Although toy or miniature electric trains exists as early as 1850 and they have been highly popular since the early 1900's, the operation of most miniature electric trains has remained essentially unchanged. Except for exceedingly technical, sophisticated and expensive systems, more than one engine could not be operated independently and simultaneously on the same section or block of trackage. The basic miniature electric train "system", as a minimum, consists of the following components:
(1) A locomotive or engine which contains an electric motor which operates on either direct or alternating current (DC or AC), flanged wheels suitable for running on miniature track, at least two of which are electrically conducting and electrically isolated from each other for DC powered motors and at least one of which is electrically conducting and electrically isolated from a third isolated conductor, usually called a shoe, for AC powered motors, a gear train which connects the rotation of the motor to the wheels, thus moving the engine, and an electrical contact system which connects the two electrically conducting wheels to the two leads of the DC motor or connects at least one wheel and the shoe to the leads of the AC motor.
(2) A system of trackage consisting of two (for DC operation) or three (for AC operation) electrically conducting rails which are fixed to some form of track tie and/or road bed which electrically isolates two of the conducting rails from each other.
(3) An appropriate DC power supply whose two output leads are connected, one lead to each rail of the two rail track, or an appropriate AC power supply whose two output leads are connected, one to the center rail and the other to one of the outside rails of the three rail track.
In addition to the foregoing, the power supply, AC or DC, is usually equipped such that voltage to the track can be adjusted from zero to some maximum thus making the engine move faster or slower or stop. Some engines are equipped with miniature head lights whose brightness is proportional to the amount of power supplied to the track, since the headlight derives its power from the motor circuit.
An appealing feature of such miniature trains is that they duplicate or simulate both in appearance and operation the real, prototype railroads. For this reason, miniature electric trains are manufactured in a number of different scales. For example, in an "HO" scale engine a foot on the prototype engine is equal to 0.138 inches on the miniature of that prototype. Each "scale" has associated with it, its own track gauge. Gauge is the distance between the outermost and innermost rails of the track measured from the inside-to-inside of the rails. This, again, promotes prototypical appearance.
Toy or miniature electric trains usually include an oval of track, an appropriate electrical power supply, freight or passenger cars and one engine. This permits the trains to go around and around the track. To improve interest and enjoyment, the operator can add more track and another engine with more freight or passenger cars so that two separate trains can be independently operated at the same time, as in a prototypical railroad.
However, if two engines are placed on the same track oval, (assuming the power supply has the capacity to run both engines), both engines will move in the same way. Both will go forward, backward or stop at the same time and, given different engines with different loads, one will eventually overtake the other. This does not achieve the goal of prototypical operation, i.e., of having two engines independently operated on the same track at the same time.
Another alternative is to place a second engine on the track and connect a second power supply. This is no better than the first situation. The engines still do the same thing. Moreover, they can receive too much power, burning out their motors, or electrical shorts can occur between the power supplies, burning both the supplies and the motors out.
A third alternative is to electrically insulate one half of the oval of track from the other and connect separate power supplies to each half. This, too, does not achieve the goal of simultaneous, independent operation of two trains on the same section of track.
Still another attempt to solve the problem is called "cab control" or "block control". In "cab control" or "block control" systems, the power supply is connected to each separate insulated section or "block" of track as the train moves into that section, from section to section, while at the same time disconnecting any other power supply from the sections to be controlled. For even a modest size model railroad and two trains operating at the same time, literally hundreds of feet of complex wiring, soldering, switches and insulating procedures are required in addition to the construction of the structure and control panels necessary to mount all the electrical components of wires. In order for a train to proceed along the track from section to section the operator must constantly operate the switches which successively connect and disconnect his power source. More important, no two trains can occupy the same track section or block at the same time. The goal of prototypical operation is not achieved.
In recent years there have been still other attempts to achieve the goal of operating more than one train simultaneously on the same trackage. Such attempts have involved even more complications and expense. For example, a special power supply is arranged to provide a number of AC signals to the rails. As many as six different signals (frequencies or pulse codes) are generated. A special receiver tuned to one of the six signals is installed in an engine. The received AC signal is then converted to DC by a special rectifier component in the engine and then fed to the engine's DC motor. This system will and does operate trains independently on the same trackage but it is expensive, requires complex electronics, and must be installed by the buyer. Special service is required for repairs. One can only use receiver equipped trains. The receiver/rectifier components to be installed in the engines do not fit in all types of engines and each installation requires different installation techniques.