Auto-Reversing a yard that enters the mainline in a WYE using DCC

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#1
I'm having some troubles coming up with a solution for this and hope that someone can help. I'm modeling the Central Midland, which is an Atlas track plan. The yard is attached to the double mainline using a WYE. Control is coming from a Digitrax Super Empire Builder. I've read about auto-reversing modules, such as the AR1(I'd like to stay with Digitrax products), that allow for polarity reversal by sensing differences in polarity as a truck enters a reversing section separated by an insulated track joiner. I see how this could work for my situation except for the fact that it claims only one train can be operated in the reversing section. I have two issues with this. 1) With this being a yard I need to be able to control 2-3 different trains at the same time which could be entering and leaving this area at any given time. 2)I've divided the layout, including the yard, into blocks to allow for block detection to be used for automatic signaling and automatic computer control in the future. What are my options?
 
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Iron Horseman

Well-Known Member
#2
've read about auto-reversing modules, such as the AR1(I'd like to stay with Digitrax products), that allow for polarity reversal by sensing differences in polarity as a truck enters a reversing section separated by an insulated track joiner. I see how this could work for my situation except for the fact that it claims only one train can be operated in the reversing section. I have two issues with this. 1) With this being a yard I need to be able to control 2-3 different trains at the same time which could be entering and leaving this area at any given time.
Well, I would say the dispatcher needs to be on their toes and not allow trains to leave the area simultaneously. OR As I recall that layout has a dual wye. Put one auto reverser on each one. Finally, this would be a worse problem in DC, how does the Atlas wiring instructions say to deal with it. Just replace their reversing switches with an auto-reverser.

2)I've divided the layout, including the yard, into blocks to allow for block detection to be used for automatic signaling and automatic computer control in the future. What are my options?
I don't understand why this would be an issue? A block detector doesn't care which "polarity" is on the rails, just that there is some current passing through.
 

fcwilt

Active Member
#3
You can have more then one train IN a section that is controlled by a auto-reverser. The issue is when trains are crossing the gaps between the reverse controlled section and the other sections.

If a train is trying to leave the reverser controlled section the reverser tries to set the polarity right. If ANOTHER train is trying to ENTER the section then reverser is going to try to set the polarity right for it as well. But it can't satisfy the conditions at both ends - the require opposite polarity settings.

The issue happens with a train that is long enough to span the entire section controlled by the reverser - the front of the train is trying to leave while the rear of the train is trying to enter.

Having a double wye makes things tough because you could have one train trying to go one way out of the yard onto the mainline and another train go the other way.

Check out the thread "Central Midland reversing section" - that describes the correct solution - I believe.
 
#4
I can suggest that you look at DCC specialties PSX-AR. Solved my problem with the reverse polarity issue. In my Central Midland that I recently tore down I only needed the polarity reverse leaving the yard or ontering the yard from the left (west). Entering and exiting from the right (east) had no polarity issue. Yes the reversing section has to be at least the length of the train entering and exiting. The PSX-AR has adjustments for voltage sensing that are also extremely usefull. I had no luck with several reversers until I installed two of the PSX-AR and then it ran flawlessly. Best place for support with DCC Specialties equipment is Tony's Trains. Alsoo check with DCC Specialties on their web site. Somewhere on this forum is a discussion under "Central Midland" about this subject. DCC Specialties and Tony's Trains will help you with your block detection question. BTW, you don't have to stay withh Digitrax equipment as I believe there are more solutions for situations like yours available much better tha Digitrax. Don't misunderstand, the Digitrax DCC system is a good one but there are a whole host of accesories available from others to support your layout beyond Digitrax.
Thanks
Wayne
 
#5
The issue happens with a train that is long enough to span the entire section controlled by the reverser - the front of the train is trying to leave while the rear of the train is trying to enter.
A clarification should be made here. It's not the entire TRAIN that's the issue, only the locomotives. If you have a MU consist that's longer than the reversing section it will run into the problem as described, i.e. the reversing section trying to match polarity on both ends and of course failing. As long as the LOCOMOTIVES fit within the length of the reversing section you're fine. You're also fine if you have locomotives on both ends or at the front and the middle of the train (as is prototypical in some trains) as long as they are set at a distance that doesn't allow them to hit opposite ends of the reversing section at the same time. In other words, the lead locos would have to either be still in the reversing section when the separated loco hits it, or be completely out of the reversing section when that happens. The only way you get in trouble is if you have two locos crossing the opposite gapped ends of the reversing section at the same time. Avoid that and you're golden.

EDIT: This info is only correct if your rolling stock has plastic wheels. Look below to see fcwilt's further info, and I've also posted a link below to the quad-gapping method of isolating a shorter reverse loop for rolling stock with metal wheels.
 
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#7
Thank all of you for your feedback. I was obviously over complicating the problem. I misunderstood the capabilities and use of the auto reverser. When I read the specs I believed it was only capable of operating one train in the auto reversing section. I didn't realize that the real issue was only with having two trains cross the boundary at the same time. As for my discussion about the blocks. I was concerned there may be power limitations that wouldn't allow me to power the entire yard using the AR1. Thanks again for all your feedback.
 

fcwilt

Active Member
#9
If you have metal wheels on your rolling stock AND your reversing sections are shorter then the train you are going to have problems unless you take precautions.

When a section of track controlled by a reverser is of opposite polarity to the adjacent uncontrolled section, the rails on each side of the insulating gaps are, naturally, of opposite polarity. It is the short created when a metal wheel bridges this gap (either rail) that activates the reverser causing it to try and change the polarity to eliminate the short. It matters not if the wheel is on a loco or a car.

I have not experimented with this but you MAY be able to "quad gap" the track. That is to say you would double gap each end of the reversing section in TWO places a short distance apart. The short section of track would have NO power.

There are a number of assumptions that are being made here. You would need to check all of your locos and cars to see if the meet the "criteria".

- The wheels on the same sides of the trucks on your non-loco rolling stock are NOT connected electrically.

- The wheels on the same sides of the trucks of your locos ARE connected electrically.

- The length of the shortest truck (actually axle to axle spacing) among all of your locos is LONGER then the dead section of track.

The idea is that one wheel of a truck on the loco would be on one side of the dead gap while another wheel on the same truck would be on the other side of the dead gap. The wheels, being electrically connected, would create the short required to activate the reverser.


I checked ONE of my cars and ONE of my locos (a GP7) and verified the assumptions above - hardly a meaningful sample. A simple ohm meter can be used to determine if you have wheel-to-wheel conductivity.

Good luck.
 
#10
If you have metal wheels on your rolling stock AND your reversing sections are shorter then the train you are going to have problems unless you take precautions
That's actually a good point, and one I didn't consider. Since I'm using N-scale, most of my rolling stock has plastic wheels, and I tend to forget that HO, I guess, has a much greater prevalence of metal? It actually drives me crazy when I get any rolling stock with metal wheels, and I end up replacing them and selling the metal on eBay. I know there are some advantages to metal, in theory, but to me they're very much outweighed by the problems they cause, not only on a reversing section but even on some turnouts.

The reversing section issue isn't a problem for me, luckily, since I'm just using different power districts instead of actual reversing sections, but before I realized I could do that I had originally planned to have some. I know and distinctly remember that in all the research I did that everything was always worded very specifically as to just the locos fitting within the reversing section, but maybe they were making the same plastic-wheels assumption that I was making for rolling stock? Dunno, but what you say definitely makes sense.

EDIT: See page 2 (and post #11) for a link to info about constructing reversing loops, wyes and turntables, and further explanation of fcwilt's quad-gapping method.
 
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#11
Was determined to find something that would bear out fcwilt's hypothesis (or something similar) as an apology for giving incomplete information. Turns out the double-gaps are *exactly* what's required to deal with a shorter reversing section and metal wheels on rolling stock. I knew it logically made sense, but wanted someone else to back it all up.

Some good how-to info if anyone's looking to reverse, wye, or turntable something (short reversing section info at the end of the document):
http://www.waynes-trains.com/site/dcc/DCC Basics PT4.pdf
 

fcwilt

Active Member
#12
You didn't believe me? You didn't trust my theory? I'm hurt - deeply hurt - I may just sulk awhile. ;)

...

OK done sulking.

Now where were we?

I don't know for sure that lighted cars would cause a problem. I will have to experiment a bit.

I built a simple LED based polarity tester to quickly determine what voltage is on the track or across a gap. It consists of a pair of jumper leads, a couple of resistors and a red LED and green LED wired up so that one polarity lights the red LED and the other polarity lights the green LED. DCC being "AC" lights them both.

Anyway being LEDs the tester doesn't draw much current. It is NOT enough activate my DCC Specialties PSX-ARs.

So the same may apply to lighted cars.


But 6 wheel passenger trucks can be quite long - my somewhat suspect visual memory tells me they are as long as a 4 wheel loco truck - so there could be problems with them.


OK back to the idea of having the two reversing sections span one leg each of the wye and a stretch of the mainline - that way it can likely be as long as needed - and all these problems go away.


Whew!
 
#13
The use of metal wheels should not be an issue if the gap is made in such a way so the wheel does not touch rails on either side of the gap at the same time. Using a razor saw to make the gap will not work as the wheel will still touch both rails. Using an insulated joiner should do fine as the wheel will be supported by the insulated material and not touch both rails.

If your reversing section of track is longer than any train that will go into it, then how the gap is made will not be an issue.
 

fcwilt

Active Member
#14
The use of metal wheels should not be an issue if the gap is made in such a way so the wheel does not touch rails on either side of the gap at the same time. Using a razor saw to make the gap will not work as the wheel will still touch both rails. Using an insulated joiner should do fine as the wheel will be supported by the insulated material and not touch both rails.
You are correct but some insulating joiners do not prevent the wheel bridging the gap. For example, the ones made by Peco for their code 83 line - the plastic separator that keeps the rails apart is not as tall as the rail - thus you get a space into which the wheel can drop and create the short.

You can, of course, cut your own gaps and make your own spacers out of, say, styrene BUT you need to be careful. I tried this on a 30" radius curve thinking all would be well but the curve "sprung" at bit at the gap creating a bit of a kink.

This was with Peco flex track which is very nice but the individual "spikes" are not very strong and they couldn't hold the curve at the gap. I found that if I wanted to have a gap on a curve with Peco I needed to slide the rail out of the ties, pre-curve the rail to close to the desired radius and then slide the rail back into the ties. It was a bit tedious but the rail slides easily into the Peco ties - you just have to take your time.
 
#15
this is the age old problem of wyes, but simple DPDT switches do wonders. Simple wiring of the turnout switches to change track polarity can be done. You will just put it into your operating scheme how to run a train over the wye watching for when you change the polarity switch. I've had thoughts of LED signals wired direct to the track at the track breaks that light up when polarity is wrong. So you watch your signals. And important to have your track length longer that the required train for the "reversal" track.
 
#16
I find this thread interesting, WHY?

Note: I am into N scale & its mostly DCC, Digitrax Xtra.

Because have an extension of my switch-yard main track that has an extra TO that forms a reverse... ie entering the yard on the normal end, then it loops around the round-house, then the series of turnouts for the yard-switching tracks (typical ladder set-up.) This over 15" section of track leads back to my freight main-line such that it reverses.

I guess another way to put it is I have a reversing loops that happens to also serve as the main switch yard track as well. I double isolated the reversing section at both ends and is longer than my longest AC12 cab forward steamer & tender. Passenger cars do not run on this mainline, so even lighted pass cars / metal wheels are not an issue. I have two separate (double) main-lines and the freight and passenger trains are on separate DCC systems as well (another topic).

I am thinking of getting a auto-reverse module to handle the reverse loop and maybe double as reversing control for my turntable.

JD.
 





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