For some time I've been wanting to make accurate comparisons of the actual pulling power of different brands and types of model locos. The classic GHP Tractometer is now a rare collectible and the weight/pulley method isn't always good for the motor. My local electronics store has some small, general purpose linear strain gauges available for under $10. Since a strain gauge is the major instrument in a dynamometer car, I wondered if it would be possible to accurately measure drawbar pull on a model loco the same way. My thought was that it could be built as a static testbed with a coupler attached to the strain gauge. The electronics side could be either a simple multitester reading the resistance and then calculating the drawbar pull, or possibly an analogue to digital converter plugged into a computer. Has anybody ever tried this? Anybody familiar with strain gauges in general and how useful they would be for typical loco drawbar forces? Cheers David
I have been using a hand held digital fish scale I purchased at a local sporting goods store. Quite accurate and works very well. I just lay it flat on the rails and connect it to the loco coupler. It gives the result to the nearest 1/10 of an ounce.
I dropped into my nearest fishing shop and they had a cheap digital scale. The only problem was it was graduated in multiples of 20 grams (0.7oz). There are more accurate ones available but they aren't cheap. Cheers David
If you install the strain gauge properly, it will give you an accurate readout. We used strain gauges all over airplanes during flight testing and they were very valuable to us. Try it.
Any tips on the associated circuitry to give a meaningful reading? I thought it might be possible just to take resistance and calibrate with known weights, but I'm sure a more useful output isn't too hard. In theory it should even be possible to make a working dynamometer car. And relay the data via Bluetooth! Cheers David
Dumber than dirt, works under motion. I think it was under $20 less the trucks and couplers.... Works great for my purposes.
