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Drawbar performance tests

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Some drawbar performance figures for my engines.

 

Test Rig
The test rig is a length of straight track with a freely-rotating drum at one end. The drum is arranged with its top in line with the couplers on the engines. The track matches the track on my layout, which is Peco Streamline code 75, so the coefficient of friction with the wheels should be similar.
blogentry-14389-0-69039900-1487369211_thumb.jpg
(For completeness, the green-liveried Roco shunter here did not run in Britain, but the yellow-liveried one did)
blogentry-14389-0-68631600-1487369223_thumb.jpg

 

A length of cotton thread passes from the engine drawbar (coupler), over the drum and down to a pan to hold some weights. The empty pan is lightweight so I can test the least-powerful engines - I am using a foil tray. The weight of the cotton thread is negligible.

 

I built my rig from materials I had to hand, and the drum is a canister for 35mm film. A pulley would be possible instead of a drum. The only important dimension is to keep the cord parallel with the track. It seemed a good idea to include a length of N gauge track as well as the H0, but of course this needs to be rather higher to keep the alignment with the drum unless I drill two fresh holes to lower the axle for the drum.

 

Test Protocol
1. Place the test rig on a table so the track is truly level and the drum is overhanging the edge of the table
2. Place the engine on the track and run the cotton thread across from the drawbar (coupler) to the drum and down to the tray.
3. Add weights onto the pan until the engine begins to slide towards the drum, then remove weight until this movement just stops.
4. Apply power and try to drive the engine away from the drum without wheelslip.

 


- If wheelslip occurs, remove more weight and repeat.

- When the engine will drive away on the cusp of wheel slip, the total mass of the pan and its weights equals the drawbar pull.

5. Remove power and measure the weight of the loaded pan.

 


Engines with traction tyres need care to avoid overloading the drawbar with too many weights.

 

It is worthwhile to measure the weight of the engine as well, in case you feel like adding some extra weight in the future. I am using pocket digital scales for weights up to 200 g, and kitchen digital scales for heavier items - though they seem to agree with each other at lower weights.

 

Test Results (revised: 19 February 2017)

 

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Conclusions (revised: 19 February 2017)

 

I had a few surprises, especially the old and new Roco EE shunters. It is worth remembering that H0 rolling stock weighs about a third less than similar 00 stock, so a bogie coach is around 110 g instead of 160 g. Therefore the drawbar pull from an H0 engine can be quite a bit less than a similar 00 model and still give a respectable performance on the layout. In particular:

  • One Fleischmann Warship manages an astonishing 120g pull with its original wheels and traction tyres, but my modified engine with Ultrascale wheels can only do a fraction of this. I had an idea for a project to put two motor bogies into a Warship, but it really isn't worth trying. If I try to work up another of these engines I'll see if I can find someone with a lathe to turn down the flanges on the original wheels, and keep the traction tyres.
  • I subjectively felt the Mehano class 66 was the most powerful loco I'd ever had, but the tests show the Warship has more power, and the S160 will haul at least as much on the layout. In fact, the S160 will propel six bogie coaches up a 1:20 gradient with a 24- to 18-inch reverse curve, without a murmur, with four or more of the coaches always on the gradient.
  • It is more difficult to get numeric test results models with traction tyres, because they don't slide under a static load.
  • I built my LB&SCR E1 from a rather tired Hornby Terrier, and put some lead ballast inside the body - and it out-performs my unmodified Terrier which seems to be much fresher chassis.
  • Conversely, balancing a 1oz or 2oz weight on top of the Rivarossi S100 doesn't make for a scrap of improvement under load on the layout - just more wheelslip. With the track the same for everything, I'll conclude that either the profile of the wheels is different, or they are made from a more shiny metal. The limitation is surely a lack of traction, not a lack of power from the motor or losses through the gear train.
  • My Roco S160 has Fleischmann 'Profi' couplers and this makes it difficult to attach the thread for the test. I am reducing myself to using the scale drawbar hook instead, and although I have seen the engine pull away with a load of 95 g I am unhappy to repeat this for fear of breaking the hook. So I will say "more than 75 g" for the time being. I have added the test results for the Hornby B17 for comparison because I feel this is one of the finest models Hornby have ever made, but for drawbar performance there isn't really a meaningful comparison with the Roco.

 


- -

 

I have posted some test results for 00 gauge engines on the Roco S160 thread here.

 

- Richard.

  • Informative/Useful 1


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