Need help with wiring DCC reverse loop

[AussieAlex90]

Hey everyone, first time wiring up a Hornby DCC layout (still in planning stages) the track layout I have come up with is attached. As you can see there is a "reverse loop" on the inside track, can someone give me some guidance on how to wire up the R8238 Hornby DCC reverse loop module to work in this situation?

 

Thanks in advance guys!/media/tinymce_upload/680d19f209c1335a90304804e40452c7.jpg

[Chrissaf]

It's explained in detail with drawings and diagrams here.

[RDS]

Isn't that reverse loop too short to work with the RL Module?

I thought the loop had to be longer than the longest train that would ever enter it

[Fishmanoz]

 Hi Alex, for a start, welcome to the forums.  Then let me say, I don't think your question really properly addresses your problem and therefore neither Chris or RDS have answered it for you.  Chris has answered the simple RL question with his link to the Brian Lambert content on RLs which does tell you how to wire one.  RDS gets a little closer to the mark because the RL does have to be longer than the longest train, so you have to have one that is.  But this is still not your problem, I don't think.

 

I think the problem is that it isn't possible to find a simple loop on this layout.  For a start, the loop here runs from either side of the top left crossover point between the long siding the around via the inner loop and part of the long siding until it returns to the other side of that point.  You have to isolate this loop from the rest of the layout with IRJs on both rails of both outlets to this point on the right hand side.  Then you wire in the RLM somewhere inside the loop, just as Brian Lambert tells you.

 

If that were all, it would be simple, but it's not.  The complication is that there are 2 other entry/exit points to the loop.  The first is the top right point joining the long siding to the inner loop.  The Second is the inner/outer loop crossover just to the right of the inner loop/long siding crossover.  So you have to isolate at these points too: on the inner loop side of the top right point and between the points in the inner/outer crossover.

 

Now for the next complication arising from this: you must not have more than one train entering or exiting the loop simultaneously. Given the amount of your layout contained within the loop, this is probably impractical.  I think it unlikely you will have trains on the 2 crossovers at the same time, and I am going to assume you won't - in fact for the solution I'm going to suggest, you can't. But it is likely you will have trains on one of those crossovers and the top right point at the same time.  Given you do, the single large isolated section can't work.  What you will have to do is to split this into 2 isolated sections by putting more IRJs on each rail somewhere around the inner loop curve at the right hand side.  I think it probably best at the lower 45 degree joint, or at 4:30 if it is considered a clock face.  And remember that each of these isolated sections must be longer than your longest train, so you will have to check that.

 

So how do you run 2 isolated sections you ask.  The answer is you need 2 RLMs, one on each section.  The only way of avoiding this is if and only if you leave it as one isolated section and only one train enters or leaves at any one time.  Only you will now if you can operate your layout with this limitation. 

 

So Alex, have I defined your problem correctly?  And everyone, have I correctly defined the solution to that problem?  I may be talking through one of Graskie's hats again, but I think not on this occasion, even if I did start on this before my morning coffee.

 

PS.  If we are lucky, Chris may interpret my words into one of his excellent diagrams to better explain, assuming he can understand what I've said.

[AussieAlex90]

Thanks for the answers guys! I think my question may have been defined, Although it may be a little out of my league to actually implement!

Now I wouldnt say I'm new to modelling, I am however new to the electrical side of the house, especially DCC. I have only just finished adding Decoders to my 2 larger engines and tested then with the hornby select unit. Am I right in assuming that by longer than my longest train you are including coaches? (as they have metal wheels). I had planned on running two larger locos (both A3 4-6-2's) simultaneously on the main lines, whilst using the long siding for a smaller 0-6-0 freight engine. 

Originaly I had planned to wire up the layout with the long siding isolated from the main line. As shown in the diagram below, Green being the isolation points and the purple being the section attached to the "Reverse Loop" module, However I am not even sure if this would work, and I could find no evidence of anyone trying something like that.

Thanks again guys, I may have to have a little fiddle with the layout and see what else I can come up with. 

 

/media/tinymce_upload/1bf19f345f0c528e449c02e729b54a41.png

[Chrissaf]

PS.  If we are lucky, Chris may interpret my words into one of his excellent diagrams to better explain, assuming he can understand what I've said.

.

Now you have let the genie out of the bottle.......your wish is my command........diagram on its way!!!

 

[Chrissaf]

Fishy, firstly I struggled to fully understand the solution you described. So I have added a grid numbering scheme to Alex's diagram. That way, if you think you can improve on Alex's OWN solution, then you can provide X,Y coordinates for the elements of your solution. For example fit IRJs at position B12 & C12.

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That said, I can not see anything wrong with Alex's OWN solution, so this is the one I have used as the basis for my revised drawing. Unless someone can see something obvious I have missed, Alex's solution will work, provided two locos do not try to enter and/or leave the RLM protected track section at the same time via points at B22 and C10. I think this is unlikely as both of these potential routes terminate in the long siding.

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/media/tinymce_upload/92d9ee10e332223202cab721a9a28ab5.jpg

[Fishmanoz]

Hi Alex, yes the isolated section must be longer than loco plus carriages.

 

Yours looks OK except you have the problem that effective length of your section is only from C10 to C20, the lower part of the long siding not counting, and I suspect that is too short.

 

That gets me back to mine which starts with IRJs at B10 on the left and follows around through B21, B23, C16 and ends with IRJs at C10.  It also needs to be isolated with IRJs at A/B21, D16 and C12.  Then if you want to have more than one training entering/exiting at the same time, you split it with more IRJs at F27 and use 2 RLMs, one on each half.

[Chrissaf]

Fishy, there is one flaw in your argument that I can see. If a train is longer than the track section between C10 and C20 then it will bridge across the straight ahead part of the C10 point. Now given that the IRJ at C10 is in the turn right part of the point and not the straight ahead route of the point, that turn right path is blocked by the long train on the C10 to C20 section straddling across the C10 point (straight ahead point route). Thus it would be impossible for IRJs at both C10 and B20 to be bridged at the same time in that particular scenario.

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Obviously if a train is left straddling the IRJ at B20 then the RLM integrity fails, but that would be the same if a train was left stationary across any RLM protected section IRJs on any layout design.

[Chrissaf]

Further to last post above: I do conceed that if two trains are heading for the long siding at the same time via the two section entry points (points at C9 & B22)  then IRJs at positions C10 & C20 could be bridged at the same time. Or if one train is entering the long siding at C20 whilst another train is exiting the long siding at C10, then the IRJs could also be bridged at the same time. It would be down the Alex to ensure only one train moves in / out of the RLM protected section at any one time for the RLM to work reliably.

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This would be the exact same issue on a bog standard RLM loop design if you had multiple trains entering / leaving the protected section at the same time, so in that respect, Alex's situation is no different.

[Fishmanoz]

Chris, you have it spot on, I'm wrong.  Alex, your suggested isolated section will work fine and is long enough because the lower section of the long siding does count.

 

You do have a higher risk though of two trains entering/leaving at the same time as a train from/to the outer loop could be entering/leaving at C10 at the same time as one to/from the inner loop is crossing at C20.

 

Mine will work and would allow for simultaneous entry/exit at C10 and C20 with 2 RLMs but I think all too complicated. Stick with yours and don't allow 2 trains to enter/exit at the same time.

[AussieAlex90]

Thanks Chrissaf! 

As I said before I wasn't sure if a reverse loop module could work in that particular way, and it is a lot easier to wire up (as per your diagram). I know the issue is with two trains entering the long siding, however I only plan to have the smaller 0-6-0 loco use the sidings for "Shunting". So it shouldnt be to much of a problem. 

Thanks again for everyones answers.