I am using Digitrax for my 24'x24' around the room DCC HO layout. I would like to know if and how one wires reverse loops within reverse loops, crossovers, and runarounds. My Forum code name is HHPATH56 Bob Hahn
would be easier to help you if you could post a picture of your layout ... as "new eyes" may help you find that your "reverse loops within reverse loops" really aren't as complicated as you make them sound, and are in fact just one single reverse loop because they all connect at points 'A' and 'B'.
-Dan
Builder of Bowser steam! Railimages Site
Bob,
Mine is wired much the same as standard DC common rail. One difference being replacing DPDT with an automatic reverser, such as as AR, if you want--in some cases I still use the DPDTs. A LOT of people like to use a wiring bus. I do not, but have soldered rail joints in many places and feed blocks from when the layout was DC. We have over 300' of track and no power issues.
Richard
You use a device that automatically flips the polarity. Here is a page that discusses Reverse Loops and what you need to know about them.
The Original Poster's layout is very complex and apparently much or all of it was built before any of it was wired, if I understood his earlier posts correctly. He's posted this sketch of it many times:, but perhaps the layout has changed in the interim.
This will likely be pretty involved to untangle from a wiring perspective, with some reversing sections that may be shorter than a train length or which could be easily entered by multiple trains at the same time.
Although some people on this forum inexplicably object when a book is suggested, it certainly would not hurt to have the basic knowledge provided by a title such as: Basic DCC Wiring for Your Model Railroad: A Beginner's Guide to Decoders, DCC Systems, and Layout Wiring
Good luck.
Layout Design GalleryLayout Design Special Interest Group
cuyama Although some people on this forum inexplicably object when a book is suggested, it certainly would not hurt to have the basic knowledge provided by a title such as: Basic DCC Wiring for Your Model Railroad: A Beginner's Guide to Decoders, DCC Systems, and Layout Wiring
I am not one to object when a book is suggested, but I think it is safe to say that this fine book will not answer the OP's questions about wiring nested reverse loops.
If the diagram that cuyama posted is the OP's current track plan, then indeed it is a complicated layout for wiring purposes.
What I always find helpful is to draw a two-rail track diagram with a different color for each of the two rails. Anywhere that two different colored rails join together is a point of reverse polarity that must be resolved.
Rich
Alton Junction
richhotrainI am not one to object when a book is suggested, but I think it is safe to say that this fine book will not answer the OP's questions about wiring nested reverse loops.
Agreed, but it would at least give him the basics upon which to build. My sense from his earlier posts is that he has not had previous experience with DCC. Starting from a blank slate and trying to wire that layout would be daunting. With the book under his belt, at least the OP would know what others are talking about.
In any case, the best approach, though painful, for the OP may well be to eliminate some of the nested reversing connections -- which would have been easier before the layout was built, of course.
They key to a complex layout is being able to abstract the ideas presented in the basic wiring book to the more complex - to be able to see where those basic elements appear in the complex plan. That's the hardest part for most people. Drawing each rail in a different color without lifting the pen is probably the best visual aid. As for DCC or not, that's really a non-issue with reversing sections, a reversing section is a reversing section, DC or DC, and needs to be gapped the same way. The sole difference is that typically the 'polarity' is reversed in the isolated section with DCC whereas in DC typically the main is reversed after the train is in the isolated section and before it comes back out. There are of course a few exceptions, and in DCC it doesn;t really matter where you do the polarity match, since the 'polarity' does not affect the direction the train runs like in DC.
The reverse section should be long enough to accomodate the longest train with metal wheels and/or lighted cars that will run through it - you can't be matchign polarity at the entrance and exit at the same time, as would happen with the loco leaving the section while lighted cars or cars with metal wheels are still crossign the gaps at the entrance. There are some alternate options like making the reverse section extremely short which is mentioned in some places although seems to have largely disappeared.
For really complex situations they did add a nice feature to the PSX-AR that allows two autoreversers to be palced next to each other. Usually when you do this, everythign comes to a standstill as both reversers attempto to change the polarity and end up on oppiste sides - kind of liek a seesaw, only one side cna be up at a time. There is a slave connection option for the PSX-AR so that if they are wired like this, one will make the other one hold off on switching so they can reach a matching situation. For loops within loops, this is probably the best bet.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Howdy
Reading your post on this Randy was interesting. You mention a extremely short reversing section. I did this on my n scale project and it worked fine. I made it about 16" long figuring I would never have a consist longer than that. Unless I used a pusher from behind I guess. Just thought about that one. Anyway, I thought because all of my other wheels are plastic and I doubt I will ever have a lighted car I would be safe.
My wondering here is would it matter if other car wheels were metal and or lighted to the auto reverse module? It's not like they are wired to the dcc brains in the loco's. The trucks are plastic as well as the couplors so there would be no direct link. Still thinking here though.
Would it mess it up because with metal wheels and axles on the rails shorting out the signal. As in some of the metal wheels are in the loop and some are on the other side. Or both?
I hope I made some sense with this question.
By the way, Thanks for the info a few months ago on Tam Valley servos. They work very well on my turnouts. I bought the decoder and mounting brackets with them and was impressed all the way around.
Ron
The metal wheels can bridge a gap, justone wheel - and if the polarities are mismatched, the reverser will attempt to flip. SO far so good. But then when the metal wheel bridges the gap onthe other side of the isolated section - same thing. Now if the cars are spaced int eh train such that one metal wheel is bridging the entrance gap and one the exit - problem. Granted, pretty rare, even with a whole train of metal wheel cars.
There is yet another option to go along with this, that is making the gap longer than just a narrow saw cut - greater than the contact length of any wheel. You don;t want an air gap int he rail that long, every car will bounce and likely derail at speed, so the missing chunk of rail needs to be filled in with something. Or, and this is harder to keep together, probably, make 2 gaps a short distance apart. Short enough so the loco pickup wheels can span it so there are no dead sections to stall the loco, but longer than a wheel diameter. The center peice of rail will be hard to keep in place though when doing something like that. Also it used to be recommended for some autoreversers to slightly stagger the gaps, by about a wheel diameter, not like oen gap here and the other rail gapes 6 inches away. That depends ont he autoreverser being used, some tell you to be sure the gaps are as directly across from one aother as possible, others say the staggered approach will work fine.
I wonder when I look at CUYAMA's post of the OP's track plan if some of the curves and elevations are workable?
On the lower left the return curve seems to be drawn in approximately 2 1/2 feet diameter. If I am correct, that translates into a 15" radius.
In the center left there is a curve that is elevated over the yard but there appears to be less than six feet of track from the last turnout to where the loop crosses over the yard, and the radius of the curve seems to be about three feet. That is a steep grade, but I guess not impossible with short trains.
In the upper left and upper right corners there appear to be hidden loops with impossibly small radii.
It would appear that any switching in the upper most yard cannot be done without fouling the main. Likewise with the second yard from the top unless the tracks closest to the aisleways are not main lines.
All of my observations may be moot if the layout has been built and these issues have been addressed. If so, more power to the OP. I hope he posts some updated layout plans and pictures of his work.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
I am glad I am in HOn3 where there is nothing but a single track main and a giant yard has 4 switches.
On a 2 foot shelf layout, I can't have a loop or even a wye, just an old 54' turntable and a two stall engine house/ car shop.
The layout offered up here for study, crams a lot of stuff on top of itself. It makes my head hurt to even think about the reversing situations that present themselves here. Though, as mentioned, this would best be broken down into simple chunks to figure out what you have.
If I can't fix it, I can fix it so it can't be fixed
I'm trying to get a handle on this reverse loop wiring question. So I'll start with this posting of Randy's and as some questions.
rrinker They key to a complex layout is being able to abstract the ideas presented in the basic wiring book to the more complex - to be able to see where those basic elements appear in the complex plan. That's the hardest part for most people. Drawing each rail in a different color without lifting the pen is probably the best visual aid. As for DCC or not, that's really a non-issue with reversing sections, a reversing section is a reversing section, DC or DC, and needs to be gapped the same way.
They key to a complex layout is being able to abstract the ideas presented in the basic wiring book to the more complex - to be able to see where those basic elements appear in the complex plan. That's the hardest part for most people. Drawing each rail in a different color without lifting the pen is probably the best visual aid. As for DCC or not, that's really a non-issue with reversing sections, a reversing section is a reversing section, DC or DC, and needs to be gapped the same way.
Did you mean to say here DC or DCC?
The sole difference is that typically the 'polarity' is reversed in the isolated section with DCC whereas in DC typically the main is reversed after the train is in the isolated section and before it comes back out. There are of course a few exceptions, and in DCC it doesn;t really matter where you do the polarity match, since the 'polarity' does not affect the direction the train runs like in DC.
In other words the reverse section needs to be long enough to accomodate the longest train?What exactly happenswhen a multiple lash-up of locos comes to this 'reversing point',....with one loco over into the new section, while following ones have yet to arrive at that point??
And if you have a pusher loco at the tail end, what happens (or what accomodations are required for it??)
For really complex situations they did add a nice feature to the PSX-AR that allows two autoreversers to be palced next to each other. Usually when you do this, everythign comes to a standstill as both reversers attempto to change the polarity and end up on oppiste sides - kind of liek a seesaw, only one side cna be up at a time. There is a slave connection option for the PSX-AR so that if they are wired like this, one will make the other one hold off on switching so they can reach a matching situation. For loops within loops, this is probably the best bet. --Randy
Brian
My Layout Plan
Interesting new Plan Consideration
railandsail I'm trying to get a handle on this reverse loop wiring question. So I'll start with this posting of Randy's and as some questions. Did you mean to say here DC or DCC? If the 'polarity' does not affect the direction of the train in DCC, why is it neccessary to reverse the polarity? What exactly happenswhen a multiple lash-up of locos comes to this 'reversing point',....with one loco over into the new section, while following ones have yet to arrive at that point?? And if you have a pusher loco at the tail end, what happens (or what accomodations are required for it??)
If the 'polarity' does not affect the direction of the train in DCC, why is it neccessary to reverse the polarity?
What exactly happenswhen a multiple lash-up of locos comes to this 'reversing point',....with one loco over into the new section, while following ones have yet to arrive at that point??
2. Regarding polarity, under DCC power, a decoder must convert AC voltage to DC voltage so polarity becomes relevant. The signal running to the decoder and back to the command station cannot be interrupted or else a short will be created. So, it is critical to maintain the proper polarity in DCC.
3. Yes, in most instances, the reverse section needs to be long enough to accomodate the longest train.
4. When a multiple lash-up of locos comes to the 'reversing point' as you call it, with one loco over into the new section, while following ones have yet to arrive at that point, if the polarities don't match between the two sections, the auto-reverser will flip the polarity inside the reversing section so that the polarities do match. So, in your example, movement will not be interrupted since the presence of a potential short will be immediately corrected by the auto-reverser.
5. If you have a pusher loco at the tail end of a train, the lead loco will have triggered the auto-reverser so the polarities match as the pusher loco reaches the reversing section and no short will be encountered.
I hope that helps to answer your questions.
The key to understanding a reverse section in DCC is that the polarity will be reversed, if necessary, inside the reverse section. to match the polarity of the adjacent sections of track. I use the term 'if necessary' because polarity inside the reversing section will not always be reversed (or mismatched) relative to the adjacent sections of track. It all depends upon the track configuration that requires a reverse section.
Since the function of an auto-reverser is to match mismatched polarities, once the polarities are matched they may remain matched as the train exits the reverse section. Every reverse section has an entry point and an exit point but depending upon the direction of the train approaching the reverse section, the entry point and the exit point may be reversed. So, a train may enter a reverse section in which the polarity matches the section of track that the train is leaving.
When I first got into DCC, I too had to re-conceptualize what exactly was going on, and I think the following might help elaborate on Rich's point #2.
So we all know that on DC, 1 rail is always positive and 1 rail is always negative. Electricity therefore always travels from the negative rail, through the motor, to the positive rail. Its obvious here why reversing sections are a problem: if the reversing section is set to match the entry end, then on the exit end your positive rail connects to a negative rail and a short occurs when your loco hits that point.
DCC does still have polarity, with one rail you can think of as positive and one as negative. The important conceptual change is that that polarity reverses rapidly, on the order of 8 to 10 thousand times per second. But for any (and every) one of those given 1/10,000th of a second intervals, the normal rules apply: you have a positive rail and a negative rail, and in a reversing section, one end will be aligned with the next section of rail while the other end will not be aligned. Wait 1/1000th of a second, and your positive rail has become a negative rail, but this is true for ALL of the rails on your layout, and the mismatched end of your reversing section is still mismatched.
So that's my advice for conceptualizing what is going on with DCC wiring: basically, freeze time and call one rail positive and one negative (or rail A and B, or red rail and blue rail, etc).
Jason
This thread is almost six years old .... I'm really hoping the OP got his layout running by now !
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
Mark R. This thread is almost six years old .... I'm really hoping the OP got his layout running by now ! Mark.
Maybe originally, but railsandsails revived it with valid questions of his own.
Mark R.This thread is almost six years old .... I'm really hoping the OP got his layout running by now !
I missed that and went looking at the OP's old posts, hoping for a better pic of his track plan. Couldn't figure out why his posts were from 2014 and before.
Cuyama pointed out that it was built and indeed there are pics in his photobucket account of this ambitious track plan.
Maybe it's a function a wide angle lens, but I see kinks in a lot of his pictures and he did not protect his track work from plaster and scenic material spills
I made the same mistake on my first layout. Dried hydrocal is a pain to deal with on track work. I feel bad for the OP. 2" blue painters tape could have prevented that.
Henry
COB Potomac & Northern
Shenandoah Valley
There's definitely a kink and bad S curve on the far left of the double slip. ANd a really bad kink on the near left of the double slip. I think it comes from trying to get parallel to the other tracks too quickly.
On a complex plan with lots of reverse coonnections - I keep cooming back to my plan so far, which is your basic dogbone if unraveled. If I have say 6 crooossovers along the length of double main, I COULD have a lot of reverse sections. Or, yooou simplify and wire both mains the same, since with DCC the direction of travel of the loco is not dependent on the track polarity, which makes exactly none of the crossovers a reverse section in any way. The end loops are where the reverse sections go, just two of them (now that I have changed to plain linear staging tracks and just one loop around, instead of multiple concentric loops).
The operative word - simplify. Simplify whenever possible and reduce the number of reverse sections and thus reduce the number of gaps that are needed.
This is why re-animating these long-dead threads is counterproductive. Posters get caught up in the original post and the re-animator’s point (if he or she has one) is missed.
It wasn't my intention to bash the OP. I still feel bad for him as there is a lot of track work, buildings, time and energy that went into getting as far as he did.
It is informative in that too much complexity is a bad thing. And execution counts.
If he corrected the problems and figured out how to wire it, it would have still been tough to figure out how to get a train from point A to point B.