Reverse loops

[Porkster]

Being an enthusiastic new comer to this hobby I have designed an ambitious layout that gives me all the features I am looking for. I know that my design incorporates several reverse loops but I am not sure if it will work or not using reverse loop relays. Are there any experts out there who would allow me to email my design to them for comment and advice? Cheers the Porkster 

[Fishmanoz]

Can't think of any reason it won't work with RLM/s. Post a copy of your layout, plenty here to help.

[Porkster]

Can't think of any reason it won't work with RLM/s. Post a copy of your layout, plenty here to help.

Hi, thanks, I'm happy to do that but not sure how? Do you know,cheers

[mjb1961]

Hi ,,,if you are going to need RLMs you should pop over to Hattons website as they are selling Hornbys RLMs for £12 ,,,,,that's a very good price ,,,,mjb

[Porkster]

Hi ,,,if you are going to need RLMs you should pop over to Hattons website as they are selling Hornbys RLMs for £12 ,,,,,that's a very good price ,,,,mjb

Cheers, thank you. Porkster

[Chrissaf]

Posting an image is easy.

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First thing you need to do is get the image of your layout into a suitable image format. It needs to be a .JPG or .JPEG

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If you have a scanner, then you could scan the page of a track plan book or a track plan printout directly into a JPG. If you can get an image of the track plan on your PC screen then you could use Windows inbuilt screen capture utility to do similar. Windows utility is called 'Snipping Tool'. Go to your Windows Start menu and type 'Snip' in the search box. You should see 'Snipping Tool' listed in the search results box. Once you have captured the image, just make sure to use the 'Save As' function to select .JPG as the Snipping Tool defaults to save as .PNG

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Once you have got the JPG on your PC, then in the forum 'Reply' text box at the bottom of this page. Write any text you want to have included followed by a couple of carriage returns to place the mouse cursor well below the text, then click the 'upload an image' tool - see screen shots below:

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/media/tinymce_upload/a79009daca5de815235fc1abf102bc6f.jpg

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A dialogue box opens. Click the 'Choose File' button and navigate to your saved JPG image. Follow the prompts and the rest should be obvious what to do.

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/media/tinymce_upload/f690d8419f35ea74c2e0bd0fc9cfa508.jpg

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Being a weekend and a relatively newbie poster, the image needs to be checked (moderated) before it will appear. Probably Monday now. To check if the image has been accepted by the system. After clicking the Green Reply button to save your post, scroll up to the top of the page and a message should be there saying something like 'your image has been saved successfully but needs to be moderated'.

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This previous post shows how I and Fishy did a similar 'find my reverse loops' service for a previous forum member. See the 7th post down on the page linked below:

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https://www.hornby.com/uk-en/forum/post/view/topic_id/15147/?p=3

[Porkster]

[snip]

 

Chris, thank you for all of your help and advice. I have followed the above and finally got the layout plan in jpg however for some reason I was unable to reply to your post on my Mac. I have no prob on my iPad, only my Mac so apologies but I will try again today. In the meantime I have read all of your information plus searched google for what ever I could find. From this I think the message is to simplify the layout and avoid RL's unless absolutely necessary. Would that be fair comment?. Maybe introduce a turntable for additional interest and train reversal? Cheers the Porkster

[Chrissaf]

I think the message is to simplify the layout and avoid RL's unless absolutely necessary. Would that be fair comment?

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In principle yes, but reverse loops are not that difficult to deal with once you understand them. Hence the request to post an image of your proposed layout so that we can analyse the layout for you. Adding a TT, can for some, in a DCC environment be more onerous than just dealing with the reverse loops in the first place.

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[Porkster]

I think the message is to simplify the layout and avoid RL's unless absolutely necessary. Would that be fair comment?

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In principle yes, but reverse loops are not that difficult to deal with once you understand them. Hence the request to post an image of your proposed layout so that we can analyse the layout for you. Adding a TT, can for some, in a DCC environment be more onerous than just dealing with the reverse loops in the first place.

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Hi Chris, I have tried again today to try and post through my mac but for some reason it won't accept any type ( input ) . I can bring up the site and login all ok, bring up the topic but cant type anything into the reply window?? Really sorry as I would like to share this will you along with the version I have progressed to that has eliminated the RV's. I am interested in your comment re TT. I know they are effectively an RV so I assume an RV relay arrangement will be required, but are there other considerations that I have overlooked. regards the Porkster

[Chrissaf]

OK your MAC seems to be a stumbling block in getting your layout design posted in this forum thread.

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Plan B, if you are able to get your layout image JPG into an emailable attachment. Then send it to Adam (Hornby forum administrator) and request him to post it into this thread on your behalf. Adam's e-mail is forum@hornby.com

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Re: TurnTables.

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There are a lot of variables concerning TTs that vary depending upon brand and type. Traditionally, TTs are made to suit better a DC Analogue layout environment. As they rotate the rails on the rotating bridge reverse. In a DC layout this is not an issue as there is no power connected to the bridge, else any loco sitting on it would be trying to move.

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In DCC, track power is permanently on. In principle there are two types of TT, the ring type and the split ring type. Both types have the potential to produce short circuits on a DCC layout as they rotate. The split ring type have the additional issue of introducing dead track positions as the bridge rotates. Not very helpful if you have a sound loco on the bridge with an idling engine (steam hissing or diesel tick over).

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Thus for a DCC environment, most TTs will need to be modified in some way. The exact nature of the modification will depend upon the type of TT they are. There are some TTs on the market that are made DCC friendly at the factory, but these are few and far between.

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The modification usually involves isolating the track lead-ins to the TT, and maybe supplemented (optionally) by fitting a Reverse Loop Module as well.

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This site here gives more information.

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http://www.brian-lambert.co.uk/DCC%202.html#Turntables

[Porkster]

OK your MAC seems to be a stumbling block in getting your layout design posted in this forum thread.

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Plan B, if you are able to get your layout image JPG into an emailable attachment. Then send it to Adam (Hornby forum administrator) and request him to post it into this thread on your behalf. Adam's e-mail is forum@hornby.com

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Re: TurnTables.

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There are a lot of variables concerning TTs that vary depending upon brand and type. Traditionally, TTs are made to suit better a DC Analogue layout environment. As they rotate the rails on the rotating bridge reverse. In a DC layout this is not an issue as there is no power connected to the bridge, else any loco sitting on it would be trying to move.

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In DCC, track power is permanently on. In principle there are two types of TT, the ring type and the split ring type. Both types have the potential to produce short circuits on a DCC layout as they rotate. The split ring type have the additional issue of introducing dead track positions as the bridge rotates. Not very helpful if you have a sound loco on the bridge with an idling engine (steam hissing or diesel tick over).

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Thus for a DCC environment, most TTs will need to be modified in some way. The exact nature of the modification will depend upon the type of TT they are. There are some TTs on the market that are made DCC friendly at the factory, but these are few and far between.

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The modification usually involves isolating the track lead-ins to the TT, and maybe supplemented (optionally) by fitting a Reverse Loop Module as well.

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This site here gives more information.

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http://www.brian-lambert.co.uk/DCC%202.html#Turntables

Chris, thank you for all of that information, I think the learning curve has just become a lot steeper! I. certainly did not realise there were so many implications with TT's. Like they say " nothing's easy". I will send the layout plans to Hornby as you have suggested and look forward to your comments. Thank you too for putting me on the Brian Lambert's site, wow, what a great site for a wealth of wiring info. I work my way through it. Cheers once again the Porkster

 

[Chrissaf]

Just for info, Brian Lambert is in fact our very own forum member 'FlashBang'. So if you see a suggestion made by FB in response to a question, then you can assume it is gospel and coming straight from the horses mouth so to speak. Also, be aware that Brian's wiring diagrams cover 'all and sundry' and 'are all things to all men'. In other words, it is not necessary to implement every wiring option Brian documents, not everything will be relevant to your particular layout.

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PS - Just a clarification point of forum etiquette. It would assist everyone greatly if using the 'Blue Button with the White Arrow' was avoided. That is not a 'Reply to this Post' button. Scroll down the page and write your reply in the empty reply text box and click the Green Reply button instead. Helpful, with my posts in particular as they tend to be long ones and the Blue button duplicates all the previous text unnecessarily.

 

[Fishmanoz]

Just on TTs, not all are old DC designs like Hornby's. Some are designed for DCC and work out of the box via an accessory decoder including with RM.  just need to be aware if they are slipring design with opposite phase on half the outlets. Doesn't mean you need an RLM, just that you need to wire them correctly.

 

One user here, Yelrow who is towards the non-tech end of the spectrum, was able to get his working first time.  Second time he used it, he had phase issues with his outlet wiring and solved them with a cheap RLM.

[Porkster]

Hi Chris, thank you for your heads up on FB. Your comment re the blue button is taken on board, my apologies to everyone regards the Porkster

[Howbi]

@Porkster.........I can't see any reverse loops in either diagram, they are all continuous loops so no polarity conflicts as far as I can see.........another will surely confirm or deny shortly......... 😀..........HB

[poliss]

Could be a reverse loop on the turntable, depending upon how it's wired. Nothing anywhere else. If you were to straighten it out it would just be large ovals with some sidings. 😆

[Chrissaf]

Porkster, I will do a full analysis later of the top drawing and give a fuller reply in due course, but just a couple of initial comments.

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There are no RLs in the main layout track on the diagram with the TT.

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Could be a reverse loop on the turntable, depending upon how it's wired.

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Agreed - I covered the TT potential for a RL in a previous reply.

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I think that there ARE RLs in the top diagram due to the quite complicated cross-over arrangement at the 9 pm clock position, but I need to give it a bit more thought first before saying yah or nay. Remember my definition of a RL, is a loop where a loco can come back to its starting point on the same piece of track but facing in the other direction. This, at first glance, looks like it can be done via the cross-overs at the 9 pm position. I need to extract the diagram from the forum page so I can magnify it in another application to look closer in detail.

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The only limitation is that you cannot have more then one train (loco plus rolling stock) entering OR leaving a RLM protected section at the same time. This is why a RLM protected section MUST be longer than the longest train. There is no restriction on having more than one train WITHIN a protected section provided they don't both try and leave it at the same time.

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Just to correct a misconception. In DCC using a RLM to reverse the phase of the DCC signal DOES NOT result in the loco changing direction of travel. Once a loco has been given a command to go either 'forward' or 'backward' then the reversal of the track phase (to use the term polarity is technically incorrect) does not affect that locos direction.

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This misconception may have arose because in a DC analogue layout reversing the polarity (polarity is the correct term to use for DC, not phase) does indeed cause the loco to travel in the other direction.

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[poliss]

Yes, you're right. Following it around with my mouse, I can see it now. Could even be two on the yellow line if you follow it round and reverse through the points at 9 o'clock.

[Chrissaf]

There are four clear Reverse Loops, there may be more, but any others over and above the four I have documented below (such as for example the three [a, b & c] variations around RL3) would just be variations around the same four core ones. In order to provide the maximum flexibility of train movements around the layout I recommend at least four Reverse Loop Modules are fitted. See final diagram. From a Reverse Loop perspective, Porksters proposed first drawing layout (non TT one) is not actually that onerous. The reverse loops are pretty basic. They all centre around the three way crossover point at the 9 pm position.

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The exact location of the Insulated Rail Joiners (IRJ) could be adjusted from that shown in the bottom drawing to suit the maximum expected length of a train (loco plus all rolling stock).

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/media/tinymce_upload/a2a1cd9c9a327c19524053c6cfa567f3.jpg

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/media/tinymce_upload/0c3e667e6a9d31919f22a9fe0de5ef56.jpg

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[Howbi]

Expertly diagnosed, Chris, I realised I was wrong about an hour after my post whilst having lunch in Milton Keynes with SWMBO...........amazing how things click after the event.......it's an age thing.......... 🤔........HB

[poliss]

I blame it on the fluorescent yellow dazzling my ancient eyes. 😎

[Porkster]

Well we got there in the end thanks to Chris and Adam. Thank you all for your comments. Chris,  I need to study your comments in more detail. The way I see it is that the complicated section of track at the 9 o'clock position is effectively one track. Once imagining that I think you can see the 4 and maybe 5 RL's more clearly. I have to study in detail to understand the reasons for your location of the RLM's they are not where I thought they would be. I don't think I fully understand the workings of the RLM.

I think the advantage if the second option over the first is that there would be no train movement restrictions thus leading to more flexible running of loco's etc while at the same time not loosing anything as both layouts look very similar. It also introduces the use of a TT which looks like a fun thing to have. Does anyone prefer one layout over the other? Cheers the Porkster

[Porkster]

Ha Ha , I used the yellow to brighten up your day, cheers

[Chrissaf]

I don't think I fully understand the workings of the RLM.

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Porkster and anybody who is interested,

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How a RLM works.

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Put simply, an RLM is a current sensing device. The DCC Signal is a digital square wave with an average frequency of about 7Khz to 12Khz [One Khz (kilohertz) is 1,000 cycles per second]. The digital square wave is a form of AC (Alternating Current), because it is AC, the signal voltages changes (reverses) every half cycle, therefore it has no polarity. This means technically that the signal has phase instead of polarity. The DCC signal passes through a diode in the DCC decoder (rectified) to convert the alternating square wave into DC pulses. This is why changing the phase (reversing the DCC signal orientation on the track) does not cause the loco to reverse direction. The diode in the DCC decoder works the same regardless of the input phase of the DCC signal. The decoder counts the pulses and the measures the length of them (time base) to decode what the command being transmitted by the DCC signal is.

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Anyway, I digress.....getting back to the RLM theory.

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The DCC input side connects to the main track part of the layout, this could be a direct connection to the track or a direct connection to a DCC Bus. Because this connection routes back to the output terminals of the controller, its phase is fixed and never reverses.

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The output of the RLM connects to the protected section of track. The protected section of track must be electrically isolated from the main track layout, hence the need for the IRJs. Any current that is drawn by a loco on the protected section therefore must pass through the RLM. The phase of the DCC signal on the protected section will be in phase with the adjacent fixed track at one end of the protected section, but 180 degrees out of phase at the other end of the protected section. Which end is in phase and which end is out of phase can switch back and forth - see explanation below.

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Two scenarios can occur:

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First consider a loco passing from the fixed phase track to the protected track section at the track joint where the two opposing and adjacent track DCC voltages are in phase. Because both sections of track are in phase, there is no short circuit, thus just the normal loco current will be passing through the protecting RLM monitoring that particular IRJ track joint. The current does not reach the RLM trigger level and nothing effectively happens. The loco just continues on its journey as normal.

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Now consider the loco approaching the exit point of the RLM protected track section. At this IRJ joint, the opposing track rails will be at opposite phase. At the instant when the first wheel set bridges the IRJ a 'short circuit' will occur. As with any 'short circuit' the current being drawn will start to increase rapidly. If the RLM was not present, the short would cause the controller to trip out.

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Anyway, back to the plot.

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As said before. All current flowing into the RLM protected section passes through the monitoring RLM. The RLM will have a trigger current set. The value of this trigger current will depend upon the brand and model of the RLM, but in the UK is typically just under 2 amps.

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This is the reason that the Hornby 1 amp controller power supply used with the eLink and Select is not recommended to be used with NON Hornby RLM brands as the controller power supply will trip before the RLM trigger current is reached, the Hornby 4 amp power supply should be used. The Hornby brand RLM has a switch position for layouts using the 1 amp power supply.

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Back to the plot again.

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Once the short circuit trigger current within the RLM is reached. The RLM reacts by reversing the phase of its OUTPUT. The phase being reversed, now removes the short circuit condition at the loco location and the current returns back to the normal ambient background current being drawn. Because the RLM has reversed its output phase, the end of the protected track section that was originally in phase with the adjacent opposing track now becomes out of phase. Thus, the next loco to cross that end of the protected track section IRJ will be the one to trigger the RLM again.

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As trains enter and leave the protected section, the RLM switches its output phase through 180 degrees and back again to match the phase of the fixed track that the train is either leaving from or joining to. This switching happens extremely fast, we are talking micro-seconds. Not even a  sound loco will notice the phase reversal, and continue on its way without the slightest audio glitch or hesitation.

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A RLM will only work on a DCC layout. A DC based layout will need a different solution.

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[poliss]

Phasers set to stun. 😎