Nether Madder and Green Soudley Rly

[BWsTrains]

11 hours ago, Nearholmer said:

I’m slowly forgetting basic engineering knowledge here, but isnt the coefficient of friction (COH) independent of area of contact?

 

Leaving that aside, if it is true that modern RTR 00 locos really can’t pull the skin off a rice pudding (COH variable according to chef), that feels like a topic to be delved into and solved.

 

The wheel material will definitely be important, it being very well known, for instance, that bright-plated wheels on nickel-silver rail have a very low COH.

 

The old 0 scale favourite is cast iron for wheels, but modern sintered steel (not plated) seems very good too, it retaining a very tiny amount of roughness. 

 

Very good point here for you to test Martin.

[St Enodoc]

8 hours ago, Stubby47 said:

 

I take it back, obviously there are much more silly ideas...

PSMT...

[chuffinghell]

The basics of the coefficient of friction are as illustrated below

 

[St Enodoc]

21 minutes ago, chuffinghell said:

The basics of the coefficient of friction are as illustrated below

 

Something strange about that diagram.

 

E. Schrödinger.

[Regularity]

1 hour ago, St Enodoc said:

Something strange about that diagram.

 

E. Schrödinger.

Or possibly, nothing strange at all.

(Works like a charm!)

[Nearholmer]

Chuffinghell’s diagram prompts me to calculate.

 

If your offending loco weighs 100g, on a 1:30 gradient, i.e. 1.91 degrees, it’s effective adhesive weight will be cos1.91 x 100  = 99.9g, so assuming a coefficient of friction of 0.2 it can exert pull of just under 20g before slipping.

 

Your train weighs 360g, so to pull the loco itself and the train up the same slope needs sin1.91 x (100+360) = 15g PLUS whatever is needed to move it on level tangent track (say 1% of mass =3.6g) PLUS whatever is needed to overcome flange friction arising on the curve (say another 3.6g) = 22.2g

 

So, even with a fairly decent coefficient of friction, which 0.2 is, it will spin its wheels on the gradient as the last couple of wagons move off the level and contribute part of their mass to the load.

 

The 165g J94 loco can exert a pull of 33g under the same conditions, while it plus the same train need 25g, so it has a bit in hand. It can probably be trusted with three or four more wagons.

 

All subject to a fair few assumptions, and to corrections by others if I’ve done my sums wrong, but  I think it illustrates the point.
 

Notice particularly how sensitive it all is to coefficient of friction, which is why traction tyres help - I think they probably yield coefficients greater than 1, whereas really shiny wheels might yield 0.1.

 

All other things being equal, big 0-6-0 or 0-4-0 tank engines is better, cos all the weight of the water (or in models, Mazak) in the tanks  is adding to adhesion. Loaded carrying wheels simply waste adhesive weight.

 

You might find that those chubby little Pecketts, particularly the 0-6-0ST, actually do better than light tender engines.

 

PS: it’s just struck me that you can measure coefficient of friction by using a spring balance to skid a loco along the track, and dividing the pull needed by the loco weight. Must go to the fishing shop and buy a small, cheap spring balance!

 

 

Edited October 23, 2019 by Nearholmer

[RedGemAlchemist]

2 minutes ago, Nearholmer said:

If your offending loco weighs 100g, on a 1:30 gradient, i.e. 1.91 degrees, it’s effective adhesive weight will be cos1.91 x 100  = 99.9g, so assuming a coefficient of friction of 0.2 it can exert pull of just under 20g before slipping...

Whoooosh.

[Malcolm 0-6-0]

All this talk of adhesion and the use of magnets when combined with electronic pulses leads inexorably to the creation of a railgun, which would then lead equally inexorably to the dubious and perhaps unique honour of being the first model train builder to be shut down by the anti-terrorism authorities.  

 

"But your honour I was only recreating an Edwardian era shunting yard in OO scale" may go down as one of the weaker defence pleas in living memory     

 

 

[St Enodoc]

4 hours ago, Regularity said:

Or possibly, nothing strange at all.

(Works like a charm!)

Up the bottom or down the top, I don't mind how you spin it.

[Martin S-C]

12 hours ago, BWsTrains said:

 

Very good point here for you to test Martin.

 

10 hours ago, Nearholmer said:

Chuffinghell’s diagram prompts me to calculate.

 

If your offending loco weighs 100g, on a 1:30 gradient, i.e. 1.91 degrees, it’s effective adhesive weight will be cos1.91 x 100  = 99.9g, so assuming a coefficient of friction of 0.2 it can exert pull of just under 20g before slipping.

 

Your train weighs 360g, so to pull the loco itself and the train up the same slope needs sin1.91 x (100+360) = 15g PLUS whatever is needed to move it on level tangent track (say 1% of mass =3.6g) PLUS whatever is needed to overcome flange friction arising on the curve (say another 3.6g) = 22.2g

 

So, even with a fairly decent coefficient of friction, which 0.2 is, it will spin its wheels on the gradient as the last couple of wagons move off the level and contribute part of their mass to the load.

 

The 165g J94 loco can exert a pull of 33g under the same conditions, while it plus the same train need 25g, so it has a bit in hand. It can probably be trusted with three or four more wagons.

 

All subject to a fair few assumptions, and to corrections by others if I’ve done my sums wrong, but  I think it illustrates the point.
 

Notice particularly how sensitive it all is to coefficient of friction, which is why traction tyres help - I think they probably yield coefficients greater than 1, whereas really shiny wheels might yield 0.1.

 

All other things being equal, big 0-6-0 or 0-4-0 tank engines is better, cos all the weight of the water (or in models, Mazak) in the tanks  is adding to adhesion. Loaded carrying wheels simply waste adhesive weight.

 

You might find that those chubby little Pecketts, particularly the 0-6-0ST, actually do better than light tender engines.

 

PS: it’s just struck me that you can measure coefficient of friction by using a spring balance to skid a loco along the track, and dividing the pull needed by the loco weight. Must go to the fishing shop and buy a small, cheap spring balance!

 

 

This is waaaay more than I want (or think I need) to think about. I just want the bloomin' engines to haul the blasted trains up the ruddy 'ills!

 

Anyhow, a foul cold that has wrapped its moist clutches around my tubes for the last two weeks now, ever since some unknown carrier gave it to me at the Milton Keynes show (thank you so much, whoever you were, not a wise idea to take your germ-laden self to a huge public gathering was it?), I am now making the most revolting coughing up phlegm noises all the time so have chosen to cancel my weekends wargaming in France, which is a real blow as we only do this 3 times a year and each time its an extravaganza of great food cooked by the host and his lovely wife, fine wines, cheeses and so on... plus beer, friends and wargames. So I'm very annoyed indeed to miss it but I can't inflict the noises I'm making right now on my mates all weekend.

This means I'll be at home and will do some more testing of locos and weights and things.

I think I'll start by creating a train of fixed (desirable maximum) weight and having all my engines pull it. Those that fail will be given a base plate magnet bypass operation.

Edited October 24, 2019 by Martin S-C
tirreble spolling

[chuffinghell]

4 minutes ago, Martin S-C said:

 

This is waaaay more than I want (or think I need) to think about. I just want the bloomin' engines to haul the blasted trains up the ruddy 'ills!

 

Anyhow, a foul cold that has wrapped its moist clutches around my tubes for the last two weeks now, ever since some unknown carrier gave it to me at the Milton Keynes show (thank you so much, whoever you were, not a wise idea to take your germ-laden self to a huge public gathering was it?), I am now making the most revolting coughing up phlegm noises all the time so have chosen to cancel my weekends wargaming in France, which is a real blow as we only do this 3 times a year and each time its an extravaganza of great food cooked by the host and his lovely wife, fine wines, cheeses and so on... plus beer, friends and wargames. So I'm very annoyed indeed to miss it but I can't inflict the noises I'm making right now on my mates all weekend.

This means I'll be at home and will do some more testing of locos and weights and things.

I think I'll start by creating a train of fixed (desirable maximum) weight and having all my engines pull it. Those that fail will be given a base plate magnet bypass operation.

 

Sorry to hear you've had to cancel your trip  hope you're feeling better soon

[Nearholmer]

Yes, miserable having that sort of thing, saps the will rather, so I hope it clears up soon.

 

The horribly damp weather doesn’t help - it’s annoyed the heck out of me.

 

Autumn hasn’t performed as required so far this year - notable lack of crisp, bright mornings, where a picturesque mist clears to reveal brightly coloured foliage. Wall to wall b mid grey!

[RedGemAlchemist]

21 minutes ago, chuffinghell said:

Sorry to hear you've had to cancel your trip  hope you're feeling better soon

Seconded. Hope you're feeling better soon Martin. 

 

 

[Martin S-C]

I feel fine! I am just making so many terrible sounds it would be socially unacceptable to spend 72 hours in a wargames room with 8 other people.

[chris p bacon]

16 minutes ago, Martin S-C said:

I feel fine! I am just making so many terrible sounds it would be socially unacceptable to spend 72 hours in a wargames room with 8 other people.

 

Couldn't you be the field hospital........

[Martin S-C]

If the field hospital made the sound effects I'd be providing, the wounded would go elsewhere - probably limp back into the fight and keep going.

Edited October 24, 2019 by Martin S-C

[St Enodoc]

26 minutes ago, chris p bacon said:

 

Couldn't you be the field hospital........

 

17 minutes ago, Martin S-C said:

If the field hospital made the sound effects I'd be providing, the wounded would go elsewhere - probably limp back into the fight and keep going.

Perhaps you could be the artillery.

[Regularity]

15 minutes ago, St Enodoc said:

 

Perhaps you could be the artillery.

You're fired!

[Martin S-C]

This conversation is quickly going down the tubes.

[Caley Jim]

20 minutes ago, Martin S-C said:

This conversation is quickly going down the tubes.

I thought that it was what was coming up the tubes that was the problem! 

 

Jim 

[mpeffers]

Are model locomotive wheels generally steel?

 

Outlandish suggestion with no metallurgical research, but I seem to remember similar metals have a higher coefficient of friction than dissimilar ones so would steel rails give better adhesion on the gradients than nickel-silver ones?

[Martin S-C]

That may well be valid on 50+ tons of real loco but I would think with the minimal masses and forces we're dealing with it would not be a factor. In any case, as stated before I am not going to be changing any loco wheels! If I can't get a loco to climb the grades with a useful load it goes in the for sale box.

[Nearholmer]

If you ferret about on-line, you will find tables of coefficients for pairs of materials and, yes, steel on steel is good, taking all of the other qualities of the material into account, which is why the real thing uses steels.

 

It's a pretty uncommon combination for model railways these days, because (a) it tarnishes really easily, and (b) its not a great combination from an electrical viewpoint.

 

I am fairly certain that at least one maker of fine scale wheels uses steel tyres, and I think that one can obtain fine scale steel rail, but the latter especially needs very tender care.

 

In the 1930s and before, cast-iron wheels on steel rail was a common, and very effective, combination. The rail was, of course, tin plated in the case of "toy" track, but usually wasn't in the case of "scale" track, and you can still find examples of both tinplate and scale track from that period in good condition. But, in the late 1930s "German Silver" rail, what we now know as nickel silver, began to be made for keen hobbyists, and it was so much better that it quickly swept the board for serious use.

 

Hornby Dublo track uses steel rail (plated, but what with I'm not certain), likewise early Triang and others, but if you read Railway Modellers from the 1950s, everyone spent a lot of time moaning about how quickly it tarnished!

 

[Nearholmer]

"If I can't get a loco to climb the grades with a useful load it goes in the for sale box."

 

Very sound thinking IMO.

[Harlequin]

14 minutes ago, Martin S-C said:

That may well be valid on 50+ tons of real loco but I would think with the minimal masses and forces we're dealing with it would not be a factor. In any case, as stated before I am not going to be changing any loco wheels! If I can't get a loco to climb the grades with a useful load it goes in the for sale box.

 

Makes sense! Personally, I would make the cut-off sooner: if it can't climb the grades with a useful load without relying on the magnets-and-steel bodge it would go in the box. Save a lot of faffing around!

 

You could apply route restrictions like the GWR. Some locos cannot be rostered on some routes. That might save a few from the guillotine!?