Traction Test Stands

[Anonymous]

I would like to test the drawbar pull of different engines and mu setups. Does anybody have plans, or know of magazine articles addressing this?

[ndbprr]

well the real railroads use a dynanomter either fixed or in a car with fairly sophisticated electronics. I remember seeing a gizmo MR used back in the fortys to test engines that basically consisted of a coffee can with a string that hung over the end of a table. a track had a pulley with a rolller bearing mounted so the string would go from vertical to parallel to the center line of the track. it was then tied to the coupler of the engine being tested. stall and slip could be determined by adding weight to the can. you are probably pushing the limits to some degree in this area. I think most of us use the trial and error method of determining engine capacity on our railroads.

[Paul3]

justair wrote:

QUOTE: I would like to test the drawbar pull of different engines and mu setups. Does anybody have plans, or know of magazine articles addressing this?

I built one of these for my RR club. The heart of it is a 1lb. capacity spring scale that is fairly accurate (increments in 1/4 oz.). We got one from a mail order catalog for about $40, IIRC.

This scale is mounted on our "torture track", a device that all locos and cars must pass before they can registered and used on our layout for operations. The 4' torture track is mounted on roadbed on a dried, straight, non-warped piece of 1x4" pine (painted and sealed to prevent any future warping). On the extreme right is the scale on a homemade wooded bracket that holds the scale vertically (a must as most spring scales will not operate accurately unless vertical). The track is club standard flex track, Walthers Code 83.

About half way down, we have a Kadee magnet (to test coupler operation), a NMRA clearance guage (to test to make sure all the cars will fit in our tunnels and platforms), some 3" long metal bars along the inside of both rails (to catch any "narrow" wheel sets), a 3" section of handlaid track brought in to the narrowest point (to catch "broad" wheel sets), a small section of flangeway (to catch any overly-large wheel flanges), and at the very end on the left, a coupler height gauge consisting of two horizontal bars (if the coupler fits between the bars, it's ok).

The scale is mounted such that it is above a teflon pulley (bought at a Home Depot, used for door slides) that is mounted on a teflon bushing (reducing friction as much as possible). Attached to the scale is some high quality string or twine of fairly good size (for string). This drops from the scale, around the pulley and towards the loco. The pulley, BTW, is set up so that the string is at coupler height as it leaves the pulley.

Attached to the end of the string is a piece of "piano wire" bent into a "J" hook that's been flattened out (so that it couples to the Kadee perfectly). The top of the "J" has been bent to have the string in the middle of coupler height.

To test a loco, place it near the scale, couple the string to the loco, and turn up the juice. Watch the needle on the scale, and record the results.

Having said all that, there are things to watch out for that will affect the scale test:
1). Make sure the track is clean
2). Make sure the wheels are clean (dirt adds traction)
3). Some new locos come with a wheel coating that adds traction, but later falls off under a load (like Atlas).
4). Watch the progess of the scale. If it's bouncing around, the wheels are usually dirty
5). Don't take the first reading as gospel. Chances are, as the loco spins the wheels, the reading will drop, sometimes as much as a full ounce or more.

Most locos these days pull around 3 to 4 oz., some more, some less.

For a loco article, MR or RMC did one a l-o-o-ong time ago. Check out the "Index of Magazines" link at the top of this page.

ndbprr wrote:

QUOTE: I remember seeing a gizmo MR used back in the fortys to test engines that basically consisted of a coffee can with a string that hung over the end of a table.

While this method can work, it's very time consuming and frustrating to attempt (I know because I tried that first). Imagine the set up: you have the container for the weights (that must be weighed empty), then you have a stack of weights (that all should be measured for accuracy). Next, you test the first engine. You guess that it will pull 2 oz. You put in that much weight (minus the container), and give it a go. If it does, you go back and add another ounce and try again. It pulls it, so you add another ounce. Now it doesn't pull it. Then you have to remove an ounce, and add a half ounce. If it pulls it, try it again with 3/4 of an ounce. At this point, if it works, it's rated for 3.75 ounces. If it doesn't, it's only rated for 3.5 oz.

And all that is just for one engine! Yeech.

It's definetely worth getting a scale for such tests, believe me, where you measure once and only once to get a good reading.

Paul A. Cutler III
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Weather Or No Go New Haven
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