This is a 5" gauge dynamometer car I built jointly with John Lyas. Externally, it is a replica of a prototype owned by the South Australian Railways, used for measuring both the output power of locomotives and the drag required by a given consist over a given section of track. The small one does exactly the same, but uses electronic sensors and a laptop computer. The first picture shows our car displayed adjacent to the original prototype at the National Railway Museum. The prototype was repainted in the 1950s.
The next shows it being used for locomotive efficiency testing.
Here is a typical output from the dynamometer car, as it appears on the computer screen. The speed graph (metres/second) comes from a DC tachometer driven from the wheels. The distance travelled (metres) is derived from an optical gap sensor on one axle. The force (newtons) comes from an electronic strain-gauge load cell mounted behind the drawbar. The drawbar power (Watts) is derived by multiplying the force by the speed. The data is acquired via analog to digital converters accessed from a USB port on the laptop. Originally I wrote the software in Turbo Pascal. I have since converted it to a Windows application written in Borland Delphi.
And for comparison, here is the truly wonderful mechanical computer and chart table inside the original…
Members of the South Australian Society of Model and Experimental Engineers conducted a day of locomotive testing, to measure the thermal efficiency of nine 5" and 7.25" gauge locomotives.
It was such a success last year that we did it again...
Third SASMEE trial 27/8/2005
Fourth SASMEE trial 23/6/2007
Fifth SASMEE trial 27/6/2009