Forty years ago, when I was in graduate school working on my Master’s Degree, I was told that a caboose cost about $1 million to purchase, maintain, staff, and fuel to drag around the countryside over its lifetime. At the time, I worked for an engineering firm that developed the embedded software for a prototype End of Train Device (EOTD). This piece of hardware (with its pair, the Head of Train Device – HOTD) is responsible for nearly every caboose in North America finding its way to the railroad boneyard (sigh).
The purpose of the caboose was to provide the conductor a place to monitor the brake pipe pressure on the last car of the train. Brakes on a train don’t work the same way that brakes on a car work; brakes on a car work in a positive fashion – pushing on the car’s brake pedal increases the pressure in the brake line, pushing the brake pad or shoe up against a disc or rotor. On modern trains, brakes (every axle of every car has a set) work in a negative (fail-safe) fashion – the brake shoes are pushed up against the rotor by a spring, and the pressure in the brake pipe pushes the shoe away from the rotor.
Pressurized air generated by the locomotive is fed into a closed pipe that runs the length of the train. Releasing the brake pipe pressure allows the spring to push the shoe against the rotor. It is important that the pressure in the brake pipe is maintained while the train is moving – a small leak in the brake pipe can cause the brakes to be applied (partially or wholly) on some, or all, of the axles. Over time, this generates an enormous amount of heat (both from the shoe rubbing on the rotor, and from the wheel being dragged, rather than rolling). This can cause the wheel to flatten, or even start a fire.
By the early- to mid-1980s, a number of organizations were developing a low-cost replacement for the caboose. Ultimately, the EOTD was able to measure brake pipe pressure, transmit this pressure data to the HOTD, and even respond to a command received from the HOTD to open a valve to dump the brake pipe pressure in an emergency situation. If the brakes are applied suddenly from the front of the train only, heavy cars in the back of the train could derail when their momentum pushes into the cars ahead of them. If the brakes are applied only from the end of the train, the locomotive could keep pulling, stretching the train until a knuckle breaks.
A pair of M-Duino 19R+ GPRS-GSM PLCs is a perfect fit for this task. The EOTD monitors pressure sensors connected by I2C or SPI, reports position and velocity using a GPS sensor, controls a brake pipe valve operated by a relay, two-way communications to the HOTD via GPRS, all controlled by plenty of horsepower provided by the Mega2560 Arduino computer. The HOTD has similar functionality, additionally with an RS-485 communications link to the engine control system, and a push button digital input used by the locomotive engineer to dump the brakes in an emergency.