DRIVE UNITS

Technical Field

The present disclosure generally relates to a drive unit comprising a wheel. In particular, a drive unit for an automated guided vehicle and an automated guided vehicle comprising a plurality of drive units, are provided.

Background Automated guided vehicles (AGVs) are typically self-powered, self-driven vehicles used to transport materials and other items from one location to another, without the need for a driver on the vehicle. AGVs are commonly used in manufacturing sites, warehouses, post offices, libraries, port terminals, airports, and some hazardous locations and specialty industries. CN 108909436 A discloses an independent steering driving wheel for an all round autonomous mobile platform. The driving wheel comprises a traveling mechanism, a damping mechanism, a stress supporting mechanism and a steering mechanism. The traveling mechanism is driven by a hub motor.

Different types of AGVs may have different propulsion requirements. Some AGVs can manage with relatively simple types of propulsion, such as a differential drive. AGVs for more demanding applications may require a propulsion system with more accurate and versatile maneuverability. One example of such application is where an AGV carries an industrial robot of some kind that works in collaboration with the AGV. A drive unit for an automated guided vehicle may comprise a steering motor and a wheel motor. A gearbox may be provided between the steering motor and a driven steering member. A gearbox may also be provided between the wheel motor and a wheel. Gearboxes are however complex and expensive in order to provide silent operation and required positional accuracy. Reducing backlash and noise in gearboxes further adds costs and complexity.

A drive unit for an automated guided vehicle may alternatively comprise a Mechanum wheel, also known as a Swedish wheel. Although a Mechanum wheel can be driven by a single motor, Mechanum wheels are mechanically complex and problematic to drive on dirty and/or uneven surfaces.

Mechanum wheels are also noisy, which is unacceptable in many

applications. Summary

One object of the present disclosure is to provide a drive unit for an automated guided vehicle, which drive unit has a simple design.

A further object of the present disclosure is to provide a drive unit for an automated guided vehicle, which drive unit has a cost-effective design. A further object of the present disclosure is to provide a drive unit for an automated guided vehicle, which drive unit has a compact design.

A still further object of the present disclosure is to provide a drive unit for an automated guided vehicle, which drive unit enables an accurate

maneuverability and/or a high degree of maneuverability for the automated guided vehicle.

A still further object of the present disclosure is to provide a drive unit for an automated guided vehicle, which drive unit enables a flexible design of the automated guided vehicle.

A still further object of the present disclosure is to provide a drive unit for an automated guided vehicle, which drive unit is relatively silent during operation. A still further object of the present disclosure is to provide a drive unit for an automated guided vehicle, which drive unit solves several or all of the foregoing objects in combination.

A still further object of the present disclosure is to provide an automated guided vehicle comprising a plurality of drive units, which automated guided vehicle solves one, several or all of the foregoing objects.

According to one aspect, there is provided a drive unit for an automated guided vehicle, the drive unit comprising a driven steering member rotatable about a steering axis; an electric steering motor arranged to directly drive the driven steering member about the steering axis; a wheel rotatable about a wheel axis perpendicular to the steering axis; and an electric wheel motor arranged to directly drive the wheel about the wheel axis.

The drive unit constitutes a steered wheel drive unit with direct drive motors for both propulsion and steering of the wheel. Due to the direct drive of the driven steering member by means of the steering motor, the driven steering member rotates with the same speed as the steering motor. Conversely, due to the direct drive of the wheel by means of the wheel motor, the wheel rotates with the same speed as the wheel motor. Since the drive unit does not comprise any gear transmission between the steering motor and the driven steering member or between the wheel motor and the wheel, the drive unit is made simple, compact and cost-effective. For example, the number of shafts, bearings and moving parts in the drive unit can thereby be reduced.

The wheel motor forms a gearless direct drive of the wheel which has a drive connection to the wheel without intermediate connection of a transmission. Conversely, the steering motor forms a gearless direct drive of the driven steering member without intermediate connection of a transmission.

The drive unit has two degrees of freedom. The wheel axis constitutes a first degree of freedom and the steering axis constitutes a second degree of freedom. The steering axis may be vertical and the wheel axis may be horizontal during operation of the drive unit in the automated guided vehicle. The wheel may be a traction wheel, e.g. for contacting a floor in order to drive the automated guided vehicle. A wheel stator of the wheel motor may be directly or indirectly connected to the driven steering member. Furthermore, the wheel stator may be rigidly connected with respect to the driven steering member. The wheel motor may be arranged radially inside the wheel with respect to the wheel axis, and axially inside the wheel with respect to the wheel axis. When the wheel rotates about the wheel axis, it may also rotate relative to the driven steering member.

When the wheel motor is arranged inside the wheel, the wheel motor is a hub motor. The wheel motor may thus be an outrunner. An axis of the wheel motor may be concentric with the wheel axis.

The drive unit may further comprise a steering bearing arrangement arranged to rotationally support the driven steering member about the steering axis and to axially support an external load on the drive unit, such as the entire external load on the drive unit, along the steering axis. The steering bearing arrangement may be constituted by one or more bearings of the steering motor. Thus, one or more bearings of the steering motor can be utilized to also axially support an external load on the drive unit.

The external load on the drive unit may comprise a part of the load of a support structure of the automated guided vehicle, and a part of a load on the support structure. For an automated guided vehicle comprising four drive units, each drive unit may carry approximately a quarter of the load of the support structure and approximately a quarter of the load on the support structure. The steering bearing arrangement may comprise an axial steering bearing (with respect to the steering axis) and a radial steering bearing (with respect to the steering axis), and/or any combinations thereof. According to one example, the steering bearing arrangement comprises a radial steering bearing and an axial-radial steering bearing. The steering bearings may be rolling-element bearings. Each steering bearing may be connected to the driven steering member and to a steering shaft of the drive unit. The steering shaft may be rigidly secured to a support structure of the automated guided vehicle. The entire external load on the drive unit can be transferred through the steering bearing arrangement. The design of the drive unit can thereby be made even more simple and cost-effective.

The drive unit may comprise a wheel bearing arrangement arranged to rotationally support the wheel about the wheel axis. The wheel bearing arrangement may radially support (with respect to the wheel axis) an external load on the drive unit, such as the entire external load on the drive unit. The wheel bearing arrangement may be constituted by one or more bearings of the wheel motor. Thus, one or more bearings of the wheel motor can be utilized to also radially support an external load on the drive unit.

The wheel bearing arrangement may comprise two radial wheel bearings (with respect to the wheel axis). The wheel bearings may be rolling-element bearings. Each wheel bearing may be connected to a wheel shaft of the drive unit and to the wheel, such as to a hub of the wheel. The entire external load on the drive unit can be transferred through the wheel bearing arrangement. The design of the drive unit can thereby be made simpler and more cost- effective. The steering motor may comprise a steering stator and a steering rotor, and the wheel motor may comprise a wheel stator and a wheel rotor. In this case, the steering rotor and the wheel stator may be rigidly connected with respect to each other. The steering rotor may be directly connected to the driven steering member, for example to a base part thereof. The wheel stator may be rigidly connected to, or integrally formed with, a wheel shaft. The wheel shaft may in turn be rigidly connected to the driven steering member, for example by direct connection to one or more arm parts of the driven steering member.

The steering motor may comprise a steering stator, a steering rotor and steering coils. In this case, the steering coils may be provided on the steering stator. Alternatively, the steering coils may be provided on the steering rotor. Signal cables and power cables to the steering motor and to the wheel motor can thereby be jointly provided in the driven steering member.

The wheel motor may comprise a wheel stator, a wheel rotor and wheel coils. In this case, the wheel coils may be provided on the wheel stator. This variant simplifies the cabling to the wheel coils and thereby reduces costs of the drive unit.

The drive unit may further comprise a wheel sensor device arranged to determine a rotational position of the wheel about the wheel axis; and wheel drive electronics for controlling the wheel motor. In this case, the wheel sensor device and the wheel drive electronics may be arranged radially inside the wheel with respect to the wheel axis, and axially inside the wheel with respect to the wheel axis. The wheel drive electronics may be configured to control rotation of the wheel motor by means of pulse width modulated (PWM) control. The wheel sensor device may comprise a high -resolution encoder. For example, the wheel sensor device may comprise a Hall effect wheel sensor and a multipole wheel encoder ring. The wheel encoder ring may comprise at least 32 poles, such as at least 64 poles, such as at least 128 poles.

The drive unit may further comprise a wheel circuit board, and the wheel sensor device may comprise an active part and a passive part. In this case, the wheel drive electronics and the active part of the wheel sensor device may be arranged on the wheel circuit board. By providing the wheel drive electronics and the active part of the wheel sensor device on the common wheel circuit board, cabling can be reduced or eliminated and the drive unit can be made more compact. The wheel drive electronics and the active part of the wheel sensor device may for example be soldered onto the wheel circuit board. The passive part of the wheel sensor device may be connected to a hub of the wheel.

The wheel circuit board may for example be arranged between two wheel bearings along the wheel axis. The wheel circuit board may be annular and disc-shaped. In this case, the wheel circuit board may be substantially concentric with, or concentric with, the wheel axis.

The steering motor may comprise a steering stator and a steering rotor, and the steering stator may be arranged inside the driven steering member. The steering stator may be arranged radially inside the driven steering member with respect to the steering axis, and axially inside the driven steering member with respect to the steering axis.

In this case, also the steering motor may be said to constitute a hub motor. According to this variant, the steering motor is thus an outrunner. The steering stator may for example be arranged inside a base part of the driven steering member. In this case, the steering rotor may be rigidly connected to, or integrally formed with, the driven steering member. An axis of the steering motor may be concentric with the steering axis. The steering motor may however alternatively be an inrunner. The drive unit may further comprise a steering sensor device arranged to determine a rotational position of the driven steering member about the steering axis; and steering drive electronics for controlling the steering motor. In this case, the steering sensor device and the steering drive electronics may be arranged inside the driven steering member, for example inside a base part thereof. The steering drive electronics may be configured to control rotation of the driven steering member by means of pulse width modulated (PWM) control.

The steering sensor device may comprise a high-resolution encoder. For example, the steering sensor device may comprise a Hall effect steering sensor and a multipole steering encoder ring. The steering encoder ring may comprise at least 32 poles, such as at least 64 poles, such as at least 128 poles.

The drive unit may further comprise a steering circuit board, and the steering sensor device may comprise an active part and a passive part. In this case, the active part of the steering sensor device and the steering drive electronics may be arranged on the steering circuit board. By providing the steering drive electronics and the active part of the steering sensor device on the common steering circuit board, cabling can be reduced or eliminated and the drive unit can be made more compact. The steering drive electronics and the active part of the steering sensor device may for example be soldered onto the steering circuit board. The passive part of the steering sensor device may be connected to the driven steering member, such as to a base part of the driven steering member.

The steering circuit board may for example be arranged between two steering bearings along the steering axis. The steering circuit board may be annular and disc-shaped. In this case, the steering circuit board may be substantially concentric with, or concentric with, the steering axis.

The driven steering member may comprise a base part and at least one arm part extending from the base part. The steering motor may comprise a steering stator and a steering rotor, and the steering stator may be arranged inside the base part. Alternatively, or in addition, the drive unit may further comprise a wheel shaft connected to the arm part. In this case, the wheel motor may be connected to the wheel shaft.

The driven steering member may comprise a base part and the steering sensor device and the steering drive electronics may be arranged inside the base part. That is, the steering sensor device and the steering drive

electronics may be arranged radially inside the base part with respect to the steering axis, and axially inside the base part with respect to the steering axis.

The steering axis may intersect the wheel axis. Alternatively, the steering axis may be offset with respect to the wheel axis while still being perpendicular to the wheel axis.

The drive unit may be modular. The modularity of the drive unit enables the drive unit to easily be connected to different parts of a support structure of an automated guided vehicle, for example in order to change a configuration of the automated guided vehicle. Thereby, the flexibility of design of the automated vehicle can be improved. Also the wheel motor and the steering motor may be modular. Thus, the wheel motor and the steering motor, and optionally the associated

electronics, may be of identic, or substantially identic, shape and size. In this way, the steering motor can be switched to be used as the drive motor and vice versa. For example, the base part of the driven member may be of identic, or substantially identic, shape and size as the hub of the wheel.

According to a further aspect, there is provided an automated guided vehicle comprising a support structure and a plurality of drive units according to the present disclosure connected to the support structure. By means of the drive units, the AGV is provided with omnidirectional motion capability.

Brief Description of the Drawings

Further details, advantages and aspects of the present disclosure will become apparent from the following embodiments taken in conjunction with the drawings, wherein: Fig. 1: schematically represents a perspective view of an automated

guided vehicle comprising a plurality of drive units;

Fig. 2: schematically represents a perspective view of one example of a drive unit for the automated guided vehicle; and

Fig. 3: schematically represents a cross-sectional view of a further

example of a drive unit for the automated guided vehicle.

Detailed Description

In the following, a drive unit for an automated guided vehicle and an automated guided vehicle comprising a plurality of drive units, will be described. The same reference numerals will be used to denote the same or similar structural features.

Fig. 1 schematically represents a perspective view of an automated guided vehicle (AGV) 10. The AGV 10 comprises a plurality of drive units 12. The AGV 10 further comprises a platform 14. In Fig. 1, the AGV 10 comprises four drive units 12. The AGV 10 may however comprise fewer than four drive units 12 or more than four drive units 12. Each drive unit 12 comprises a wheel 16. The wheels 16 are traction wheels for driving the AGV 10 on a surface, such as a floor.

The platform 14 constitutes one example of a support structure for the AGV 10. The platform 14 of this example comprises a horizontal support surface.

One further example of a support structure is a frame. In this case, various devices can be attached to the frame.

The platform 14 can carry a load, for example an industrial robot (not shown). The robot may comprise at least one manipulator operable in three or more axes. The AGV 10 and the robot may be moved simultaneously when carrying out a task by the robot.

The drive units 12 are modular. Due to their modularity, drive units 12 can be added to, and/or removed from, the platform 14. The drive units 12 may be connected to different sections of the platform 14. Thus, the number of drive units 12 and their placement on the platform 14 can be tailored for a specific application. In Fig. 1, each drive unit 12 is connected to a corner of the platform 14.

The AGV 10 further comprises a central control system 18. The central control system 18 is provided in the platform 14. The central control system 18 is in signal communication with each drive unit 12 via controller area network (CAN) buses (not shown). The central control system 18 may also comprise a battery (not shown) for powering each drive unit 12.

Fig. 2 schematically represents a perspective view of one example of a drive unit 12 for the AGV 10. In addition to the wheel 16, the drive unit 12 comprises a driven steering member 20. The wheel 16 is rotatable about a wheel axis 22. The driven steering member 20 is rotatable about a steering axis 24. The wheel axis 22 is perpendicular to the steering axis 24. Moreover, the wheel axis 22 intersects the steering axis 24. In Fig. 2, the wheel axis 22 is horizontal and the steering axis 24 is vertical. The wheel axis 22 and the steering axis 24 provide two degrees of freedom for the drive unit 12. The drive unit 12 further comprises an electric synchronous wheel motor 26. The wheel motor 26 is arranged to rotationally drive the wheel 16 about the wheel axis 22. The wheel motor 26 is arranged to directly drive the wheel 16, i.e. without any intermediate gearing between the wheel motor 26 and the wheel 16. The wheel motor 26 is arranged inside the wheel 16. The wheel motor 26 thereby constitutes a hub motor or outrunner.

The drive unit 12 further comprises an electric synchronous steering motor 28. The steering motor 28 is arranged to rotationally drive the driven steering member 20, and consequently also the wheel 16, about the steering axis 24. The steering motor 28 is arranged to directly drive the driven steering member 20, i.e. without any intermediate gearing between the steering motor 28 and the driven steering member 20.

The driven steering member 20 of the example in Fig. 2 comprises a base part 30 and an arm part 32. The arm part 32 extends from the base part 30. In Fig. 2, the arm part 32 extends vertically downwards from the base part 30. The steering motor 28 of this example is arranged inside the base part 30.

The steering motor 28 thereby constitutes a hub motor or outrunner. The steering motor 28 may however alternatively be an inrunner. The driven steering member 20 may be produced by means of additive manufacturing, such as 3D printing.

Fig. 3 schematically represents a cross-sectional view of a further example of a drive unit 12 for the AGV 10. The drive unit 12 in Fig. 3 differs from the drive unit 12 in Fig. 2 in that the driven steering member 20 comprises two arm parts 32 extending from the base part 30. As can be gathered from Fig. 3, the drive unit 12 has a simple mechanical structure and can be produced at low costs.

The steering motor 28 comprises a steering stator 34 and a steering rotor 36. The steering motor 28 further comprises steering coils 38 arranged on the steering stator 34. The base part 30 of this example is a cylindrical housing. The steering rotor 36 comprises a plurality of magnets attached to the interior of the base part 30. In this way, the driven steering member 20 is an integral part of the steering rotor 36.

The drive unit 12 further comprises a steering shaft 40. In this example, the steering shaft 40 is integrally formed with the steering stator 34. The steering shaft 40 is concentric with the steering axis 24. Signal cables and power cables from the central control system 18 may be routed through the steering shaft 40 to the steering motor 28.

The drive unit 12 further comprises a steering bearing arrangement 42. The steering bearing arrangement 42 rotationally supports the driven steering member 20 about the steering axis 24. In addition, the steering bearing arrangement 42 axially supports the entire external load on the drive unit 12, such as a vertical downward force from the platform 14 acting on the steering shaft 40. The steering bearing arrangement 42 supports both rotation of the steering motor 28 about the steering axis 24 and axial forces along the steering axis 24. Thereby, the bearings of the steering motor 28 can be effectively utilized to also support external loads on the drive unit 12.

The steering bearing arrangement 42 of this example comprises a radial steering bearing 44 and an axial-radial steering bearing 46. The radial steering bearing 44 is arranged vertically above the axial-radial steering bearing 46. One race of the radial steering bearing 44 is secured to an upper steering flange 48 of the base part 30 and one race of the radial steering bearing 44 is secured to the steering shaft 40. One race of the axial-radial steering bearing 46 is secured to a lower steering flange 50 of the base part 30 and one race of the axial-radial steering bearing 46 is secured to the steering shaft 40. The steering shaft 40, the radial steering bearing 44 and the axial-radial steering bearing 46 are dimensioned to handle the entire load on the drive unit 12.

The radial steering bearing 44 and the axial-radial steering bearing 46 are rolling-element bearings such as ball bearings or roller bearings. As shown in Fig. 3, each of the upper steering flange 48 and the lower steering flange 50 protrudes towards the interior of the base part 30.

The drive unit 12 further comprises a steering sensor device 52. The steering sensor device 52 determines a rotational position of the driven steering member 20 about the steering axis 24. The steering sensor device 52 comprises an active part, here constituted by a Hall effect steering sensor 54, and a passive part, here constituted by a multipole steering encoder ring 56. The steering encoder ring 56 may for example comprise 128 poles. The steering sensor device 52 thereby constitutes a high-resolution encoder for accurate determination of a rotational position of the steering rotor 36 and the driven steering member 20 about the steering axis 24.

The steering encoder ring 56 is concentric with the steering axis 24. As shown in Fig. 3, the steering sensor device 52 is arranged inside the base part 30.

The drive unit 12 further comprises steering drive electronics 58. The steering drive electronics 58 controls the operation of the steering motor 28, for example by means of PWM control. As shown in Fig. 3, the steering drive electronics 58 is arranged inside the base part 30.

The drive unit 12 further comprises a steering circuit board 60. The steering circuit board 60 is flat and annular around the steering axis 24 and the steering shaft 40. As shown in Fig. 3, the steering circuit board 60 is horizontally oriented. The steering circuit board 60 is arranged between the radial steering bearing 44 and the axial-radial steering bearing 46 along the steering axis 24. In this example, the steering circuit board 60 is arranged between the steering stator 34 and the axial-radial steering bearing 46 along the steering axis 24.

The Hall effect steering sensor 54 and the steering drive electronics 58 are provided on the steering circuit board 60, for example by means of soldering. Fig. 3 further shows two transistors 62 provided on the steering drive electronics 58. The steering encoder ring 56 is connected to the driven steering member 20. In the example in Fig. 3, the steering encoder ring 56 is connected to the lower steering flange 50.

The drive unit 12 further comprises a steering homing switch 64 for homing the steering motor 28. The steering homing switch 64 comprises a steering homing sensor 66 and a steering homing magnet 68. The steering homing sensor 66 is provided on the steering circuit board 60. The steering homing magnet 68 is provided on the base part 30.

The wheel motor 26 comprises a wheel stator 70 and a wheel rotor 72. The wheel motor 26 further comprises wheel coils 74 arranged on the wheel stator 70. The wheel 16 comprises a hub 76. The wheel rotor 72 comprises a plurality of magnets attached to the interior of the hub 76. In this way, the hub 76 is an integral part of the wheel rotor 72. The hub 76 may be of identic, or substantially identic, design as the base part 30. The drive unit 12 further comprises a wheel shaft 78. The wheel shaft 78 is concentric with the wheel axis 22. Signal cables and power cables from the central control system 18 may be routed through the wheel shaft 78 to the wheel motor 26. The signal cables and power cables to the wheel motor 26 may optionally also be routed through the steering motor 28, such as through the steering shaft 40.

In this example, the wheel shaft 78 is integrally formed with the wheel stator 70. The wheel shaft 78 is secured to each arm part 32, in Fig. 3 to a lower end of each arm part 32. As a consequence, the wheel stator 70 is rigidly connected to the steering rotor 36. The wheel stator 70 and the steering rotor 36 thereby move together as one unit around the steering axis 24 during operation of the AGV 10.

The drive unit 12 further comprises a wheel bearing arrangement 80. The wheel bearing arrangement 80 rotationally supports the wheel 16 about the wheel axis 22. In addition, the wheel bearing arrangement 80 radially supports (with respect to the wheel axis 22) the entire external load on the drive unit 12, such as a vertical downward force from the platform 14 acting on the wheel shaft 78 via the steering shaft 40 and the driven steering member 20. Thereby, the bearings of the wheel motor 26 can be effectively utilized to also support external loads on the drive unit 12. The wheel bearing arrangement 80 of this example comprises a first radial wheel bearing 82 (to the left in Fig. 3) and a second radial wheel bearing 84 (to the right in Fig. 3). One race of the first radial wheel bearing 82 is secured to a first wheel flange 86 of the hub 76 and one race of the first radial wheel bearing 82 is secured to the wheel shaft 78. One race of the second radial wheel bearing 84 is secured to a second wheel flange 88 of the hub 76 and one race of the second radial wheel bearing 84 is secured to the wheel shaft 78. The wheel shaft 78, the first radial wheel bearing 82 and the second radial wheel bearing 84 are dimensioned to handle the entire load on the drive unit 12. The first radial wheel bearing 82 and the second radial wheel bearing 84 are rolling-element bearings such as ball bearings or roller bearings. As shown in Fig. 3, each of the first wheel flange 86 and the second wheel flange 88 protrudes towards the interior of the hub 76.

The drive unit 12 further comprises a wheel sensor device 90. The wheel sensor device 90 may be of the same type as the steering sensor device 52. The wheel sensor device 90 determines a rotational position of the wheel 16 about the wheel axis 22. The wheel sensor device 90 comprises an active part, here constituted by a Hall effect wheel sensor 92, and a passive part, here constituted by a multipole wheel encoder ring 94. The wheel encoder ring 94 may for example comprise 128 poles. The wheel sensor device 90 thereby constitutes a high-resolution encoder for accurate determination of a rotational position of the wheel rotor 72 and the wheel 16 about the wheel axis 22. The steering sensor device 52 and the wheel sensor device 90 enable high-performance control of each drive unit 12, and thereby also of the AGV 10. The wheel encoder ring 94 is concentric with the wheel axis 22. As shown in Fig. 3, the wheel sensor device 90 is arranged inside the hub 76.

The drive unit 12 further comprises wheel drive electronics 96. The wheel drive electronics 96 controls the operation of the wheel motor 26, for example by means of PWM control. As shown in Fig. 3, the wheel drive electronics 96 is arranged inside the hub 76.

The drive unit 12 further comprises a wheel circuit board 98. The wheel circuit board 98 is flat and annular around the wheel axis 22 and the wheel shaft 78. As shown in Fig. 3, the wheel circuit board 98 is vertically oriented. The wheel circuit board 98 is arranged between the first radial wheel bearing 82 and the second radial wheel bearing 84 along the wheel axis 22. In this example, the wheel circuit board 98 is arranged between the wheel stator 70 and the second radial wheel bearing 84 along the wheel axis 22.

The Hall effect wheel sensor 92 and the wheel drive electronics 96 are provided on the wheel circuit board 98, for example by means of soldering. Fig. 3 further shows two transistors 62 provided on the wheel drive electronics 96.

The wheel encoder ring 94 is connected to the hub 76. In the example in Fig. 3, the wheel encoder ring 94 is connected to the second wheel flange 88. The drive unit 12 further comprises a wheel homing switch too for homing the wheel motor 26. The wheel homing switch too comprises a wheel homing sensor 102 and a wheel homing magnet 104. The wheel homing sensor 102 is provided on the wheel circuit board 98. The wheel homing magnet 104 is provided on the hub 76. The drive unit 12 further comprises an accelerometer 106. The accelerometer 106 determines acceleration of the wheel 16. In this example, the

accelerometer 106 is provided on the wheel circuit board 98.

While the present disclosure has been described with reference to exemplary embodiments, it will be appreciated that the present invention is not limited to what has been described above. For example, it will be appreciated that the dimensions of the parts may be varied as needed. Accordingly, it is intended that the present invention may be limited only by the scope of the claims appended hereto.