Any experience with 5" radius curves?

[squirrelhunter]

I'm thinking of building a T Trak module of a cement unloading facility and the prototype uses a tightly curved track to reach it.

So I figure I have real estate 10" deep to work with- so I'm considering a 180 degree 5" radius curve. I'd use some variety of switcher and 2 bay cement hoppers for rolling stock, at very low speeds.

My gut feeling is this is probably "a bridge too far", but I thought I'd seek the collective wisdom of the Railwire.

Here's a link to the aerial photo of the prototype:
https://maps.app.goo.gl/JvZzUYPFUCitBv5w7

Edited for right link to map

[mmagliaro]

I'm afraid this doesn't answer your question about whether a 5" radius curve is even usable, but looking at the photo of the prototype you linked, that 180 degree "turn-around" curve looks to be about a 340' radius (about 25.5" radius in N Scale).  We all have to compress things, but is there some reason you have to go all the way down to a 5" radius?  Is it solely to accomodate squeezing this thing in a standard-depth T-Trak module?

[randgust]

I had a working Nn3 T-TRAK triple down in Altoona, with 127mm curved Rokuhan track on it (5"), and my new Nn3 Climax A pushing log cars around an oval that just barely fit on a 14x34 footprint. and still clear the two front T-TRAK main lines.   No scenery yet, just a demo track for my Nn3 Climax.  Simple oval with a spur, that was all.

I am using Showcase Miniatures 24' log cars, flat cars, a 36' Bachmann Civil War box with Nn3 trucks under it, and a few other similar cars.

Mark Graulty ("Narrowminded") is working on a functional, 4=wheel mine locomotive, I've seen the chassis, and he already has functional 4-wheel Nn3 RP-printed dump cars.

On my Climax, the secret is a 25:1 gearhead, along with 8x8 pickup, for a reliable and slow locomotive.   But it will go around those curves as an oval that fit on a Ttrak module, worked well all day.    You could probably do a diesel body on the chassis I've developed, not impossible at all.

Mike Wong (MK) was taking a lot of photos of it, so were a couple other folks that were going to be posting video.

I really don't think you could make it work with standard gauge, but if you're willing to go Nn3, and stay around the 25' range for equipment, it can be done.

[squirrelhunter]

Max, the module depth is the constraint. I have some 13" deep modules I would use for this, but by the time I account for the two main tracks, 3.75 inches of that is gone. I am planning to compensate with by using foam core to create and overhang to get to a full 14 inches deep, which would leave 10.25 inches between the back of the module and the inside main track.

If I went beyond 14" I'd probably need to make some "companion" modules that are narrower than normal so the combined back to back width of the modules wouldn't exceed 28".

The narrowness of T Trak modules can really be killer sometimes- if I thought I could get in even 7" curves I'd probably just go for it.

[squirrelhunter]

Randgust, that's helpful- I did some looking online at the various tight radius track from Japanese mfgs and I was curious how well it worked.

Also it sounds like the equipment that will work on 5" track is just below what I am thinking about, which would be something like an Atlas S2, MT SW1500 or SW 1200 with 2 bay covered cement hoppers from IM, MT, Athearn or Fox Valley.

I haven't been able to figure out a way to get the double mains and a 7" radius curve on a module without also having to build "narrow" modules to go behind to stay in the 28" max  width for back to back modules

[randgust]

It was so tight on the T-TRAK geometry for a triple that I had to move the Nn3 line up close to the inner main to prevent equipment from hitting, and then build out to the absolute rear edge of the width limits, including cutting the skyboard out to get an addition 1/4" of depth at the back of the oval!   But it did work.

I do 8" curves on my 18x36 Hickory Valley module and all the 40' boxcars have had to be slightly modified to keep the wheels from hitting the center sill.

Some of the Tomytec chassis will handle ridiculous curves, but you'll want to use a one-truck drive and put a gearhead in there because the worm-to-worm gear reduction still results in a rocket sled on rails.

Are you sure that mining operation isn't already narrow gauge?

The basic Rokuhan track is pretty good as it looks like a Z version of Kato Unitrak.   They have two turnouts; the sharp one that has a 5" diverging and one that is more like a #4.  I had nothing but grief on the sharp one as there was a built-in kink from the points to the frog that kept piling the Rokuhan truck up, it worked fine on the longer turnout.

Mark is working on turnouts that will be in the same geometry, just better made using real rail on tie strip.

Your real enemy on the locomotives you're looking at is coupler swing even if the trucks can handle it; the distance between the truck center and the coupler space is fixed and you may have real issues with the locomotives leveraging the car off on curves.   I have issues with 8" using a SW8 chassis.    If the couplers were truck mounted you have a chance.

If you are really insisting on standard gauge I'd also look at the Bachmann 44-tonner.   That's a really good chassis, slow speed, 8x8 pickup and drive.   Very short, prototype was designed to handle sharp curves.

[MK]

Mike Wong (MK) was taking a lot of photos of it, so were a couple other folks that were going to be posting video.

Pictures are up and that photo turned out good. 

[Sharky_McSharknose]

For rolling stock, 2-bay PS-2, Airslide, H30, and 2-bay ACF Centerflow covered hoppers are ≤40' long and appropriate for cement service.

The latest (2015) version of the Bachmann Plymouth switcher would likely negotiate the 5" curves. It's DC-only. A Z-scale decoder can be fitted though.

https://web.archive.org/web/20151002191201/http://home.comcast.net/~orrrbrit/decoders/switcher.html
https://kennethsnscale.wordpress.com/projekt-bachmann-mdt-plymouth-industrial-switcher/

Or you could get a BLI Baldwin Centipede. With all the articulation it has, I'd bet it could take 5" curves, easy. 

[dem34]

The latest (2015) version of the Bachmann Plymouth switcher would likely negotiate the 5" curves. It's DC-only. A Z-scale decoder can be fitted though.

https://web.archive.org/web/20151002191201/http://home.comcast.net/~orrrbrit/decoders/switcher.html
https://kennethsnscale.wordpress.com/projekt-bachmann-mdt-plymouth-industrial-switcher/

Or you could get a BLI Baldwin Centipede. With all the articulation it has, I'd bet it could take 5" curves, easy. 

And as a little bonus, that plymouth can usually be bought for like $20.

And yeah no kidding with the BLI centipede, heres a pic of mine.

[squirrelhunter]

Thanks for the input everyone- I think I may try to re conceive this idea without the turn back loop, I don't think I could execute it in a way that would fit what I want to do...maybe if I sleep on it I'll think of a new angle...

[ryan_wilkerson]

I grew up about 20 minutes from that prototype. I never noticed it even after virtual railfanning through google maps. You could always change to Free-moN and design it true to the prototype!
Ryan

[Faire to Midland]

What do you think the odds of getting a Bachmann 4-6-0 around a curve this small are? 

I am considering a wye in my track plan for turning a light locomotive and wanted to make it as small as possible  I noticed Tomix makes mini turnouts that are approximately 5.5" radius and wondered if it would even be possible to use those.

[narrowminded]

Make some up with some flex track to be sure.  And @randgust 's  comment about couplers, their length, mounting, and position relative to the truck pivot may prove to be a bigger issue than the radius. 

If the basic radius testing with a loco proves acceptable then further testing of the rolling stock that you might be interested in running with some actual intended transitions should be made up to be sure they will behave as a coupled train.  Gentle radius transitions (easements) and short straight sections between any right/ left transitions can often fix issues should they surface and this can all be mocked up with some flex pieces before to commit to foam. 

[randgust]

When you start pushing things to extreme radius curves like this you'll discover a whole new collection of headaches, and the other thing is that you absolutely must be able to operate at creeping speed - which makes electrical pickup as important as tracking.

The tight wye will probably drive you just as crazy as any turntable would.  In situations that tight railroads almost always opted for a turntable even when it seemed impossible.   The one at North Creek NY is half-bridge over the riverbank, still there.  Just no room for anything.

Some of the tightest 'real railroad' curves you'll ever see are on the old B&M industrial spur lines in Lowell, MA.   I have track charts for that and the one shocker was that there was a turntable just long enough for a locomotive and one car - to make a 90-degree turn and head down an alley to get to an industry.   It's the only application I've ever seen of a common-carrier freight railroad using a turntable outside of a terminal, and that's pretty nuts, but the canals got there first and the railroads had to build around them.

[nkalanaga]

The MILW's BiPolars could take ridiculous curves.  Reportedly one went through a 12 inch kink, caused by a fallen tree, with the rails bent into a "U", without derailing.  This was while pulling a passenger train, and the front truck of the first car also made it over, before the train could be stopped.

page 117, "The Milwaukee Electrics", Noel Holley