# Not-quite-a-wye DCC question



## riderdan (Jan 2, 2014)

I've actually poured the concrete and have the track laid out on my "Not-quite-a-wye" that I asked for input on in another thread. I decided to flip the orientation, as it eliminated a reverse curve from the inner loop of track.

Here's the current layout:









The track labeled with a green "C" on the very bottom is the main-line loop of my layout. The track labeled with the blue "A" is an inner loop that goes past my industries. This will allow me to run two trains simultaneously without having to do collision detection, detect occupied blocks, etc. In front of my station and service yard are a set of crossovers that would allow a train to switch from one loop to the other, if that were needed/desired.

The Not-quite-a-wye (labeled with the red "B") will allow me to reverse trains without resorting to the "hand of god" method--and I just think it looks neat 

Anyway, in tracing this out for DCC, I believe that the entire section labeled "B" needs to be isolated from the rest of the layout and attached to a DDC reversing module. Before I start putting on track joiners, I thought I'd get some input from the experts here. If more (or less) needs to be isolated, please let me know!

Thanks,
Dan


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## East Broad Top (Dec 29, 2007)

How do A and C connect? As I trace it, the topmost rail of A (as seen at the lower right) becomes the lowermost rail on C below it. If those two tracks are joined by a turnout, that will result in a short, and then "B" will need to be isolated by a reverse loop module. I'd place the gaps at the B-C switch and also just south of the diamond crossing. 

If they do not connect, or connect via a 180-degree horseshoe, then there's no reverse loop and you're good to go. 

Later,

K


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## riderdan (Jan 2, 2014)

I guess I should have posted a clearer overview of the whole thing...










From what you're saying, I think the take-away is that "B" needs a reverser


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## Totalwrecker (Feb 26, 2009)

ABC through cross over is a 3 sided wye= SHORTS


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## East Broad Top (Dec 29, 2007)

Yep. Isolate along B just after the switch where it leaves C and just south of the diamond crossing. If you're running long trains with lit coaches, you want to make sure you can fit the entire train inside the isolated section between those two points. If you can't, then consider modifying the diamond crossing so the two tracks are electrically isolated from each other. (They may be already.) If you do that, then the entire "B" track can be isolated. 

Later,

K


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## Greg Elmassian (Jan 3, 2008)

use isolated crossing and use autoreverser on a and b.... b alone is too short.

greg


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## Dan Pierce (Jan 2, 2008)

Or make B longer by going inside A farther or crossover B and connect up to C.


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## riderdan (Jan 2, 2014)

Thanks for all the input.

B is long enough for my longest train to pass through without touching C and A at the same time (I tend to run short, 5-6 car trains, since my layout is small) and the crossover is isolated. So is putting the reverser on B enough?

D


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## CliffyJ (Apr 29, 2009)

One other question Dan, will you use automatically-thrown switch machines, and if so, what kind? Just curious.


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## Greg Elmassian (Jan 3, 2008)

Technically if the section is longer than the longest train, B would be fine. 

If you just run one train at a time, no issue.

I would do it differently so on the occasion I ran longer trains, or more than one train in the inner loop, it would be better doing A and B my opinion.

Greg

Greg


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## riderdan (Jan 2, 2014)

CliffyJ said:


> One other question Dan, will you use automatically-thrown switch machines, and if so, what kind? Just curious.


Cliffy,

The switches are manual at the moment. The crossovers from the main line to the inner loop, and the one switch from the mainline that's a leg of the wye, are all within about one foot of the edge, quite reachable. The switch that's farthest away is the one at the top, where A and B come together. Luckily, I'll only ever throw that in the case of a "reverse"--so it's no problem at the moment. There are also two sidings for "industries" (my motorcycle factory and a lumber mill) but at the present I'm not actually doing any operations, so they're not being used.

I was following your thread about remote-mounted switch actuation with some interest, as I really don't like the looks of the LGB/Piko/Proline drive mechanisms. I think I mentioned on there that I've been trying out different ideas--but I'm still undecided. My current thought is a take on what you did: I'll use a servo to drive a stainless rod inside a brass tube for actuation. I'll rigidly mount the tube to the structure that houses the servo and the ties at the switch to reduce play. I don't have any awkward places where I couldn't fit a trackside building within 12 or so inches of the switch. If the brass tube is down near ground level, the groundcover should cover it quite handily.

There was no hurry until all the switches were in.

Also, I'm leaning away from using DCC (only) to control the switches. On one hand, I like the idea of being able to set routes or throw the switches from the cab, but it seems to me that the mechanics of "select accessory mode-->enter accessory address-->throw switch-->return to locomotive control mode" is rather cumbersome. So I think I'm going to get a couple of the Tam Valley servo/decoder units that allow for an optional physical button to throw the switch. Then I'll remotely mount the units in track-side structures, and put buttons in "panels" set into the side of the raised bed so I can throw them "by hand" when that's preferred.

I'm not terribly close to doing any of this, of course. I have more landscaping to do (I can't ballast/level the whole thing until the dirt's at the right level), a mountain to build, several locos to install decoders into, four structures to work on, etc. Plus my Christmas train (composed of an LGB locomotive and some New Bright cars, and my "bubble elephant" car) needs to be done in a month or so.

Maybe when it's too cold to work outside this winter, after Christmas, I'll take another stab at it.


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## riderdan (Jan 2, 2014)

Greg Elmassian said:


> Technically if the section is longer than the longest train, B would be fine.
> 
> If you just run one train at a time, no issue.
> 
> ...


Thanks Greg. I would only ever run two trains in roundy-round mode, with one doing the outer loop and the other the inner loop, and never the twain shall meet. My longest train is my LGB mallet, a baggage car, and three passenger cars. The whole thing easily fits on the reversing section.

As an update, I hooked up the reverser and everything worked fine.


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## JackM (Jul 29, 2008)

I've always seen it written that the length of the isolated section must be longer than the longest train. Am I correct that this is a somewhat overstated "rule"?

The isolated section need only be longer than the loco or locos that will pass thru the isolated section, lest they short. If the rest of the train is merely, say, a line of boxcars with plastic wheels, there is no concern as to where they are. Correct? The only exception to that is if it's a passenger train with lighted cars. Correct?

I feel that I'm missing something. The bunch of boxcars (presuming they have plastic wheels) can't short anything, so I don't see a problem. Metal wheels momentarily bridging the gap between sections would the be the problem?

I don't want to hijack this thread, but it seems that a lot of layouts COULD get by without a lengthy wye if willing to avoid metal wheels. This would be helpful for layouts under the Xmas tree. No?

JackM


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## riderdan (Jan 2, 2014)

Jack, that's a good question. I agree that is seems like the only thing that requires reversing is the locomotive, so as long as the isolated section is longer than the length of the loco wheelbase, it would be OK.

One thought I had was that some people have pickups on their cars that provide extra contacts for their locomotive (through the LGB power plugs, for instance) so that might be an issue. I run a car like that behind my LGB Mallet because it only has wheel brushes and can have pick-up problems sometimes.

Hopefully someone who knows will chime in.


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## Totalwrecker (Feb 26, 2009)

I imagine a lighted caboose could reverse the polarity at a bad time.....


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## Greg Elmassian (Jan 3, 2008)

Jack, you are a good study, you are exactly correct.

Even a single car that might momentarily trip the reverser won't always cause an issue.

It's basically if you are shorting TWO sets of insulated gaps at the same time. Even then good autoreversers will just wait a bit and come back, since good ones also have short circuit protection. The trains might stumble a bit.

Remember that a DCC loco's direction is irrespective of the "polarity" of the track, it can adapt instantly to a reversed polarity. All that really happens is an interruption to the current data packet it is receiving.

Greg


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## CliffyJ (Apr 29, 2009)

Greg Elmassian said:


> It's basically if you are shorting TWO sets of insulated gaps at the same time. Even then good autoreversers will just wait a bit and come back, since good ones also have short circuit protection. The trains might stumble a bit.
> Greg


That's interesting Greg, I'd not thought about that. I stagger my rail joints just to help the curves be smoother (with flex track). But the PSX-AR units perform flawlessly, when one wheel crosses the gap, and then (after a pause) a wheel (on a different axle) on the other side.

For testing the autoreverser and wiring and whatever, on a number of occasions I've used a screwdriver or some other metal thing close to hand, to bridge the gap between the insulated rails either on the same side, or on opposite sides. The reverser has always cooperated. One touch was all that it took to trigger the phase change. I have turnouts controlled by this process, so it's easy to see.

Rather than a timing-based circuit then, I suspect that upon encountering one bridging of an insulated gap, the reverser detects whether the phase on the other side of the gap is in alignment. If not, the reverser brings the loop's phase into its opposite state. In other words, it is detecting a phase misalignment, and flipping the loop's phase such is dected. Any subsequent bridging, even on the other rail, merely confirms that phase alignment is already in place. Just my guesses though, you're far more knowledgeable in all this. 

To Jack's great point, if the train is longer than the insulated gap, each wheelset beyond the borders of the insulated leg (on either end) would feed the reverser conflicting signals. I guess that a short will close things down in that case. But if not, either the earth's core, or maybe some circuitry on his layout (I forget which) might collapse, and it'll be Jack's fault. 

CJ


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## Greg Elmassian (Jan 3, 2008)

The PSX-AR is very smart, the best on the market, evidenced by how many clubs use them. It will even handle nested reversing loops.

You are exactly right in your assessment of how it works Cliff, although most people do suggest you do not stagger the insulated joints.

From a practical perspective, if nothing else is "trying" the autoreverser, the reverse will happen (if needed) at the first insulated joint "hit" after that, then everything is already in the right phase, so the next insulator "hit" in a "staggered" setup does nothing.

Greg


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