Motion System Design

Microdrive delivers delicate motion

From little kids to kids at heart, model train enthusiasts are passionate about their hobby and crave as much realistic detail as possible to be packed into their miniature replicas. While older generations of model trains were roughly molded from tin, intricate detail is expected from modern designs. Besides the aesthetic value, today's focus is increasingly on realistic handling. Modern electronics allow the latest models to be controlled digitally, eliminating complex wiring and various power supplies.

As a leading designer of sophisticated model train systems, Nuremberg, Germany-based Fleischmann recently developed a new model — a highly intricate 1:160 (N gauge) miniature replica of the Bavarian 70 series locomotive (BR 70) from 1930. Even the lettering measuring just tenths of a millimeter high can be read perfectly with a magnifying glass. Major advances also include the drive technology, with professional model makers at Fleischmann bringing microdrive specialist Faulhaber Group, Clearwater, Fla., into the design phase. In the new model, a microdrive links the electronics to the mechanisms, enabling delicate shunting operations to be accurately replicated.

Building an N-gauge model train system involves working with tiny units. In this case, the BR 70 locomotive is just 57.8 mm long when measured buffer to buffer. The locomotive's undercarriage and body are die-cast metal with additional plastic parts, which allows even the smallest details to be faithfully replicated in series production. To match the original, realistic lights are integrated using tiny, warm-white LEDs that automatically switch to the direction of travel.

Regarding the drive design, certain mechanical and physical conditions had to be taken into account. As on full-scale locomotives, traction (and on the model, power transmission) between the wheel and track is a crucial factor. A small motor generates only low torque, but requires high engine speed, which must then be geared down relative to the scale and size of the drive wheels. All of this must function reliably and out of sight for many years while taking up minimal space.

In the case of the BR 70 with a weight of just 36 g and a relatively high engine speed, quiet operation is also important. Even the slightest rotor imbalance can cause vibrations and resonance in the railway system on which the model rails are laid. This issue was resolved by deploying a high-precision flywheel, with a wobble of just 0.03 mm, on the motor shaft. The flywheel (and motor) are as large as the locomotive body permits — so the flywheel, which stores kinetic energy, maximizes running performance even during very slow track-switch shunting operations. This is particularly important when there are brief interruptions in the power supply from the track.

Beyond toy trains, modern microdrives can be customized for virtually any scenario. For more information, visit MicroMo, the North American contact for Faulhaber Group, at or call (800) 807-9166.

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