WO2022097084A1

WO2022097084A1 - System and method for determining distance travelled by a model vehicle

Info

Publication number: WO2022097084A1
Application number: PCT/IB2021/060268
Authority: WO
Inventors: Philip Elphee Williams; Peter John Jones
Original assignee: Mr Innovations Limited
Priority date: 2020-11-05
Filing date: 2021-11-05
Publication date: 2022-05-12
Also published as: GB202105910D0; GB202017507D0

Abstract

A system outputs a signal indicative of a distance travelled from a datum, by a model train over a train track with an electric conductor. The conductor is arranged in a square wave form below the train track and has an electric current flowing in it. A model train is fitted with a transducer that detects a variation in a magnetic field strength (H) arising from the electric current in the electric conductor and derives an instantaneous magnetic field strength (H) which is proportional to a distance between the transducer and a maximum magnetic field strength (H) occurring where the electric conductor crosses the train track. Zones are defined between two adjacent crossovers of the electric conductor and a counter counts zones which correspond to the number of zones through which the model train has travelled. When this distance is added to a distance, corresponding to a proportion of a zone through which the model train has travelled, the total distance measured from the datum is derived.

Description

System and Method for Determining Distance Travelled by a Model Vehicle

Field of the Invention

The invention relates to a method of determining a distance travelled by a vehicle, such as a model train or a model car, over a defined path or track. More particularly, but not exclusively, the invention also relates to a method of determining the speed of the model train or model car, over the defined path or track.

Background

The invention is particularly well suited for use with a toy or model vehicle, such as a toy train or model train or carriage, as the invention provides a precise indication of the location of the model train or carriage within a model railway layout.

Verifying the location of model trains, within a model railway layout or installation, has been difficult especially with larger railway layouts. Where model railway installations were separated into several independent zones each zone required its own wiring and control unit. As a consequence of this, the cost of complex model railway installations was often very expensive, particularly as the size and complexity of model railway installations grew as each zone required a dedicated control system and its own wiring. Therefore as the size and complexity of model railway layouts grew the ability to locate the precise whereabouts of a train became increasingly difficult.

The present invention overcomes these problems and eliminates the need for complex wiring and so removes the cost of additional controllers.

Because it was often difficult to locate the position of a train it was also difficult to determine its speed. An object of the present invention therefore is to identify the location, and the rate of change of location (speed) of a moving vehicle, such as a model train or car which moves over a surface, such as a track or roadway defined on a playing surface.

Prior Art

United States patent application number US 2011/294391 (Todd) discloses a system including a toy car and track or a model train set. The system has a power supply, controller, track, and moveable object(s) such as a toy car or train which contain a permanent magnet or one or more electrical conductors acting as electromagnets, positioned so as to travel general parallel to the surface of the track.

The controller has operator interfaces such as switches and/or a potentiometer(s) for speed/motion input. The track consists of one or more printed circuit boards with conductive traces configured such that the controller energises them. Current passes through the traces in a repetitive sequential order which causes the moveable object to be propelled along the track due to the Lorentz force generated by the electromagnetic field acting on its magnet.

United States patent application number US 2010/0130096 (Baarman et al) discloses an inductively powered toy vehicle and an associated track with inductive charging segments. The vehicle includes a secondary coil, a drive motor, an electrical power storage device connected between the secondary coil and the drive motor and a wireless communications unit. The charging segments may include a primary coil, a sense circuit operable to detect the presence of the vehicle based on a change in detected impedance of the primary coil and a power control unit operable to provide a time-varying current to the primary coil when the vehicle traverses the charging segment.

The primary coil is positioned within a race track adjacent an upper track surface. The vehicle drive motor may be operable at first and second speed settings, and a remote control device provides operating instructions to the vehicle wireless communications unit.

Japanese patent application number JP 2003052105 (Matsushita Electric) describes a system that detects the speed of a moving body. Markers are installed at intervals along a path over which the moving body travels. The body is provided with a marker detecting means for detecting the markers and a speed-calculating means. Data, such as distance travelled, speed and position can be obtained accurately using the markers.

None of the aforementioned systems discloses a system which enables precise location of a vehicle, such as a model train or model car, which travels over a track.

An object of the invention therefore is to provide a system which may be installed quickly and easily into a model train installation which provides a precise indication of the ;location of the train.

Another object of the invention is to provide a system that is able to be retrofitted to an existing system in order to simplify its operation.

A further object is to provide a system that is simple to use, and which provides a digital output of instantaneous location data, from which the speed and precise location can be obtained.

A yet further object of the invention is to provide a system, which in a preferred embodiment, includes a battery powered device capable of being carried in or fitted to a model train carriage or model train engine and whose battery is easily replaced.

Statement of the Invention

According to a first aspect of the invention there is provided a system which outputs a signal indicative of a distance travelled from a datum, by a model train over a train track with an electric conductor, arranged in a serpentine form below the train track, when an electric current flows through the electric conductor; the system includes a model train which is fitted with a transducer that detects a variation in a magnetic field strength (H) arising from the electric current in the electric conductor and wherein the instantaneous magnetic field strength (H), at a model train location, is proportional to a distance between the transducer and a maximum magnetic field strength (H) occurring where the electric conductor crosses the train track; a zone is defined between two corresponding points, such as adjacent crossovers, of the electric conductor with respect to the train track; and a counter counts the number of zones through which the model train has travelled; and when added to a distance, corresponding to a proportion of a zone, through which the model train has travelled, a processor provides the total distance measured from the datum, wherein the proportion of the zone, through which the model train has travelled, is derived from a magnetic field strength measured at the model train location and a local negative or positive rate of change of the magnetic field strength is sensed and used to derive the proportion of the zone, through which the model train has travelled.

Preferably an alternating current is fed to the serpentine loop and is arranged to establish a magnetic field (H) which has a uniquely identifiable magnitude at every position in the zone.

The variation in the magnetic field (H) is sensed as a varying field strength by the transducer on the model train as the model train moves through the zone between crossovers.

Ideally the varying magnetic field strength is in the form of a cosine wave and the uniquely identifiable magnitude is derived from the field strength and the rate of change of field strength with respect to location in the zone (dH/d(d)).

The advantages of having a high frequency carrier signal are that it maintains the voltage induced in the transducer, even when the model train is stationary. In addition the high frequency ensures that the field measured is not affected by any additionally induced voltage arising as the train moves through the zone. In other words the change in magnetic field arising from the high frequency carrier signal (dH/dt) is much faster than that magnetic field variation detected by the model train (dH/d(distance moved from crossover)). The choice of carrier signal frequency should also be many times (typically tens of thousands) greater than a maximum modulation frequency which is associated with the motion of the train.

EMF = dH/dt N (where N is number of turns of the coil in the transducer)

Model train motors are controlled using pulse width modulation (PWM) which operate at frequencies typically up to 20 KHz. These produce a very high magnetic field which is associated with fundamental and higher harmonics arising from the train motor. In order to allow narrow band filtering, as described below, the chosen carrier signal frequency has to be significantly greater than 20 kHz.

Another advantage of having a very high carrier signal frequency is that it eliminates interfering magnetic fields arising, for example from the Earth’s magnetic field.

Ideally the variation in the voltage induced in the coil is in response to a change in magnitude of the magnetic field strength (H) and a processor associates these variations with maximum and minimum field strengths which occur at crossovers and therebetween.

The local magnetic field strength (H) is detected by the coil, as an induced voltage (Vo) at a position between two crossovers and the fact that the Vo is proportional to the cosine (Vo/Vmax), where Vmax is the maximum induced voltage occurring at a crossover, is used to derive a signal indicative of the position of the train, even when it is stationary.

Thus the induced voltage (Vo) at a position can be expressed as a ratio of a portion travelled within a zone with respect to the total zone distance (d) as Hmax cos (o), where o is expressed as d x (360)/max is used to derive the proportion of the zone, through which the model train has travelled, as described below. The invention improves the accuracy of locating a model train within an installation which enables greater flexibility when positioning accessories, such as points and level crossings; station furniture, such a lights; and ancillary items, such as signal boxes or water tanks, which are typically used in complex model train layouts and whose function depends upon the location of model train in order to create an authentic model railway experience.

In addition, the present invention enables close control of individual trains within a complex installation due to the capability of precisely locating each train with respect to a reference or datum.

In a particularly preferred embodiment data is transmitted from the model train by a radio frequency (RF) transmitter to a controller which includes a processor. The controller activates accessories and switches on and switches off other functions of a system derived from data obtained by the invention. For example, automatic safety features may be integrated into a model railway installation control system. For example, a collision sensing means may be provided which prevents two or more trains, on the same section of track, from colliding with one another. This has sometimes occurred when one train stops unexpectedly, or the exact location of each train was not known. The present invention when used in conjunction with control software prevents this problem from occurring.

In a preferred embodiment a remote receiver is preferably included in a master controller that operates in accordance with software and extracts train identity data and train location data from signals received from RF transmitter in the train.

Data from the processor may be used to control a network of trains and/or signals and/or other accessories or peripheral devices. Data is ideally transmitted by modulating an RF signal carrier in an RF transmitter or an infra-red (IR) transmitter, or by a wireless communication device, such as a Bluetooth (RTM) wireless protocol device. Information with respect to the train position may be transmitted to the master controller by a different method from the one used by the master controller to communicate to the train. In this sense full duplex communication is achieved between the master controller and the train by communication via separate channels.

Ideally the electric conductor is arranged in a regular serpentine form below the train track by folding or bending a wire in the form of a square wave whose duty cycle is dimensioned so as provide a series of crossovers substantially in the form of a rectangular square wave below the track. In this way the invention is suitable for retrofitting to existing railway installations, simply by lifting a section of track and placing the folded wire between the track and a mounting board on which the track rests. Continuity can be tested at any time to ensure the integrity of the folded wire.

In a preferred embodiment therefore the folded wire is envisaged as three separate sides of a square. Where the wire crosses the track, it is ideally perpendicular to the track and ideally is parallel to the track until its next crossover. Thus a series of crossover points is established which defines distinct zones, each crossover is separated by a distance D with each crossing alternating from left to right and then from right to left.

After n number of crossovers and therefore (n-1 ) zones, the end of the wire is returned to a carrier frequency generator which generates the high frequency alternating signal. Thus a circuit has been established as an overall loop in which one side of the loop is arranged to cross below the track, n times. The distance (d) between crossovers is not critical but needs to be consistent. Preferably the distance between crossovers is a spacing of 100mm.

In some embodiments the electric conductor crosses at least one rail of the train track. Ideally the electric conductor crosses both rails of the track.

Ideally the electric conductor crosses the rail track at right angles (or at an angle substantially at right angles) to the direction of the path of train travel. This produces a magnetic field (0) which is parallel to the rail track direction. The strength of the magnetic field (0) varies as a cosine curve within a zone and this is used in order to determine the precise location of the train in a zone defined between two crossovers.

The transducer ideally includes a coil, whose axis is aligned to be parallel to the magnetic field and thereby produces a varying induced signal in the transducer in dependence upon the position of the transducer with respect to two magnetic field strength maxima, defined at each crossover.

In some embodiments a high frequency amplifier is provided to amplify an induced signal in the coil. Ideally an induced voltage signal is fed from the coil (or pick-up) via the high frequency amplifier and output as an instantaneous value for each induced voltage.

Ideally a timer is provided which derives the frequency of the number of zones counted and outputs a signal indicative of the speed of the model train.

In a preferred embodiment, which includes the high frequency amplifier, the timer may be configured to output a signal indicative of the acceleration and deceleration of the model train.

Ideally the induced voltage value is sampled by a timer and its value is stored and compared with previous values in order to determine the instantaneous position of the train in any zone. If the value is the same as a previously stored value, then the train is stationary. If the samples indicate reducing values of magnetic field (H), then the movement of the model train is towards a trough; and if the samples indicate increasing values of magnetic field (H) then the movement is towards a peak. This enables precise location within the zone, as described below.

A datum is provided from which absolute distance is measured. Preferably the datum is defined by a double loop formed in the electric conductor. Alternatively the datum may be defined by an insert, such as an additional coil, connected in series with the closed loop.

A datum may be established in a variety of ways including the use of a magnet and reed switch or an optical means. The datum may also be provided by the use of a fixed magnet on the moving train passing over a pick-up coil adjacent, or between, the rails of the track. When the train passes over the datum pick-up its signal is amplified and integrated and informs the controller that the train is at the datum point. A memory may be provided to store an integrated value indicative of the total distance travelled by the model train.

In a particularly preferred embodiment a model railway set is supplied with a controller that is adapted to operate a plurality of accessories or peripheral devices in accordance with information derived from the speed and location of the model train so that the data relating to the train position and/or its speed is used by the controller to control the accessories or peripheral devices.

These accessories or peripheral devices may be connected to a communication network and include devices such as: points, barrier crossings, lights, audible alarms, signal controls and signals all of which are addressable by the controller.

Ideally the electric conductor is in the form of a closed loop of copper wire with its own power supply which is preferably at an input terminal under supervision of an operator or a remote control command system.

A preferred embodiment of the invention will now be described, with reference to the Figures in which:

Brief Description of the Figures Figure 1 shows an overall diagrammatical arrangement showing how a wire is folded in the form of a regular square wave below each rail (shown as ghosted) of a model railway track;

Figure 2 shows in diagrammatical form magnetic field lines in each zone;

Figure 3 shows in diagrammatical form a graph of magnetic field strength (H) measured by a coil passing through the magnetic fields in the zones, corresponding to Figure 2;

Figure 4 shows an actual voltage output which corresponds to a model train moving through magnetic fields and shows the induced voltage which corresponds to the magnetic field (H) maxima and minima as peaks and troughs in the form of a cosine wave;

Figure 5A is a diagrammatical view of voltage output for a zone defined between two crossovers;

Figure 5B is a diagrammatical view of a section of railway track showing locations within the zone, between the two crossovers; which correspond to the outputs shown in Figure 5A;

Figure 6A is a block diagram of one example of an amplifier and demodulator circuit and Figure 6B is a block diagram of a higher frequency carrier frequency generator;

Figure 7A shows a signal induced in the transducer whose envelope is varying in dependence on its movement through the magnetic field within a zone;

Figure 7B shows the signal after amplification and depicts high frequency carrier signal within the envelope;

Figure 7C shows the signal after rectification where the envelope is positive, and encloses positive half cycles of the high frequency carrier signal; and Figure 7D shown the signal after the positive high frequency carrier signal components have been removed after low-pass filtering.

Detailed Description of a Preferred Embodiments of the Invention

Referring to Figure 1 there is shown in lines two rails 10 of a section of model railway track (not shown). A folded wire loop 14 is placed below the rails 10 in the form of a square wave of spacing d. The wire loop 14 has its two end terminals 16A and 16B which are connected to a higher frequency carrier frequency generator, as described below. In practice a prefabricated railway track is placed over the folded loops of wire.

A baseboard (not shown) on which the track is laid supports the folded wire loop 14 which may be stuck to the baseboard by tape (not shown). The folded wire loop 14 shows the spacing d between crossovers, that is where the folded wire loop 14 crosses each rail 10 at right angles. Arrow F indicates the direction of travel of a model train or car (not shown). The number of folded wire loops is indicated as being between fixed datum 18 to a maximum number (N) of zones.

In a practical installation the wire loop 14 is installed beneath the track. What is important is that each folded wire loop 14 repeatedly crosses the path of travel F of the model train. The baseboard (not shown) should be non-magnetic and non-ferrous. An alternating current (AC) from higher frequency carrier frequency generator 70 is fed at terminals position 16a and 16b to the wire loop 14. This establishes an alternating magnetic field around the wire 14. A coil 20 is shown whose outputs are connected to high frequency amplifier 22.

Pick-up coil 20, together with associated devices (as described below) is located on a device which is mounted in the model train (not shown) or housed in a carriage (not shown) which travels with the model train. It is important the coil is aligned to be parallel with the rails 10 and so intersect magnetic fields which are established in portions of wires 14 which cross the rails 10.

Figure 2 shows that the direction of the magnetic field H and that it is changing its polarity for each reversal of the wire loop 14 and that this gives rise to a series of peaks and troughs in magnetic field strength, as shown in Figure 3. In practice this means that there are always opposing fields at every reversal of the wire loop 14 as shown by arrows I in Figure 2. It is also apparent that field nulls result at each half wave between each crossover point as shown in Figure 3.

The model train (not shown) is fitted with a pick-up coil 20 which is set at right angles to the direction of flux (V). As the model train moves in the direction of travel F, an EMF is induced in the pick-up coil 20. The amplitude of the signal induced in the pick-up coil 20 is shown in Figure 3. The frequency of the signal induced in the pick-up coil 20 is proportional to the speed of travel of the model train.

Between each null point there is a voltage that is induced which is fed via the pick-up coil 20 to an amplifier 22. Rectifier 23 ensures all half cycles are positive. As shown in Figure 3 the signal is sent to a processor 30 which is operative to produce an output value for each instance of an induced voltage between the nulls. A counter 40 counts the instances of zones and data is stored in a memory 50, such as a random access memory. This data is relayed to the main controller (not shown) via a wireless transmitter 60.

Referring to Figures 5A and 5B the distance between crossover points A, B, C and D is arranged to be a fixed value d and the number (n) of crossover points is also known. Therefore the absolute position from the datum 18 (shown in Figure 1 ), that the model train has travelled, can be determined by counting the number of zones and added to the distance calculated by the instantaneous value of H, as described below.

One way to establish the location of the datum point 18 is to have a double loop of wire (not shown) at a distance of d/2 or to insert an extra coil (not shown) in series with the folded wire loop 14 which induces a larger signal in the pick-up coil 20 to identify the datum point 18. A further way is to have a fixed magnet on the train that induces a signal into the datum coil 18.

The above describes the arrangement for travel in the direction F. If the model train is capable of travelling in both forward and reverse directions then a further embodiment of the invention includes fitting the model train with a second pick-up coil that is arranged a known distance (such as d/3), such that the first pick-up coil 20 induces a voltage signal before the second pick-up coil (not shown) induces another voltage signals and this lag can be used to determine the direction of travel of the model train.

It is also understood that when there is travel in the opposite direction (-F) the second pick-up coil induces a voltage signal before the first pick-up coil 20 induces a voltage signal. Processor 30 is operable to interpret these voltage signals and to provide an appropriate output as described below.

The total distance moved by the model train is then derived as n x d, where d is the spacing between the crossovers in mm and n is the number of zones encountered since the datum.

Reference will now be made to Figures 5A and 5B to show how the distance travelled within a zone is calculated. The distance travelled within a zone is obtained by measuring the ratio of an induced EMF, at an instantaneous position (shown as Z, in Figure 5A) and then dividing this value by a maximum induced EMF, shown at point Y.

Thus position is proportional to cos 0 (Vi/Vmax) where Vi is the instantaneous EMF at point Z and Vmax is the maximum EMF at point Y as shown in Figure 5A and as described in greater detail below. Measurements of field strengths and whether a rate of change at a particular point Z is negative or positive, may be used to indicate where a model train is within a particular zone.

Figures 5B shows an example of a zone of 100mm. The graph shown in Figure 5A corresponds to positions in the 100mm zone. In order to derive the precise distance travelled within the zone, the relationship Vo = 0.5 (1 + cos 0) is used to determine the proportion of the total zone distance through which the model train has passed.

Therefore, where Vo is the induced voltage at a specific point, Vo = (1+ cos (Dx360/100mm) and 0 = (actual distance moved/zone distance) x 360°.

Therefore the actual distance travelled in the zone (D = 100/360) cos^-1 ((Vo - 0.5)/0.5) = 22mm in the example shown in Figure 5B. Using the information derived from the system described above, it also is possible to determine the speed, the acceleration or deceleration as well as the position of the model train. Therefore in a model railway installation this information may be used to control a number of features such as stopping distance, stopping places, points control and signal lights.

Data representing the position, speed and acceleration of the model train may be transmitted from the processor 30 to a user (operator) via any suitable means such as an infra-red or wireless communication system 60, such as via Bluetooth (RTM) protocol wireless device. Trains are therefore able to be positioned within plus or ± 1 mm in a track layout.

The description above refers to the use of an alternating current passing through the pick-up coil 20 in which an alternating current is transmitted via the folded wireless loop 14.

Figure 4 shows a typical variation in field strength between maximum and minimum and have a rate of change dV/dt is able to be used to indicate whether a train is moving forwards or backwards following amplification, rectification and low-pass filtering.

Referring to Figures 1 and 2, the magnetic or electromagnetic flux produced by the electric conductor crossing the track is substantially parallel to the direction of travel of the model train. A longitudinal axis of the transducer is substantially parallel to track lines on the train track. The transducer includes a coil of conductor whose turns are substantially at right to lines of parallel flux produced by the electric conductor when it crosses the railway track substantially at right angles with respect thereto.

Figure 6A is a block diagram of one example of an amplifier and demodulator circuit. Figure 6B is a block diagram of a higher frequency carrier frequency generator. A crystal or another high stability oscillator 95 which is connected to a power amplifier 80. Power amplifier 80 is tuned to the frequency of the crystal oscillator 95 by narrow band filter 85 and is impedance matched to a square wave conductor loop 14. The square wave conductor loop 14 is positioned in the form of a square wave duty cycle beneath the rail, as shown in Figures 1 and 2.

A search coil 20 is mounted within the train and passes over the folded wire loop 14. Two narrow range radio frequency filters 21 A and 21 B and an amplifier 22 are tuned to the high carrier signal frequency.

Rectifier 23 detects the positive cycle of the amplified signal which corresponds to the detected field strength, so as to ensure all half-cycles are positive going as shown in Figure 3.

A low pass filter 24 removes the high frequency carrier signal and allows the low frequency changes in the amplified signal, as shown in Figure 7D. Frequencies above around 10 Hz have been removed after low-pass filtering leaving only those due to the train movement or position, to reach processor 30. Processor 30 measures the signal and calculates the train position. This data is relayed to the controller via wireless link 60. The signal is expressed as Vo = 0.5 (1 + cos (distance moved x 360/zone distance)).

The aforementioned system may be used with commands and control signals in which a number of different model trains can be monitored and controlled. Knowledge of the precise location of the train is consequently used to control track infrastructure such as signals, points, barrier crossings, train stopping position, and many other features including precise train speed relative to track scale.

The remote receiver is preferably included in a master controller that operates in accordance with software and extracts train identity data and location specific data from signals received from the vehicle and uses these to control a network of trains and/or signals and/or other peripheral devices. Software is ideally compatible with existing software such as RailMaster™ control software. As in the other embodiments data is transmitted by modulating an RF signal carrier and is received at a master controller.

It will be appreciated that variation may be made to the aforementioned embodiments without departing from the scope of the invention as defined in the appended claims. For example the invention may be included in a model railway set that includes the model train which is fitted with the system for determining its speed and location. Ideally the system for determining its speed and location of the train is provided in the form of a single device mounted in a chip, with a simple replaceable cell-type battery. The chip may include electronically erasable read only memory.

Claims

1. A system which outputs a signal indicative of a distance travelled from a datum, by a model train over a train track with an electric conductor, arranged in a serpentine form below the train track, when an electric current flows through the electric conductor, the system includes a model train which is fitted with a transducer that detects a variation in a magnetic field strength (H) arising from the electric current in the electric conductor and wherein an instantaneous magnetic field strength (H), at a model train location, is proportional to a distance between the transducer and a maximum magnetic field strength (H) occurring where the electric conductor crosses the train track; a zone is defined between two corresponding points, such as adjacent crossovers of the electric conductor, with respect to the train track; and a counter counts the number of zones through which the model train has travelled and when added to a distance, corresponding to a proportion of a zone, through which the model train has travelled, a processor provides the total distance measured from the datum, wherein the proportion of the zone, through which the model train has travelled, is derived from a magnetic field strength measured at the model train location and a local negative or positive rate of change of the magnetic field strength, is sensed and used to derive the proportion of the zone, through which the model train has travelled.

2. A system according to claim 1 wherein the variation in the magnetic field (H) is sensed by the transducer on the model train as the model train moves through the zone between crossovers.

3. A system according to claim 1 or 2 wherein the electric conductor crosses the rail track at right angles.

4. A system according to claim 3 wherein the electric conductor crosses the rail track in the form of a square wave.

5. A system according to either claim 3 or 4 wherein the electric conductor crosses both rails of the train track.

6. A system according to any preceding claim wherein the transducer includes a coil which senses a variation of an induced voltage therein.

7. A system according to claim 6 wherein a high frequency amplifier is provided to amplify a voltage signal.

8. A system according to claim 7 wherein the induced voltage signal is fed via a high frequency amplifier and is output for each induced voltage.

9. A system according to claim 8 includes a timer which derives a rate of change of and outputs a signal indicative of the speed of the model train derived therefrom.

10. A system according to claim 9 includes a differentiator which outputs a signal indicative of the acceleration and deceleration of the model train.

11 . A system according to any preceding claim wherein the datum is defined by a double loop formed in the electric conductor.

12. A system according to any preceding claim wherein the datum is defined by an insert, such as an additional coil, connected in series with the closed loop.

13. A system according to any preceding claim wherein the datum is defined by a magnet. 19

14. A system according to any preceding claim wherein the electric conductor is in the form of a closed loop of wire.

15. A system according to any preceding claim includes an alternating current (AC) supply for connection to the electric conductor.

16. A system according to claim 15 wherein the magnetic or electromagnetic flux produced by the electric conductor crossing the track is substantially parallel to the direction of travel of the model train.

17. A system according to claim 16 wherein a longitudinal axis of the transducer is substantially parallel to track lines on the train track.

18. A system according to claim 16 or 17 wherein the transducer includes a coil of a conductor whose turns are substantially at right angles to lines of parallel flux produced by the electric conductor as the coil crosses the railway track.

19. A system according to any preceding claim wherein a remote receiver provides data relating to one or more model railway carriages to a controller that operates in accordance with software for providing control signals for controlling at least the following: one or more accessories or peripheral devices; the position of at least one model train and/or the speed of at least one model train.

20. A system according to claim 19 wherein the accessories or peripheral devices include: points, barrier crossings, signal controls, lights and audio devices. 20

21. A system according to either claim 19 or 20 includes: a display on which data relating to a train position and/or its speed are presented in a computer generated image format.

22. A kit includes the system according to any of claims 19 to 21 and a toy railway set with carriages, track, models, a transformer and a controller.

23. A method of using the system according to any of claims 19 to 22 to record the location of a model train or model railway carriage, comprises the steps of: placing the unpowered vehicle on rails at a datum in a model railway network; recording the datum; traversing the unpowered model railway carriage along the rails to a desired location; deriving the distance traversed from the datum to the desired location; and recording an end location by transmitting a signal indicative of the distance traversed, to the remote receiver.