Reverse loop re visited

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M

maczimb

Member
I am now in a state of total confusion.
I am in the process of converting to DCC.
HO is my scale.
I would like to use a reverse loop on my layout so that I can reverse direction without doing it by lifting and placing.
I understand the problem of "reverse polarity"
One guy I talked to said something about an electronic under table gismo and the polarity is automatically reversed when a loco passes over the area.
Guy number two said that I don't have to do a thing once I have installed DCC, this sounds real hokey to me.
Third guy had a near stroke when I mentioned REVERSE LOOP, "don't ever get into that area". However after some thought he relented and rambled on at length about a very expensive and complicated deeeee vice.
I have read some bits and pieces on the subject but I find all the articles a bit wordy and I come away more confused than when I started.
HELLLLP
Mac
 
its maybe 30 bucks or so at tonystrains. It does it all for you, it just swaps the polarity of the track. You can have the whole loop isolated and hooked to it, or a section that is a bit longer than your longest consists.

Somebody was pulling your leg as to the difficulty of it.
 


There are any number of auto reversers on the market. With DCC, it's just a matter of connecting four wires, two each at the entry and exit points of the reverse loop. It's dead easy and reasonably inexpensive. Whomever those three guys are, don't waste your time talking to them about model railroads again. :)
 
From article in Model Railroad News Vol 15, issue 4, May 2009 page 82 titled "My Conversion to DCC: part2: Preventing Short Circuits"

Autoreversers come in 2 models
- adjustable (cheaper), potentiometer to tune, if locos user varying amounts of current this will fail
- fixed (2x price)

I think the author said they tried the cheaper units and couldn't get them to work reliably for all his engines. The author users more expensive fixed, DCC Specialties PSX-AR model.
 
could someone explain this a little more?

i understand that the rails of one end of a rev loop will be of opposite polarity of the main line, and the polarity needs to match before the engine (or any other car with electrical contacts) spans the end of the rev loop and the main line.

does the gadget reverse the power of the reverse loop or the main line?

does it sense which end an engine is entering a rev-loop before it enters it from the main line?
 
For what part gets reversed...it's the part you connect the auto reverser to.

If you left the reversing loop wired statically, it would stay as wired. If you wired in the reverser to the rest of the layout, that part would get reversed by the AR when it deemed it necessary. Most of us reverse the loop itself to keep things localized.

Second question...the reverser only senses a problem where it is wired in to do that. So, let's assume you have elected to follow convention and wire it to the rails comprising your reversing loop...only. When a metal wheel crosses either gap, no matter which end, and there is a polarity mis-match, the AR automatically reverses the loop...which is what we agreed it would manage...only.

Say you ran a train successfully out one end of the loop. Doesn't matter if the AR had to reverse the loop....forget what the AR did last time...it'll remember on its own because it is reading both parts of the layout concurrently...in real time. Let it do the thinking!

Now, a day later, you run a train across the last gap crossed, but it is coming from the opposite direction...into the reversing loop instead of leaving it. Follow me?

In order for the last train, yesterday's train, to successfully cross that gap, wouldn't the polarity have had to be the same across the gap? Yes. And would it have changed for any reason if you had not used the loop since then? No.

So, our today's train encounters the gap and crosses it without any changes anywhere...the AR senses that the polarity was as it left it the previous day...properly aligned. Nothing happens and your train trundles into and down the length of the reversing loop.

Now we'll pause a bit and recall that the main tracks, the rest of the layout, does not change. The polarity is always what it is. So, when today's train gets around the reversing loop and encounters the far set of gaps, won't it encounter a reversed polarity if the first gap it just crossed was alright? Yes, it will. If the loop is a true reversing loop, and the main tracks always keep their polarity orientation from rail to rail, then one of the gap crossing must, by logic, be a faulty one.

So, our today's train attempts to bridge the far gap (by which time the rails will be mismatched [or reversed in polarity] with the ones on the other side of the gap). For a brief microsecond there is still a short, but the AR quickly detects it, and it changes the loop tracks to match those of the oncoming main layout rails that the train is entering.

It is a nifty device, and you would be well-served with a PSX-AR or something similar.

-Crandell
 
Another question. Do these electronic boards (auto-reversers) work on DC, or only on DCC? I'm really hoping somebody says DC.
Tom
 
Yes, the Circuitron AR-1 Automatic Reverser can be used to control polarity on DC reverse loops. You can read more about it at http://www.bakatronics.com/shop/item.aspx?itemid=498. It's vital that you run it off a good filtered 12 volt power supply, whcih you will have to buy in addition to the AR-1. Trying t run it off track power will smoke the electronics in about five seconds.
 


reverse polarity re visited

Thanks for all the info on the subject but I'm not done with the questions so please bare with me.
I have a sort of dog bone layout, the middle section is about 30" front to back and 72" left to right. In that area I have a west bound line and an east bound line running parallel, about 24" apart, connected on both ends by large sweeping curves.
I would like to link east line and west line with a short, diagonal section, thus enabling me to reverse direction.
I would like the reversing of polarity to happen in the short diagonal area (isolate that short piece of track) I have a bunch of stuff going on within the two large sweeping curved areas and I don't want to create any problems there.
I will install the necessary doohickies mentioned earlier
I hope my description is clear enough.
Thanks again guys.
Mac
 
Mac, I'm not clear on what you have. Is it two completely separate mainlines and now you want to add what sounds like a crossover so you can get from one line to the other? If so, that's not a reverse loop but I fail to understand how that will allow you to reverse directions. I'm kind of dense at times so a sketch or track plan would help.
 
Hi Jim.
Thanks for your response.
Let me try again to splain it.
Imagine a large obround (oval with parallel sides) track, squeezed in the middle until the two sides are within 24" of each other, then cross over from one side to the other.
I'm not conversant enough with posting pictures and not a very good photographer either.
Hope this clears it up.
Mac
 
There is one critically important matter that arises from your last post.

When the AR reverses polarity, the entire metal-axle componentry of the entire consist must be within the confines of the reversing section....that is, between the two gaps at each extreme of the section the AR is manipulating. If you have part of an engine, or even a single pair of metal wheels on any car, bridging over to the adjoining, non-manipulated rails, you will have a very cranky AR unit. It will be confused, and electronics hate confusion.

Therefore, as my be becoming more evident to you, your tiny crossover at the pinch won't allow you to have a full-sized train safely contained in the length of the reversed track....that is, between the gaps at each end of it.

You'll have to re-thunk your approach to getting a crossover to change directions at the midpoint of your oval.

-Crandell
 
Sorry, Mac, I still don't get it. How will crossng over from one track to another change the direction the train is traveling? My pea-size brain tells me there are only two ways to change direction on the fly. One is a balloon loop and the other is a wye. A balloon loop is one which the train enters a loop and then exits the loop back on to the same track it entered from. This will both change the direction of the train and create an electrical reverse loop. A wye track has two branches that come off the mainline that join together in one track, called a tail track. Thus, a train can enter one branch, go up the tail track, have the switch thrown for the other branch, and exit and change directions. This is also an electrical reverse loop. You must be doing one or the other to change the direction of your train.

You can do a rough sketch in Paint and then upload it here. Maybe Crandell has a better idea of what you're trying to do but not me. :confused:
 
Jim, depending on his initial direction of travel around the oval, he can either drive into the diagonal that connects both sides of the oval and reversed himself that way, or pass a reversed point that leads to the diagonal on the diverging route and reverse through the diagonal to past the far set of points. From that position, he can take the through route and have effected his reversal.

At least, this is what I see in my mind's eye.

-Crandell
 
OK, I think I get it now. What he wants really is a modifed form of a balloon loop. As long as his crossing track takes place right at the end of the loop, he should be able to have his whole train inside the loop before he gets into polarity trouble. Having the crossing in the section where the tracks are only 24" apart is never going to work.
 
Well thanks a bunch guys.
I was sailing along, quite oblivious to the problems and you guys had to come along and burst my bubble.
I think I could learn to dislike you guys.
I guess it's back to the drawing board.
From all of the info I have gleaned, I believe I am now better equipped to achieve my REVERSE loop.
Thanks again.
Mac
 


Mac, I was posting while you were posting your picture. That's a big help to able to see what you want. I think it will work electrically but it's not a good idea operationally. Is there some reason you need to have that crossover go through your yard ladder? It's going to make it tough to do switching since the ladder will be blocked by through trains. Can you move the crossing track to the right so it is parallel to the yard ladder but not through it? I think that would work out a lot better operationally.
 
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