Adding reversing capability to layout

A

Andrew_au

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This is a rough diagram of my current layout. It consists of
  • an outer mainline loop (green)
  • two inner loops (purple) that can be joined into a single large inner loop (green)
  • two connections to allow trains to pass between the outer and inner loops (pink)
Arrows indicate direction of travel.

RoughLayout_Annotated.jpg
As currently structured, all tracks share a common polarity, and the entire layout can be powered with a single DCC connection.

I'm thinking of replacing the LGB 13200 crossing with an LGB 12260 double slip crossing. This would allow me to run trains onto and off the two loops in either direction. However, it plays havoc with the polarity.
RoughLayout_Crossover.jpg
Plan would be to run the inner and outer loops with the same polarity (e.g. clockwise), and use reversing sections at the interchanges. This would also allow me to add additional (non-reversing) interchanges between the inner and outer loops.

Question: where do I put the reversing sections for optimal operation?
 
Set up isolating sections around the top half of the Yards and Sidings Loop, and another around the right hand end of Inner Loop B.
 
You do not say if you are DCC or not. This makes a big difference. EDIT Oops oh yes you do missed that sorry.

Ok the logical place for the Reverser would be at the double slip, isolations at all parts and feeds to the centre of the slip on the outer rails. But that will not work as effectively the only place where the revercer can do its stuff is the short length of the slip and any loco longer will span the revercer section. This does not work. You need a reverce section longer than your longest train and a set of stock with metal wheels can cause issues if the section is shorter than that longest train. Be interesting to see if others agree with me.
 
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The double slip needs to be isolated in all directions. The horizontal route through the double slip would be a short length and as dunny says normally that would be too short. However, because it is between 2 sections of correct polarity it will not be in a conflict between opposite polarities when using that route. If the reversing loop, including the double slip, is in the wrong polarity as soon as a locomotive enters the double slip, the reversing loop will switch to the correct polarity for both inside loops.

Any other route would need complete train lengths because of the conflicts of polarity.

Routes through the double slip -

- You will need the horizontal rails at each side of the double slip to be isolated (train length not an issue as above).
- The lower left hand diagonal route will need the rails isolated a train length away from the double slip.
- The upper right hand diagonal route will need the rails isolated a train length away from the double slip and also on the route upwards to the outer loop (this one doesn't need to be a train length away).
Total of 5 pairs of isolators.

AL
 
Just a note, with an autoreverser as "smart" and programmable as a DCC Specialties PSX-AR, you don't need a reversing section as long as the train, just as long as powered cars. This is why I made my suggestion of a single reversing section, and keeping it "off" the main line and the 2 inner loops. Simple.

Other less smart units may require the whole train fit in the isolated section.
 
AlanL said:
However, because it is between 2 sections of correct polarity it will not be in a conflict between opposite polarities when using that route.
Click to expand...
This is a very good point! Thanks Alan for bringing it up. It is something to keep in mind whenever a complex "reverse-loop" like Andrew's is part of the design. Drawing both rails on a diagram along with their "polarity" should help in thinking through the problem.
 
phils2um said:
This is a very good point! Thanks Alan for bringing it up. It is something to keep in mind whenever a complex "reverse-loop" like Andrew's is part of the design. Drawing both rails on a diagram along with their "polarity" should help in thinking through the problem.
Click to expand...
Yes I find that helps, though as is likely to be said polarity with AC DCC is not quite the same but using it to highlight the differences of possibly cross joining wiring certainly helps. With my line on my wiring diagrams I used to talk about Inner and Outer Rail but a + or - works just as well as does a red or black line on your drawings.
 
Thanks for all your thoughts.
Greg Elmassian said:
Just a note, with an autoreverser as "smart" and programmable as a DCC Specialties PSX-AR, you don't need a reversing section as long as the train, just as long as powered cars.
Click to expand...
Assume for a moment that each bogie is isolated from all the others (except on the loco). Is not there still a risk of short if the isolated section is bridged at each end simultaneously?

Alan & Greg correctly identify that I can treat the double switch as a critical section, and then create safe zones for when it is set to a curve. But I wonder if there's another way of thinking about the problem. I can see 3 broad solutions:

(1) Treat the double switch as the critical section

The trouble with this is that it is not sufficient to just isolate the switch. I need enough room for a significant portion of a train to be in the switch section.​
  • I'm pretty tight on room
  • I'd like for a train on a stopped leg to be able to approach the junction and stop outside it, rather than remain a long distance away to avoid providing a second train across the critical section boundary.
Greg and Alan have talked about ways of doing this. I'm not sure I can find a "good" solution without needing multiple adjacent reversing sections or a very large "safe" zone.​

(2) Treat the double switch as a thoroughfare with two controlled turnouts.

Don't put the double switch as a reversing section at all, but treat it as a main-line through the green-blue loop with a turnout to brown and a turnout to purple. This requires two reversing sections:​
  • one on the brown line, with isolators on each branch of the junction (one leading to the double switch, the other continuing the brown loop) and a third splitter someone further around that corner (like a wye)
  • one on the pink branch line
Due to the extra loops and etc, I don't think there's a clean way to put the reversing sections on the blue loops.​

(3) Make the brown / blue / green tracks match polarity and the pink tracks the "problem" sections

Consider if I switch polarity on (say) the outside track (the brown arrows) so that it matches the blue and green tracks. At this point, all paths through the double switch are "safe" except the pink track.​
​
As above, I need two reversing sections. In this case, one goes on the top brown loop (treating it like a wye) and the other on the pink branch line.​

Although the latter two solutions both require 2 reversing loop modules, I think the layout as a whole ends up being a lot cleaner, and the "one train only" sections seem natural. My only concern is whether the lower pink section is long enough, as some longer trains might be able to cross both ends.
 
Andrew, please read more carefully...... you have to have some faith in people who have direct experience, and we have gone over this specific subject several times.

I use DCC specialties PSX-AR, this is the smartest one (short detecting) on the planet, it uses a microprocessor to analyze the situation, it is programmable and has been used in thousands of layouts.

If you have a reversing section shorter than your train, but the only part of the train that has power pickups is the loco, then the "little shorts" of a wheel bridging the gap is OK, NO PROBLEM...

This is because the PSX-AR is smart, and has evolved over the years.

Other systems with sensor sections or not programmable may not tolerate this.

This is why, if you choose items properly, you don't have to follow the "longest train rule'.

I gave the caveats and set the scene, please realize we have gone from generalities and "common wisdom" to years of specific experience. I gave careful specifics in the switch yard post too, and they were missed... so, I do work hard to carefully describe and qualify when what I state differs from "common wisdom".

Best regards,

Greg
 
The LGB double slip is tricky to work with because of the all-live design. I used it for a double reverse section on my layout for a while. There is a thread exactly on this topic here: DCC Conversion Reverse Loops

I ended up having to completely isolate the double slip to get it to work for my reversing design. It was fine for larger locos, but for short locos they needed power caps in order to get across the dead rail of the double slip. Because of the amount of switching involved I decided to move the double reversing section to a dedicated section of track and replaced the double slip with the 13200 crossover. This allows me to run figure 8 using the inner loop without having to do switches every time a loco comes in and out of the inner loop.
 
Greg Elmassian said:
I have run a loco over the double slip. I was not impressed. I also model in Z scale, and double slip switches are NOT allowed in the club layout anywhere near the mainline or reversing sections.

While it looks convenient, almost every scale hates them.

Greg
Click to expand...
I'd have to agree here. They look cool and are great space savers, but they can become really problematic on more heavily utilized lines. I'd only use it use for yards at this point and definitely not on any point of a main line.
 
Does seem to be one up for the battery boys, forget cost, you can run a double slip :mask::mask::mask::mask::mask::mask:
 
LGB slips as has been mentioned in the forum before are smallish radius. The crossover causes few problems but the curves are another matter. We had one on the Ruschbahn in a station and it’s location was within a run round loop to give excess to a platform and allow further access to a yard for shunting. Thus no main line speeds were encountered. With careful slow running few problems were encountered but we never ran the 2-8-0 though it.
 
I don't have any personal experience with the double slip but I've read enough to know that they can be problematic. A perfect track base in the area would be essential.
dunnyrail said:
LGB slips as has been mentioned in the forum before are smallish radius. The crossover causes few problems but the curves are another matter. We had one on the Ruschbahn in a station and it’s location was within a run round loop to give excess to a platform and allow further access to a yard for shunting. Thus no main line speeds were encountered. With careful slow running few problems were encountered but we never ran the 2-8-0 though it.
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dunny's experience on the Ruschbahn is a case in point. If I remember, the Ruschbahn was an elevated railway with good structure to support the tracks.

Do you really NEED a double slip for interesting operations?

Why not start with a more simple track-plan and have space for future expansion ?

If you do need more complex operations could you fit crossovers instead of the double slip as my other rough sketch?

IMG_20220426_145644578.jpg
Alan
 
AlanL said:
I don't have any personal experience with the double slip but I've read enough to know that they can be problematic. A perfect track base in the area would be essential.

dunny's experience on the Ruschbahn is a case in point. If I remember, the Ruschbahn was an elevated railway with good structure to support the tracks.

Do you really NEED a double slip for interesting operations?

Why not start with a more simple track-plan and have space for future expansion ?

If you do need more complex operations could you fit crossovers instead of the double slip as my other rough sketch?

View attachment 297733
Alan
Click to expand...
Indeed it was, the slip was in a Garage based station.
 
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