Hello Janne and all!
Ah yes!
The ever lasting question!
I was concerned with that myself for a very long time, as I too love to have long and sometimes very "heavy" trains
But no longer!

All it takes is a little bit of physics!
The maximum available traction effort "T" on any given axle of a locomotive is the product of the weight " W" carried by that axle multiplied by the adherence coefficient "K" of the two surfaces in contact.

T = W x K

The important variable here is K. The higher it is, the more tractive effort can be produced

Metal wheel (clean) on metal track , K is around 0.1 to 0.15

Wheel with (clean) traction tyres on metal track , K is around 0.8 to 0.95

So for example if a bare metal axle carries 100 grams , it can contribute around 10 grams of tractive effort, but the same axle with traction tires will produce 8 to 9.5 times more !

Simply said one axle carrying a load "W" with tyres produces the same tractive effort as up to 8 or 9 "metal to metal" axles!

The other variable is the weight carried by each individual driver axle of a steam loco.

At close inspection you will be able to see that most "driver" axles are just "touching" the track, and carry mostly only their own "weight"

You can check that yourself: place one such lok on the track and try to gently lift the various axles (e.g. with a very small screwdriver)

Some axles will lift the loco (weight carriers, at least the one with traction tires) others (usually placed in the middle) will let themselves be lifted without lifting the whole loco. They are there either pushed down by gravity or a **gentle** spring (just to make sure they make good electrical contact! )

Same for pony wheels/bogies, just applied by their own weight or a gentle spring action

So what does this tell us?

1° The whole weight (or at least a vast majority...) of the loco is usually carried by two driver axles, and also with a predominance on the axle with the tires
2° The non-weight carrying axles do not contribute any significant traction effort (if any...!)
3° Since they do not contribute any significant effort , the load on the coupling rods is correspondingly very small too...and as long as there is a good alignment (90 or 120 deg) of the drivers cranks on each side, the effort on the rods is "symbolic"

And the absence of (connecting) gears is, in this case, a good idea!
No gears means no noise and "see-through" chassis and lower production cost .
All it takes is to produce the driver axles with cranks aligned properly...


Now , if you have such a loco that really underperforms, there might be problem(s) in the model itself that reduce(s) the weight carried by the actual/predominant "traction" axle.

I usually look a the (close) coupling mechanism with the tender that may bend and could lift the traction axle, or the tyres may be worn, or the "floating" axles (the one you normally could lift slightly with a screwdriver) are "stuck" and carry more weight than their own.

Or the loco is too light...but that's also happening with the real ones!

Hope this helps

Happy Easter

Jacques

We should measure the weight of these new models and compare with the weight of the older ones.
Also, in our 60's locos, the reversing unit which was in the loco added weight, the gears added weight,
and our famous 3047 DB BR 44 with the magnificent articulated chassis, had four traction tyres, if I remember...

And what about the new motors torque ?

Best Regards
Joël

Hi again,

After a quick check I found these differences between 39011 DRG BR 01 and 37951 DRG BR 03 technic related to traction things:

39011 has four traction tires. In front and rear drive wheels. Middle drive wheels are without traction tires and like Jacques described earlier it is just like that just carrying it’s own weight and moving freely upwards. Heavy metal tender but not as heavy locomotive itself. Rear axle/bogie has quite strong ”lift” as there is strong spring for it. But not so strong that it would lift loco driving wheels up of course.

37951 has only two traction tires in the rear driving axle but better traction. None of it’s driving axles are moving freely upwards. So all of it’s six driving wheels are touching tracks and supporting locomotive weight evenly. Not as heavy tender with plastic tender body. Locomotive itself without tender is slightly heavier than 39011. This one has less ”springy” rear axle/bogie.

Now I will do something else. I will build a 1 Gauge layout in our living room and run my two analog Crocodiles 5757 and 5758. I will do a very curvy track so I can enjoy Crocodiles three part body movements.

Cheers,
Janne

Edited by user 11 April 2020 21:50:05(UTC)  | Reason: Not specified

Hi Kimball

No doubt...but it's a totally different beast!
Actually, the articulated BR 50 (and BR 85 ,etc.) is made out of *two* separate (articulated) chassis and are rather like a two bogies design found in electric and diesel locos!
It would be impossible to have driven the 5 axles without the gears!
The coupling rods on the BR 50 (3084,etc..) are there "just for show" and serve no transmission purposes at all!
Is has two set of traction tires, one on each rear axle of the subchassis.

The very clever design from Märklin here (dating back to the G 800!! ) is that there is a little vertical play in the articulation.
When the engine starts pulling forward , like a car, the front axles tend to lift, which transfers all the weight on the rear axle, i.e the one with the tyres.

One would think then that when the lok is pulling in reverse it would loose traction...but no!
The front chassis (the one with three axles) will indeed tend to lift, but while doing that, it transfers weight (and traction! ) to the rear (éaxle)

You'll see, it's subtle, but truly genius.

No wonder that BR 44 with the original designs were so powerful ...and still are! (and my favorites too)

Cheers

Jacques

A problem that many modern Märklin steamers have: too much spring tension on powered axles without traction tyres, too little pressure on the axle with traction tyres.
Tests have shown that reducing the spring tension on some axles increases the tractive effort very much.

It is surprising how much a modern Märklin DHG 500 with just one powered axle can haul. It is a pity how much potential tractive effort is lost with some big steamers.

Sorry folks - you are compairing apples with pears.


"Newer design Märklin steam locomotives too fragile for pulling long trains".

is the heading for this thread. In my opinion they are not! They are only constructed more to the existing reality. Different classes for different duties. In the same way you have to think about yourself too, while running trains as a MRR.

Read the article

"On the art of designing steam locomotives"

and

"Technology in detail. In the early 1920s, the German State Railroad reclassified all their steam locomotives into 99 main class numbers. The German federal and state (GDR) railroads took over the system."

in the Märklin Insider Club News 02/2020. It is the actual one! Here is the link too:

https://www.maerklin.de/...02-2020_031620_EN_nt.pdf

My problem was related to the 3102, the metal boiler was off set and its weight was heavier towards the front bogie lifting up the rear bogie and therefore losing its traction force, I had to add a small washer to align the boiler to its rightful position where you actually tie the screw to the frame, there was enough play for the boiler (1mm) to drop in the front.

John

Bizarre that my dad's old hornby dublo locos drive all wheels through the connection rods.
You can attach hhuuggee lengths of carriages and wagons to them, get some wild wheel slip on start up just like the real thing, then it gets better as you gain speed.
All power is delivered through a worm to the rear axle, and from there to the remaining axles via connecting rods.Obviously not as fine as modern marklin, but good god, if your new trains bend their rods trying to haul loads then maybe you should look for older tougher models.

Good point!
But in fact , if you were scale it up , most model locos would be pretty powerful, because of their rubber traction tires!
The big problem with model trains is that if you were to scale the rolling resistance (even with the best brands of cars and coaches) it would look more like the train is running with the brakes on!
But again, who cares?
With most locos in my inventory I can pull a prototypical train composition (sometimes with up to 100 axles ...and up a 3 % grade, and certainly through a R2 curve on the same gradient.
What more do we need?
Cheers
Jacques