Machinedesign 2403 Scale Locomotives1199 0 0

Hobby horse

Nov. 1, 2000
Today's miniature motors are found in products ranging from office machines to medical equipment. But not too long ago, they were mainly used to power model trains. Take a ride into the past, and the future, of motors in model railroading.

Model-train hobbyists have a common goal: To simulate real-life motion, from the speed at which a train accelerates, to the load it can carry, to how it stops. A fully loaded locomotive, as you know, never stops on a dime, so why should a model? Hobbyists (or railroaders) not only demand an aesthetic representation of the real thing, they also want mechanical simulation to be true to life.

Track must simulate real track, arriving in pieces and requiring assembly just as in real railroading. Switches and bridges must operate in a miniature fashion like the real thing, and of course, the locomotive engine should operate as true-tolife as possible. In the case of motors it means acting as if they're working harder with heavy loads on inclines and producing more noise and "steam."

A model beginning

The early train models back in the 1900s were usually powered by wet-cell batteries. Those sources were soon replaced with 110-V electric transformers.

In 1934, Pittman Engineering Co., now part of Penn Engineering & Mfg. Co., produced its first batch of motors and became one of the earliest suppliers to this market. Measuring 1-5/8 x 3/4 x 1/2 in., the 100 rectangular motors were specifically designed to power HO model locomotives, says Robert Kish, marketing manager.

The company stayed in the hobby business until about 1969, when it began changing its focus to the computer peripheral market. Despite the move, the company still finds that several model train manufacturers purchase its motors. One reason is because hobbyists still feel nostalgia for the Pittman name. "Plus," says Andy Edleman of MTH Electric Trains, "our customers prefer the robust construction and high quality of industrial miniature motors."

For their high-end models, several manufacturers use industrial miniature motors. From API Portescap, Micro Mo Electronics, Pittman, and others. For their other designs, they use less expensive motors obtainable through such Asian suppliers as Mabuchi and Johnson.

Get real

In the modeling industry, everything is done to scale. No matter what the size of model train, it should act like a full-size train with a scale model load comparable to loads carried by railroads across the country. For example, if a real-world engine can carry a maximum of 50 cars, then the model engine should carry 50 model cars with scale loads. In reality, though, industrial miniature motors often provide quite a bit more power.

"We use a Pittman motor in our model of the high-speed trains of Amtrack, particularly the one for the Boston to Washington run," says Jim Weaver, Atlas Model Railroad Co. Inc. "The real trains only pull about seven cars, but at speeds to 125 mph. In our model, the motor will pull many more cars, and do so at a scale speed that exceeds the real version." Even though this goes beyond the accuracy requirements of hobbyists, they don't seem to mind. "Hobbyists will often try to see just how far they can take a model train beyond the real thing's capabilities," continues Weaver.

One very important aspect of railroading to modelers is smooth operation. Hobby manufacturers often put flywheels in the form of brass discs on the motor shaft to smooth acceleration and deceleration so that the train starts and stops more gradually. It's an aesthetic value that makes the model locomotive more realistic.

Lionel, a recognized name in model railroading, uses a Pittman 9434 that produces about 800 g-cm to pull 18 to 20 lb locomotives.

The company also manufacturers in-house two motors it uses in its higher-end models. Its Pullmor motor, an open-frame ac design, is repairable. All components, including brushes are replaceable. The motors are wound in-house, and produce an ozone smell that modelers enjoy, according to Bob Grouva, director of engineering.

Another motor, the Odyssey, is a brushless dc motor with closed-loop speed control and efficiency ratings up to 70%. Some of the unique features Lionel engineers designed into the motor are "percent duty cycle," which is used to determine how hard the motor is working at a given speed.

For example, if the train is going 20 scale miles per hour on a flat grade and then starts up a hill, the speed doesn't change but, realistically, the motor should work harder to drive the train up the hill. The Odyssey relays data to a sound system that then emits sounds similar to an actual locomotive motor straining under similar circumstances. It also increases the output of a fan-driven smoke simulator. Everything is controlled by the motor circuitry.

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When the engine crests the hill - because a real engine would have a dynamic brake - the motor begins braking itself to maintain speed. On cue, the sound unit receives information and plays the sound of a dynamic braking system.

Tomorrow's model trains point to being even more lifelike. On-board microprocessors will ensure realistic, prototypical accelerations and decelerations. For hobbyists who really want to get serious, the "smart" locomotives will even schedule their own periodic break-downs.

Going for gold

At the world model train championship in Germany last year, the Faulhaber Flash took first place. Specially designed for the race, the train achieved a top speed of 100.2 km/hr - the equivalent of going from 0 to 60 in 1.5 sec. It was also the only model to brake within 10 m, a requirement of the competition.

The train consists of a vacuum formed plastic body with a carbon-composite chassis. The remaining mechanical pieces were custom made out of aluminum at Faulhaber, GmbH, sister company of Micro Mo Electronics, Clearwater, Fla.

Inside the train were two Series 3863HO12CR dc micromotors built with neodymium magnets. The design team installed silver graphite brushes in the motors to exert a higher pressure on the commutator. Although motor life was not a concern for the race, speed was - so designers drove the motors with 60 V, five times the catalog value. By increasing the traction control tolerance to 20%, they hit maximum acceleration within 25 m.

The engineers controlled and measured the train's performance through a notebook PC. Two Hewlett-Packard HEDS encoders, one mounted on a secondary front axle directly contacting the track, and the other on the rear motor, provided feedback which the engineers used to track actual train speed, distance traveled, and actual motor speed.

Gauge matters

Modelers often use the terms "gauge" and "scale" interchangeably, but there are technical differences. Gauge is the width of the track. It refers to the distance between the track's outside rails. The O gauge is 11/16-in. in height with a width of 1.25 in., while O-27 track is 7/16-in. high by 1.25-in. wide.

Most model trains run on one or the other gauge. The difference is that curves in the O-27 are tighter than O so, the longest O-gauge cars cannot negotiate the tight corners of the O-27 layout.

Not as popular are the slightly smaller S trains, and the G (garden) trains which are bigger. Scale, on the other hand, is a measure of the size relationship between a model and its real-world prototype. For example, an O-gauge train is 1/48th the size of the real thing - that makes it a 1:48 scale.

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