Configuring reversing loops in a balloon staging yard

[GaryHinshaw]

Those of you following my Engineering thread will recognize this topic.  I am starting to think through the wiring of the reversing loops in my staging yard and I'm trying to decide how many separate reversing circuits I need for flexible operation.  Here is a schematic of the yard (omitting a few impertinent tracks):

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There are 8 balloon staging tracks (numbered from 1 to 8 from the inside out), each of which forms a reversing section of its own.  The 4 leads converge to a double-track main on the left (not shown) and black here indicates fixed polarity up to the gaps.  The meaning of red & blue is described below.

The brute force way to configure this yard is one auto-reverser (AR) per balloon track because this gives operators flexibility to enter or leave any track with minimal regard to other trains.  The only polarity constraint is that you can’t bridge the gaps at both ends of a given balloon track at the same time.  Since all tracks are longer than the longest train, this is fine.  (Note that I can't allow a train to enter one end of a given track while another train is leaving the other end of that track, but I think that constraint is unavoidable and not onerous.)

Now do I really want to purchase and wire 8 separate AR boards?  It occurs to me that I can cut the number in half with no loss of functionality by pairing up neighbouring tracks, e.g. 1 and 2, behind one AR board if I feed them with the opposite polarity, shown as red and blue in the schematic.  Suppose a train is entering or leaving track 1 on the top side of the yard.  Then it is impossible for another train to be entering or leaving track 2 on the top side at the same time because the turnout is fouled.  However, it can enter or leave track 2 on the bottom side just fine, and if tracks 1 and 2 have the opposite polarity, the AR will be perfectly happy if both of those gaps are bridged at the same time.

Am I missing anything here, or can I cut my board count by 50% without loss of functionality?

[Ed Kapuscinski]

If you're not expecting trains running into and out of the yard at the same time, you can probably get away with a single AR for the whole shebang.

Remember, the AR doesn't reverse direction or anything, all it does is reverse polarity of the rails to sync things up with the next track section. The other tracks in the staging yard aren't going to care.

If you block it correctly (sorry, I can't see the diagram to tell you where), it can also provide a handy circuit breaker for the short circuit prone entry and exit yard throats.

Thinking about it a bit more, at worst you might need two: one for each throat. Make the middle of the yard "normal". And this will mean that movements from both ends can occur independently, and you'll have handy dandy circuit breaking for each throat. Just make sure that the AR block is longer than your power consists will be. Metal wheelsets might throw a monkey wrench in the works, but tiny insulated sections, like one wheel width, might solve that issue.

If a train enters one throat, and the polarity is backwards

[ednadolski]

oh no, getting the gray circle again... 

Ed

[eric220]

oh no, getting the gray circle again... 

Same here. No photo.

[GaryHinshaw]

I see the same issue when I clear my session, even though I'm using the exact same recipe I used for this post, and I still see those images.   

Google can go jump in a lake.  Please check back later.

added - I just deleted the image from Google Photos and re-uploaded it and relinked it in the OP.  Now it does show up for me even after clearing my session.  But I can't tell you that I followed a different recipe the second time.  This whole process is too unstable for my liking... -gfh

[GaryHinshaw]

To EdK's point (and assuming people can see the schematic now), in theory this yard could be quite busy with as many as 4 trains or loco sets in the throat area at any given time.  For example, one train arriving in the upper ladder, another one departing in the lower ladder, and locos being added or taken off a train in the third (and maybe fourth) ladder.  I think to maximize flexibility - i.e. to allow for all 4 ladders to be occupied independently without having to think about polarity too much, I want to have 4 AR's, one for each pair of red/blue tracks.  I think this achieves everything I could have gotten with 8 AR's and is quite manageable in terms of cost & complexity. 

I just want to make sure I'm not missing something with this choice.

Thanks!
-gfh

P.S. To Ed's other point, if I understood it correctly: I don't want to make the ladder sections reversible because they would be short blocks that a typical train would span.

[John]

Just make the approach blocks your reversing sections .. so -- two ARs at the most ... 

[C855B]

I'm with John. I think the approach blocks are where you want the ARs. Regardless of yard and ladder activity you can't have more than two arrival/departures... unless said ladder activity makes it to the first crossover bridging the throat.

But whadda I know, given the screwed-up mess I almost did to myself.

[GaryHinshaw]

We had a discussion about this option in the Eng thread (nearly two years ago now!).  The section labelled B in the linked diagram was a possible design, but the presence of crossover 2 limited the length of that block.  (And the actual plan now has 3 crossovers in that area, so even more complicated.) The long discussion that ensued convinced me that I was better off having the balloon tracks be reversible.

For the record, I'm fine with 4 AR's.  I just want to be sure I'm not limiting my operations too much with the solution proposed above.  I don't think I am...

[C855B]

... Here is a schematic of the yard (omitting a few impertinent tracks): ...

"Impertinent" makes me chuckle every time I read it. Yes, it's the #2 definition, as in "not pertinent", but my mind always go to the #1 definition of inappropriately bold or aggressive, such as "an impertinent child". So, you have some of your trackage back-talking or sassing you?

[GaryHinshaw]

So, you have some of your trackage back-talking or sassing you?

That's what I'm trying to avoid! 

[eric220]

That's weird. At first, I couldn't see the diagram. Then a couple of hours ago I could. Now I can't again.

[GaryHinshaw]

Just cleared my session and now it's gone for me again too.  Yet the other new images in that same album persist.  Google can kiss my  ! 

Flickr, here I come. Thanks to Ryan for posting a tutorial.

[mmyers]

Can't see the drawing. How many trins will be able to cross a gap where phase needs to be changed? that's how many reversers you would need. If there is only one throat that can only be used by one train at a time, the reverser can go there. Whole yard can be in the reverse section.

[jagged ben]

Gary, I'm going to assert that with your new track plan you only need 3 ARs:  one each for the outside throats, and one for the two middle throats, since the track arrangement dictates you can't be arriving/ leaving from both inside throats at the same.  You might need to fix the picture issue for me to know for sure and/or be able to show you, if I'm not being clear.

EDIT:  after looking at your trackplan again in your build thread, you might need a couple X blocks to make this really work, which may or may not be less trouble to you than another AR. 

There's also still the question of whether 2 AR's will fight each other if you somehow power route one of the outside tracks to both yard throats (even if a train is entering/leaving only one side.  Say if you want to leave one track lined for continuous running.