WO2009043082A1

WO2009043082A1 - Vehicle navigation system

Info

Publication number: WO2009043082A1
Application number: PCT/AU2008/001114
Authority: WO
Inventors: Ian Edwards; Michael Prowse; Allan Williams
Original assignee: Protege Sport Pty Ltd
Priority date: 2007-10-02
Filing date: 2008-08-04
Publication date: 2009-04-09
Also published as: AU2008307122B2; GB201006528D0; AU2008307122A1; GB2467063B; GB2467063A

Abstract

A navigation system (30) for a vehicle, the vehicle including left and right motors (22, 24) for respectively causing rotation of left and right wheels and left and right motor drives(26, 28) for respectively driving the left and right motors, the navigation system including: an electronic gyroscope (36) mountable to the vehicle; and a control unit (32) configured to: receive an output signal from the gyroscope; derive a yaw angular velocity from the gyroscope output signal; derive a vehicle turning direction from the gyroscope output signal for non-zero yaw angular velocities; and cause the motor drives to apply a relative speed difference between the motors according to the yaw angular velocity and vehicle turning direction to thereby compensate for a change in vehicle heading.

Description

VEHICLE NAVIGATION SYSTEM

Technical Field

The present invention relates to a vehicle navigation system and method of vehicle navigation, a control unit forming part of the system and software or firmware for use with the control unit. The invention is suitable for use in applications relating to golf buggy navigation and it will be convenient to describe the invention in relation to that exemplary, but non-limiting, application.

Background

In recent times, motorised golf buggies have become increasingly popular with golfers who wish to minimise the physical effort required to play a round of golf. Such buggies generally include two large rear wheels and a third, smaller front wheel. Each rear wheel is driven by a separate D. C. motor. The golf buggy can be set to travel down a fairway in a desired direction by turning the golf buggy to a desired heading and then causing operation of the two D. C. motors at the same speed.

It can be difficult to compensate for a change in vehicle heading when the golf buggy is travelling on an inclined surface. As the golf buggy moves across the inclined surface, gravity may pull the golf buggy down the incline, causing it to deviate from its heading. It can be especially difficult to compensate for a change in heading of the golf buggy when the front wheel is a free or floating wheel. A floating wheel is able to pivot freely about a vertically extending shaft so as to self-orient in the direction the golf buggy is moving. This allows the direction of movement of the golf buggy to be changed easily, even when carrying significant weight. However, this also means that when the golf buggy is pulled down an incline by gravity, the floating wheel rotates to point down the incline, further increasing the deviation of the golf buggy from its desired heading.

A known method of compensate for a change in heading of a golf buggy is by using a compass to determine the direction in which the vehicle is moving and compensating for changes in direction. However, there are limitations in using compasses in such navigation systems. Compasses rely on the Earth's magnetic field, which varies widely in strength and angular direction depending on the region of the world. Compasses therefore may be prone to error in particular regions.

In addition, as compasses detect all magnetic fields, they are affected by magnetic fields caused by sources other than the Earth's magnetic field, such as magnets, ferrous materials or current carrying wires, which may lead to inaccuracies in the compass. Compasses also need to be tilt-compensated to take into account the attitude of the vehicle as the vehicle travels over an inclined surface. This means that tilt measurement devices need to be used in compass based systems. Compass based systems needs to calculate the tilt of the compass in order to determine the control signals to be sent to the motor drives of the vehicle. This causes a delay in sending the control signals and thereby compensating for the change in vehicle heading. Tilt measurement devices are often sensitive to vibration, such as vibrations caused by the vehicle travelling over uneven terrain or from the vehicle motors. Compass based systems need to take this vibration into account when calculating the compass tilt, further extending the delay. The visual result may be an obvious dynamic correction of the vehicle direction.

Summary of the Invention

It would be desirable to provide a navigation system for a vehicle that ameliorates or overcomes one or more disadvantages of know vehicle navigation systems.

One aspect of the invention provides a navigation system for a vehicle. The vehicle includes left and right motors for respectively causing rotation of left and right wheels and left and right motor drives for respectively driving the left and right motors. The navigation system includes: an electronic gyroscope mountable to the vehicle; and a control unit configured to receive an output signal from the gyroscope; derive a yaw angular velocity from the gyroscope output signal; derive a vehicle turning direction from the gyroscope output signal for non-zero yaw angular velocities; and cause the motor drives to apply a relative speed difference between the motors according to the yaw angular velocity and vehicle turning direction to thereby compensate for a change in vehicle heading.

A navigation system having these features has advantages over compass navigation systems, as unlike a compass, an electronic gyroscope is not dependent on the Earth's magnetic field, is not affected by magnetic sources and does not need to be tilt compensated. It provides a more accurate yet less complex means for determining the deviation of a golf buggy from a constant heading. Determining the angular velocity of the vehicle rather than its direction also has advantages, as the rate at which the vehicle is changing direction may indicate the steepness of the incline on which the vehicle is travelling. The control unit of a navigation system having these features is also able to react faster to compensate for changes in heading than a control unit in a compass based system in which tilt compensation calculations must be carried out. The navigation system is therefore more reactive to changes in vehicle heading. It may apply smaller corrections, providing a visually smoother performance.

Another advantage of a navigation system having the above-mentioned features is its lower production cost compared to compass based systems. In a preferred embodiment, the control unit may derive the vehicle yaw angular velocity by comparing the value of a property of the gyroscope output signal to a reference value. For non-zero yaw angular velocities, the vehicle turning direction may be derived by determining whether the gyroscope output signal property value is less than or greater than the reference value. The reference value may correspond to the gyroscope output signal property value when the vehicle is at rest. In order to minimise false readings, the reference value may be continuously updated when the vehicle is at rest for greater that a predetermined period.

The gyroscope output signal could be electrical, acoustic, radio frequency, infra red or another type of signal. The signal property could be the amplitude, frequency, phase or any other property of the signal. In a preferred embodiment, the gyroscope output signal is a voltage and the signal property is the amplitude of the voltage.

The system may further include a manually operable controller to enable manual control of the motor drives. The manually operable controller may, for example, be used to change the vehicle heading. To facilitate the navigation system taking the change of heading into account, the control unit may be further configured to receive control signals from the manually operable controller; override operation of the motor drives to apply a relative speed difference between the motors according to the yaw angular velocity and vehicle turning direction; and control operation of the motor drives in accordance with the control signals.

The manually operable controller may be mounted on or integral with the vehicle, or it may be separate from the vehicle and communicate with the control unit wirelessly. It may send control signals to the control unit via an electrical, radio frequency, infra red, acoustic or other signal.

In one embodiment, the vehicle is a golf buggy. The present invention is also applicable to other types of motorised vehicles, such as trolleys, lawnmowers and the like. It is applicable to any such vehicle that has at least two motor drives, to separately drive motors of a left and right wheel of the vehicle. Another aspect of the invention provides a method of navigating a vehicle. The method includes the steps of: receiving an output signal from the gyroscope; deriving a yaw angular velocity from the gyroscope output signal; deriving a vehicle turning direction from the gyroscope output signal for non-zero yaw angular velocities; and causing the motor drives to apply a relative speed difference between motors according to the yaw angular velocity and vehicle turning direction to thereby compensate for a change in vehicle heading. Yet another aspect of the invention provides a control unit forming part of a navigation system for a vehicle. The navigation system includes the control unit and an electronic gyroscope mountable to the vehicle. The control unit includes a processor and associated memory device for storing a series of instructions for causing the processor to receive an output signal from the gyroscope; derive a yaw angular velocity from the gyroscope output signal; derive a vehicle turning direction from the gyroscope output signal for non-zero yaw angular velocities; and cause the motor drives to apply a relative speed difference between the motors according to the yaw angular velocity and vehicle turning direction to thereby compensate for a change in vehicle heading. A further aspect of the invention provides a program for use with a control unit for a navigation system for a vehicle. The control unit includes a processor and associated memory device for storing the program. The program includes a series of instructions for causing the processor to receive an output signal from the gyroscope; derive a yaw angular velocity from the gyroscope output signal; derive a vehicle turning direction from the gyroscope output signal for non-zero yaw angular velocities; and cause the motor drives to apply a relative speed difference between the motors according to the yaw angular velocity and vehicle turning direction to thereby compensate for a change in vehicle heading.

The program may be firmware or software depending on the implementation of the control unit.

For a better understanding of the invention and to show how it may be performed, embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings. It is to be understood that the particularity of the drawings does not supersede the generality of the preceding description of the invention.

Brief Description of the Drawings

Figures 1 and 2 are respectively front and side views of a golf buggy equipped with a navigation system in accordance with an embodiment of the invention; Figure 3 is schematic diagram of a navigation system in accordance with an embodiment of the invention; Figure 4 is a graph showing the relationship between the output signal voltage of a gyroscope forming part of the navigation system of Figure 3 and the angular velocity of the golf buggy of Figure 1 ;

Figure 5 is a flowchart of the steps taken in a control unit forming part of the navigation unit of Figure 3 to determine a reference value corresponding to a gyroscope output signal property when a vehicle is at rest; and

Figure 6 is a flowchart of steps taken in a control unit forming part of the navigation unit of Figure 3 to compensate for a change in vehicle heading, including steps taken when a control signal is received from a manually operable controller.

Detailed Description of the Invention

Referring now to Figures 1 and 2, there is shown generally a golf buggy 10 including a frame 12 for supporting a golf bag, a floating front wheel 14, a left rear wheel 16 and right rear wheel 18, each of the wheels 14 to 18 being connected to the frame 12, and a handle 20 for manually positioning and pushing/pulling the golf buggy 10. The left and right rear wheels 16 and 18 are respectively caused to rotate by left and rights motors 22 and 24. As depicted schematically in Figure 3, the left and right motors 22 and 24 are respectively driven by left and right motor drives 26 and 28.

A navigation system 30 controls operation of the left and right motor drives 26 and 28. The navigation system 30 includes a microprocessor 32, handle control unit 34, electronic gyroscope 36 and wireless control unit 38. The microprocessor 32, handle control unit 34 and electronic gyroscope 36 are mounted on the frame 12, whilst the wireless control unit 36 is intended to be carried by a golfer to enable the golf buggy 10 to be controlled remotely. The microprocessor 32 includes a CPU 40, firmware 42 stored in a read-only memory device to be executed by the CPU 40, and volatile memory device 44 for temporarily storing data generated during operation of the navigational system 30. The microprocessor 32 acts to transmit control signals to the left and right motor drives 26 and 28 to independently drive the left and right motors 22 and 24 of the golf buggy 10.

While the navigation system 30 includes a microprocessor 32, other control units such as a microcontroller, or hard wired system could be used. Similarly, the firmware 42 could be replaced by software.

The handle control unit 34 communicates with the microprocessor 32 via a bus 46, whereas the wireless control unit 38 communicates with the microprocessor 32 via a wireless link 48. The handle control 34 includes manually operable switches 50 to 54 to enable a user to transmit "accelerate", "decelerate" and "stop" signals to the microprocessor 32. Upon receipt of these signals, the microprocessor 32 transmits control signals to the left and right motor drives 26 and 28 to cause both motors 22 and 24 to be jointly accelerated, decelerated or stopped.

By contrast, the wireless control unit 36 includes manually operable switches 56 to 64 to enable a user to transmit "turn left", "turn right", "accelerate", "decelerate" and "stop" signals to the microprocessor 32. The "accelerate", "decelerate" and "stop" signals are handled as described above. However, upon receipt of the "turn left" and

"turn right" signals, the microprocessor 32 transmits control signals to the left and right motor drives 26 and 28 to cause a relative speed difference to be applied to the motors 22 and 24 to thereby cause the golf buggy 10 to turn left or right.

The handle control unit 34 and wireless control unit 36 are two examples of manually operable controllers which enable manual control of the motor drives 26 and 28.

The electronic gyroscope 36 generates an output signal for transmission to the microprocessor 32. The voltage of the gyroscope output signal varies as a function of dθ the yaw angular velocity — of the golf buggy 10, where θ is the angular dt displacement of the golf buggy 10 from a desired heading 52, and the direction in which the golf buggy 10 turns. As shown in Fig. 4, the voltage of the output signal dθ increases linearly from a minimum value V_mn at which the yaw angular velocity — of dt the golf buggy 10 is maximal when turning left, to a maximum value V_max at which the dθ yaw angular velocity — of the golf buggy 10 is maximal when the golf buggy is dt turning right. When the yaw angular velocity — of the golf buggy 10 is zero, the dt voltage of the output signal has a reference value V_ref .

The slope of the graph shown in Figure 4 and the actual values of V_1111n , V_max and V_ref will vary depending upon the characteristics of the electronic gyroscope used in the navigation system 30. For example, the gyroscope may be a micromachined vibratory gyroscope using a vibrating mechanical element to sense rotation. The output voltage may then depend on the change in capacitance due to movement of the vibrating mechanical element. An example of the electronic gyroscope 36 that may be used in the system is the Murata MEV-50A-R electronic gyroscope. In this particular gyroscope, at a temperature of 25°C an output signal having a minimum value V_1111n Of 0 volts is generated at a maximum yaw angular velocity of -70 degrees per second and an output signal having a maximum value

V_max of 5 volts is generated at a maximum yaw angular velocity of +70 degrees per second.

It will be appreciated that electronic gyroscopes using other output signals or having different properties could be used in other embodiments of the navigation system.

In operation, the microprocessor 32 derives the yaw angular velocity from the gyroscope output signal by comparing the value of a property of the gyroscope output signal to a reference value. The microprocessor 32 derives the golf buggy turning direction from the gyroscope output signal, for non-zero yaw angular velocities, by determining whether the gyroscope output signal property value is less than or greater than the reference value. The reference value corresponds to the gyroscope output signal property value when the golf buggy is at rest.

The navigation system 10 firstly determines the reference value V_ref and stores this value in the data memory 44. As the reference value V_ref may change over time, the navigation system 30 can operate more accurately if the reference value V_ref is continuously updated. Figure 5 shows the steps which are executed by the microprocessor 32 in accordance with instructions in the firmware 42 to update the reference value V_ref . The gyroscope output signal is initially received by the microprocessor 32 at step 70. The microprocessor 32 then determines whether the golf buggy 10 is at rest at step 72 according to whether control signals are being sent to the motor drives 26 and 28 to drive the motors 22 and 24.

If the microprocessor 32 then determines that the golf buggy 10 is not at rest, the microprocessor 32 returns to step 70. However, if the golf buggy 10 is determined to be at rest, the microprocessor 32 determines at step 74 whether the golf buggy 10 has been at rest for a predetermined period of, say, 3 seconds. If so, the current value of the gyroscope output signal voltage is read by the microprocessor 32 at step 76 and stored in the data memory 44 as the reference value V_ref . Otherwise, the microprocessor 32 returns to step 70. The operations depicted in steps 70 to 76 are repeated continuously while the navigation system 30 is switched on.

Whilst in this embodiment, the navigation system 30 determines that the golf buggy 10 is at rest from the absence of control signals being sent to the drives 26 and 28, in other embodiments the navigation system 30 could determine whether or not the golf buggy 10 is at rest by the provision of a feedback signal from the left and right motor drives 26 and 28, or the left and right motors 22 and 24, to the microprocessor

32.

Figure 6 shows the steps executed by the microprocessor 32 in accordance with instructions in the firmware 42 to compensate for a change in heading of the golf buggy 10. The microprocessor 32 determines the instantaneous value of the voltage of the gyroscope output signal at step 80 and calculates an error value at step 82 by subtracting reference value V_ref from the instantaneous value of the gyroscope output signal voltage. The microprocessor 32 determines if the error value is equal to zero at step 84, thereby indicating that the golf buggy 10 is not deviating from its desired heading. In this case, the microprocessor 32 returns to step 80.

Otherwise, the microprocessor 32 determines if the error value is greater than zero at step 86, thereby indicating that the golf buggy 10 is turning right. The microprocessor 32 then applies a correction signal to the right motor drive 28 at step 88 to cause the right motor 24 to rotate faster and compensate for the turning of the golf buggy to the right. If the microprocessor 32 determines that the error value is less than zero at step 90, indicating that the golf buggy 10 is turning to the left, the microprocessor 32 applies a correction signal to the left motor drive 26 at step 92. This causes the left motor 22 to rotate faster to compensate for the turning of the golf buggy 10 to the left. The operations carried out in steps 80 to 92 are repeated continuously while the vehicle is switched on.

The value of the correction signals applied to the motor drives 26 and 28 are proportional to the instantaneous error value. In that sense, the navigation system 30 applies a simple proportional control to the motor drives 26 and 28. In other embodiments a more complex control algorithm, including integral and differential elements, could easily be applied by the microprocessor 32. A feedback signal from the left and right motor drives 26 and 28, or the left and right motors 22 and 24, could also be used by the microprocessor 32 in the algorithm.

Steps 88 and 92 could be replaced in other embodiments by other steps for applying a relative speed difference between the motors 22 and 24. For example, instead of acting to increase the speed of either the left or right motors 22 and 24 to compensate for the turning of the golf buggy 10, a correction signal could be applied to one of the left or right motor drives 26 and 28 to cause one of the motors 22 and 24 to rotate more slowly. In another alternative, correction signals could be sent to both the left and right motor drives 26 and 28 to cause one of the motors 22 and 24 to rotate faster and the other to rotate slower.

Fig. 6 also shows additional steps 100 which are executed by the microprocessor 32 in accordance with instructions in the firmware 42 when a control signal is received by the microprocessor 32 from the handle control unit 34 or wireless control unit 38. The microprocessor 32 determines whether a control signal has been received at step 102. If the microprocessor 32 determines that no signal has been received, it proceeds to step 82. Otherwise, the microprocessor 32 determines whether the control signal is a "turn left" or "turn right" signal at step 104. If so, the microprocessor 32 overrides operation of the motor drives and controls operation of the left and right motor drives 26 and 28 in accordance with the control signals by transmitting control signals to the motor drives 26 and 28. This causes a relative speed difference to be applied to the motors 22 and 24 to thereby cause the golf buggy 10 to turn left or right. Otherwise, the microprocessor 32 continues to step 82. While the vehicle is switched on, the microprocessor 32 continually determines whether a control signal has been received.

Although the navigation system has been described above in relation to a golf buggy 10, the navigation system is also applicable to trolleys, lawnmowers and the like. It is applicable to any such vehicle that has at least two motor drives, to separately drive motors of a left and right wheel of the vehicle.

It is to be understood that various alterations, additions and/or modifications may be made to the parts previously described without departing from the ambit of the present invention, and that, in the light of the above teachings, the present invention may be implemented in a variety of manners as would be understood by the skilled person.

The present application may be used as a basis for priority in respect of one or more future applications, and the claims of any such future application may be directed to any one feature or combination of features that are described in the present application. Any such future application may include one or more of the following claims, which are given by way of example and are non-limiting with regard to what may be claimed in any future application.

Claims

CLAIMS:

1. A navigation system for a vehicle, the vehicle including left and right motors for respectively causing rotation of left and right wheels and left and right motor drives for respectively driving the left and right motors, the navigation system including: an electronic gyroscope mountable to the vehicle; and a control unit configured to: receive an output signal from the gyroscope; derive a yaw angular velocity from the gyroscope output signal; derive a vehicle turning direction from the gyroscope output signal for non-zero yaw angular velocities; and cause the motor drives to apply a relative speed difference between the motors according to the yaw angular velocity and vehicle turning direction to thereby compensate for a change in vehicle heading.

2. A navigation system according to claim 1 , wherein the control unit derives the yaw angular velocity by comparing the value of a property of the gyroscope output signal to a reference value.

3. A navigation system according to claim 2, wherein the control unit derives the vehicle turning direction from the gyroscope output signal by determining whether the gyroscope output signal property value is less than or greater than the reference value.

4. A navigation system according to either one of claims 2 or 3, wherein the reference value corresponds to the gyroscope output signal property value when the vehicle is at rest.

5. A navigation system according to claim 4, wherein the control unit is further configured to update the reference value when the vehicle is at rest for greater that a predetermined period.

6. A navigation system according to any one of claims 2 to 5, wherein the gyroscope output signal property is a voltage.

7. A navigation system according to any one of the preceding claims, and further including a manually operable controller to enable manual control of the motor drives.

8. A navigation system according to claim 7, wherein the control unit is further configured to: receive control signals from the manually operable controller; override operation of the motor drives to apply a relative speed difference between the motors according to the yaw angular velocity and vehicle turning direction; and control operation of the motor drives in accordance with the control signals.

9. A navigation control system according to either one of claims 7 or 8, wherein the manually operable controller and the control unit are configured to communicate wirelessly.

10. A navigation system according to any one of the preceding claims, wherein the vehicle is a golf buggy.

1 1 . A method of navigating a vehicle, the vehicle including left and right motors for respectively causing rotation of left and right wheels, left and right motor drives for respectively driving the left and right motors and an electronic gyroscope mounted to the vehicle, the method including the steps of: receiving an output signal from the gyroscope; deriving a yaw angular velocity from the gyroscope output signal; deriving a vehicle turning direction from the gyroscope output signal for nonzero yaw angular velocities; and causing the motor drives to apply a relative speed difference between motors according to the yaw angular velocity and vehicle turning direction to thereby compensate for a change in vehicle heading.

12. A method according to claim 1 1 , wherein the step of deriving the yaw angular velocity includes comparing the value of a property of the gyroscope output signal to a reference value.

13. A method according to claim 12, wherein the step of deriving the vehicle turning direction from the gyroscope output signal includes determining whether the gyroscope output signal property value is less than or greater than the reference value.

14. A method according to either one of claims 12 or 13, wherein the reference value corresponds to the gyroscope output signal property value when the vehicle is at rest.

15. A method according to claim 14, and further including the step of updating the reference value when the vehicle is at rest for greater that a predetermined period.

16. A method according to any one of claims 12 to 15, wherein the gyroscope output signal property is a voltage.

17. A method according to any one of claims 1 1 to 16, the vehicle further including a manually operable controller to enable manual control of the motor drives, wherein the method further includes the steps of: receiving control signals from the manually operable controller; overriding operation of the motor drives to apply a relative speed difference between the motors according to the yaw angular velocity and vehicle turning direction; and controlling operation of the motor drives in accordance with the control signals.

18. A method according to any one of claims 1 1 to 17, wherein the vehicle is a golf buggy.

19. A control unit forming part of a navigation system for a vehicle, the vehicle including left and right motors for respectively causing rotation of left and right wheels and left and right motor drives for respectively driving the left and right motors, the navigation system including the control unit and an electronic gyroscope mountable to the vehicle, the control unit including a processor and associated memory device for storing a series of instructions for causing the processor to: receive an output signal from the gyroscope; derive a yaw angular velocity from the gyroscope output signal; derive a vehicle turning direction from the gyroscope output signal for non-zero yaw angular velocities; and cause the motor drives to apply a relative speed difference between the motors according to the yaw angular velocity and vehicle turning direction to thereby compensate for a change in vehicle heading.

20. A control unit according to claim 19, wherein the series of instructions for causing the processor to derive the yaw angular velocity includes instructions for comparing the value of a property of the gyroscope output signal to a reference value.

21 . A control unit according to claim 20, wherein the series of instructions for causing the processor to derive the vehicle turning direction from the gyroscope output signal includes instructions for determining whether the gyroscope output signal property value is less than or greater than the reference value.

22. A control unit according to either one of claims 20 or 21 , wherein the reference value corresponds to the gyroscope output signal property value when the vehicle is at rest.

23. A control unit according to claim 22, wherein the series of instructions further includes instructions for causing the processor to update the reference value when the vehicle is at rest for greater that a predetermined period.

24. A control unit according to any one of claims 20 to 23, wherein the gyroscope output signal property is a voltage.

25. A control unit according to any one of claims 19 to 24, the vehicle further including a manually operable controller to enable manual control of the motor drives, wherein the series of instructions further includes instructions for causing the processor to receive control signals from the manually operable controller; override operation of the motor drives to apply a relative speed difference between the motors according to the yaw angular velocity and vehicle turning direction; and control operation of the motor drives in accordance with the control signals.

26. A control unit according to claim 25, the manually operable controller being configured to communicate wirelessly, wherein the control unit is configured to communicate wirelessly with the manually operable controller.

27. A control unit according to any one of claims 20 to 26, wherein the control unit forms part of a navigation system for a golf buggy.

28. A program for use with a control unit for a navigation system for a vehicle, the vehicle including left and right motors for respectively causing rotation of left and right wheels and left and right motor drives for respectively driving the left and right motors, the navigation system including the control unit and an electronic gyroscope mountable to the vehicle, the control unit including a processor and associated memory device for storing the program, the program including a series of instructions for causing the processor to: receive an output signal from the gyroscope; derive a yaw angular velocity from the gyroscope output signal; derive a vehicle turning direction from the gyroscope output signal for non-zero yaw angular velocities; and cause the motor drives to apply a relative speed difference between the motors according to the yaw angular velocity and vehicle turning direction to thereby compensate for a change in vehicle heading.

29. A program according to claim 28, wherein the series of instructions for causing the processor to derive the yaw angular velocity includes instructions to compare the value of a property of the gyroscope output signal to a reference value.

30. A program according to claim 29, wherein the series of instructions for causing the processor to derive the vehicle turning direction from the gyroscope output signal includes instructions to determine whether the gyroscope output signal property value is less than or greater than the reference value.

31 . A program according to either one of claims 28 or 29, wherein the reference value corresponds to the gyroscope output signal property value when the vehicle is at rest.

32. A program according to claim 31 , further including a series of instructions for causing the processor to update the reference value when the vehicle is at rest for greater that a predetermined period.

33. A program according to any one of claims 29 to 32, wherein the gyroscope output signal property is a voltage.

34. A program according to any one of claims 28 to 33, the vehicle further including a manually operable controller to enable manual control of the motor drives, wherein the program further includes a series of instructions for causing the processor to receive control signals from the manually operable controller; override operation of the motor drives to apply a relative speed difference between the motors according to the yaw angular velocity and vehicle turning direction; and control operation of the motor drives in accordance with the control signals.

35. A program according to any one of claims 28 to 34, wherein the program is for use with a control unit that forms part of a navigation system for a golf buggy.

36. Firmware for use with a control unit for a navigation system for a vehicle, the firmware including a program according to any one of claims 28 to 35, the firmware being stored on a read only memory device.