How many RLM's do I need?

[SHEDINGTON]

Right guys

I planning 2 x doulbe reverse loops on my layout how many RLM's do I need ?

Please say 1 (££££££££££££)

Dodge

keep owt'os rowd

[poliss]

Sorry, you need at least two, possibly four if you're talking about four different lines.

[Fishmanoz]

Poliss is certainly right in the first instance - you need 4. But in practice, just maybe not. And we can't be sure unless we know just what your layout configuration is and how you intend to use it. 

To try to examine it for you, let's start with what a reversing loop is - it is a track configuration where, as you trace around it, you find that the left track meets up with the right track, causing a short. You can also think of it as a place where a train can start around your layout in one direction and end up coming back to this point going in the other direction. Either way, the consequence is your track is short circuited.  The only way you can avoid that short is to have a section of track in the loop, longer then your longest train (yes train, not loco) which is isolated at each end on both rails with isolating track joiners (IRJs).  Then when a train approaches this isolated section , the polarity in the section must be switched to match the polarity of the track the train is on, and it can enter without a problem. then, before it leaves the isolated section, the polarity in the section must be switched to match the polarity of the track it is leaving on outside the section. 

Hopefully so far, I have just been teaching you to suck eggs, but I wanted to make sure. Also, it is possible to control such a loop without an RLM by switching the isolated track section manually. That would mean stopping the train before it entered the section to check and adjust the polarity in the section, then doing the same thing, stop, check and adjust, before leaving. This is likely highly inconvenient and in practice an RLM will be needed. 

Now let's get to your particular layout and let me ask - how many isolated sections do you need to isolate your 2 double loops?  Depending on your track configuration, the answer may be 1 (unlikely), 2 (possibly), or 4 (probably). 

Now let's assume the answer is 4. Given this, let me ask - how many trains can you have in isolated sections at the one time?  If the answer is only ever one train, then you could run all 4 sections using one RLM. After all, there are only 2 polarities on your track, no matter where they are occurring, and one RLM can switch between them as needed. But if the answer is you can have 4 trains, one in each of the isolated sections at the one time, then you are going to need 4 RLMs to run them. And there is a possibility that your answer is that only 2 sections can have trains in them at the one time, in which case 2 RLMs will be needed. 

Now if the answer is you can isolate all your loops with only 1 or 2 isolated sections, then you will only need 1 or 2 RLMs to run them. 

So does that make complete sense and can you answer my questions to determine the number of sections and RLMs you need?  Or are you now completely confused? Or are you not confused but what I said makes no sense at all?

[SHEDINGTON]

Thanks Fishman, it is as I thought I am going to need at least 2 and maybe 4 if I want full capabitily with no limitation ie running 4 trains around at the same time 

My layout is basic at the moment, double track "rectangle" with 2 and 3 radius curves at each corner 3m x 5m, various passing loops for storage etc 

The reverse loops commence about 3/4 away along each 5m side and double back on themselves one either side bit like ears sticking in to the middle of the rectangle

I may decide that the RL's will become single loops instead of double loops with all the cross overs etc due to cost but in time leave the option open to install the double loops later, or employ the manual switching method on 1 of the tracks in each loop

A good explanation Fishmanoz understood most of it anyway thanks for the help and support you have confirmed my worst fears ..... it's gonna cost a mint, or I could suggest a as a Xmas present from my wife and get her off my back then I could stop taking the medication ............

It would be good If Hornby could design the electronics to operate 4 Reverse loops from one module like the accessory decodes,     shhhhhhh there's an idea to market but don't tell Hornby...... it'll takea a decade to get in production and another to reach market

Thanks again

Dodge 

keep owt' os rowd

[Fishmanoz]

Even if you build the double loops, I suspect practical running will mean that you can get away with one RLM per double loop by connecting the one to both the isolated sections. This will only not work if you then have a train entering either of the loops at the same time as another is exiting. The RLM won't know which way to switch and will likely trip out in some fashion.