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System 3
The locomotives at TMRC are powered by DC motors that pick up electrical power from the rails. The speed and direction of each locomotive is determined by the voltage and polarity of the voltage across the rails. In order to operate multiple trains at once, the track is divided into a number of electrically isolated sections called blocks. The task of supplying the power to each block is the job of the control system. TMRC has built three automatic control systems since the clubs founding.

The System

The first control system at TMRC was completed in 1954. Called the Automatic Cab Selection System (ACS or simply the "System" for short), it was one of the first automatic control systems built anywhere. It was able to control up to 5 trains and 30 blocks of track. Like System 2 which followed it, it was built with a variety of electromechanical relays, including a lot of surplus telephone equipment.

System 2

System 2, built between 1963 and 1966, operated the TMRC layout until January 2002. It was so reliable that it functioned with no major faults for almost 40 years! System 2 was large, the main piece being a wall of relays 6' high, 12' long, weighing over 600 pounds, and could not be readily extended to handle more blocks of track or larger numbers of trains (it was limited to 5 trains and 50 blocks of track), which was going to be a problem with the new layout in N52. Some pictures of System 2 can be found in the progress reports, especially here. As an added bonus, there is an audio file there as well.

System 3

The current control system, cleverly named System 3, is fully computer controlled through a network of circuit boards designed by club members. Rather than a single large control system, components of System 3 are distributed under the layout. Microcontroller based boards called block cards control up to eight blocks of track, while a second set of cards, called switch cards control up to eight turnouts apiece. These cards all communicate with a server program running on a computer. A separate program presents a graphical display of the state of the layout.

Major features carried over from System 2 include:

New features with System 3:

Some portions of System 3 are documented more fully in the pages listed below.

Debugging information can be found here

The following pieces currently do not have public on-line documentation:


Tech Model Railroad Club of MIT
MIT Room N52-118
265 Massachusetts Avenue
Cambridge, MA 02139

+1 617 253-3269
x3-3269 (on campus)
Email: tmrc-web@mit.edu
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