# Need help with auto reverse



## Papa&TJ (Nov 11, 2014)

Just getting started and could use a lot of help with our layout.

We have a situation were due to our cross over the polarity reverses. We are using Atlas code 83 track and DCC locos.

Please consider the following drawing and offer any and all help as to where to place the ARs if indeed we can use them.

So far we thought to maintain the tangents as the main track and auto reverse the "figure Eight".

Assuming the loco starts travel as indicated, as long as it remains on the "figure eight", all is well.

If the loco travels straight through switch #4 the tangent which is isolated will have an AR sensor at the approach to switch #3. flipping the "figure eight" polarity.

Continuing, the loco turns out at switch #1 and enters the "figure eight" all is well. If the loco travels straight through switch #1 onto the tangent which is isolated, an AR sensor will be placed at the approach to switch #2.

Does any of this make sense? Are we missing something?


----------



## fcwilt (Sep 27, 2013)

Assuming your trains are short enough to fit completely into the "diagonal" tracks then electrically isolate each diagonal from the turnouts and connect each diagonal to a AR.


----------



## Papa&TJ (Nov 11, 2014)

Thanks for your reply.
If by "diagonal" you mean the straights between the switches, does the entire train need to be on the straight? We thought only the Locos (or the intelligent device) needed to be in this area! We will other wise have to redesign this area to accommodate the expected train lengths.


----------



## fcwilt (Sep 27, 2013)

Yes I mean the straight track between the switches.


With the typical gaps or insulated rail joiners you would have in both rails at the both ends of the stretch of track ANY metal wheel that bridges a single gap will possibly trigger the AR.

That is why, without special consideration, the length of track needs to hold the entire train. 

If the train were longer then the length of track and the cars had metal wheels then it would be possible that a wheel was bridging a gap at both ends of the track at the same time. 

The AR unit would be trying to match polarity at both ends of the track - which it, of course, cannot do.


There are different ways to work around this problem but each approach solves the problem but introduces other problems of its own.


The only fool proof approach is to have the entire train fit into the section of track.


----------



## Papa&TJ (Nov 11, 2014)

Thanx again for the reply.

Since the straight section is isolated on both ends does that section of track need to be on a totally separate power source or can it be fed by the same main system power?


----------



## fcwilt (Sep 27, 2013)

You would connect the track power from your DCC command station to the power inputs of the two AR units.

The power outputs of each AR would go to one of the isolated sections.

AR units REQUIRE gaps in both rails at both ends of the section the AR unit is powering.


----------



## DonR (Oct 18, 2012)

As Wilt indicated there are work arounds so you can have whatever
length train run through a reverse loop without shorting.

One is to use a tiny dab of nail polish either side of the insulated
gap. That prevents metal wheels from spanning the gap and possibly
shorting. 

Another is to insert a tiny piece of plastic between the 2 rails so
that a metal wheel cannot touch both sides of the joint at
the same time.

And a third, while metal wheels offer better running, by using only
plastic wheels there is no possible shorting at the joiners.

However, if you have lighted passenger cars on a train long enuf to extend
over the 2 insulated joints you will have a shorting problem.

Don


----------



## fcwilt (Sep 27, 2013)

Don's suggestions can work in many cases.

However trucks with metal side frames or trucks designed for power pickup (think passenger car lighting) may have conductivity from one wheel set to another.

In these cases just preventing a short at the gap is not enough.


----------



## Papa&TJ (Nov 11, 2014)

Thanx fcwilt and DonR
Good info for starts.


----------

