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?
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.
justair wrote:
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”