Measuring Scale Speed
Measuring scale speed - it's quick and easy.
First lets look at measuring speed accurately. Usually we want to know the speed in scale miles per hour. But what we have at hand are the necessary tools to accurately measure speed in real feet per second. So the question becomes how to use them and how to convert the results into scale miles per hour.
To measure speed in real feet per second, lay two reference markers beside the track. The markers can be anything, but quarters are easily seen and are usually close at hand. Put the markers far enough apart to make timing easy, say 3 to 5 real feet in Z scale, 5 to 10 real feet in HO, 15 or more real feet in large scale. To simplify calculations, make the distance between markers an exact number of real feet.
Next, time how long it takes your train to travel from one marker to the other. A stop watch is ideal, but any watch showing seconds will do. Make sure your train is up to speed when it reaches the first marker and time how long it takes for a point on the train (say the front of the engine) to travel from marker to marker.
Finally, calculate the speed of the train. First calculate the
speed in real feet per second by dividing the distance between your markers
by the number of seconds it took to travel between them. Then multiply
the answer by the rfps-to-smph factor for your scale from the table below.
The answer is in scale miles per hour. The accuracy of this method
depends mostly on the accuracy of your time measurement.
For a quick check on speed in any scale (including full size), count how many seconds it takes a 40 foot box car to travel past a fixed point beside the track. Then divide this number into 30 to get scale miles per hour. For 50 foot box cars, divide the number of seconds into 36. This quick check works best at low speeds and is a great way to keep shunting speeds prototypically slow in a yard.
In large scale, using a factor based on scale and on a common box car
which can be used in all these scales may be more convenient. The
table below is based on the ubiquitous Bachmann box car. Pick the
factor for your scale and divide it by the number of seconds it takes
your Bachmann box car to roll past a fixed point to get its speed in scale
miles per hour. The table also shows this box car's length in the
various large scales.
As a historical note, these methods are very similar to the ways engineers and station agents measured train speeds in the days before speedometers and hot box detectors. Engineers would time the distance between mile posts, station agents would time the passage of box cars, and the railroads were run on tight schedules based on this.