Reverse Loop

[Jackfrost83]

Hi All,

 

I understand that if I have an oval of track wired to a DCC bus system and want to add a crossover between the two long sides of the oval I must fit a Reverse Loop Module to allow trains pass across without shorting.

 

All the advice I have read suggests that the isolated section controlled by the module must be long enough to accommodate the train passing through it. My question is - what if this is not possible because the track is too short? Is there another possible solution? I model steam and in OO gauge.

 

Thanks

[melmerby]

The auto reverse module will reverse the 'polarity' whilst the train is in that section.

For that to work no vehicles should be straddling both ends at the same time.

e.g. if you had a train with pickups and lights on all vehicles, as the loco exits the reversing section the reverse module will switch the track to suit, if a vehicle with lights is at the other end straddling the entry point, you will get a short circuit.

 

EDIT

If however the only vehicle with pickups is the loco it will work.

You could still get problems as a wheelset bridges the insulated gap.

 

P.S.

You must either have

a) very long trains

or

b) very short track.

Edited May 2, 2023 by melmerby

[RobinofLoxley]

It would be safer Jack if you posted your track plan here so that the best place for the reverse module can be identified. Some times its not where you think. However if your trains will bridge the junction it should be OK if you have plastic wheels. I didnt realise some of my carriage wheels were actually metal. This isnt shorting across the axle but when the wheels bridge a gap that otherwise has an insulated fishplat or something similar

[Jackfrost83]

Thanks for advice so far - here's a screen shot of my track plan. The outermost lines form a continuous loop of track in a dog bone-type shape. The lines branching off into the middle are to a terminus station within the dog bone shape. I hope this makes sense.

 

The highlighted section of track is where I anticipated placing a reverse loop module.

[RobinofLoxley]

OK, so you are referring to the parallel tracks on the right hand side. This is quite complicated - too complicated for me in fact. The outer and inner loops are linked in DCC. I think as an alternative that you make the entire dogbone the reversing section but I stand to be corrected.

[ITG]

58 minutes ago, RobinofLoxley said:

OK, so you are referring to the parallel tracks on the right hand side. This is quite complicated - too complicated for me in fact. The outer and inner loops are linked in DCC. I think as an alternative that you make the entire dogbone the reversing section but I stand to be corrected.

That’s is what I’d suggest, although there’s a twin track to consider, which presumably adds complication, as you could presumably have a train on each track, at different stages of the transition through or past the polarity change. I therefore think I know what the problem may be, but necessarily yet got to the solution!

Ian

[WIMorrison]

This looks like it could actually be rather simple, however I need to see the whole track plan. If, as I suspect, it is a dog bone type of layout then you are looking in the wrong place to place a reversing loop.

 

Please post the whole plan then we can make valid comments, without it any advice will be incorrect.

[Jackfrost83]

Thanks again - here is the whole track plan. The track with the orange background is already built and exists today in a closed loop around the outside of an attic. It's wired in the traditional "black to back" (being the outside) fashion. The track with green background is the proposed extension.

 

I hope this makes sense

[WIMorrison]

I think you need 2 x reversing loops for this layout given the complexity of the throat design - they are the red lines on this drawing.

 

 

There are lot of sources for cheap, but effective auto reversers.  This is one and is available from James.

 

BLOCKSignalling DCC Autoreverser REV1 - dcctrainautomation.co.uk

[Jackfrost83]

Thank you - I think that makes sense

 

What I’m struggling to get my head around is the wiring for the station itself. Which way round do I wire the droppers?   One way or another a loco entering the station will have to switch - or am I over thinking it completely and it’s a non issue?

[WIMorrison]

Get a old wagon and paint one side red and the other black, or blue and green or pink and yellow - colours don’t matter.

 

place the wagon on the layout and never take it off, simply move it around and always wire to the same side with the same wire.

 

the effect of those two red stripes is to break that end loop into two long sidings which will break the reverse situation you have created.

 

hopefully someone else will confirm. I think they are correct but it might also need some at the other end.

[melmerby]

IMHO the only thing that needs an autoreverser is that link line in your first extract of the layout. The restb is just part of the same loop.

Cannot you re-arrange the propsed track to make it longer?

[Grovenor]

1 hour ago, WIMorrison said:

I think you need 2 x reversing loops for this layout given the complexity of the throat design - they are the red lines on this drawing.

 

 

There are lot of sources for cheap, but effective auto reversers.  This is one and is available from James.

 

BLOCKSignalling DCC Autoreverser REV1 - dcctrainautomation.co.uk

Sorry but the red sections on this drawing are not going to do the job on their own, they would work if you add two more, on  the right hand side of the orange section where the up and down arrows are. The section of dogbone between the two pairs of reversing sections and the station would all be wired to the same polarity as the bottom side of the dogbone.

[RobinofLoxley]

1 hour ago, WIMorrison said:

Get a old wagon and paint one side red and the other black, or blue and green or pink and yellow - colours don’t matter.

 

place the wagon on the layout and never take it off, simply move it around and always wire to the same side with the same wire.

 

the effect of those two red stripes is to break that end loop into two long sidings which will break the reverse situation you have created.

 

hopefully someone else will confirm. I think they are correct but it might also need some at the other end.

I dont think you are quite right. I have tried and failed to edit the track plan and post it back, unfortunately. But my point is that breaking the connections where you propose doesnt convert the plan to a form of loop with sidings because the actual reverse loops are on the left hand part of the plan and come together at two right hand turnouts at the left end of the station complex. In this case, surely, the breaks could be on the left hand loops on the long sections of track, two different possible positions.

 

1 hour ago, melmerby said:

IMHO the only thing that needs an autoreverser is that link line in your first extract of the layout. The restb is just part of the same loop.

Cannot you re-arrange the propsed track to make it longer?

The point we're trying to solve is to have long enough sections being flipped to hold complete trains. Perhaps the turnouts that form the crossing at one end of the originally proposed break could be moved a long way to the left, close to the large group of sidings. May not be convenient for the OP as its in an already built area.

[Grovenor]

See my post above. When you put connections across the middle of a dogbone then both ends become return loops not just one of them. With the double track it is difficult to have just one by the junction except by using the original short version which limits your train options.

[Curlew]

Instead of just the short link line, make the whole terminus one reversible section. No need to do anything to the outside loops.

[Mike Buckner]

This  should do it. Isolate all crossing areas at the nearest track joiner inside the red line, and power the whole terminus area by the auto-reverser.

 

Subject to the rule that no more than 1 train should have any of its vehicles crossing the red line at any time.

 

 

[Curlew]

27 minutes ago, Mike Buckner said:

This  should do it. Isolate all crossing areas at the nearest track joiner inside the red line, and power the whole terminus area by the auto-reverser.

 

Subject to the rule that no more than 1 train should have any of its vehicles crossing the red line at any time.

 

 

What I meant, but you explained it far more comprehensively than me. It seems to me to be the only solution - and a very simple one too!

 

You will need to make sure that trains don't  arrive and depart simultaneously on certain routes at the terminus though. Arriving and departing on the double track approach will be fine, but one departing on the double track and another arriving from the single line approach at the same time won't work. Easy enough to remember though. Not really a problem.

Edited May 2, 2023 by Curlew
add

[RobinofLoxley]

If the only way to wire it up is per @Mike Buckner then its time to redesign the track plan. If you have a busy terminus as designed, one of the features of such a design is parallel arrivals and departures, my personal opinion is that it would become at least very frustrating for operations if that wasnt actually possible.

[ITG]

1 hour ago, RobinofLoxley said:

If the only way to wire it up is per @Mike Buckner then its time to redesign the track plan. If you have a busy terminus as designed, one of the features of such a design is parallel arrivals and departures, my personal opinion is that it would become at least very frustrating for operations if that wasnt actually possible.

I agree. I’m not sure there is another effective way of wiring the reverse loop with that track plan. Could you not make that short length of track longer by extending where it joins the (existing on yellow) circuit much further north. That way it should house a full train length, and thus the reversing section could be on that single line. Imho, unless you can run trains non-stop through a reversing section, you may as well have polarity switches which have to be thrown whilst the loco is static.

But - and this may not be an issue for the OP - doesn’t it mean that an arrival would come via the double track, but depart via the single track, and vice versa, in order to reverse the train to get back to the station. Unless, the whole train was fiddled in what I assume is a fiddle yard.

There is some comparison with a layout that I’m about to begin construction. I have a roundy, but with a through station disguised as a terminus (2 through lines pass under the station building, plus run round loops and terminating roads), and a double junction off the roundy, to a storage yard which continues on to a reverse loop. Thus back to the storage yard, and back onto the roundy, and return to station.

Ian

[RobinofLoxley]

Agree. Basically a clockwise running train would be forced to run wrong line on the approach. Or the whole access junction is moved up so the now extended yellow track section is long enough to hold a full length train. Then you have a third line running next to the main tracks which will look odd but be functional.

[DCB]

# Mike Buckner 's wiring will work for one engine in steam  operation.  It's when  simultaneous arrivals / departures  are occurring that the whole lot will short out. At some stage you have to change polarity under the train.  Using auto reversers on the lines next to the arrows look promising .  I can't see an easy way to automate the "Blue" section but using the point motor for authority will work and the green and orange ones should work

Edited May 3, 2023 by DCB

[KingEdwardII]

I think that the way to attack this problem is to break it down into separate parts and deal with each separately.

 

I consider the track plan as containing 2 major parts:

 

1. The terminus itself and the out-and-back loop on the left (in orange above).

2. The loop that encircles the terminus, on the right (in green above).

 

For the out-and-back loop on the left, there must be a reversing section for each of the inner and the outer tracks. The most obvious place to put these are on the right hand side of the orange area, since the track there is clear of turnouts and looks as if it is long enough to accommodate the longest train running on the layout.

 

For the encircling loop on the right, a reversing section needs to be inserted for each of the inner and the outer tracks. The sections identified by @WIMorrison above look suitable - lacking pointwork and long enough to accommodate the longest trains.

 

So - I make that 4 reversing sections, with appropriate hardware to handle the reversal of polarity as trains transition them.

 

Yours,  Mike.

[Grovenor]

Thank you Mike, exactly what I said several posts back. Its the only reasonably simple solution that avoids any restrictions on the operation.

[Harlequin]

What about this, folks?

 

The auto-reverse section indicated is long enough for a whole train and allows all the useful simultaneous movements in/around the terminus except one: You can't have something running through the section on the outer circuit while a train is departing from the terminus onto the inner circuit.