Roundhouse: How much will these things pull?

[Keith S]

Just wondering if anyone knows just how much a Roundhouse engine or one of similar size/boiler pressure will pull? My friend has a Mercer traction engine and has "youtubed" a video of it pulling his five year old daughter around on a little wagon. Yesterday I had my "Billy" set up in a hangar at work on a temporary track and we tried to load up the two wagons as much as possible. We got a five-gallon bucket about a quarter full balanced on the wagons before I started to worry about the IP wheels and solebars. The engine of course required a bit higher regulator setting, but still only a tiny fraction above "off".

I wonder what it would pull before the wheels slipped too much to move. If you try to hold the engine back with your hand, it just churns away like a mad thing trying to get away. Would it pull a man? A small woman? Two five-year-olds? I guess a Mercer traction engine has more tractive effort due to the gearing, but it's only got one cylinder and a pot-boiler, and is probably lighter.

What have you pulled with your little engines?

[TheChestnutLine]

and of course don't forget there are no brakes in 16mm or g scale  ;)

Except for Mr Bond's railway of course!

[MuzTrem]

On one gala at the Woodrow Light Railway (not Pauly's - the "other" WLR!), we put together a train of 70 axles, which IIRC, our "Millie", "Russell" and "Fowler" were each able to haul individually. Unfortunately, the train was a mix of bogie and 4-wheel stock and we had no means of accurately measuring its weight. Nevertheless, it gives some idea of what can be done!

[TonyW]

Years ago, a friend of mine used the "unshared" rails on a 3.5inch/5inch circuit to run a 16mm/scale loco. He didn't try to make it pull him though.

[Sir haydn]

Funny you should say that Tony. Mick Mobley did the same thing but pulled himself and his wife with john campball NGG16

[Chris Bird]

Well an Accucraft 2 cyl Shay wil certainly start and pull 250lbs on a 1:100 gradient! This was on heavy aluminium rail using the 45mm gap between the 5" and 7 1/4" rails on my test track.

The loco is, of course, geared and the rail gave excellent adhesion so there was little slipping.

I know it was 250 lbs because I picked up the brake van and stood on the scales!

You can see it here:

http://www.youtube.com/watch?v=iJi7MBVzugg

Cheers
Chris

[Keith S]

I've seen that video. That is amazing.

I'm not about to try riding behind the locomotive, I agree with "other Keith" that it would probably damage the rails and definitely the little wagons. What was actually going through my head was how many little wagons the engine could handle around the garden, and also all the guys at work asking things about horsepower and tractive effort (they are aeroplane mechanics). We tried encumbering it next with an aeroplane shock absorber weighing 50 lb, and it couldn't make progress, but the load was only shared by the four axles on the two wagons, so I'm sure there was a lot more friction than if it had, say four wagons or more.

I've also noticed that once the locomotive drips oily water on the rails, it's "game over" when it comes to pulling heavy things.

THis all seems kind of juvenile, I can picture you guys shaking your heads at the idea of me having "tractor pulls" with a roundhouse engine or trying to ride behind it. It will be pulling normal things like wagons from now on, this was just its "trials" phase.

[GTB]

What was actually going through my head was how many little wagons the engine could handle around the garden, and also all the guys at work asking things about horsepower and tractive effort (they are aeroplane mechanics).

Science content warning...........

On reasonably clean rail the kinetic co-efficient of friction between common metals used for wheels and rail will be about 0.2, so the drawbar pull of our little locos will be about 1/5 of the weight on the drivers (half that if the track is oily).

I have a small digital hand scale (modern equivalent of a spring balance) which makes measuring drawbar pull and rolling resistance quite easy.

I've recently done some measurements on my 0-4-2 Baldwin and it has a drawbar pull of about 300g. Total roadworthy weight is actually 2.5kg, so the drawbar pull should be higher, but it is tail heavy and the sprung trailing truck is taking a disproportionate amount of the weight.

The few wagons I have at present are lightweight and have a rolling resistance of 10g, so theoretically the Baldwin could pull about 30 of them on flat straight track without slipping.

On a 1:30 grade, the drawbar pull would be reduced to 220g, as it has to lift it's own weight, as well as the train. The wagons weigh 180g each, so now require 16g to move them on the grade and the load would be down to 14 wagons, or about half the load on the flat.


Power is fairly meaningless at this size. Easy to calculate for an electric, but for a steamer you need a long straight hill and know the train weight, gradient and speed to measure developed power.

Small motors and worm gears aren't very efficient and the average battery powered loco would be doing well to develop 10W at the wheels.

If I do the calculation for the Baldwin steamer pulling those 14 wagons up a 1:30 grade at a scale 20mph, the theoretical power needed is only about 5watts at the driving wheels. Drawbar power is about 3watts, the other 2watts are needed to lift the loco up the hill.

More fun to just keep adding wagons until the loco slips.....

Regards,
Graeme

[MTA]

I've had my Roundhouse Katie haul 10kgs of weights in four Accucraft open wagons, on an approximate gradient of 1 in 80. That's a sure fire way of showing off the effect of a Summerlands Chuffer!

[Keith S]

The chuffer really does sound good when the engine is loaded up. I think the most appreciated feature of the engine when I brought it to work was the chuffing sound it made. People didn't seem to believe it was actually steam-powered until they heard the sound it made.