Double Reverse Loop ?

[HooliganHedgehog]

Until now I have steered clear of reverse loops but I am now considering a total rebuild and would like the ability to turn trains around and back again.  I thought I understood the principle of the Reverse Loop Module, but I have totally confused myself trying to design a track plan.  This is probably painfully obvious to you guys but is this/media/tinymce_upload/6ea3eb66a04c2e6da134b4fc33e93d2e.jpg diagram workable and is this just one Reverse Loop Section ?  This will be just one section of the layout with other connections to a main outer loop, sidings passing loops etc, but not involving any other reverse loops.   I am using Hornby Elite and Railmaster and have a Hornby RLM R8238 on order.  Also, am I right in thinking other trains in this same section  of track are unaffected ( as long as not in the actual reverse section of track).  Thanks.     

[Chrissaf]

There are two reverse loops in your layout as drawn.

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I am assuming that your intention was to use the single R8238 RLM you have ordered as per Drawing A below. If you are, then the protected RLM section (shown in red) is TOO SHORT. The RLM protected section of track should (best engineering practice) be longer than your longest train (loco PLUS rolling stock with metal wheels being hauled).

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Drawing B shows a work-around that could work, but it relies on you ONLY operating one train at a time. The other rule about Reverse loop design, is that only one train can enter or leave a RLM protected section at a time. Drawing B only works because of the cross link shown in Blue. The end loops (left in original black colour) also need to be longer than the longest train. If you are going to run more than one train at a time, then you need to implement the design in Drawing C.

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Drawing C shows the preferred RLM solution, but this requires TWO R8238 RLMs. This assumes that the end loops are longer than your longest train. The blue section in the middle is the part of the track layout directly powered by the DCC controller.

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Personally, I would implement Drawing C anyway, even if you were only intending to operate one train at a time to future proof and comply with best engineering practices.

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EDIT: After re-reading your original posted text.

Your original drawing post indicates that this is only a concept drawing, and your actual planned layout is different i.e has a second oval, passing loops and sidings not shown on your drawing, re-post with an accurate layout plan showing ALL your proposed track for me to do a proper RLM evaluation on. One needs to assess the WHOLE layout for the impact on reverse loops before designing a reverse loop plan. It is not as simple as your original post drawing infers. You may need up to four R8238 RLMs. I need to see your whole layout plan to confirm or not.

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/media/tinymce_upload/03413bc4772526119fba4f06536b7f5b.jpg

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[HooliganHedgehog]

Thank you so much Chrissaf, that makes perfect sense..   The whole layout will be 16' x 4' in two layers.  The lower layer will be for my underground trains which will appear out of tunnels at stations and cuttings, and also through a cut-out in the upper layer where there will be sidings and maintenance area etc.   The upper layer will be an oval with sidings and passing loop as mentioned, some of which will be behind a backdrop as a sort of fiddle yard. The idea being a train disappears through the backdrop and a while later a different train rejoins the scene whilst the original dwells a while out of sight.. I am not sure I will be able to produce an accurate track plan in advance as things like board supports and point positions will to some extent determine where the underground section is visible etc.  I would like the outer loop to join the inner loop / reversing loops by way of sissor points between where you have shown RLM1 & RLM2  Mostly still in my head right now, just trying to work out feasibility.  This Reverse Loop thing was driving me mad.  I understood about the train length and intended the 'too short' section to be longer in real life, but then I couldn't decide if it was 1 or 2 loops.  Thanks again for your clear explanation.  

[Chrissaf]

I am currently writing a 'Reverse Loop' tutorial PDF to add to my existing 'Track Extension Pack' PDF. The intention is to post it on the forum (Hornby DCC sub-forum) when ready - anticipated during March. It will be invaluable to you when you are in a position to have a clearer understanding of the exact geometry your layout will take. From what you have described so far ie. the underground layer with tube trains and the overall layout size. It sounds impressive, and I look forward to seeing some photos of it in the "Let's see your layouts" thread.

[HooliganHedgehog]

Sorry, me again Chrissaf.  Re-reading your answer, the point against my original sketch was the length of the Reverse Section.  Would it be OK otherwise ?   I have had a first crack at a proper plan, which is based on my original idea ( and probably why I got so confused over the Reversing Section(s)).   Good practice or not, would it work with the two points and track in between being controlled by the RLM ?   From your explanation, to do it properly will be fairly complex as it seems to then involve the whole layout?    I have also attached a couple of photos from my present layout showing the underground station and a cutting and my proposed track for the lower level./media/tinymce_upload/1b6775f2b8ec110974ed6b76b24299fb.jpg/media/tinymce_upload/a2fc2384464b8909590d4d3dd582c788.jpg

/media/tinymce_upload/71d022998f715f8f82e39b0896e3c556.JPG/media/tinymce_upload/17da08654657c682d8bdecf64b5f2384.JPG/media/tinymce_upload/8c75b9798979e327ce9ef039a6ff1b77.jpg

[Chrissaf]

Although Option1 below looks to be the simplest (which is your preferred option). I would only use that option if you can reasonably well guarantee that only one train will be entering or leaving the middle protected section at a time.

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Option 2 (my preferred option) gives a lot more train movement flexibility and would allow two trains on the inner oval. But with the same caveat that only one train entering / leaving each individual RLM section at a time. However, fine tuning of the exact IRJ locations i.e. being just far enough apart on the two individual protected sections to be longer than your longest planned train should make that caveat a non-issue.

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Note the short Blue & Brown lines on each side of the track on the main upper and lower ovals. These lines represent the physical polarity of the track power connections. Notice how in Option 2 the upper inner oval track rails are reversed compared to the upper outer oval track rails (see blue dotted circle). If these power connections are reversed from that shown, you will get a short on the main track. This is key to the Option 2 plan working.

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What you can't do with Option 2 is add any form of oval to oval cross-over points between the two main ovals at the top i.e in the layout track section where the blue dotted circle is. To do so will create an instant short. If you did want to do that, an additional two RLMs will be needed and all four end loops would need to become protected RLM sections with their own dedicated additional IRJs. The very top two power connections in the blue dotted circle represented by the Blue & Brown line bars would need to be reversed too. Alternatively, if you added these cross-overs to the Option 1 plan, then they would just need to have IRJs on the cross-over where the points faced each other. I don't think you are planning on implementing these additional cross-overs, but I mention them just in case. Adding this track amendment to the Option 1 plan, would just make it easier to break the RLM design rule about only one train entering or leaving a protected section at a time, so probably not a good idea to implement anyway. But would be fully supportable in Option 2 if the additional two RLMs were added.

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/media/tinymce_upload/79bfd31f59c51fbd85ef2bdb6ed6870b.jpg

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I've given you the options with the Pros and Cons of each. Which one you adopt is your choice.

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Thanks for the photos by the way.

[HooliganHedgehog]

Thanks Chris. It took me a while, but I think I understand it all now and I tend to agree Option 2 is best. Just need to get started now but feeling bad about dismantling the old layout which took so long to get to where it is now and was a steep learning curve.     Thanks again,   John

[Chrissaf]

Good luck..!

[HooliganHedgehog]

Hi Chris,  sorry, me again  !!    Well, after overcoming several design flaws .....  mainly access problems during assembly and point motor positioning, I am getting to the point of test running some trains.  I have gone with Option 2 for the reverse loops. Now I might be 'over thinking' this as it is my first attempt at Reverse Loops, so I'd rather be safe than sorry.   I understand the need to ensure only one train enters a Reverse Loop at a time, but would it be a problem if a train were long enough to enter the second loop before completely clearing the first? 

Thank Chris.

[Chrissaf]

On the basis of the design being compliant with Option 2.

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.....but would it be a problem if a train were long enough to enter the second loop before completely clearing the first?

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No, that would not be problem provided the front carriage (loco) of the train and the last carriage of the train including all intermediate carriages do not share any electrical connection to the wheels of the different coaches.

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In essence, the track gap between two different RLM protected track sections (i.e the documented Option 2) only needs to be longer than your longest loco or loco plus any attached rolling stock that has electrical pickups that supplement the loco pickups.

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Put more simply, if only the loco has electrical pickups for the loco motor. And optionally any attached carriages have electrical pickups for internal coach lighting, but there is NO inter-coach to loco wiring connecting the rolling stock together, then that should be OK.

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Although not yet published directly on the forum. My RLM Tutorial PDF can be downloaded from this link:

https://btcloud.bt.com/web/app/share/invite/yYK2gzPXT4

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When the link opens, click the file in the top left corner to download.

 

[HooliganHedgehog]

Thank you Chris.  That is what I hoped, but as I said ... over thinking !    

[Fishmanoz]

Are you sure you have that logic correct Chris?  Seems to me it works like this:

 

-  track between the 2 loops is of fixed phase, only the isolated sections change phase by action of the RLMs

 

-  as a train exits loop 1 its RLM switches phase to match the track between the loops

 

-  as the train enters loop 2 its RLM does similarly. Now both loops and the track between are on the same phase

 

-  given this, you effectively have a variant of Drawing B with one loop, rather than Drawing C with 2 loops?  And the same operational limitation - no other train entering or leaving either loop while the first train is crossing between the loops and has not cleared either.

[Chrissaf]

And the same operational limitation - no other train entering or leaving either loop while the first train is crossing between the loops and has not cleared either.

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That is correct. The 'rule' about only one train entering / leaving a RLM protected section at a time always needs to be considered. I was looking at the question from the point of view of the train itself that is bridging the fixed phase section**. That train will not have an issue traversing the RLM sections, providing (as you say) another train elsewhere is not leaving / entering one or other of the two RLM protected sections at the same time. Once you start adding RLMs into a layout, there will always be the inevitable operational compromises that will need to be made.

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Note** which I took the question to be relating to.

[Fishmanoz]

Hi Chris, I didn’t make my point clear did I?  You said the interloop track being shorter than the longest train is not a problem if there is no electrical connectivity along the length of any train crossing.  I’m saying there is no problem full stop ...... but you can’t also have any other training entering or leaving either loop at the same (except you can if your proviso applies).

 

Haven’t had the time to look at your RL tutorial yet but I’m sure it will be of high quality and cover the subject thoroughly, you don’t do half measures, at least not on this forum.  So I don’t know if you’ve covered this or not, or in this way - best practice says that the isolated section should be longer than the longest train, but not significantly longer.  A significantly longer section, either by extension of a single track, or by having long branches of track coming from the section, introduces the operational possibility that 2 or more trains may enter or leave the isolated section at the same time.  This cannot be allowed as the RLM cannot handle more than one train entering or leaving at any time.

 

What I am suggestion is the addition here is the “not significantly longer” statement.