DRIVE MODULE

Abstract

This invention relates to a drive module. The drive module includes a base and a steering assembly rotatably mounted to the base. The steering assembly is selectively rotatable about a predetermined steering axis and carries a drive train. The drive train is configured to provide a multi-stage drive reduction of the drive train and the drive train is adapted to support a wheel such that a centre of a contact patch of the wheel is laterally offset from the steering axis.

Claims

1. A drive module, including: a base; a steering assembly mounted to the base and selectively rotatable about a steering axis; a drive train carried by the steering assembly; and a wheel operatively associated with the drive train; wherein at least a portion of the steering assembly and the drive train is spaced from the steering axis, thereby to form a void about the steering axis in which the wheel can be mounted.

2. (canceled)

3. A drive module according to claim 1, wherein the drive train provides a multi-stage drive reduction.

4-8. (canceled)

9. A drive module according to claim 1, wherein an auxiliary drive reduction mechanism is provided between a driving actuator and the drive train carried by the steering assembly.

10. A drive module according to claim 1, wherein the drive train includes a first gear set having a pair of spur gears arranged and configured to be rotatably driven by a driving actuator, wherein the first gear set includes a first spur gear meshingly engaged with a second spur gear, the axis of rotation of the first spur gear is coaxially aligned with the axis of rotation of the driving actuator, thereby to define the steering axis about which the steering assembly rotates.

11-12. (canceled)

13. A drive module according to claim 4, wherein the drive train includes a second gear set having a pair of gears arranged and configured to be rotatably driven by the first gear set, the second gear set includes a bevel gear set, wherein a connecting rod extends between the second spur gear of the first gear set and a first bevel gear of the second gear set, wherein the second spur gear, the connecting rod and the first bevel gear are arranged rotate in unison about a common axis.

14-15. (canceled)

16. A drive module according to claim 5, wherein the first gear set has a first drive reduction ratio (R.sub.1) and the second gear set has a second drive reduction ratio (R.sub.2).

17. A drive module according to claim 5, wherein the first drive reduction ratio of the first gear set is greater than or equal to the second drive reduction ratio of the second gear set.

18. A drive module according to claim 5, wherein the first drive reduction ratio of the first gear set is less than or equal to the second drive reduction ratio of the second gear set.

19-20. (canceled)

21. A drive module according to claim 1, wherein the wheel is mounted to the drive train such that a centre of a contact patch of the wheel is laterally offset from the steering axis, wherein the offset between the steering axis and the centre of the contact patch of the wheel is determined by the following equation: $\frac{d_{\mathrm{offset}}}{r_{\mathrm{wheel}}}=\underset{i=1}{\overset{n_{\mathrm{gearsets}}}{.Math.}}.Math..Math.\frac{n_{\mathrm{teeth}.Math.\_.Math.i.Math.\_.Math.\mathrm{input}}}{n_{\mathrm{teeth}.Math.\_.Math.i.Math.\_.Math.\mathrm{outpu}.Math.t}}=R_{\mathrm{final}}$ where: d.sub.offset is the offset between the steering axis and the centre of the contact patch of the wheel r.sub.wheel is the radius of the wheel n.sub.gearsets is the number of gearsets mounted on the steering assembly and is equal to or greater than 1 (i.e. n.sub.gearsets1) n.sub.teeth_i_input is the number of teeth on the ith gearsets input gear n.sub.teeth_i_output is the number of teeth on the ith gearsets output gear R.sub.final is the final speed ratio of the multi-gearset configuration

22. A drive module according to claim 1, wherein the steering assembly includes a steering arm mounted for rotation relative to the base.

23. A drive module according to claim 10, wherein the steering arm has a receiving formation in which the drive train can be mounted, whereby the steering arm acts as a mechanical support for the drive train to maintain the relative positioning and alignment of the drive train components.

24. A drive module according to claim 10, wherein the steering arm is adapted to support the wheel to one side of the steering arm, wherein the steering arm has an asymmetrical profile, thereby to facilitate the lateral offset of the contact patch of the wheel from the steering axis.

25. (canceled)

26. A drive module according to 10, wherein the length of the steering arm and/or connecting rod is selectively adjustable.

27. A drive module according to claim 1, including a control unit is-provided for selectively controlling movement of the drive train and steering assembly, wherein the control unit includes a drive system for controlling movement of the drive train, the drive system including a driving actuator adapted to provide drive inputs to the drive train, thereby propelling the wheel in a forwards or a reverse direction.

28. (canceled)

29. A drive module according to claim 14, wherein the control unit includes a steering module for selectively controlling movement of the steering assembly, the steering module including a steering actuator adapted to provide steering inputs to the steering assembly, thereby steering the wheel in a left or right direction.

30. A drive module according to claim 15, wherein the steering module includes a reduction gearbox associated with the steering motor, the reduction gearbox of the steering module having a steering shaft for driving a steering gear mechanism, thereby to control movement of the steering assembly.

31. A drive module according to claim 16, wherein the steering gear mechanism is arranged within the base and adapted to provide a further drive reduction to facilitate control of the steering assembly.

32. A drive module according to claim 17, wherein the steering gear mechanism includes a pair of steering spur gears mounted in intermeshing engagement so as to rotate in opposite direction to each other, the pair of steering spur gears including a first steering gear operatively coupled to the steering shaft such that, upon activation of the steering motor, rotation of the steering shaft causes a corresponding rotation of the first steering gear, and a second steering gear driven in an opposite direction to the first steering gear, wherein the second steering gear is operatively coupled to the steering assembly to cause a corresponding movement thereof.

33. (canceled)

34. A drive module according to claim 18, wherein the second steering gear is connected to the steering assembly by a coupling element, the coupling element being fixedly connected at one end to the second steering gear and at its other end to the steering assembly, whereby the coupling element and the steering assembly form an interconnected unit in which all components rotate in unison about the steering axis upon activation of the steering motor.

35-36. (canceled)

37. A drive module according to claim 1, wherein rotation of the steering assembly about the steering axis causes a corresponding rotation of the wheel about the steering axis such that the wheel rolls about its axis of rotation.

38. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0115] Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0116] FIG. 1 is a perspective view of a first embodiment of a drive module according to the invention;

[0117] FIG. 2 is a side view of the drive module of FIG. 1;

[0118] FIG. 3 is front view of the drive module of FIG. 1;

[0119] FIG. 4 is a cross-sectional view of the drive module taken along line A-A of FIG. 2;

[0120] FIG. 5 is an exploded perspective view of FIG. 1, showing the control unit, steering assembly and wheel in more detail;

[0121] FIG. 6 is a perspective view of an embodiment of a robotic ground based vehicle, incorporating four of the drive modules of FIG. 1;

[0122] FIG. 7 is a perspective view of an embodiment of a personal transportation vehicle/wheelchair, incorporating four of the drive modules of FIG. 1;

[0123] FIG. 8 is a perspective view of an embodiment an automobile, incorporating four of the drive modules of FIG. 1;

[0124] FIG. 9 is a perspective view of a second embodiment of a drive module according to the invention, in which the steering assembly incorporates dual concentric splines as part of a suspension mechanism;

[0125] FIG. 10 is a cross-sectional view showing a part of another embodiment of a drive module according to the invention, in which the drive train includes a gear shifting mechanism associated with a drive input shaft;

[0126] FIG. 11 is a cross-sectional view showing a part of another embodiment of a drive module, in which the drive train incorporates an additional intermediate gearset;

[0127] FIG. 12 is a cross-sectional view showing a part of another embodiment of a drive module according to the invention, in which the drive train incorporates a bevelled upper gear set and a non-parallel connecting shaft extending towards the wheel hub;

[0128] FIGS. 13A-13B show perspective views of embodiments of a steering assembly with details of the sign of the wheel offset for a given gearset configuration;

[0129] FIG. 14 is an exploded perspective view of the steering assembly of the drive module; and

[0130] FIG. 15 is an enlarged cross-sectional view of a control unit of the drive module.

PREFERRED EMBODIMENT OF THE INVENTION

[0131] Referring initially to FIGS. 1 to 5, the invention in a first embodiment provides a drive module 1 including a base 2, a steering assembly 3 rotatably mounted to the base 2, a drive train 4 (FIGS. 4 and 15) carried by the steering assembly 3 which is selectively rotatable about a predetermined steering axis (X-X). In the illustrated embodiment, the drive train 4 is configured to provide a two-stage drive reduction, and is adapted to carry a wheel 5 such that a centre of a contact patch of the wheel is laterally offset from the steering axis (FIG. 4). The wheel 5 is advantageously formed of a suitable material and with a suitable profile to provide the wheel 5 with desired characteristics to suit the intended application, optionally incorporating integral treads or tyres as required for the intended application of the drive module 1.

[0132] The drive module 1 is in the form of a swerve drive unit having omni-directional functionalities and capabilities, in terms of both driving and steering actions. To provide the drive module 1 with omni-directional steering capabilities, the steering assembly 3 is mounted to the base 2 so as to be selectively rotatable through 360 degrees relative to the base 2 about the steering axis. The steering assembly 3 can rotate both in a clockwise direction and a counter-clockwise direction about the steering axis (when viewed from above) to steer the drive module 1 in a desired direction. It will be appreciated that the rotation of the steering assembly 3 about the steering axis causes a corresponding rotation of the wheel 5 about the steering axis such that the wheel rolls about its axis of rotation (e.g. as defined by a drive shaft).

[0133] The ability of the wheel 5 to roll around the steering axis (as opposed to skid) arises from the lateral offset of the wheel, whereby the wheel is advantageously positioned to the side of the line of travel of the wheel as defined by the centre of the contact patch of the wheel (when the vehicle is viewed from the front). As described in further detail below, this characteristic of the swerve drive module 1 is particularly advantageous when only a steering input is provided to the drive module (i.e. when there is no driving input). In addition, the mechanical decoupling of the steering and driving axes allows independent control of the steering and driving axes without the need for controller based decoupling throughout the entire controllable driving and steering axis velocity range.

[0134] In the illustrated embodiment, as best seen in FIG. 4, the drive train 4 carried by the steering assembly 3 is a reduction mechanism in the form of a mechanical gear arrangement configured to provide the two-stage drive reduction. The drive train 4 has a first (top) gear set 6 associated with and arranged to be driven by an input driving actuator of a drive unit 7. The first gear set 6 is in the form of a pair of spur gears and provides a first stage drive reduction of the drive train 4.

[0135] The drive train 4 includes a second (bottom) gear set 8 having a pair of bevel gears arranged and configured to be rotatably driven by the first (top) gear set 6. The second gear set 8 provides a second stage drive reduction of the drive train 4. In the illustrated embodiment, the second gear set 8 is directly driven by the first (top) gear set 6 by way of a connecting rod 10 extending between the first and second gear sets (6, 8).

[0136] The first (top) gear set 6 has a pair of spur gears including a first spur gear 11 meshingly engaged with a second spur gear 12 such that rotation of the first spur gear 11 in a first direction causes a corresponding rotation of the second spur gear 12 in an opposed second direction.

[0137] The axis of rotation of the first spur gear 11 is coaxially aligned with the axis of rotation of a driving actuator of the drive unit 7 and the steering axis about which the steering assembly 3 rotates in use to steer the drive module 1. In the cross-sectional view of FIG. 4, the first and second spur gears (11, 12) are mounted to the steering assembly such that each gear lies in a generally horizontal plane, with the steering axis extending in a generally vertical direction. In this layout of the first gear set 6, the axis of rotation of the first spur gear 11 is in parallel spaced apart relation to the axis of rotation of the second spur gear 12.

[0138] The second (bottom) gear set 8 includes a first bevel gear 13 arranged in parallel spaced apart relationship to the second spur gear 12 of the first gear set 6, and a second bevel gear 14 meshingly engaged with the first bevel gear 13. The second spur gear 12 is connected to the first bevel gear 13 by the connecting rod 10 such that these elements rotate in unison about the same vertical axis of rotation (i.e. an axis which is offset from and in parallel relation to the steering axis).

[0139] The second (bottom) gear set 8 is configured such that the axis of rotation of the second bevel gear 14 is orthogonal to the horizontal axis of rotation of the first bevel gear 13, and thus that of the connecting rod 10 and the second spur gear 8.

[0140] The first (top) gear set 6 has a first drive reduction ratio (R.sub.1) determined by reference to the number of teeth on the first spur gear (n.sub.1) and the number of teeth on the second spur gear (n.sub.2). The second (bottom) gear set 8 has a second drive reduction ratio (R.sub.2) determined by reference to the number of teeth on the first bevel gear (n.sub.3) and the number of teeth on the second bevel gear (n.sub.4).

[0141] The drive train 4 has an output driven member in the form of drive shaft 15 for supporting the wheel 5 for rotation. The drive shaft 15 is attached to and co-rotates with the second bevel gear 14 by actuation of the drive unit 7. The drive shaft 15 and the second bevel gear 14 are coaxially aligned with one another, and thus with the axis of rotation of the wheel 5. The drive shaft is connected to the second bevel gear and the wheel by a power transmission element such as a mechanical key (not shown) such that the draft shaft, the second bevel gear and the wheel co-rotate in unison about a common axis (i.e. the wheel axis).

[0142] The second bevel gear 14 has a bore 16 through which the drive shaft 15 extends such that a first end of the drive shaft 15 is adapted to support the wheel 5 and an opposed second end of the drive shaft 15 is supported by a bearing 17 mounted within the distal end of the steering assembly 15. In the illustrated embodiment, the drive shaft 15 advantageously extends through the bore 16 such that the first and second ends of the drive shaft 15 are positioned on opposite sides of the second bevel gear 14. Accordingly, the output/second bevel gear 14 of the drive train 4 is arranged between the connecting rod 10 and the wheel 5, thereby providing a compact arrangement to the drive module 1.

[0143] In the illustrated embodiments, the steering assembly 3 includes a single-sided rigid L-shaped steering arm 18 mounted for rotation relative to the base, to enable steering of the driving module 1. As best seen in FIG. 4, the steering arm 18 has a receiving formation in the form of an internal hollow cavity 19 in which the first and second gear sets (6, 8) and the connecting rod 10 of the drive train 4 are mounted. In this way, the steering arm 18 acts as a structural support for the drive train 4 to maintain the relative positioning and alignment of the various components of the drive train. The first gear set 6, the second gear set 8, and the connecting rod 10 of the drive train 4 are housed entirely within the steering arm 18 such that the steering arm 18 acts a cover for the drive train 4, protecting the geared mechanisms and inhibiting ingress of dust and debris.

[0144] The L-shaped steering arm 18 has a first arm 20 at its proximal end and adapted to be mounted in close proximity to the base, and a second arm 21 extending orthogonally from the first arm 20 to its distal end. The single-sided configuration of the steering arm 18 is such that the wheel 5 is supported to one side of the second arm 21 of the steering arm. It will be appreciated that the one-sided configuration of the steering arm 18 advantageously and readily facilitates mounting of the wheel 5 in the laterally offset position from the steering axis.

[0145] In the illustrated embodiment, the length of the first arm 20 is less than the length of the second arm 21. The length of the first arm 20 is fixed to facilitate the desired offset mounting position of the wheel 5, and to provide the drive module 1 a compact configuration.

[0146] The length of the second arm 21 can be set to accommodate the radius of the wheel and provide a desired clearance gap between the top of the wheel 5 and the first arm 20 and/or to provide a desired ground clearance for the particular terrain of the intended application of the drive module 1.

[0147] Referring to FIG. 4, the first gear set 6 is housed within the first arm 20 at the proximal end of the steering arm 18, and the second gear set 8 is housed towards the distal end of the second arm 21 of the steering arm 18, with the connecting rod 10 extending between the first and second gear sets along the second arm 21.

[0148] As is most clearly shown in FIGS. 3 and 4, the L-shaped configuration of the steering assembly, together with the associated stepped, staggered or otherwise offset arrangement of the drive train to complement the shape of the steering assembly, advantageously forms an open area or void about the steering axis, thereby ensuring that neither the steering assembly nor the drive train interfere with the wheel and thus do not determine the offset positioning of the wheel relative to the steering axis. In particular, the steering assembly and drive train do not interfere with the top and upper half portion of the wheel.

[0149] Referring to FIGS. 4 and 5, a control unit 25 is provided for selectively controlling movement of the drive train 4 and steering assembly 3, and thus the drive module 1 as a whole. As foreshadowed, the control unit 25 has a drive unit 7 for controlling movement of the drive train 4. The drive unit 7 includes a driving actuator in the form of an electric drive motor 26 for providing drive inputs to the drive train 4 to rotate the wheel 5 and thereby propel the drive module 1 in a forwards or a reverse direction as required.

[0150] The drive motor 26 has a drive motor shaft 27 which is coaxially aligned with, and operatively connected to, the first spur gear 11 of the first (top) gear set 6. By this arrangement, activation of the drive motor 26 will rotate the drive motor shaft 27 and cause a corresponding rotation of the first spur gear 6, and thus the wheel 5 via the drive train 4 to propel the drive module 1.

[0151] For self-propelled autonomous applications of the drive module, the drive unit 7 preferably includes computerised control modules, power regulators and/or associated electronic components, operating in accordance with predetermined drive control algorithms and methodologies, to control the velocity and acceleration of the drive motor 26.

[0152] In addition to the driving unit 7, the control unit 5 has a steering module 28 for selectively controlling movement of the steering arm 18. The steering module 28 includes a steering actuator in the form of an electric steering motor 29 adapted to provide steering inputs to control inputs to the steering assembly to steer the wheel 5 in a left or right direction as required, in use. To provide greater flexibility and control over the range of control inputs that can be applied to the drive module, the drive unit 7 and the steering module 28 are advantageously independently operated such that the driving unit 7 can provide driving inputs whilst the steering module 28 is in an inactive state. Similarly, the steering module 28 can provide steering inputs whilst the driving unit 7 is in an inactive state.

[0153] In the illustrated embodiment as best seen in FIG. 4, the steering module 28 includes a reduction gearbox 30 associated with the steering motor 29. The reduction gearbox 30 of the steering module 28 has a steering shaft 31 for driving a steering gear mechanism to control movement (rotation) of the steering assembly 3.

[0154] The steering gear mechanism is arranged within the base 2 of the drive module 1, and is adapted to provide a further drive reduction to facilitate selective and precise control of the steering assembly 3. In the illustrated embodiment, the steering gear mechanism includes a pair of steering spur gears mounted in intermeshing engagement so as to rotate in opposite direction to each other. The pair of steering spur gears includes a first steering gear 32 and a second steering gear 33.

[0155] The first steering gear 32 is operatively coupled to the steering shaft 31 such that, upon activation of the steering motor 29, rotation of the steering shaft 31 causes a corresponding rotation of the first steering gear 32. The second steering gear 33 is driven by the first steering gear 32 in an opposite direction to the first steering gear 32 and is operatively coupled to the steering assembly 3 to cause a corresponding movement thereof.

[0156] The second steering gear 33 is connected to the first arm 20 of the steering arm 18 by a hollow tubular coupling element 34. The tubular coupling element 34 is fixedly connected (directly or indirectly) at its proximal end to the second steering gear 33 by suitable connecting elements or fasteners (e.g. screws) and at its distal end to the first arm 20 of the L-shaped steering arm 18. In this way, the second steering gear 33, the coupling element 34, and the steering arm 18 form an interconnected unit in which all components rotate in unison about the steering axis upon activation of the steering motor 29.

[0157] The second steering gear 33 and the coupling element 34 are mounted within a hollow interior space of the base 2 so as to be coaxially aligned with the steering axis (i.e. as defined by the drive motor shaft 27). The coupling element 34 is in the form of a hollow tubular member having a passage through which the connecting member of the drive module passes (to couple the drive motor shaft 27 to the first spur gear 11), thereby facilitating the coaxial alignment of the various components with the steering axis.

[0158] The base 2 has an open passageway 35 defined about the steering axis and arranged to allow the tubular coupling element 34 of the steering module 28 to pass therethrough. Two friction reducing elements in the form of roller bearings 36 are mounted within the open passageway to facilitate the relative rotation between the base 2 and the coupling element/steering assembly upon activation of the steering motor.

[0159] For self-propelled autonomous applications of the drive module 1, the steering module 28 includes computerised control modules, power regulators, feedback encoders and/or associated electronic components, operating in accordance with predetermined steering control algorithms and methodologies.

[0160] With reference to FIG. 5, the various components of the drive unit 7 and the steering module 28 are mounted to a mounting board 37 so as to form a control unit 38 which can be releasably mounted to the base 2 by suitable fastening means (e.g. screws). A protective cover 38 is detachably mountable over the control unit.

[0161] The lateral offset between the steering axis and the centre of the contact patch of the wheel advantageously allows the wheel to roll when the steering assembly is rotated about the steering axis when the drive motor 26 is inactive and no drive input is applied to the wheel via the drive train (any braking mechanism is released such that wheel is free to rotate about its drive axis).

[0162] It has been found that the following general kinematic equation can be applied to the reduction gear train carried by the steering arm in order to calculate the preferred offset between the steering axis and the centre of the contact patch of the wheel. That is, the follow general equation can be advantageously be used to define the system geometry for the gearset configuration of the drive train and steering assembly:

[00005]$\frac{d_{\mathrm{offset}}}{r_{\mathrm{wheel}}}==\underset{i=1}{\overset{n_{\mathrm{gearsets}}}{.Math.}}.Math..Math.\frac{n_{\mathrm{teeth}.Math.\_.Math.i.Math.\_.Math.\mathrm{input}}}{n_{\mathrm{teeth}.Math.\_.Math.i.Math.\_.Math.\mathrm{outpu}.Math.t}}=R_{\mathrm{final}}$

[0163] where: [0164] d.sub.offset is the offset between the steering axis and the centre of the contact patch of the wheel [0165] r.sub.wheel is the radius of the wheel [0166] n.sub.gearsets is the number of gearsets mounted on the steering assembly and is equal to or greater than 1 (i.e. n.sub.gearsets1) [0167] n.sub.teeth_i_input is the number of teeth on the ith gearsets input gear [0168] n.sub.teeth_i_output is the number of teeth on the ith gearsets output gear [0169] R.sub.final is the final speed ratio of the multi-gearset configuration

[0170] Where the drive train includes a multi-stage drive reduction having two or more stages of drive reduction, the number of gearsets is equal to or greater than 2 as follows: [0171] n.sub.gearsets is the number of gearsets mounted on the steering assembly and is equal to or greater than 2 (i.e. n.sub.gearsets2)

[0172] It is to be noted that, in the above equation, n.sub.gearsets defines the number of gearsets that are actually mounted to the steering assembly. Any auxiliary gearsets that are mounted to the non-steered mount point of the drive module are independent of the system geometry and are not used in the above equation.

[0173] In the illustrative example of a drive train having two gear sets, the above general equation can be expressed as follows:

[00006]$\frac{d_{\mathrm{offset}}}{r_{\mathrm{wheel}}}=.Math.\frac{n_{\mathrm{teeth}.Math.\_.Math.1.Math.\_.Math.\mathrm{input}}}{n_{\mathrm{teeth}.Math.\_.Math.1.Math.\_.Math.\mathrm{outpu}.Math.t}}\frac{n_{\mathrm{teeth}.Math.\_.Math.2.Math.\_.Math.\mathrm{input}}}{n_{\mathrm{teeth}.Math.\_.Math.2.Math.\_.Math.\mathrm{outpu}.Math.t}}$

[0174] In practical applications, however, there may be a number of imperfections and nonlinearities (e.g. in the tyre to ground interaction, manufacturing errors, tyre deformation etc.) which could give rise to additional factors that may need to be considered following application of the above simple kinematic equations in practice. For example, with a given wheel construction with an estimated or predicted degree of deformation, the above formula could be modified or approximated to account for a difference between unloaded and loaded radius values, where the radius of the wheel in the formula is taken to be the loaded radius. That is, in the above formula, r.sub.wheel may be replaced with:

r.sub.loaded=r.sub.unloadedy.sub.deformation [0175] where y.sub.deformation is the estimated deformation of the wheel.

[0176] In some cases, an empirical determination of the system geometry based on experimentation and measurement, in conjunction with the above formula, may produce more practical results for implementation. Accordingly, it may be preferred in some cases to choose or refine the system geometry values d.sub.offset, r.sub.wheel, or R.sub.final based on a mathematical model or empirically. In such cases, we can define an equation as follows that optimises for more complex real world interactions:

[00007]$\underset{d_{\mathrm{offset}}.Math.,r_{\mathrm{wheel}}}{\arg .Math..Math.\min }.Math.f\left(d_{\mathrm{offset}},r_{\mathrm{wheel}},R_{\mathrm{final}}\right)$

where f is an objective function to be minimised, and may incorporate a combination of measures including, but not limited to: [0177] The amplitude of the axial and radial run-out in the central steering shaft for each value of d.sub.offset, r.sub.wheel and R.sub.final [0178] The torque power, energy or time required to steer the wheel for each value of d.sub.offset, r.sub.wheel and R.sub.final [0179] The stresses in the mechanisms when steering for each value of d.sub.offset, r.sub.wheel and R.sub.final [0180] The damage or wear to the ground or tyre when steering (e.g. soil compaction depth, tyre wear rate etc.) for each value of d.sub.offset, r.sub.wheel and R.sub.final

[0181] Since typically the value of r.sub.wheel and R.sub.final will be limited or pre-defined, this equation can in many cases be simplified to:

[00008]$\underset{d_{\mathrm{offset}}}{\arg .Math..Math.\min }.Math.f\left(d_{\mathrm{offset}}\right)$

[0182] FIG. 6 shows a further embodiment of the invention, in which four of the drive modules of FIGS. 1 to 5 are mounted to a chassis 40 to form a self-propelled autonomous robotic ground based vehicle 45.

[0183] FIG. 7 shows a further embodiment of the invention, in which four of the drive modules of FIGS. 1 to 5 are mounted to a chassis 40 with a chair 41 to form a, a personal transportation vehicle or wheelchair 46.

[0184] FIG. 8 shows a further embodiment of the invention, in which four of the drive modules of FIGS. 1 to 5 are mounted to a chassis 40 to form an automobile 47.

[0185] In further embodiments, one or more additional wheels may be incorporated between, in front of or behind the drive modules for stability, supplementary drive capacity, additional load bearing capacity, or other specific purposes. Any such additional wheels may be driven or free-wheeling, and may optionally incorporate steering mechanisms. In one particular variation, one or more additional wheels are supported for rotation on a common axis, either inboard or outboard of the wheels of the drive modules.

[0186] Control of the drive modules may be partly or fully automated as part of an overall environmental scanning, route planning, and control methodology, optionally operating systematically in conjunction with a plurality of like or complementary autonomous vehicles.

[0187] In one embodiment, the chassis is adapted to support one or more solar panels, to provide primary or supplementary electric power for the drive and steering motors and thereby extend vehicle runtime. In some embodiments, the chassis may have a support platform mounted thereon and adapted for use as a launch pad for one or more other supplementary or autonomous vehicles such as UAVs, UGVs, AUVs or other teleoperable devices.

[0188] In some embodiments, the drive module includes components and systems whereby the vehicle is adapted to function autonomously or substantially autonomously, as an omni-directional mobile platform for a robot. Examples of such components and systems include: [0189] sensors suited to the intended application (such as ranging, imaging, localisation or inertial sensors), [0190] actuators or instruments suited to the intended application (such as manipulators, robotic arms, pan/tilt mechanisms, agricultural planting, weeding, spraying or harvesting mechanisms, drilling or mining tools, firefighting tools including water nozzles or chemical sprayers, weapons systems, medical instruments or devices, research or analytical instruments or tools, or lifting and positioning tools for logistics or materials handling), [0191] lighting systems (such as laser, UV, IR, LED or floodlighting systems), [0192] energy generation or conservation equipment (such as solar panels, sails, wind turbines or fuel cells), and/or [0193] ancillary electronic equipment (such as computers, data storage media, communications or navigation equipment, antennas or networking components).

[0194] In various embodiments, the drive module could advantageously be employed in, but not limited to, the following types of vehicles: [0195] Mining and Construction: Trucks, loaders, tractors, forklifts, bulldozers, cranes, graders, draglines, haul trucks, excavators, tunnel-boring machines, scissor lifts [0196] Defence/Military: personnel carriers, tanks, target training vehicles, bomb disposal robots [0197] Agricultural Vehicles: tractors, agricultural robots [0198] Space: planetary rovers, shuttle transporters [0199] Stevedoring: straddle carriers, container transporters [0200] Transport: cars, trucks, buses [0201] Logistics: warehouse transport vehicles and robots [0202] Aquatic: amphibious or surface vehicles [0203] Motorsport: racing vehicles [0204] Aerospace: landing gear or motion systems on aerial vehicles or aerial vehicle handling vehicles (e.g. pushback tractors or tugs) [0205] Personal Mobility: wheelchairs, scooters, skateboards, utility vehicles [0206] Medical: Patient beds, mobile assisted patient rehabilitation walking vehicles (e.g. with a harness), surgical or monitoring equipment vehicles [0207] Other: Generic robotic bases, telepresence robots.

[0208] It will be appreciated that the invention in its various preferred embodiments provides a drive module with a number of inherent and unique features and advantages. In particular, the ability to determine the extent of wheel offset by way of a generalised kinematic equation significantly reduces the time associated with designing, testing and developing swerve drive units for various applications. In addition, the ability to apply this system geometry to modules incorporating multistage reduction drives housed within a steering assembly provides improvements in the degree of accuracy of control, in particular during low speed applications.

[0209] Furthermore, the use of multi-stage reduction drives within the steering assembly advantageously obviates the need for additional and often bulky gearboxes associated with the drive motor, as relatively large gear reductions can be obtained through the drive train. This in turn results is a relatively compact system geometry having a reduced foot print, and provides a drive module which is robust and relatively simple to construct and is scalable. The use of a single-sided steering arm improves access to the wheel and thus gives rise to ease of service, maintenance, and repair.

[0210] The use of multi-stage reduction drives within the steering assembly is also advantageous over single reduction drives since they allow for the wheel to be located closely to the steer rotation axis which minimises the swept volume of the steering wheel, reduces moment loads on mechanical components, reduces the steering or steer holding torque requirements, provides a near constant footprint geometry and allows for greater clearances between the sidewall of the tyre and the supporting mechanics. This arrangement can also assist in providing a better balance in the design of swerve drive units, particularly between the requirement of a changing vehicle footprint and large swept volume of the steering wheel against that of smooth, efficient and simple operation of the system. In these and other respects, the invention represents a practical and commercially significant improvement over the prior art.

[0211] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.