Author Topic: body mounting couplers  (Read 1962 times)

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asciibaron

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body mounting couplers
« on: December 29, 2008, 09:52:17 AM »
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i'm on the fence if i should body mount couplers.  can someone push me one way or the other?

my layout will have a minimum radius of 16" and mostly i'll be running cars 50' or less - some tofc flats, auto racks, and auto parts cars.

-Steve
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Ian MacMillan

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Re: body mounting couplers
« Reply #1 on: December 29, 2008, 03:08:53 PM »
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16" isn't bad but there might be some problems with the 89'ers. I would do a few and run them around a set of 16"s to see how it works out. I am going body mounted, but I'm using a minimum radius of 32", with most being 40"...so I'm not much help in pushing you either way.
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asciibaron

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Re: body mounting couplers
« Reply #2 on: December 29, 2008, 03:22:20 PM »
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16" isn't bad but there might be some problems with the 89'ers. I would do a few and run them around a set of 16"s to see how it works out. I am going body mounted, but I'm using a minimum radius of 32", with most being 40"...so I'm not much help in pushing you either way.

i would probably leave the couplers alone on the long cars to make life easier.  i'd like to have a more prototypical look on my rolling stock.
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3rdrail

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Re: body mounting couplers
« Reply #3 on: December 29, 2008, 03:40:45 PM »
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You're going to have to go one way or the other. Backing a train with mixed truck and body mounts around a curve less that 30" is asking for a derailment. Also, coupling is impossible except on straight track.

Before you make the leap to body mounts, consider your tank and hopper cars. Many of these require scratchbuilding new ends on which to attach the draft gear.  Body mounted couplers are prototypically correct, but more work is involved. Whether it's worth it is your personal decision.

ednadolski

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Re: body mounting couplers
« Reply #4 on: December 29, 2008, 04:08:32 PM »
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Do you have any gradients?  Anything that puts a truck-mount coupler(s) into compression is an invitation to a derailment. With truck-mount couplers and DPUs, it can be a trick to move a train uphill.   

wm3798

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Re: body mounting couplers
« Reply #5 on: December 29, 2008, 04:11:33 PM »
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At 16" you may not run into this much, but I've got 15" minimums, and there are certain combinations where cars want to walk over the rail.  Usually this involves a body mount with a long extension (such as an SD-40 or a 60' auto parts car) and a body mount with a standard extension.  Sometimes the longer car with a body mount will pick a truck-mount, but not always.  This can happen when the train is moving forward, too.
One way to prevent this as much as possible is to have a section of 18" easement going into your 16" curves.
Still, it may fluctuate on a case by case basis.

Lee
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Walkercolt

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Re: body mounting couplers
« Reply #6 on: December 30, 2008, 01:39:12 AM »
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It'd be great to say that body-mounted N-couplers are the "best", but it doesn't quite work that way. They look better, and on shorter cars with our obsenely tight curves(compared to the prototype) they work well. On longer cars, with our curves, problems start. We have a nearly 70" radius on one of our N-TRAK modules. Body mounted couplers can cause problems on passenger cars on it. The sharpest curve an SD-40-2 can negotiate at 25 MPH is about a 4 FOOT radius. Our cars are so much lighter(closer to "scaled down" real cars) than HO and larger scales, the closer we make our cars like the prototype, the more they act like prototypical cars. Does that make any sense? We should have #10 turnouts in yards, and #16 or longer with movable point frogs on the mains, and 7' curves, but that's not fesable. Converting tankcars and hoppers to body mounts is usually frustrating at best. As of yet, there isn't a perfect answer, and I doubt there ever will be. What works best for you is the only answer.

ednadolski

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Re: body mounting couplers
« Reply #7 on: December 30, 2008, 10:57:11 AM »
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It'd be great to say that body-mounted N-couplers are the "best", but it doesn't quite work that way. They look better, and on shorter cars with our obsenely tight curves(compared to the prototype) they work well. On longer cars, with our curves, problems start. We have a nearly 70" radius on one of our N-TRAK modules. Body mounted couplers can cause problems on passenger cars on it. The sharpest curve an SD-40-2 can negotiate at 25 MPH is about a 4 FOOT radius. Our cars are so much lighter(closer to "scaled down" real cars) than HO and larger scales, the closer we make our cars like the prototype, the more they act like prototypical cars. Does that make any sense? We should have #10 turnouts in yards, and #16 or longer with movable point frogs on the mains, and 7' curves, but that's not fesable. Converting tankcars and hoppers to body mounts is usually frustrating at best. As of yet, there isn't a perfect answer, and I doubt there ever will be. What works best for you is the only answer.

A 10-degree prototype curve scales out to 43" radius in N scale, so it's hard for me to imagine how a 70" radius could cause problems for any kind of equipment unless there is some other issue at work.  (Is your 70" curve superelevated?)  I don't have curves anywhere near a 4-foot radius, but I have no problems running SD40-2 or any other long CC diesels with body-mount couplers, down to a 16" radius on a 2.08% grade.

Weight is a secondary consideration, what you really want is a geometry that allows the wheel treads to remain in contact with the railheads at all times.  With truck-mount couplers, running them in compression will make the truck want to spin and thus derail (adding weight to prevent that is a limited solution and has other drawbacks).   With body-mount couplers, if you mix long- and short- overhang cars on tight curves, you will likewise have a geometry issue -- the heavier car will "win", but adding weight to the lighter car won't fix the fundamental geometry problem in that case.


inkaneer

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Re: body mounting couplers
« Reply #8 on: December 30, 2008, 02:56:15 PM »
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"Trade off " is still very much a viable concept in Nscale, more so than in any of the larger scales.  I once considered going the body mount with metal wheel route then decided that my time, energy and money would be better spent in doing something that had more tangible and observable reults.  In the end it is up to you.  Some people just can't live knowing that their rolling stock has truck mounted couplers.  I am not one of them and even though I run Ntrak with rather broad curves I still use truck mounted couplers.  However, I do close the gap between my ABBA units and I do weight my cars above the NMRA specs.  The latter was caused by the use by Atlas in using metal castings in their fishbelly and offset side hoppers.  This cause some problems with the lighter MTL hoppers. 

pfs

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Re: body mounting couplers
« Reply #9 on: December 30, 2008, 06:58:35 PM »
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......i'd like to have a more prototypical look on my rolling stock.

Sounds like you should go for body mount then.

Walkercolt

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Re: body mounting couplers
« Reply #10 on: December 31, 2008, 12:45:37 AM »
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I meant a prototype SD-40-2. Left my participle dangling, I guess. The sharpest mainline curve in the BNSF scales out to over 8 foot radius, with the marked exception of the Tehachapi Loop which would be about 5 1/2 feet across with a 25MPH speed restriction. Any trackage over 45MPH the curves are about 10-12 foot radius in N-scale. 65MPH trackage curves are about 20 feet in N. I'm using the current BNSF Rulebook and John Armstrong's formula for converting degree of curvature to radius(which isn't exact, but close enough for hand-grenades and model railraods). There are drawbacks to truck-mounted couplers and to body-mounts in N scale. I can back a 100 car train with truck mounted couplers on our N-TRAK layout, a couple of hundred feet, usually without incident, not always. Consistancy in car weights is important, more than NMRA "Specs", and heavy cars at the end of a train is a recipe for problems. Empty MT 33' hoppers are not my best friend either.

Ed Kapuscinski

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Re: body mounting couplers
« Reply #11 on: December 31, 2008, 01:21:14 AM »
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Don't forget that throttle application and other train handling techniques also play a large roll.

A jerky start will do a good bit of damage, while smoothly taking in the slack will yield much better results. These are all things I have learned over 26 years "on the job".

davefoxx

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Re: body mounting couplers
« Reply #12 on: December 31, 2008, 05:12:24 PM »
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On my layout, my curves average a 13-15" radii, but in one spot it's closer to 12 3/4" to clear a bridge.  That said, I body-mount my couplers where I can and have no problems with derailments caused by the body-mounts.  In fact, just last week, I ran a test train after body-mounting couplers on an 89' MT auto rack (my longest car) and coupling it up to an Intermountain 2-bay hopper (my shortest car).  Neither car derailed, and I even ran them through a #5 cross-over.  Seems to me that there is a lot of side-to-side play in N scale couplers, so S curves seem, to me, to be a little more forgiving in our scale.

Since I have two stub yards on my layout, I end up pushing cars often.  The only cars that give me an occasional coupler-related problem (i.e., when pushing) are my Atlas tank cars, which do not have a provision for body-mounts and still retain their truck-mounted couplers.

Hope this helps,
Dave

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