S Curve Dangers

@BillYo414 posted:

I want to add a section to my mainline that would include a cross over made from #10 or #8 Turnouts, to a 3" straight, to an 0-128 curve. This would result in an S curve. The 0-128 bends in the opposite direction of the turnout. I've read this sort of track arrangement can cause some problems but this are very gentle curve sections.

Am I asking for trouble?

I don't think this would be a problem. A lot depends on what you are running too. Is this on a main line, yard?

Try a mock up and run some trains through it to test.

That 3” straight in the setup will help a lot. If you can redesign the setup to use a 6” straight, that would be even better. However, using #8 or #10 switches into an O-128 curve is a nice, easy, broad curve. I think you’ll be fine.

I agree that it should be fine… that’s very gentle overall.

S-curves are primarily an issue with body-mounted couplers.  HO cars have these, and HO is far and away the most popular scale, so S-curves in general get a bad reputation.  With our 3-rail truck-mounted couplers, gentle S-curves like you describe are not an issue at all.  Now if you run body-mounted Kadee couplers, then testing would be in order.

I agree with everyone else; you should be fine, but if you can squeeze a little more straight, that would be good.

I made mock ups like Bob suggested, but my concern was steep grades with curves near the top and bottom.  Try your scenario as a mock up to ease your mind.

Here's a track diagram:

I don't know why I didn't post this before. Nonetheless, we're looking at the red line.

@RSJB18 this would be on the mainline. I wouldn't expect to be high balling through it though.

@Rich Melvin @GregK the extra distance on the straight could be worked in there I think. I think the technical term here is a run around track. I don't know that mainlines typically included a run around track but I thought it would be nice to have in my case.

@Bob Body mounted couplers could be an option eventually. They're not high on the priority list at the moment. Do you know if the body mounted couplers just can't sway far enough?

@Mark Boyce maybe Santa will bring me a #10 haha

Thanks everyone for the help!

Bill, You never know what Santa will bring.  On the other hand, he may bring you coal for the furnace!! 

Your red line looks practically straight.  I don't see any problem at all! 

I'm not one to complain about Santa's offerings @Mark Boyce but I suppose that line is rather straight now that I look at it. I guess I was thinking in terms of parts instead of looking at what is right in front of me.

We will give you the benefit of the doubt, Bill.  S-curves are a No No; is all we have heard for a lifetime! 

Bill, while not an exact duplicate to your trackage. A standard Ross double crossover with a #8 turnout. I can back through the crossover onto the leg of the #8 with no issues. I run Kadee’s on everything. I think you will have no issues with your arrangement.

@Dave_C thanks! That's good timing too because I was looking at what I might gain from using #8 instead of #10. I thought #10 might be good just because this is on the mainline. I think I'll be able to go through them faster than smaller pieces.

I'm not sure I'd worry about it. You're playing in huge radii as far as 3 rail stuff goes.  

That said, you could eliminate the S curve by flipping the lower side switch and moving it into the curve (the curved leg of the switch is the lower line and your crossover is the straight leg of the switch).  Would probably involve some flextrack and a bit of rail splicing. Very doable if you're at all handy laying track.

Alternately, if you cut the switch back all the way to the ends of the point rails and roll directly into that curve (flex tracking an easement into it would be even better) without there being any straight at all.  

A curved switch would be really ideal for that spot, but you'd have to lay that in there by hand. Not saying it cant be done though...

I tinkered a bit more after @Boilermaker1's comments.

I did manage to squeeze a #241 Ross 0-120/0-96 curved turnout in there with a #220 Ross #8 turnout. You can see that in the first picture. Hopefully these screenshots are big enough.

You can (hopefully) see the lack of alignment in the next two photos. That puts me into uncharted territory. I'm not sure how much of a sudden angle change model trains will tolerate. I suspect I'll be ok but I'm interested in hearing opinions if anybody has experience with this. I would basically lay the tracks over each other and just cut along a plane so the rails can be connected.

I'm certainly not opposed to laying my own switches. I have to make at least one of my own crossovers. I'm a little intimidated by bending the rails if it's a curved switch. I would probably make this a project down the road if I decided to go this route.

One operational caveat of S-curves I find to be particularly troubling...backing movements for the train.

Pulling the train through an S-curve, IMHO, is relatively easy in comparison.  But for truck-mounted couplers (we're focusing on O3R, now), at the peak 'misalignment' of two cars being pushed through an S-curve, the truck centers are totally misaligned and the conjoined couplers are creating a twisting leverage of the two trucks leading to an outward derailment.

If you are pushing but a car or two through the S, the leveraging force on that misalignment probably isn't so bad.  But if you're nursing a 12-car 20th Century backwards into the station, that pairing of couplers between the head-end baggage car and its adjacent passenger car is going to be painfully taxed by the preceding load of another 10 cars subject to the relentless push of steam/diesel power.

Of course, with the typical generous+ flanges on the wheels and properly weighted (?) cars, derailment will probably be a rare exception.  Right?     (I guess its just those lingering memories of decades ago...backing a long string of HO cars all featuring 'talgo' truck-mounted NMRA couplers through 'Snap-Track' S curves .)

#8 or #10 switches with a bit of straight betwixt?...I agree, you should be OK...pull or push.

@BillYo414 posted:

I tinkered a bit more after @Boilermaker1's comments.

I did manage to squeeze a #241 Ross 0-120/0-96 curved turnout in there with a #220 Ross #8 turnout. You can see that in the first picture. Hopefully these screenshots are big enough.

You can (hopefully) see the lack of alignment in the next two photos. That puts me into uncharted territory. I'm not sure how much of a sudden angle change model trains will tolerate. I suspect I'll be ok but I'm interested in hearing opinions if anybody has experience with this. I would basically lay the tracks over each other and just cut along a plane so the rails can be connected.

I'm certainly not opposed to laying my own switches. I have to make at least one of my own crossovers. I'm a little intimidated by bending the rails if it's a curved switch. I would probably make this a project down the road if I decided to go this route.

Don't bind yourself to the footprint of the switch that is sold to you.  Once you pass the frog, you can cut off the rest of it and use all of the extra space you've created to fit the two switches together (i.e. give yourself a lot more distance to make up the angle difference). Your true distance to finagle with is between the red lines.  You should be able to gently pull that slight angle difference in over that kind of distance.

The other thing you can try if you dont want to cut it, is to unspike all 3 rails from the 120 leg of that switch except for maybe the 3 ties after the frog, move them (print yourself a rail gauge to keep the spacing correct) and respike the rails down, lined up with the #8 diverging leg.  MicroEngineering Medium Size spikes are a good choice for doing this. Get the MicroMark Spiking pliers, it makes it easier.

I don't know if Steve would do it (it would not surprise me at all if he does), but it could be worth calling and asking if he could make the switch and leave the rails extra long for you to do this without that little piece of track in the middle.  

@dkdkrd posted:

If you are pushing but a car or two through the S, the leveraging force on that misalignment probably isn't so bad.  But if you're nursing a 12-car 20th Century backwards into the station, that pairing of couplers between the head-end baggage car and its adjacent passenger car is going to be painfully taxed by the preceding load of another 10 cars subject to the relentless push of steam/diesel power.

It could be a dozen or so hoppers (some Atlas die cast) with live coal loads. It could get interesting!! I can't get over how much more momentum I have with 12 empty hoppers. The momentum setting on the CAB2 doesn't even matter. I had trains pulling 3-6 cars as a kid because that's all I had but now I got trains with weight haha it's wild!

I never thought to unspike the rails @Boilermaker1 That's not a bad plan! I would feel much more comfortable doing that than trying to roll my own. I wonder if the #8 or 120/96 curve switch is a lower volume piece that might be a good candidate for a custom request.

I appreciate the help everybody. Definitely opened my eyes to some other possibilities.

Boilermaker, that is a good idea pulling the spikes and respiking.  

Bill, I chopped off long ends of a number of my switches to get everything to fit like suggested.

Looking at the angle mismatch again, I think you actually need to pull the #8 into like a “7.9” to get it to work.  Should be pretty doable.