that means... Basically, each locomotive has only so much horsepower and
traction. This means that a single locomotive can only pull a certain
number of cars. In the case of my 3 truck shay, that's around 7 short
coal cars. Any more than that and the shay just sits there and spins its
wheels (all 12 of them).
In the real world, let's say an engine can pull 10 cars. If the railroad
needs to move 15 cars, they hook 2 engines together to do the job. Since
modern engines are electronically controlled, the control systems are
also linked and the 2 engines operate as one. The engineer in the
primary engine operates the controls and the second engine mirrors them.
This is what I did this morning for the first time. I hooked another
engine to the front of the shay and hooked 12 cars together. Without the
second engine, the train did not move at all. When I made a consist and
linked the engines, the train now moves with ease.
Since I run DCC (digital cab control) on my layout, I control each
engine independently on one electronic controller. I told the controller
that the 2 engines are a consist, and the control signals sent to the
primary engine are obeyed by the secondary engine as well. I can consist
up to 4 engines with my controller I believe. With analog controls, it
is much harder to do this unless the engines are identical. Otherwise,
they would want to run at 2 different speeds. With the digital controls,
if the 2 engines run at different speeds, it is possible to program the
speed tables in the on-board control chip so that the 2 engines match in
speed and acceleration. This is so cool to see in operation.
