How an Electric Train Works
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Model Trains Imitate the Real World
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A railroad locomotive in the real world uses electric power, generated by an onboard diesel engine or carried by overhead wires or a third rail, to run a "traction" motor that drives its wheels. No electricity is carried by the rails, except for small amounts of current used to operate signaling devices along the tracks. Model train locomotives simulate the operation of real ones with motors that run off electricity transmitted through the rails of the track.
DC-Powered Trains
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For many years, most American model train locomotives have operated from 12 volts of direct current, or DC, as standardized by the National Model Railroad Association. Some foreign train manufacturers such as Märklin (Germany) use alternating current or AC systems, and their trains are electrically incompatible with American brands. Voltages can vary in different scales of model trains, and no one power pack is usable for all scales. While locomotive motors and headlights function on DC, accessories such as streetlights and turntables usually run off AC.
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How Model Train Locomotives Run
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DC is transmitted by wires from a "power pack" to the rails on the tracks. In the two-rail systems that power most scales, one rail has positive polarity and the other serves as the ground. The locomotive wheels serve as the conduit for this electricity. The positive charge passes through the wheels to the motor and is discharged through the opposite wheels into the negative rail. The 027 scale, familiar from collectible Lionel trains, has a third rail in the center of the track which serves as the ground while the outer rails are positive.
Mechanics of Locomotion
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The power transmitted through the rail and locomotive wheels is conveyed by wires to a DC motor which spins at various speeds governed by the rheostat (called the "throttle") on the power pack. The motor drive shaft is the first part of the drive rod assembly. A linkage connects the drive shaft to a "worm gear." The spinning worm gear is connected to a gear box that sits on the axles of the locomotive's wheels. Teeth on the axles are driven by the gears and the locomotive is propelled forward or backward, depending on the directional setting on the power pack.
A New Refinement: Digital Command Control
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Simple DC power, which has been used for a century in powering model trains, has some disadvantages. Electrically insulated sections or "blocks" of track allow independent control of several trains, but within any one block locomotives can run only in one direction and at one speed. Digital Command Control (DCC), a recent development in the hobby, allows for separate electronic impulses to be sent through the rails to decoders wired into each locomotive. On one piece of track, up to 9,999 locomotives can theoretically be run at varying speeds and directions using DCC, creating the flexibility for much more realistic operation. Along with this refined control, wireless "walkaround throttles" have given operators the freedom to follow their train around a layout instead of standing at the main power pack. DCC, now the hottest growth area in model railroading, has also given rise to extremely accurate sound systems that faithfully reproduce not only horn and bell sounds, but the roaring engines of specific locomotives, including idling and gear-shifting sounds.
Unusual Ways to Power Locomotives
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A few advanced hobbyists have devised interesting alternatives to using the rails for power. One of these, used by a few who model overhead wire (known as catenary), is to make the wire carry power just as in the real world. However, this is a rare and unusual modification, and the vast majority of modelers use the standard power systems.
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