Reverse Track/Loops Question

Model Railroader Layouts and layout building
1

I have read a bit about reversing in DCC and had a couple questions. I hope I word it correctly…

I read about reversing track on John Armstrong’s book so that a train doesn’t just go around an oval in the same direction all the time.

  1. Is this the same “Reverse” as what I am reading in this forum from time to time about having to wire DCC correctly in order for reversing to work?

  2. Do I have to wire differently if I want to have what John Armstrong talks about? I have a feeling that these are two different animals…

I guess I am not sure what the recent threads I’ve read mean when they talk about wiring for reverse so that it mirrors a prototypical situation…one person mentioned they received instructions from Tony at Tonys Trains about how to wire it properly…made me nervous that there was going to be a little more involvement in hooking up DCC.

Maybe someone could give me (or direct me to) a 101 class on “Reversing”. I just assumed you put an engine on the track and tell it to go forward or reverse no matter where it was on the track…

2

ANy time you have a situation where a train can head one direction on a section of track and then come back facing the opposite way, it is a reversing section. A turntable is an obvious one. So is a simple loop - connect both legs of a turnout and you can see how the train will go in one way and come out the other. A diagonal line connecting opposite sides of an oval will do this as well. A wye is alittle less obvious - it requires you to back up but if you trace the lines through it you will see that a train can go in on any leg and come back out on that same leg facing the opposite direction - thus it is a reversing section. As track plans get more complicated you can get reversing sections that aren’t so obvious at first glance, but they are all a variation of one of the basics. Another way to tell is to trace over one rail. It doesn’t matter which one, but pick one and trace over it and never lift your finger. If at any point tracing around the rail you end up touching the opposite rail, you have a reversing section. For example, a reverse loop is shaped like a P. Put your finger on the left rail of the leg of the P and start following it around. You will end up on the right rail in the leg.

–Randy

3

a Reverse loop allows a train to enter a loop in one direction and leave by the same track it came in on.
(OK, your track wouldn’t be a sloppy as my free hand drawing :slight_smile: )

It can be wired for DCC with an auto-reverse unit or you can use a toggle switch (see example below)

4

All good explainations so far guys. I’d only like add a web site to reference when working with DCC. It covers these issues and many more. Just about any question you’re going to come up with regaurding DCC is covered here: http://www.wiringfordcc.com/wirefordcc_toc.htm . Of particular interest to you will be the sections on turnouts.

5

May be redundant, as I haven’t read wiringfordcc.com, but here is another site with lots of good basic tutorial information. http://www.loystoys.com/MiscHTML/dcc-topics.html This is the Topics page, but you can navigate to his home page to see what else he has. He does do a lot of description on each product page, to tell you how to use it, what it is for, how to hook it up, etc.

FT

6

Thanks! One other question…I have narrowed my choices down to Digitrax (Zephyr or Super Empire…not sure yet) and NCE (Power Cab or Power Pro…again, not decided yet).

I see something in the Walthers Catalog about auto reversing capability…I think on both the Zephyr and Power Cab. Does that cover my needs?

I will definetly be doing some reversing on my track.

Another question on my two choices. I understand what happens when I enter in a 3rd engine with the Power Cab. What happens with the Zephyr system? I don’t think I will go beyond 3 trains on my 7 x 13 foot layout.

Mike/Nightshade

7

While we’re on the subject of reverse loops, I’ve seen the auto-reversers for DCC, but does anyone make one for good old DC?

8

I don’t think there are any commercial versions for DC available. In DC, the polarity of the rails provides direction information, in DCC it does not. For this reason, a DC auto-reverser cannot use the short circuit created when metal wheels bridge the insulated gap between rails of opposite polarity as a detection mechanism. A DC locomotive bridging the gaps of opposite polarity on the same rail will either try to reverse itself or stop (or both).

So a DC auto-reverser requires at least 2 position detection setups - the first to match the polarity of the reversing section to the main line before the train enters the reversing section, and the second to match the polarity of the main line to the train exiting the reversing section while the train is completely contained in the reversing section.

There has never been a standard way of doing position detection in 2 rail DC model railroading. There have been various train current detection systems (Twin T and successors), IR, optical, magnetic reed switches, and weight sensitive contacts used at one time or another. Very few of these detection systems have proved to be 100% reliable in practice.

And since each approach to the reversing section must have a detection system, plus the reversing section itself, making a “universal” DC auto-reverser would be impossible from a practical point of view. Also, the expense of the detection plus the relays or solid state switching unit to throw both main and reversing section polarity as required lead most MRs right back to Mark 1 eyeball detection and manually thrown direction toggle switches.

While given the time and $$, a DC auto-reverser is quite easily doable on a case-by case