Undercarriage for a tracked vehicle

Abstract

A tracked vehicle comprises an undercarriage 100 having a main body 101 with a longitudinal axis, four track assemblies 105a-d and four arms 140a-d. The four arms 140a-d extend from the main body 101

Description

Field of the invention The invention relates to an undercarriage for a tracked vehicle, in particular to an undercarriage for heavy machinery and military vehicles. Background A conventional tracked traction system may use a rigid two-tracked system, with both tracks operating in the same plane fixed to the rotating main bearing. The main chassis of the upperworks or superstructure is structurally rigid and can include the control cabin, gear boxes, hydraulic pumps, hydraulic tanks and related equipment. The upperworks can be connected on top of the lowerworks (i.e. the undercarriage) by a rotating bearing, where the undercarriage can include structural beams, side frames, and drive motors, rollers, idlers, chains and plates for the tracks. When tracked machines operate on uneven ground, their tracks act as a single, loadbearing plane with a plate face that contacts the ground. The machine’s rotating upperworks also follow the ground plane defined by the tracks’ plate faces. As the machine moves over uneven terrain, the tracks - fixed to the upper works and lacking an independent counteractive system - conform to the ground’s uneven profile, limited by the rigidity of the steel tracks. This irregular terrain profile is transmitted to the machine and its operator, with speed of movement further affecting the operator's ability to control the machine. At low speeds, control is generally maintained, while at medium to high speeds, control becomes difficult. This effect is seen in equipment such as drilling and piling machines, cranes, excavators, main battle tanks, and other track-mounted machines like Howitzer artillery. When deployed on uneven ground, the two-track system lacks flexibility, resulting in the machine missing low points and riding over crests, which transmits movement to the entire machine body. If the ground is inclined, the tracked machine will follow this slope regardless of the orientation of any attached tools. In machines with a rotating upper works or turret, such as piling machines with a leader and drilling string, the vertical alignment of the drilling string is compromised when the upper works rotate, even when the machine is stationary. In current piling and drilling machines, the vertical alignment necessary for accurate pile placement can be lost as the leader is rotated, disrupting its initial alignment. For maximum pile load-bearing capacity and integrity, concrete piles need to remain vertical to prevent any load eccentricity. It is an aim of the present disclosure to provide improvements to undercarriages for tracked vehicles. Summary of the invention An aspect of the disclosure aims to provide an undercarriage for a tracked vehicle, the undercarriage comprising any or all of the following features: a main body having a longitudinal axis; four track assemblies; and four arms extending from the main body, each arm of the four arms being configured to pivotably couple a corresponding track assembly of the four track assemblies to the main body to facilitate steering of the tracked vehicle; and wherein each track assembly of the four track assemblies comprises: a first part coupled to its corresponding arm; and a second part configured to receive a track of the track assembly; wherein the first part is coupled to the second part such that the second part can pitch and roll relative to the first part. Providing an undercarriage having four track assemblies may provide improved stability. It may also provide redundancy, because if one track assembly is damaged then the tracked vehicle may be operated using the three remaining track assemblies. The arrangement can also provide a tracked vehicle in which each of its four track assemblies can steer (i.e., in the yaw direction), pitch and roll relative to its corresponding arm. This may provide an undercarriage that can better compensate for undulations in terrain to maintain an upperworks of the tracked vehicle at a desired orientation, for example level with a horizontal plane. The longitudinal axis may be parallel to the driving direction. The longitudinal axis may be in a horizontal plane. At least one track assembly may comprise a third part. Each track assembly may further comprise a third part. The third part may be configured to couple the first part to the second part. The third part may be rotatably coupled to the second part to facilitate rotation of the track assembly relative to the corresponding arm about a pitching axis. The rotation of the second part about the pitching axis may be constrained by contact between the first part and the second part. The third part may be rotatably coupled to the first part to facilitate rotation of the track assembly relative to the corresponding arm about a roll axis. The third part may comprise a first bore. The first bore may be configured to receive a shaft of the first part. The third part may be coupled to the second part by a bearing. The rotational axis of the bearing may be transverse to the first bore. The third part may comprise two cylindrical portions. The cylindrical portions may intersect one another. The third part may comprise a single integral component. The third part may comprise two intersecting cylinders. The longitudinal axes of the intersecting cylinders may be perpendicular to each other. The second part may comprise a frame. The frame may be configured to support the track. The track may be supported on the frame by a plurality of rollers mounted to the frame. At least one track assembly of the four track assemblies may further comprise an actuation member. The actuation member may be configured to raise a portion of the track of the at least one track assembly out of contact with the ground to facilitate slotting with an adjacent track assembly of the four track assemblies. Each arm of the four arms may be configured to facilitate independent pivoting of each arm with respect to the main body. At least one arm of the four arms may comprise a pivotable coupling. The pivotable coupling may be configured to facilitate a range of rotation of the track assembly relative to the main body of at least 90 degrees, preferably at least 100 degrees, preferably at least 110 degrees. Each arm may comprise a proximal portion connected to the main body; a distal portion connected to a corresponding track assembly; and a pivot joint between the proximal portion and the distal portion. The pivot joint may be arranged to facilitate pivoting of the proximal portion to the distal portion in a single plane. This may facilitate the portions being pivotable relative to one another about a single pivot axis. The pivot axis may be a vertical axis. The proximal portion may be extendable. The proximal portion may comprise a telescopic assembly. The telescopic assembly may facilitate extending and retracting of the track assembly with respect to the main body. The telescopic assembly may comprise hydraulic cylinders. By providing extendable arms, this can provide for increased stability. This can also provide the advantage of allowing the centre of gravity of the tracked vehicle to be adjusted, for example by independently extending different arms by different degrees. This may be particularly beneficial if one of the four track assemblies is malfunctioning, because this track assembly could be removed while the tracked vehicle could be operated using the remaining three track assemblies. Each arm may extend from the main body at an angle measured with respect to the longitudinal axis of approximately 40 degrees. The angle may be at least 10 degrees, preferably at least 20 degrees, preferably at least 30 degrees, preferably at least 35 degrees. The angle may be between 20 degrees and 60 degrees from the longitudinal axis, preferably between 30 degrees and 50 degrees from the longitudinal axis, more preferably between 35 degrees and 45 degrees from the longitudinal axis. The main body may comprise four comers. Each arm may extend outwards from the main body from a corresponding corner of the four comers. An aspect of the disclosure also provides a tracked vehicle comprising the undercarriage as described hereinabove. Brief description of the drawings Embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a plan view of an undercarriage according to the present disclosure in a compact configuration; Fig. 2 is a plan view of the undercarriage of Fig. 1 in an expanded configuration; Fig. 3 shows the undercarriage of Fig. 2 in a steering configuration; Fig. 4 shows the undercarriage of Fig. 2 in a lateral drive configuration; Fig. 5A is a schematic diagram of a first part and third part of an articulation joint of a track assembly according to the present disclosure; Fig. 5B additionally shows the second part of the articulation joint; Fig. 6 is a plan view of an articulation joint according to the present disclosure; Fig. 7 is a side view of a track assembly according to the present disclosure; Fig. 8 is a rear view of a track assembly according to the present disclosure; Fig. 9 is a side view of part of an articulation joint according to the present disclosure; Fig. 10 is an end view of part of articulation joint according to the present disclosure; Fig. 11A is a side view of adjacent track assemblies according to the present disclosure in a stacked configuration; Fig. 11B shows the adjacent track assemblies in an unstacked configuration; Fig. 12 is a schematic block diagram illustrating a system for controlling the pose of a tracked vehicle according to the present disclosure; Fig. 13 is a functional block diagram illustrating a system for controlling a tracked vehicle according to the present disclosure; and Fig. 14 is a functional block diagram illustrating a traction control system for a tracked vehicle according to the present disclosure. Detailed description of the drawings Embodiments of the disclosure relate to an undercarriage for a tracked vehicle. A tracked vehicle is one which contacts and moves along the ground using tracks, instead of, for example, wheels. Such tracks may be termed continuous tracks, caterpillar tracks or endless tracks. Examples of tracked vehicles include those found in military vehicles such as tanks, or construction vehicles such as pile drivers. In such examples, the undercarriage typically has two parallel tracks disposed on opposite sides of a chassis. The tracks cannot pivot relative to the main body which means that, to steer, the tracks can be driven at different relative speeds. In one example of the disclosure, an undercarriage has a main body or chassis with four track assemblies. Each track assembly has a continuous track driven by a motor. Each track assembly is connected to the main body via an arm. The arm includes an elbow joint so that the track assembly can pivot relative to the main body, for example to facilitate steering. The arm can also provide an extended configuration and a retracted configuration, so that each track assembly can be brought closer to or further away from the main body, for example by using a telescopic assembly. Each track assembly is configured to rotate about a roll axis and a pitch axis relative to the arm. Therefore, since each track assembly can rotate in the yaw axis by virtue of the pivoting joint, this allows each track assembly to rotate in all three orthogonal axes. The pitching and rolling can be facilitated by an articulation joint between the arm and the track assembly. The articulation joint can include a first part and a second part. The first part is fixed to the arm, for example rigidly fixed so that no rotation is possible. The second part defines a frame of the track assembly which is the part around which the track can be mounted. The first part is coupled to the second part to facilitate pitching and rolling relative to the first part. The articulation joint can achieve this by including a third part, which may comprise intersecting cylinders. A first of the intersecting cylinders is rotatably mounted around a shaft of the first part, so that the third part can rotate about a roll axis relative to the first part. A second of the intersecting cylinders is rotatably mounted to the second part, so that the third part can rotate about a pitch axis relative to the second part. In this way, the first part can pitch and roll relative to the second part. Since the first part is fixed to the arm and the second part defines a frame of the track assembly, this configuration permits the tracks to pitch and roll relative to the corresponding arm, thereby allowing the tracks to follow uneven terrain. Figure 1 shows an undercarriage 100 for a tracked vehicle. The undercarriage 100 comprises a main body 101. The main body 101 has a generally rectangular form and has a longitudinal axis 103. The longitudinal axis 103 may be considered a ‘Y’ axis. Accordingly, an axis in the horizontal plane that is perpendicular to the longitudinal axis may be considered an ‘X’ axis. A vertical axis which is perpendicular to the X and Y axes may be considered a ‘Z’ axis. The main body 101 is configured to receive the upperworks (not shown) of the tracked vehicle. For example, the undercarriage 100 may be configured to support the upperworks of a tank (including the main hull and the guns, etc.), or the upperworks of a pile driver (including the operator’s cab and the leader, etc.), or the upperworks of other types of tracked vehicles. The undercarriage 100 comprises a main bearing 106 at a central portion thereof. The main bearing 106 has a rotational axis that is normal to the main body 101. In this way, the undercarriage 100 can be rotatably coupled to the upperworks such that the upperworks, or at least a portion thereof, can rotate relative to the main body 101. The undercarriage 100 also comprises four track assemblies. The track assemblies are configured to support the main body 101 over the ground, for example to facilitate movement of the undercarriage 100 over the ground so as to permit driving of the tracked vehicle. The four track assemblies comprise a first track assembly 105a, a second track assembly 105b, a third track assembly 105c and a fourth track assembly 105d. The track assemblies are arranged in a rectangular array with respect to the main body 101. In the arrangement shown, taking the top of the page of Figure 1 to be the “front” of the vehicle, the track assemblies may be arranged such that: the first track assembly 105a is at a front left position of the main body 101; the second track assembly 105b is at a front right position; the third track assembly 105c is at a back left position; and the fourth track assembly 105d is at a back right position. As such, each of the track assemblies may be arranged at a separate corner of the main body 101. The four track assemblies may all be configured in the same manner and may comprise the same components and arrangement of such components. It will be appreciated that an aspect of one track assembly may be orientated differently (e.g. mirrored) to that of a different track assembly. For brevity, the description will refer to a track assembly 105, which can refer to any one of the four track assemblies and may refer to each of the four track assemblies, as appropriate. In particular, features disclosed in relation to the track assembly 105 may apply to all four track assemblies. The track assemblies are connected to the main body 101 via a plurality of arms. In the arrangement shown, the undercarriage 100 comprises four arms, such that each track assembly is coupled to the main body 101 by one of the four arms. The four arms comprise a first arm 140a, a second arm 140b, a third arm 140c, and a fourth arm 140d. For example, the first track assembly 105a is connected to the main body 101 via the first arm 140a, and the second track assembly 105b is connected to the main body 101 via the second arm 140b, and so on for the other arms. The four arms may all be configured in the same manner and may comprise the same components and arrangement of such components. It will be appreciated that an aspect of one arm may be orientated differently (e.g. mirrored) to that of a different arm. For brevity, the description will refer to an arm 140, which can refer to any one of the four arms and may refer to each of the four arms, as appropriate. In particular, features disclosed in relation to the arm 140 may apply to all four arms. The arm 140 extends from the main body 101 at an angle of approximately 40 degrees to the longitudinal axis 103 in the horizontal plane (i.e. when viewed from above). As shown in Figure 1, each arm extends from the main body 101 at an angle corresponding to the position of its associated track assembly. For example, the arm 140 extends diagonally from the main body 101 towards the front left to couple the first track assembly 105a to the main body 101. As will be described, the arms are extendable between a retracted and an extended position. In Figure 1, the arms are in the retracted position such that the undercarriage 100 is in a compact configuration. Figures 2 to 4 show the undercarriage 100 in an expanded configuration. In particular, Figure 2 shows additional detail of the arm 140. The arm 140 comprises an upper arm 141 and a forearm 143. The upper arm 141 is disposed at a proximal end of the arm 140 (i.e. the end that is closest to the centre of the main body 101) and the forearm 143 is disposed at a distal end of the arm 140 (i.e. the end closest to the corresponding track assembly). The upper arm 141 is configured to facilitate the extension of the arm 140 so as to bring the corresponding track assembly 105 into an extended or retracted position. This can be achieved by the upper arm 141 comprising a telescopic arrangement comprising at least two telescopic sections. In the arrangement shown, the arm 140 comprises three telescopic stages: a first stage 141a, a second stage 141b, and a third stage 141c. The first stage 141a is arranged at the distal end of the upper arm 141 and the third stage 141c is arranged at the proximal end of the upper arm 141, such that the second stage 141b is coupled between the first stage 141a and the third stage 141c. The three telescopic stages comprise hollow shafts which are nested together to provide the telescopic arrangement. In particular, the first stage 141a has a smaller cross sectional area than the second stage 141b such that the first stage 141a can be slidably received within the second stage 141b. Likewise, the second stage 141b has a smaller cross sectional area than the third stage 141c such that the second stage 141b can be slidably received within the third stage 141c. The three stages may each comprise a hollow shaft that is substantially cylindrical or cuboidal, for example. In either case, one or more shafts may be tapered to facilitate the compact configuration. In the arrangement shown, due to the angle at which the arm 140 extends from the main body 101, the proximal end of each stage is tapered to facilitate nesting in the retracted position (see Figure 1). Similarly, the distal end of each stage may be tapered to facilitate nesting in the retracted position, in particular to facilitate abutment against the corresponding track assembly 105. The arm 140 also comprises an extension control device 144. The extension control device 144 is configured to control the extension and retraction of the arm 140. The extension control device 144 may be connected between the first stage 141a and the third stage 141c to control the separation therebetween. In the arrangement shown, the extension control device 144 is a hydraulic cylinder. The hydraulic cylinder is disposed within the channel provided by the hollow shafts of the three stages of the upper arm 141. The arm 140 may also comprise a reel 148. The reel 148 can be configured to store excess cable when the arm 140 is in the retracted position, for example to ensure that there is sufficient length of cables for communications (e.g. electrical communications) between the track assembly 105 and the main body 101. At the proximal end of the upper arm 141, the third stage 141 c is coupled to the main body 101 via a shoulder joint 146. The shoulder joint 146 can comprise one or more pins received in one or more holes to pivotably couple the arm 140 to the main body 101, in particular via the third stage 141c. In the arrangement shown, the shoulder joint 146 is configured to facilitate pivoting of the arm 140 about a horizontal axis that is perpendicular to the arm 140. In other words, the shoulder joint 146 is configured to provide pivoting of the arm 140 in a vertical plane. The undercarriage 100 may comprise an elevation control device 147. The elevation control device 147 may be configured to control the pivot angle of the arm 140 with respect to the main body 101, in particular to control the elevation of the track assembly 105 with respect to the main body 101. In this way, the elevation control device 147 may be configured to actuate and / or damp pivoting motion between the arm 140 and the main body 101. The elevation control device 147 may be a hydraulic cylinder. In the arrangement shown, the elevation control device 147 comprises a pair of hydraulic cylinders arranged between each arm 140 and the main body 101. As best seen in Figure 3, the upper arm 141 is coupled to the forearm 143 by an elbow joint 142. The elbow joint 142 is configured to provide a pivotable coupling in the arm 140. In particular, the elbow joint 142 can facilitate pivoting of the forearm 143 relative to the upper arm 141 about a vertical axis (i.e., normal to the page of Figure 2). In this way, the forearm 143 can yaw relative to the upper arm 141 and the main body 101. The arm 140 may further comprise a yaw control device 145. The yaw control device 145 is configured to control the pivot angle of the elbow joint 142. In the arrangement shown, the yaw control device 145 is arranged between the upper arm 141 and the forearm 143 to control the pivot angle therebetween. In this way, the yaw control device can be configured to actuate and / or damp pivoting motion between the upper arm 141 and the forearm 143. The yaw control device 145 may be a hydraulic cylinder. As shown in Figure 3, the elbow joint 142 allows each track assembly to pivot independently with respect to the corresponding upper arm 141 and the main body 101. As such, the pivotable coupling provided by the elbow joint 142 can facilitate steering of the tracked vehicle. In the example configuration shown, for a driving direction “up the page”, the undercarriage 100 can be steered to the right. As best seen in Figure 4, the elbow joint 142 can permit a pivoting range of at least 90 degrees. In other words, the undercarriage 100 can be configured such that each track assembly 105 can be moved between a first position (see Figure 2) that is parallel to the longitudinal axis 103 and a second position (see Figure 4) that is perpendicular to the longitudinal axis 103. As such, as well as driving in a direction that has at least a component parallel to the longitudinal axis 103, the arms 140 of the undercarriage 100 can be arranged to drive the tracked vehicle along a lateral axis (e.g. perpendicular to the longitudinal axis 103). Figures 5A to 10 illustrate how the arm 140 can be coupled to its corresponding track assembly 105 to facilitate pitching and rolling relative to the arm 140. With particular reference to Figures 5A to 6, this can be achieved by an articulation joint. The articulation joint comprises a first part 110, a second part 120, and a third part 130, as best seen in Figure 5B. The first part 110 comprises an articulation member 111. The articulation member 111 comprises an articulation fork 111a and an articulation shaft 111 b. As shown in Figure 5A, the articulation fork 111a is substantially arcuate or C-shaped. The articulation fork 111a has two ends comprising apertures (see Figure 6) configured to receive the articulation shaft 111b. The apertures may be splined apertures 115 (see Figure 10). The ends of the articulation fork 111a may comprise frustoconical portions 116. The articulation shaft 111b is configured to connect between the two ends of the articulation fork 111a. In this respect, the articulation shaft 111b can be fixedly connected to the articulation fork 111a, for example such that no rotation therebetween is possible. This may be achieved by the articulation shaft 111b comprising splines along the longitudinal axis of the shaft, wherein the splines are configured to couple with corresponding splines in the apertures of the articulation fork 111a. As shown in Figure 6, the articulation shaft 111b is fixedly connected to the articulation fork 111a by at least one end plate 113. The end plate 113 is connected to the articulation shaft 111b by at least one screw received in a threaded hole of the articulation shaft 111b, so as to secure the articulation shaft 111b with the articulation fork 111a. As shown in Figure 6, the arm 140 is connected to the track assembly 105 via a plate connector 112. In particular, the plate connector 112 is configured to couple the forearm 143 to the articulation joint of the track assembly 105. In more detail, the plate connector 112 can provide a direct connection between the forearm 143 and the first part 110 of the articulation joint, particularly the articulation fork 111a. The plate connector 112 may be fixed between these components by a plurality of bolts 112a. As best seen in Figure 5B, the second part 120 of the articulation joint comprises a frame 121. The second part 120 is illustrated in a schematic manner in Figure 5B so as to illustrate how the components can move relative to each other, but it will be appreciated in relation to the later figures that the second part 120 can be configured to receive the track of the tracked vehicle. The frame 121 comprises a plurality of walls. The walls may be arranged in a cuboidal manner. The walls may be solid walls, or may be notional walls, i.e. imaginary planes bounded by the edges of the frame 121. In the arrangement shown, the frame 121 comprises a front wall 121a, a rear wall 121b, a top wall 121c, a bottom wall 121 d and a side wall 121e. The frame 121 also has an opening 121f, which may be disposed opposite the side wall 121 e, so as to provide an opening in which the first part 110 and the third part 130 can be received. The second part 120 is arranged to be pivotably connected to the first part 110 such that the second part 120 can pivot about a pitch axis 130a relative to the first part 110. Also, the second part 120 is configured to be pivotably connected to the first part 110 such that the second part 120 can pivot about a roll axis 110a relative to the first part 110. The pivotable connections may be provided by the third part 130. In particular, the second part 120 may be configured to be connected to the first part 110 via the third part 130. As best shown in Figure 5A, the third part 130 can comprise intersecting cylinders. In particular, the third part 130 may comprise a first cylinder 131 and a second cylinder 132. The first cylinder 131 may be integral with the second cylinder 132, for example by forming the two cylinders from a cast, welded and / or machined component. The first cylinder 131 may be longer than the second cylinder 132. The first cylinder 131 may have a smaller diameter than the second cylinder 132. The second cylinder 132 may intersect the first cylinder 131 approximately halfway along the axial length of the first cylinder 131. The third part 130 may comprise a bore, which may be defined through the first cylinder 131. The bore may be configured to receive the articulation shaft 111b. The third part 130 may be connected to the first part 110 by mounting the first cylinder 131 around the articulation shaft 111b, for example via the bore. In this way, the first cylinder 131 can be arranged about the roll axis 110a. The second part 120 may be connected to the third part 130 by a rotatable connection between the second cylinder 132 and the side wall 121 e of the frame 121. In this way, the second cylinder 132 can be arranged around the pitch axis 130a. With further reference to Figure 5B, it can be envisaged that by virtue of the third part 130 being rotatably mounted on the articulation shaft 111b, the second part 120 and the third part 130 can rotate about the roll axis 110a relative to the first part 110. The second part 120, by virtue of its rotatable connection with the third part 130, can rotate about the pitch axis 130a, relative to the first part 110 and the third part 130. Given that the first part 110 is fixedly connected to the arm 140, it will be appreciated that the articulation joint facilitates the second part 120 pitching and rolling relative to the arm 140. In further detail, Figure 6 shows how the third part 130 is mounted to the first part 110. The first cylinder 131 is provided around the articulation shaft 111b using at least one bearing 134, which may be a roller bearing such as a spline bearing. The third part 130 may comprise a roll control device 133. The roll control device 133 may be configured to control and / or damp rolling motion between the third part 130 and the first part 110. This may be achieved by the roll control device 133 comprising a disc brake in association with a biasing member. The articulation joint may comprise a thrust washer 136 provided between the third part 130 (e.g. the first cylinder 131) and the first part 110 (e.g. the articulation fork 111a). The thrust washer 136 may be configured to space the first cylinder 131 from an inner surface of the articulation fork 111a. Figure 7 shows a track assembly 105 from the side. As described previously, the track assembly 105 comprises an articulation fork 111a and an associated articulation shaft 111b which are coupled to the frame 121 via the first cylinder 131 and the second cylinder 132. Figure 7 also shows that the second part 120 is rotatably mounted to the third part 130 via a mounting bearing 135. The mounting bearing 135 may comprise a roller bearing, for example having an outer race fixed to the frame 121 (e.g. to the side wall 121 e) and an inner race fixed to the third part 130 (e.g. to the second cylinder 132). The track assembly 105 may also comprise a pitch control device 137. The pitch control device 137 may be a hydraulic cylinder provided between the second part 120 and the first part 110, in particular between a top wall 121c and an end of the articulation fork 111a, such that it is aligned along the roll axis 110A. The pitch control device 137 may be configured to control and / or damp pitching motion between the second part 120 and the first part 110. As shown in Figure 7, the track assembly 105 comprises components of a continuous track 124, also known as an endless track ora caterpillar track. The track 124 comprises a series of track plates 125, mounted to the frame by a track chain 126, and configured to roll around the frame 121 by a plurality of track rollers 127, an idler 123, and a drive motor 122. For example, the track assembly 105 may have eight rollers 127 mounted to the bottom of the frame 121 (e.g. to the bottom wall 121 d). It will be appreciated that the track assembly 105 may have a different number of rollers, such as four, five, six, seven, nine, or ten rollers 127, for example, which could together be configured to distribute the load of the track assembly 105. In the arrangement shown, the drive motor 122 is arranged at an opposite longitudinal end of the track assembly 105 to the idler 123. The drive motor 122 is configured to drive the track plates 125 around the frame 121 via the track chain 126. Given that the track 124 is mounted around the frame 121, it will be appreciated that references to the second part being pivotable with respect to the first part 110 and the third part 130 will also apply to the track 124. For example, the articulation joint facilitates pitching of the track 124 relative to the first part 110 (and therefore relative to the forearm 143) about the pitch axis 130a. As illustrated in Figure 7, if it is considered that the drive motor 122 is at the front of the track assembly 105, then the track 124 can be seen to be pitched downwards by virtue of the front of the articulation fork 111a being at the top of the frame 121 (e.g., closer to the top wall 121c than to the bottom wall 121 d) and the rear end of the articulation fork 111b being at the bottom of the frame (e.g., closer to the bottom wall 121 d than to the top wall 121c). In view of the articulation joint, it will be appreciated that the track 124 can rock up and down (e.g. in the manner of a seesaw) about the pitch axis 130a, for example via the mounting bearing 135 between the second part 120 and the third part 130. It will also be appreciated that the movement of the frame 121 about the pitching axis 130a is constrained by contact between the frame 121 and the articulation member 111. As such, the range of rotation about the pitching axis 130a may be constrained by contact between the first part 110 and the second part 120. The track assembly 105 also comprises an actuation member 128. The actuation member 128 is configured to move the idler 123 between a raised and a lowered position. This will be described later in relation to Figures 11A and 11B. Figure 8 shows the track assembly 105 from the rear, for example along the roll axis 110a. As described previously, the track assembly 105 comprises the articulation member 111, the plate connector 112 to connect the articulation member 111 to the forearm 143, the articulation shaft 111b and the frame 121. As also described previously, the track assembly 105 comprises track plates 125, a track chain 126 and track rollers 127. The track assembly 105 is shown in Figure 8 in a left roll position relative to the arm 140, and relative to a horizontal level 150. As described previously, such rolling motion can be achieved by the rotatable connection between the third part 130 and the first part 110 about the roll axis 110a. The track assembly 105 in Figure 8 also shows a roll control device 133. This may be an alternative roll control device 133 to that described in relation to Figure 6. In the arrangement shown in Figure 8, the roll control device 133 comprises a series of three connected cylinders arranged in a Z format. This may also be configured to control and / or damp the movement of the second part 120 relative to the first part 110 about the roll axis 110a. Figure 9 shows a side view of the first part 110 (without the articulation fork 111a) and the third part 130. As described previously, the third part 130 can be mounted to the articulation shaft 111b by at least one bearing 134. The third part 130 may comprise a roll control device 133 which may be disposed within the second cylinder 132, similar to that shown in Figure 6. Figure 10 is an end view of the articulation fork 111a. Also shown is the plate connector 113 for connecting the first part 110 to the corresponding arm 140, in particular to the forearm 143. The articulation fork 111a comprises a splined aperture 115 configured to receive the articulation shaft 111b. Figures 11A and 11B each show a schematic side view of two adjacent track assemblies. The adjacent track assemblies may be the first track assembly 105a and the third track assembly 105c, which are the front left and back left track assemblies in Figure 1. The first track assembly 105a comprises a drive motor 122a and an idler 123a. Likewise, the third track assembly 105c comprises a drive motor 122c and an idler 123c. In the arrangement shown, the track assemblies are arranged such that the idlers 123a, 123c are facing each other. As mentioned in relation to Figure 7, the track assembly may comprise an actuation member 128. The actuation member 128a of the first track assembly 105a is configured to raise (see Figure 11A) and lower (see Figure 11B) part of the track assembly 105a. In particular, in the first track assembly 105a the actuation member 128a is coupled to the idler 123a and is configured to pivot the idler 123a between the raised position shown in Figure 11A and the lowered position shown in Figure 11B. Given that part of the track 124 is mounted around the idler 123a (see Figure 7), the actuation member 128a can be configured to raise part of the track 124 above the ground. In this way, the actuation member 128 can raise a portion of the track out of contact with the ground. This may allow the track assemblies 105a, 105c to stack more closely together because the raised portion of track of the first track assembly 105a can be positioned above the lowered portion of track (i.e., on the ground) of the third track assembly 105c. In particular, this may allow the adjacent track assemblies to slot together, for example by creating a space under the raised portion of the first track assembly 105a under which the corresponding track portion of the third track assembly 105c can be received. It will be appreciated that, by symmetry, the foregoing also applies to other adjacent track assemblies, such as the second track assembly 105b and the fourth track assembly 105d. An example of how the undercarriage can be operated will now be described. Starting from the configuration shown in Figure 1, the undercarriage 100, which may be part of a tracked vehicle, can drive similarly to a two-tracked vehicle. For example, the undercarriage 100 can drive backwards and forwards (i.e. along the longitudinal axis 103) by driving the tracks 124 of the track assemblies 105 in an appropriate direction. The undercarriage 100 can turn by driving the tracks 124 at different speeds. For example, a right turn can be achieved by rotating the left hand side tracks 105a, 105c faster than the right hand side tracks 105b, 105d, or by driving the right hand side tracks in a forward direction and driving the left hand side in a rearward direction. The arms 140 can be extended using the extension control device 144 to move the undercarriage 100 to its expanded configuration as shown in Figure 2. The undercarriage can be driven in a similar manner to the configuration shown in Figure 1, but in the expanded configuration the undercarriage can also be driven by pivoting the track assemblies 105 relative to the corresponding arm 140, as shown in Figure 3. To drive the undercarriage 100 in a lateral direction, the track assemblies can be pivoted so as to be orientated transverse to the longitudinal axis 103, as shown in Figure 4. The centre of gravity of the undercarriage 100 can be selected in the horizontal direction by altering the degree of extension of each arm (e.g. by adjusting the extension of the hydraulic cylinders 144), and in the vertical direction by altering the elevation of the arms 140 (e.g. by adjusting the extension of the elevation control device). When the undercarriage 100 moves over non-flat terrain, for example when approaching an upslope, the track 124 of the track assembly 105 can pitch upwards about the pitching axis 130a using the rotatable connection between the first part 110 and the second part 120, provided by the third part 130. In particular, with reference to Figures 5B and 7, the frame 121 (around which the track 124 is mounted) will pitch up about the pitching axis 130a relative to the third part 130 when the track assembly 105 approaches an upslope. Therefore, the first part 110 and the arm 140 will not pitch relative to the main body 101. Similarly, when the undercarriage 100 approaches a side slope (e.g. a slope having a slope direction that is transverse to the driving direction), the track 124 can roll in a corresponding direction about the roll axis 110a using the rotatable connection between the first part 110 and the second part 120, provided by the third part 130. In particular, with reference to Figures 5B and 8, the frame 121 will roll about the roll axis 110a, which will cause a corresponding roll of the third part 130 in view of the mounting bearing 135. Due to the third part 130 being rotatably mounted on the first part (e.g. by the first cylinder 131 being rotatably mounted around the articulation shaft 111b), the first part 110 and the arm 140 will not roll relative to the main body 101. Figures 12 to 14 illustrate aspects of how the undercarriage 100 can be controlled. An aspect of the disclosure provides a system for controlling an undercarriage 100, such as the undercarriage 100 described herein. The system may comprise various controllers and sensors, which may or may not be part of the undercarriage 100 itself. In some examples, the undercarriage 100 comprises various sensors for monitoring the relative position of components. The sensors may provide sensing data to a controller, which may be onboard the undercarriage 100 or may be in the tracked vehicle, or may be in a remote location wirelessly connected to the undercarriage 100. Figure 12 is a schematic representation of how the upperworks of a tracked vehicle can be connected to the lowerworks (i.e. the undercarriage) using a plurality of elevation control devices. Figure 12 also includes a block diagram of how the undercarriage can be self-stabilised. In the arrangement shown, the elevation control devices comprise pairs of hydraulic cylinders, for example as discussed in relation to Figure 2. The system may be configured to use inverse kinematics to control the arms 140. In this respect, the system may include sensors to detect the length and / or pressure of the hydraulic cylinders which form the elevation control devices. The system may be configured to use this information to determine a pose of the upperworks and / or the lowerworks. The system, for example using an engine control unit (ECU), may use the pose information to provide control inputs to the elevation control devices to reach a desired pose. The system may be configured to control the arms 140 based on information processed by the controller. In one example, the undercarriage is used with an artillery gun. It will be appreciated that the tracked vehicle will experience recoil when the gun is fired. Using the sensors and the control system, the tracked vehicle may be configured to actively respond to such forces, for example by rotating the track of one or more track assemblies to prevent the tracked vehicle toppling over. Figure 13 is a functional block diagram to show communicative connections between components of an example control system. In particular, Figure 13 illustrates the inputoutput process control for the system. The system includes a track control module (TCM). The TCM is communicatively coupled with the motor of each track assembly. In particular, each motor may be a low speed, high torque drive motor including a brake. The TCM may also be communicatively coupled to a rotary encoder, hydraulic control, a reverse valve, and an X- and / or Y-axis hydraulic cylinder brake. The TCM is part of a group which may also include an arm control module (ACM), an engine control unit (ECU) and a machine-to-machine module (MCM). The group is communicatively coupled to an input which may provide various system and environmental information. The system information may include the angle of each track in the pitch / roll / yaw directions; the position of a traction toggle switch; engine throttle position; engine torque; drive position; vehicle tilt; vehicle incline; zero-point moment. The system information may also include information about the upperworks, for example in the case of a pile driver tracked vehicle the information may include the slew and leader angle and position; the position and velocity of a cable; the pile number and length. The environmental information may include wind data from an anemometer; precipitation data; air temperature; sub soil conditions. The group may also be communicatively coupled to an overturn indicator with traction control and an anti-lock braking system (ABS). The group may also be communicatively coupled to an output. The output may include an actuator solenoid; an actuator pump or motor input; a slip indicator or overturn indicator; a traction off light; a drive pump; and / or shift solenoid valves. The group may also be connected by radio to the upperworks systems, which may include a demountable cab connected by a MCM connection. The MCM may be communicatively coupled to a display touch screen with input; a keyboard; GSM communication (i.e. Global System for Mobile Communications); global positioning system (GPS) communication; joy stick with rotation; pedals with rotation; camera and / or microphone. In one example in which the tracked vehicle is a piling machine, details of the proposed foundations may be received by one or more vehicles on a construction site. These details may be at least one of subsoil report information of soil material strengths, depths, thickness of material, ground water level, pile material type (e.g. concrete, steel or wood), diameter, length, cutoff, depth, concrete mix, number of piles, pile layout, pile sequencing, GPS location, site location, date, time and tool types. Such information may be accessible by multiple vehicles on a single site. Figure 14 is a functional block diagram of a traction control system for the undercarriage. The track control module (TCM) is communicatively coupled between the ECU and the ACM. The TCM is communicatively coupled to a pressure load sensor for each track assembly. Each pressure load sensor may be communicatively coupled to a track roller pressure sensor for each track, which may include a plurality, for example six, track pressure sensors (TPS). The arm control module (ACM) is communicatively coupled to each arm, in particular to the arm cylinder (AC), which may be the extension control device 144 of Figure 2). The ACM is communicatively coupled to a pressure load sensor and an arm deflection position sensor. The ACM may also be communicatively coupled to an encoder configured to measure the length of wire / cable spooled out from the reel (e.g. the reel 148 in Figure 3). 5 It will be appreciated from the above description that many features of the different examples are interchangeable and combinable. The disclosure extends to further examples comprising features from different examples combined together in ways not specifically mentioned. Indeed, there are many features presented in the above examples 10 and it will be apparent to the skilled person that these may be advantageously combined with one another. 15

Claims

1. An undercarriage for a tracked vehicle, the undercarriage comprising:a main body having a longitudinal axis;four track assemblies; andfour arms extending from the main body, each arm of the four arms being configured to pivotably couple a corresponding track assembly of the four track assemblies to the main body to facilitate steering of the tracked vehicle;wherein each track assembly of the four track assemblies comprises:a first part coupled to its corresponding arm; anda second part configured to receive a track of the track assembly;wherein the first part is coupled to the second part such that the second part can pitch and roll relative to the first part.

2. The undercarriage of claim 1, wherein each track assembly further comprises a third part configured to couple the first part to the second part.

3. The undercarriage of claim 2, wherein the third part is rotatably coupled to the second part to facilitate rotation of the track assembly relative to the corresponding arm about a pitching axis.

4. The undercarriage of claim 3, wherein the rotation of the second part about the pitching axis is constrained by contact between the first part and the second part.

5. The undercarriage of any of claims 2 to 4, wherein the third part is rotatably coupled to the first part to facilitate rotation of the track assembly relative to the corresponding arm about a roll axis.

6. The undercarriage of any of claims 2 to 5, wherein the third part comprises a first bore configured to receive a shaft of the first part.

7. The undercarriage of any of claims 2 to 6, wherein the third part is coupled to the first part by a bearing whose rotational axis is parallel to the first bore.

8. The undercarriage of any of claims 2 to 7, wherein the third part is coupled to the second part by a bearing whose rotational axis is transverse to the first bore.

9. The undercarriage of any of claims 2 to 8, wherein the third part comprises two cylindrical portions.

10. The undercarriage of any preceding claim, wherein the second part comprises a frame, wherein the frame is configured to support the track.

11. The undercarriage of claim 10, wherein the track is supported on the frame by a plurality of rollers rotatably mounted to the frame.

12. The undercarriage of any preceding claim, wherein at least one track assembly of the four track assemblies further comprises an actuation member, the actuation member being configured to raise a portion of the track of the at least one track assembly out of contact with the ground to facilitate slotting with an adjacent track assembly of the four track assemblies.

13. The undercarriage of any preceding claim, wherein each arm of the four arms is configured to facilitate independent pivoting of each arm with respect to the main body.

14. The undercarriage of any preceding claim, wherein at least one arm of the four arms comprises a pivotable coupling configured to facilitate a range of rotation of the track assembly relative to the main body of at least 90 degrees.

15. The undercarriage of any preceding claim, wherein each arm comprises:a proximal portion connected to the main body;a distal portion connected to a corresponding track assembly, and a pivot joint between the proximal portion and the distal portion.

16. The undercarriage of claim 15, wherein the pivot joint is arranged to facilitate pivoting of the proximal portion to the distal portion in a single plane, for example such thatthe portions can pivot relative to one another about a single pivot axis.

17. The undercarriage of claim 15 or claim 16, wherein the proximal portion is extendable.

18. The undercarriage of claim 17, wherein the proximal portion comprises a telescopic assembly to facilitate extending and retracting of the track assembly with respect to the main body.

19. The undercarriage of claim 18, wherein the telescopic assembly comprises a hydraulic cylinder.

20. The undercarriage of any preceding claim, wherein each arm extends from the main body at an angle measured with respect to the longitudinal axis of approximately 40 degrees.

21. The undercarriage of any preceding claim, wherein the main body comprises four comers, and wherein each arm extends outwards from the main body from a corresponding corner of the four comers.

22. A tracked vehicle comprising the undercarriage according to any preceding claim.

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