-feedback system comprises a hydraulic force- feedback actuator hydraulically connected to the output actuator to provide force- feedback corresponding (e.g. proportional) to the force applied by the output actuator. Other plumbing arrangements are possible. In one advantageous variant, the bleed- down orifice 263 is eliminated and both ends of the feedback actuator 253L are fluidly connected to the high-pressure end of the output actuator 93L. In this variant, whilst the output leg is weight-bearing, the lower-pressure end of the actuator 93L is held at a constant pressure, which in this example corresponds to a reservoir pressure of the hydraulic system. As such, the pressure on the high-pressure side of the actuator 93L linearly varies with respect to the load applied by that actuator. By exposing both ends of the actuator 253L to this pressure, the actuator 253L exerts a force corresopnding to the product of the pressure on the high-pressure side of the actuator 93L and a cross- sectional area of a rod of the actuator 253L. In this way, a relatively robust and inexpensive actuator can be used as the force-feedback actuator and to scale down the force-feedback. This in turn enables the crank portion 255L to be extended (or the knee control unit 147L' to be otherwise reconfigured) to improve the fidelity of the force- feedback.

A drawback of this variant is a loss of the force-feedback that occurs when a lower end of the actuator 93L is pressurised (and the top end is dropped to reservoir pressure) to lift the output leg. This means that the operator cannot feel just how hard the leg is being pulled up. The inventor regards this as a compromise worth making for improved feedback whilst the output leg is load-bearing.

Similar hydraulic force-feedback may be employed in connection with the other joints. By way of example, in connection with the ankle control system of Figure 18, the flex mount 107L and cable 187L might be eliminated by replacing the spring 185L with an actuator akin to the actuator 253L and plumbed in parallel to the actuator 105L.

While the above description refers to one embodiment of the vehicle, it will be appreciated that other embodiments can be adopted by way of different combinations of features. Such embodiments fall within the spirit and scope of this invention. Furthermore, various elements of the technology disclosed herein may well be employed in other contexts. By way of example, various details of the control system 7 may be employed in the context of walking vehicles other than bipedal vehicles (e.g. in the context of a quadruped). Indeed, various aspects of the control system may be employed in entirely different contexts. The flex mounts may be conveniently employed in other contexts, perhaps unrelated to vehicles, where force-feedback is desirable. The term "comprises" and its grammatical variants has a meaning that is determined by the context in which it appears. Accordingly, the term should not be interpreted exhaustively unless the context dictates so.