Re: Auto Reverse Segments in DCC



I realize that in a previous discussion we covered most of the questions about auto-reversing segments in DCC.  And I apologize if this is redundant.  

I understand that an AR segment must be longer than one’s longest train.  

Q.1.  Does that minimum AR segment length include steel-wheeled non-powered cars, e.g., metal-wheeled passenger cars without any decoders, lighting or powered accessories?

In practice, you will probably get away with longer trains with just metal wheels not connected electrically to other axles at least 99% of the time. In the remaining <1%, there may be a short reported - or not if you're lucky. If not, you won't even notice anything amiss at all. But it's still not a good idea. If you add in the system that some people use to stagger the gap between left and right rail (which I am 100% sure is pointless, but does no harm normally) then the 99% will drop significantly, in line with the length of the staggered bit.

I also understand that a non-reversing segment must separate two AR segments, i.e., two AR segments should not be connected directly to one another. 

Q.2.  What is the minimum length of the intervening non-reversing segment?  I believe I recall the consensus being at least the length of one’s loco (or multi-loco powered consist).  Is that correct?

That is certainly safe. Even one loco OF a powered consist is plenty. Shorter will work, but there is no set shortest distance. Stick to the length of your shortest loco and you'll be good (although if you push a train instead of pull things need to be looked into more carefully).

If the answer to Q2 is a distance shorter than the answer to Q1, why aren’t those answers inconsistent?  What is the explanation for the difference?  

Q1 is about how one autoreverser works, whereas Q2 is about preventing two AR sections  from in-fighting. It's like asking for the difference between inflation and the exchange ratio between dollar and euro. They are both about money, but there is no other relation.

I believe I recall that one can have more than one train in an AR segment at the same time, so long as no two trains are attempting to enter/depart the AR segment simultaneously.

Q.3.   Is that correct.   (In theory I understand why and am just seeking confirmation.)

That is correct. It's all about not crossing both gaps simultaneously.



Thanks in advance.  

Bill D
N&W Steam Only

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