# Calling DCC gurus: Techniques for "short" reverse loops.



## Greg Elmassian (Jan 3, 2008)

OK, so comments not limited to gurus, but kind of a technical subject, so WAGs are really not solicited.

This question is DCC only, using autoreversers. 


I know about how you want your train fully into a reverse loop before it hits the "gaps" to leave it. Of course the ideal case, so lighted cars and cabeese are no problem.


But on a shorter reverse loop, and with the potential for lighted cars, and jsut the situation of metal wheels going over insulated joints, what's the "rules" on how to hand a reverse loop that the entire train will not fit into?

I hope I can entice Bob Grosh and George Schreyer and Bullet Bob, and the like to come on in here (and apologies to all the other guru's whose names I forgot!!)


Regards, Greg


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## George Schreyer (Jan 16, 2009)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

this is a problem. The issue is when there is a car or loco crossing the gap at one end and another car or loco crossing the gap at the other end. The reverser cannot deal with this. At the end that is polarity matched, a loco can bridge Rail A to Rail A, no problem because the polarity is matched. If at the same time, another loco or lighted car is crossing the other gap, THAT car will be connecting Rail A to Rail B because that is the mismatched end. 

Result, short and shutdown.


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## StanleyAmes (Jan 3, 2008)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

The better solution is to rethink where the reverse loop really is. Think outside the box on this on as the "loop" can oftem be in a totally different place then it would be in a traditional DC layout. 

Stan


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## Trains West (Oct 4, 2008)

how do you have a train longer then the loop without the engine hitting the the rest of the train ???????


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## Greg Elmassian (Jan 3, 2008)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

I use the term "reverse loop" euphemistically, for any section of track that could reverse the direction of a train. 

Not alll "reverse loops" are loops, you could have a track connecting diagonally across a simple oval, and call that track a reverse loop. 

Stan, I think you're intimating that you consider track "outside" of the loop for the autoreverser. I have considered that and also have done this for a solution, but I KNOW how to do that, I'm looking at the problem as described. 

One possible (partial) solution is to have a short dead section so that wheels cannot short the track out by "jumping" the gap. This does nothing for lighted cars. So, if you had a freight train, and the only powered car was a loco, this would solve the problem. 

A lighted caboose would foil your plan. 

But, you are still in trouble with a lighted passenger train. 

More ideas? 

Regards, Greg


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## Semper Vaporo (Jan 2, 2008)

You slam on the brakes to bunch up the slack!









The insulated joints between the loop and the switch leads are not "at" the switch but set in some amount... sometimes really close to the switch and if so, then your comment is true, but sometimes the joints could be several feet from the switch, giving plenty of room for a train to be longer than the isolated section.


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## Greg Elmassian (Jan 3, 2008)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

Ha ha! 

Back to the question, I CAN solve the problem if I can make the section longer than the train. No brainer. 

But, electrical solutions to the problem as described is what I am after, something I do NOT know. 

Regards, Greg


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## Trains West (Oct 4, 2008)

but the little part in the center of a loop is not the auto reverse section 


this is what you think needs the auto reverse 















but this is what should have the auto reverser hooked to it 














why whould you make it harder then it needs to be?


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## Greg Elmassian (Jan 3, 2008)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

You guys are really insistent on telling me what I already know... you did not pay attention to my response to Stan. 

If you don't have ideas on what I am asking, then, at least, don't tell me what I keep telling you I don't want to solve and already know. 

Greg


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## Trains West (Oct 4, 2008)

I read it 

MY question is why are you trying to make it harder then it should be ????

why dream up some convoluted way to make it work when it is simple ......move the joint and make the block longer ?????


and if you know all of this then what is the point of this whole thread ....

it is like asking someone to reinvent the wheel ....

or are you just hoping someone has some magic way to stop shorts when none of the big DCC companies do .......


here is an idea ....... power all of the cars from the loco and run plastic wheels


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## Steeeeve (Sep 10, 2008)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

I'm not sure if this would work but what if you did a series of reserving loops that are each the size of the space between the back pick up wheels of one car and the front pick up wheels of another. I'd guess you have to have a minimum of three reserving sections. I haven't thought it all out yet but Lets say you have section M (main) followed by A,B,C which are the reversing areas and then M again. 
M1--A--B--C--M2. 

When loco enters A from M1 than a will switch to be correct. It will probably then enter B and do the same. Now the backs wheels have to be just in B when loco enters M2. You have A empty (gap between loco and first passenger car wheels). B matches with C and M2. When the passenger car enters A it will switch and so fourth and so on..you have always have to have reversing area empty. 

the problem with this is you have two reserving units tied to one section of track. I'm not sure how this would play out. It also assumes consistent dimensions of certain train cars.

Again this is just a first thought idea while I'm at work so don't rip me for it " align="absmiddle" border="0" /> Just trying to help haha.


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## Greg Elmassian (Jan 3, 2008)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

Steeeeeve: I was thinking this might be the only way, is basically another autoreverser. The reason for this thread is that it's easy to go by the "rule" of loop longer than train, and of course, as I stated and all the others have said, find a way to try to make your loop longer. 

But in the "impossible" cases, I have been wondering if there was not some "trick". 

It's interesting to think about. I have a reason for asking, besides minimizing the number of autoreversers, I want to minimize the number of separate power districts. I also intend to run pretty darn close to the max current in my power districts, so all of this has to be considered. 

Regards, Greg


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## Steeeeve (Sep 10, 2008)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

It can't just be one more auto reverser because you can still run into the same problem of either having the two reversing sections being the length of the train (thus making the second one useless) or you will short again. My idea is basically a series of small reverse areas where each car/loco will have one small section of track between it at all times while in the auto reverse "area". You have to have a minimum of 3 auto reversers. Way overly complicated I admit but it seems like it could work given the right circumstances. 

Of course the best solution is to have a train manufacturer create some function that can handle the short....I assume this is possible but for a different topic " align="absmiddle" border="0" />


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## bobgrosh (Jan 2, 2008)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

That's why they make plastic wheels.


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## Steeeeve (Sep 10, 2008)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

This is not possible if you have lighted cars.


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## K27_463 (Jan 2, 2008)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

Actually , it can be done with lighted cars. Takes modification of each car however. Create a dead section of track longer than the longest truck wheelbase. Not car wheelbase, but truck. By dead this means both rails insulated on both ends of the section. Power must be bridged over this section of course with jumpers from before to after this dead track, unless this dead section is at the very end of the reversing section. Now, modify each car so that each truck picks up both rails and feed to lights. Use Diodes to block lighting interconnect from each truck to the lighting circuit, likely will take a bridge in order to cover both direction polarity. 
Now as each truck enters the dead section , it becomes electrically inactive, and cannot interfere with any polarity reversal. Reversal cannot be done while locos are crossing, but should work with cars modified in this way. Anyone find any holes in this ? 

Jonathan


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## StanleyAmes (Jan 3, 2008)

Depending on the the technology in the auto reverser you can have all blocks be auto reversing blocks. With many units when you enter a block it is that block that will see the short faster then the one the locomotive is alreading drawing current. In this approach the leading block will reverse to the polarity of the preceeding block and the following blocks will have no need for a further reverse, thus preserving the requirement that under the train no auto reversals will take place.

Stan


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## Semper Vaporo (Jan 2, 2008)

Posted By K27_463 on 02/12/2009 2:46 PM
Actually , it can be done with lighted cars. Takes modification of each car however. Create a dead section of track longer than the longest truck wheelbase. Not car wheelbase, but truck. By dead this means both rails insulated on both ends of the section. Power must be bridged over this section of course with jumpers from before to after this dead track, unless this dead section is at the very end of the reversing section. Now, modify each car so that each truck picks up both rails and feed to lights. Use Diodes to block lighting interconnect from each truck to the lighting circuit, likely will take a bridge in order to cover both direction polarity. 
Now as each truck enters the dead section , it becomes electrically inactive, and cannot interfere with any polarity reversal. Reversal cannot be done while locos are crossing, but should work with cars modified in this way. Anyone find any holes in this ? 

Jonathan


Something like this?


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## Steeeeve (Sep 10, 2008)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

modification to cars is much more complicated than even my idea.


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## George Schreyer (Jan 16, 2009)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

Greg, accept the condition that a reversing section shorter than a train is a problem. There is a small matter of physics involved that you won't be able to get around without special attention to all your rolling stock. 

"You can't fool Mother Nature" 

or Schreyer's Corollary 

"Nature is a Mother" 

- gws


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## Greg Elmassian (Jan 3, 2008)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

Dang, you mean I cannot repeal the laws of physics? What is the world coming to. 

My initial thought when starting this thread was a "dead section" slightly longer than my longest powered car, which would be a USAT streamliner. Jonathan's suggestion shortens the dead section to a truck length, but I would have still to consider locomotives, a few of which are pretty darn long. 

It's either that or more autoreversers. 

Thanks for the ideas all, it is an interesting discussion. 

Regards, Greg


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## KVBarkley (Jan 9, 2009)

*RE: Calling DCC gurus: Techniques for "short" reverse loops.*

DCC doesn't care about polarity, right? It will make the train go "forward" no matter the polarity of the DC, correct? 

Why not put a 4-way bridge at every truck/pickup? No matter what the polarity of each truck/pickup, the master buss will have the same polarity. 

The dead-zone between polarity reversals only needs to be a truck long. 

ETA: oops, never mind, I did not read that other post just the first one on this page...I did not peak, honest!


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