Quote from: Luke Piewalker on February 22, 2014, 11:13:49 AM
I was always under the impression such things were more of an issue for the American modellers because of the prototypically long trains they tend to run.

That is quite true, it's more of an issue for American modellers. The prototype trains over here are often quite long, often 100 or more freight cars in a single train, which can stretch a mile. To duplicate the prototype trains and make it look realistic, American modellers run longer consists, then is normal in England. Because of those longer consists, the mismatch between body mounted and bogie mounted (truck mounted in American parlance)  does cause problems for American modellers.

Here in North America, almost all new locomotives being made have body mounted couplers, while the vast majority of freight cars (in N scale) are equipped with truck mounted couplers. So if you have a typical train with 2 to 4 locomotives (all with body mounted couplers), and 25 to 50 freight cars (usually all with truck mounted couplers), it does cause stresses to build. It's normally fine when you run in the forward direction, but can often cause problems running in reverse. The locomotive will usually push the first freight car coupled to it, and force it to derail. It has to do with the sideways pressure from the mismatch of body and truck mounted couplers. The couplers want to naturally follow a particular line by themselves. On a curve, body mounted couplers tend to run toward the outside rail, which is very evident in long freight equipment. While truck mounted couplers (on a curve) tend to stay closer to the middle, between the two rails. And when you combine body and truck mounted couplers connected together in a long train (especially with the sharp radius curves people are usually forced to operate with), it can cause derailments to happen. The curves we modellers are forced to use (such as 9 or 11 inch) are extremely sharp compared to the prototype. A sharp prototype curve would be huge, even in N scale. Even a 20 inch radius curve, although great for N scale, is extremely sharp compared to the prototype.

It's a very common topic on American forums. Truck mounted couplers don't like to be pushed in long trains (anything over about 15 to 20 freight cars). For many serious American modellers, truck mounted couplers and body mounted couplers do not play well together. The experts often advise, you pretty much need to go all one way or all the other, for smooth and reliable trains. They advise from personal experience, not to mix and match body and truck mounted.

The problem has something to do with the sideways stress that is caused, by the different angles that the different sets of couplers line up with, when going through sharp curves. With body mounted couplers the sideways forces (the stresses) are transferred from the couplers to the body (or chassis) of the equipment, resulting in fewer derailments compared to having the sideways pressure transferred from the couplers to the trucks (bogies). 


But getting body mounts to work right in not always easy.  The main issue is getting the couplers to line up correctly on the centerline of the car. Usually what happens is, broader radius curves are required for body mounts on American trains. This is to help deal with the reduced angles the trucks (bogies) can move around, because a body mounted coupler can get in it's way. If all the couplers are body mounted, they should all be at the centerline of the freight car, and should (more or less) align for easy coupling. The only time this is a problem is if you're coupling a significantly short car (like 25 foot long) to a significantly long car (like 80 feet long) on a curve. In that situation it helps to have very broad curves, and perhaps also a car of intermediate length coupled between them.

Edited to show a picture and a video that explains in more detail.




BODY MOUNT COUPLERS vs TRUCK MOUNT COUPLER

Last link is just a google search about this topic. You will find lot's of opinions.

https://www.google.com/#q=body+vs+truck+mount+coupler

Howard

Quote from: D1042 Western Princess on February 22, 2014, 07:34:49 AM
Hello Howard, welcome to the site. As a fellow new member (I only joined a few days ago) I can confirm the friendliness and helpful attitude of fellow members - I have already taxed their patience to the limit with foolish (but totally genuine) questions re computers and had nothing but a lot of help in return.
As to your problem I  have shunted all kinds of trains in all kinds of scales from N up to "12" to the foot" (I am a professional railwayman - Conductor, in US parlance) and would echo what most others have said.
There are several principle factors to be taken into account, the main of these being track laying - really take your time with that, the better laid the fewer problems. To test it take a few short wheel base wagons (I used 10 16 ton mineral wagons) and GENTLY push them by hand around the layout making sure ALL rail joints are covered. Push from the last (or first depending on how you see these things!) vehicle as if your hand was the locomotive. Any faults will soon be shown up (the leading wagon will derail) and the problem joints should be attended to as soon as you find them so they are not forgotten. It only takes one misaligned rail join to ruin the perfect layout.
My other main suggestion is shunt SLOWLY, very slowly. In real life Class 08 shunters, the standard British shunting engine (switcher), are limited to a maximum of 15 MPH for a good reason. To give an idea of how slow 9 feet of track is (about) 0.25 mile in N and at 15 MPH a loco should take about a minute to cover that distance.
Less important, but will add to reliability of running, is do not be tempted to save space by using minimum radius curves or points (turnouts) unless space is really restricted. The tighter the curve the greater the problems you may encounter. Always go for at least medium radius even in yards if you can.
Finally keep your track and wheels clean as it will aid slow running.
As to the question of couplings it is rare, at least since the 1960s, to run bogie and non bogie stock together but it does happen. In model form it should not be a problem particularly if you follow my suggestions re track and speeds above.
Good luck, happy modelling.
Greg.

Thank you for all the advise, I greatly appreciate and agree with you. It surely helps to carefully test each track joint. As you say, by pushing some wagons around by hand, to detect any trouble spots. And yes I agree, going slow in shunting. And making sure the track and wheels are clean. And I would also recommend checking that everything (both track and wheels) are to proper gauge. And I also agree with your comments about track radius, to a degree. It would really depend on how "sharp" the track and points are, in comparison to the equipment being run. I would imagine a class 08 diesel can handle sharper curves, compared to a class 44, 45 or 46 diesel.  A tram could go around tiny curves by comparison, because they do in real life also. 

Howard

Hi Howard,
Yes, you are quite right about Classes 44/5/6/ (and of course Class 40s) which were not built for tight curves in real life, but large locomotives did not necessarily mean large radius curves. The Western (Cl.52) for example could get down to 4.5 chain radius (which is still OVER 7 feet in N  ) which just proves your point and makes my "tightest" (on view) curve of 4 feet, and even more so "large radius" turnouts, seem ridiculously tight although huge for a model layout.

Quote from: D1042 Western Princess on February 23, 2014, 07:58:50 AM
The Western (Cl.52) for example could get down to 4.5 chain radius (which is still OVER 7 feet in N

I think you mean 297 feet! One chain in 66 feet.

Your point stands of course; some big engines could negotiate surprisingly tight curves when travelling dead slow.

Cheers, NeMo

Quote from: D1042 Western Princess on February 23, 2014, 07:58:50 AM
The Western (Cl.52) for example could get down to 4.5 chain radius (which is still OVER 7 feet in N

Quote from: NeMo on February 23, 2014, 08:37:02 AM
I think you mean 297 feet! One chain in 66 feet.

Cheers, NeMo

by my reckoning, 4.5 chains =297 feet on the prototype. At 2mm:foot that equates to (near enough) 1ft 11.5 ins on the model...

Imagine the uproar there would be if Farish were to announce there models were only usable on over 2ft radius!

Quite right; misread the post. Thought it said the real Class 52 went around 2 ft curves!

Cheers, NeMo

Someone has got their wires crossed somewhere. I think it might be me.
80 CHAINS TO THE MILE, I was thinking 80 yards to the chain.
Humble apologies.  That makes my 4 foot curve far more lifelike. Thanks all.

I'm sometimes amazed at the ridiculously tight curves model trains can get around. It's helpful when designing a layout, I don't need to use entirely prototypical curves, or I might be forced to use T scale. Luckily I don't have to worry that a new N gauge loco might require a 20 inch radius curve, lol. They all can get around sharper curves, then the prototype could handle. Just think, those original Arnold and Minitrix locos from the 1960's were designed to handle 7 inch radius points and curves. Same with the early British and American N scale. But it was still good to use wider curves were there is enough room to make it possible. There are some large N scale American diesels (such as SD70, etc) that will bulk at anything smaller then 11 inch, and just barely run on 11 inch. But really, those diesels should be on at least 14 inch.

Now compare that to some old style 3 rail Lionel trains, which are O gauge. The sharpest Lionel curves are called 0-27, which can fit on a board about 29 inches wide. The actual radius is about 13 inches. Some of those 0-27 Lionel trains look ridiculous on track that sharp, but they run on it.