# Reverse loop??



## Sehender1 (Jan 21, 2015)

So crossovers have a me a bit confused when it comes to reverse loops. 
I'm using Bachmann #6 crossovers, and have plotted out what looks to me like a reverse loop... but I'm not sure.. 
I think it's a reverse, starting at the far left, where the turnout abuts the vertical crossover, and ending where the right turnout abuts the left turnout just past horizontal crossover in the middle. 
Is that right? 
Any ideas? 


Also: I'd be hooking this up with an auto-reversing module. Are there any limitations with that? If, for instance, there were more than one train inside the reverse loop, would that cause a problem? 










Many thanks in advance of any advice!!!


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## flyboy2610 (Jan 20, 2010)

You do indeed have a reverse loop. I can't be much help with the wiring, though, never having used one.


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## DonR (Oct 18, 2012)

I Agree with Flyboy...it is a reverse loop created by
the crossover. 

It would not be good to have two locos in the
reverse loop at the same time. Actually, the
problem is when one loco spans an insulated joint,
and the other loco does it also you would
have a short circuit.

To avoid that you want to have an isolated section
long enough for your longest lighted passenger train,
but no longer. That would likely avoid the 2 loco problem.
It would be your choice anywhere in that loop.

The isolated section would be fed by a reverse loop
controller.

We had another crossover caused reverse loop situation
last week that was resolved by using a Double pole double
throw relay controlled by the crossover motors instead
of a reverse loop controller.

Here is the drawing and resolution of last weeks 
reverse loop.

http://www.modeltrainforum.com/showthread.php?t=30193&page=2

RT Coker's black/red drawing shows how it was done.

Draw your layout using RED for the outside rails and
BLACK for the inside rails. You'll see where there is
a 'short' when either crossing is set to divert.

We may have to do something similar with this layout.

Don


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## Sehender1 (Jan 21, 2015)

This is super helpful.. 

So, another question: Can I just arbitrarily limit the size of the reverse "loop"? 
In other words, drawing on the example I have here, what if the "loop" were nothing more than the length of my longest passenger train, for instance, along the left side of the drawing? 
Say, above the right turnout at far left, but no further than the last straight piece along the top of the layout? 










The idea, if I'm understanding, is to switch polarity BEFORE you create the mismatch... As long as the "loop" section is long enough to fit one train, it doesn't need to be any longer... right? 
Shortening to that length, and placing in that position, would also eliminate the chance of more than one train being in the loop. 


Let me know if I'm off-track here.. (sorry for the pun! lol)


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## DonR (Oct 18, 2012)

Your layout's reverse loop problem is complicated by
the two crossovers. As I suggested, redraw your layout
using Red and Black pencils for each track rail and you'll
see that there is a polarity conflict when you set the points of
either turnout to cross over. 

Your layout is actually one large loop as was last weeks.
If there were no crossovers there would be no polarity
conflict. 

Normally, a crossover is between two parallel tracks where
the left rail of both tracks is BLACK and the right rail of both
tracks is RED so there is no conflict. Your parallel tracks are 
really two sides of an oval, thus the two tracks are of
opposite polarity.

If the two crossover tracks were long enough they could
be isolated and fed by reverse loop controller, but cannot
be as drawn.

I'm still mulling just how to overcome the problem. Anyone
with an easy solution chime in.

Don


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## Sehender1 (Jan 21, 2015)

Yes - I think I see. 

So if you consider the section bounded by the two crossovers as the main line, with regular polarity on the crossovers, I think the solution becomes clear. 

If you trace around the loop with red/black, the conflict comes in just one spot, just above the vertical cross over on the left, where the right turnout is. 
The leg that goes off to the right, back into the "main loop" is just fine. But where the other loop comes down into the straight leg of the right turnout, there's a conflict. So isolating a section of that other loop is probably the solution.. 
I'll prob take the layout to a guy here who's really great with these kinds of questions, and ask him... 
but the red/black method makes great sense to me..


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## johnfl68 (Feb 1, 2015)

Don,

If the section in the top left did not connect to the two crossovers (pretend it isn't there for a moment), then there would be no issue with the crossovers, correct? Assuming they are wired with the parallel tracks red black red black as you would normally do for any dual track situation.

So if the section of track that is in the upper left (I assume the breaks in the track have just not been filled in yet) is the length of his longest train, why not make that section the reverse section? Wouldn't that work?

John


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## Sehender1 (Jan 21, 2015)

johnfl68 said:


> Don,
> 
> If the section in the top left did not connect to the two crossovers (pretend it isn't there for a moment), then there would be no issue with the crossovers, correct? Assuming they are wired with the parallel tracks red black red black as you would normally do for any dual track situation.
> 
> ...


What John said... I think he's right.
The problem doesn't occur until the left section comes back down into the "regular loop." If I isolated that left section and had the trains switch polarity there, it should work... right?? lol.


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## DonR (Oct 18, 2012)

No guys. As you can see below. If there were no
crossovers you would have a simple oval. However,
the polarity mismatch occurs
when you set the points of either of the turnouts to divert.

It's a poor drawing but you can see the problem.

The GREEN marks are where insulated joiners go.

Remember: Everything below the turnout pair, lower left
is a loop thus completing an oval.










This is the first thought of how to do it:

The entire lower loop would be MAIN.
The lower right hand track would be MAIN up and
around the curve to the next GREEN mark.
The Short middle track between the GREEN marks
would be MAIN. (the reason is you can't have the
isolated loop abut itself)
The entire upper loop would be isolated and fed by
the REVERSE LOOP CONTROLLER.
It is entirely far too long and invites a short circuit
if a 2nd loco enters the Isolated section.

I'm not at all pleased with this solution so if any of
you see another method, chime in.

Don


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## johnfl68 (Feb 1, 2015)

Don:

Like I said, don't think of it like a loop.

If you take the track section that is separate in the upper left corner, and just pretend it isn't there, then how would you wire the layout?

Everything would be a normal dual track layout (where the crossovers are) that goes to a single track layout past that. Everything would be wired normally.

Now you add the upper left section as the Reverse section, it is the ONLY part that would need to flip track polarity.










Sorry for the quick crude drawing.

John


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## Sehender1 (Jan 21, 2015)

Ok. So MY art is worse, but tell me if I'm wrong here. 

If I didn't have the reverse in play at all, this is how the wiring would look for this layout. Essentially a straight line of track (with a curve, yes) with two crossovers at either end. 










I don't think crossovers are wired so that either side is opposite polarity. (red is not on the inside of both sides of the crossover, for instance) Or so that when the points are diverted, they are. They connect the black to black, and red to red, and insulate contact with the opposite, right? 

So all I would be doing here, by adding the loop, would be reversing the polarity of that "loop" section before it comes back around to meet up with the original loop. 
Like so: 









I think this is what John is saying would happen. It's also in line with the idea that the crossovers don't switch polarity - either on their own, or because of the loop, which will be totally insulated from the "main loop". (On the drawing, there should also be a line, for spacers, on the far left of the drawing, above that right turnout.) 

AGain, apologize for the drawings.. lol.. 
This is fun, and I really, really appreciate the help..


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## Sehender1 (Jan 21, 2015)

johnfl68 said:


> Don:
> 
> Like I said, don't think of it like a loop.
> 
> ...


Again: John on the spot with a much clearer drawing. But essentially the same thing I'm arguing. Thanks!


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## DonR (Oct 18, 2012)

Nope guys.

Your red/black drawing is wrong
in the lower left.

You are showing the rail polarity as if the
tracks at the lower left crossover were
parallel. They are not. The right track is actually
the return of the left track after it has gone around
the loop. Thus, the BLACK OUTSIDE RAIL of the left track
should be the same COLOR as the OUTSIDE RAIL of
the right track. 

To prove this simply draw a simple RED/BLACK loop below that
lower left crossover. Then you will see the conflict. For
purpose of illustration: The outside rail should be BLACK 
all the way around the entire LAYOUT MAIN LINE. The Inside
rail would be RED. 

Now, if I have misinterpreted your partial original drawing and
there is no loop connecting the tracks in the lower left I would
take another tact. Tell us what is below where the track drawing
ends. Is it a loop or do the tracks come to an end somewhere?

Don


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## Sehender1 (Jan 21, 2015)

ok. 
Actually, I think that's not right, Don. 

AS I showed in the first "drawing," if you don't have the top portion of the layout at all, you'd have NO problem. And if you insulate the "return" of that one track from the lower crossover, you're not introducing a problem. 

Isolating that left top of the track (and inserting a reverser in it) eliminates the polarity conflict. 

Again - the key is looking at it WITHOUT the reverse loop. My former layout (now dismantled) had something quite similar to the setup without that loop. Polarity doesn't reverse inside the crossover, unless it is connected to the reversing loop. Insulating it from that loop keeps the crossover in the main. Right???


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## johnfl68 (Feb 1, 2015)

I don't know how else to explain it. It's not a loop, it's closer to a wye.

I don't know why you keep trying to make it a loop, the tracks in the lower left are parallel.

I give up.


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## DonR (Oct 18, 2012)

John, hang in there.

Sehender:

What does the layout look like in the area below
the bottom crossover? On your drawing you simply
show the tracks ending at the crossover and I'm
certain that is not the case.

Draw the complete lower layout for us and connect
it to the drawing we've been looking at. 

That missing information is why we all three are not on
the same page. We are each 'seeing' a different layout.

Don


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## Sehender1 (Jan 21, 2015)

Thanks for hanging in with me, Don. Obviously want to get this right. 

So, below the cross over is a second, independent reverse loop, that would be wired separately, with its own reverse module.. 

I've stripped down much of the rest of the layout to show the various "districts" that would be created. The red lines mark the beginning and ends of the small "reverse loop" sections in the layout.. I didn't show the bottom of the layout initially because I KNEW that was a reverse loop, and had to be wired that way. My question was really about the top section.. 

I'm fairly certain this is right.. But again, very interested in your opinions, Don, and in John's.


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## DonR (Oct 18, 2012)

Pre she ate getting all of it.

But, it is what I thought you were doing.

Again, in utter simplicity, you have one big 'oval'.

If it were not for the crossovers you would not
have a reverse loop.

Now, draw that lower loop in Red and black to
meet the upper section. That is where you find
that the black outside rail on the right track of the crossing
is opposite to the black outside rail on the left track of the crossing
as in my red/black drawing. Thus when you set the points
to divert (cross over) you encounter a short circuit...Red and Black
meet. It does the same in the middle track to oval crossover.
This is why using a simple short isolated section somewhere in
the upper loop is no help. We have to resolve the mismatch
of polarity at the crossovers.

The isolated section created by the FIVE insulated joints
in my drawing is far too long. 

Here is my suggestion to keep your basic plan but shorten
the isolated section. We move the crossover from the
middle track/oval connection. Place it just above the lower crossover
creating a double crossover. The entire lower loop would
be MAIN as would the right hand track up and around the upper loop
to a point near the upper left hand curve. The ISOLATED 
section would be ONLY the lower left hand turnout and all
tracks upward to where we want it to end. 

It would require insulated joiners just below the lower left hand
turnout, between the left and right hand tracks at the right
lower right hand turnout and finally at the point in the
upper loop where we want the isolated section to end.

The double crossover created would give you either way
access to either track as well as full reversing action.

If you wanted the middle track to have a 2nd exit to the
Main, connecting it to the topmost track would maintain
the polarity but would require another insulated joiner
at it's left turnout since it will be same polarity as the main.

Would this work for you?


John:

We now know that the previously not shown bottom part of
the layout is a simple loop which makes the entire layout
one big oval with the crossovers creating the reverse loop.

I truly understand where you are coming from. You are thinking
of a crossover in the usual track situation where there are two
parallel tracks, each having a red right rail, and a black left rail.
As you see by my drawing that is not the case since the parallel
tracks in this layout are actually two sides of an oval, thus, as in
my drawing, the left rail on the left track is black and the left rail
on the right track is red. Thus when the crossover is set to divert
you encounter a short. The middle track and the crossover to 
the oval are the same conflict as the lower crossover.

Don


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## Sehender1 (Jan 21, 2015)

Ok. 
Going to try this again.. I think I see what you're saying, but what you're not accounting for is the SECOND reverse loop that's included at the bottom, which solves the red/black switching problem. 

So... let's start from the beginning. 
Here's the layout without the reverse loops.. Essentially, if you eliminate the curved rails, you'd just have a straight piece of track. 
Can we agree that THIS layout would require no special wiring? 









Red and black never get switched here... Even when the points in the crossovers are set to divert, you're not creating a reverse loop... 



Ok. 
Now let's add the loops, both of which cause a conflict, switching the position of red and black and introducing short circuits. 
BUT... to prevent the shorts, we add insulators at the points of the red lines, and wire the two newly created sections with auto-reverse modules. 









Does this make sense???


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## Sehender1 (Jan 21, 2015)

Here's another way to look at it.. with the red/black layout.. 

First, the layout without any loops in it.. 









AGain, no need to resolve any potential shorts in this layout. Even with the crossovers diverted, this layout works without special wiring. This would be the main power district. 

Now, let's add the loops: 








This, of course, would cause a short on both ends if you just hooked the track up. But by insulating at the points of potential conflict, and wiring the two separated districts with an auto-reverse module, we mitigate the shorts. THey don't happen.. 
Your theory is that, when the crossovers are diverted, they're creating their own switch in polarity. I'm not sure that's so - pretty sure they're insulated to keep red and black from touching, or switching. 
But even if they WERE doing what you're saying, it wouldn't matter, because the districts where the polarity is flipped are completely insulated from the section with the crossovers. 

Right?


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## DonR (Oct 18, 2012)

Yes I do agree.

If you have the 2 isolated sections, each controlled by a
reverse loop controller as shown in blue on your
drawing, your layout would work fine. You would want
each to be long enough to accomodate your longest
lighted passenger train.

By using those 2 isolated sections you can then make the
crossovers actual parallels with the rails of both tracks the same 
polarity, thus eliminating the mismatch when points are diverted.

Don


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