reversing loop - will this work

[JDW]

David's post pretty much sums up what I was saying, but much more graphically and colourfully, well done that man!  

[Chimer]

Just a thought ..... this is going to sound weird but, for DC with cab control, I can't see anything wrong with it at first glance:

 

Make the circle and its immediate approach and departure tracks an electrically isolated section.  Feed it from a separate power supply, which could even be uncontrolled and left permanently on for clockwise running.

 

As a train approaches this section, have the sections it approaches from and will depart to switched to the same controller.  If it's going to use the circle to reverse, reverse this main controller while the powered bits are on the circle section.  If it's going straight through, don't!

 

You will obviously get variations in speed, especially if two straight through trains going in opposite directions are on different sectors of the circle at the same time, but I'm guessing this is going to be tucked away in the darkest corner where it's less likely to be noticed.

 

If running long trains with multiple pickups, the circle section will need to include sufficient lengths of approach and departure track to ensure all the pickups are clear of the main controller's sections when you reverse it.

 

The operator clearly needs to pay attention when using the circle to reverse a train, but I would assume it will be standard operational procedure to stop most other traffic when doing so  .

 

Cheers

 

Chris

Edited November 14, 2017 by Chimer

[Harlequin]

If the layout were DCC (which the Grandkids would love because of the sounds and the lights) then an off-the-shelf DCC auto-reverser could probably be used and, if so, that would allow continuous running through the reversing section of track with no manual switching (i.e. just drive the train through any route you want).

 

It is usually recommended that the reversing section is long enough to hold the entire train to avoid the possibility of accidental shorts and that might be tricky to achieve with the designs shown above - but it might be easy. Just needs to be thought about...

 

Edit: I "forgot to use the subjunctive..." ;-)

Edited November 14, 2017 by Harlequin

[34theletterbetweenB&D]

As far as I can see, there isn't really a "reverse loop" here in electrical terms at all, assuming that the twin track circuits aren't connected by a crossover for example... 

That's the crucial understanding. A reverse loop is only created if there is a crossover between the two tracks. And all you have to do is make a fully isolated section of one point in any crossover:  and make the supply to that isolated section by a DCC reverse loop module. (The isolated section will need to include a length of plain track leading into the point if the point is shorter than the pick up span of the longest vehicle or train.)

 

That looks like the problem I had with my loft layout, similar concept nearly impossible to make work. John KS plan works with steam rank locos, however lots of diesels and steam tender locos have pickup one side of the loco and one side of the tender or one side leading bogie the other side trailing and wont get across the join between two separate transformers.

 

The easiest way to make the loop work is with common return cab control with the common rail the right hand rail, so with double track the rails adjacent to each other are common return. 

 

With this and insulfrog points you don't need isolators.

 

This is fine until you introduce crossovers between the two tracks at which point you need to abandon common return and switch both -ve and +ve feeds, however stopping to switch controllers before running across a crossover is easier than trying to do it half way around a return loop..

It's rather more complicated in DC, and especially if using older model designs which split the current collection over two vehicles or bogies each picking up from one rail only, don't bother would be my suggestion: this concept plays to DCC's strengths, and the large majority of current RTR models which pick up from both sides.

 

Sometimes it is best to just move on...

Edited November 14, 2017 by 34theletterbetweenB&D

[Harlequin]

A DCC auto-reverser could be wired like this:

 

(The green cross-marks are isolators and the green tracks are powered by the auto-reverser.)

 

We have to assume that the inner and outer roundy-round lines use the same convention for wiring "polarity" and so if you follow one of the rails around either of the reversing loops in this diagram you will see that "plus" would meet "minus". So there is an electrical reversal here and that's why some sort of reversal control is needed.

 

(I know that DCC doesn't have "polarity" or "plus" or "minus" - I'm just using those terms to illustrate the point.)

 

As "34*" said, this is a case where DCC makes life much easier.

Edited November 14, 2017 by Harlequin

[JDW]

I see where some people are coming from, but think it's getting over complicated.  For DC, providing there are no other crossovers, For trains turning back around the loop, surely all that's needed is to set the points, ensure one (DC) controller is off, and use the other one to drive the train, just like on any other basic train set where you have 2 concentric circles connected by a crossover.  Providing the red and black (to use David's colours on page 1) rails are the correct way around, there should be no issue.  You could probably even get around needing any sort of common return and use individual controllers by using isolating fishplates on each end of the black rails that form the circle (ie just before the points) and use a simple three-way switch to select controller 1 < off > controller 2 depending whether you were running trains around the main line or the loop.  

[Hoover50005]

A DCC auto-reverser could be wired like this:

Auto-reverser.png

 

(The green cross-marks are isolators and the green tracks are powered by the auto-reverser.)

 

We have to assume that the inner and outer roundy-round lines use the same convention for wiring "polarity" and so if you follow one of the tracks around either of the reversing loops in this diagram you will see that "plus" meets "minus". So there is an electrical reversal here and that's why some sort of reversal control is needed.

 

(I know that DCC doesn't have "polarity" or "plus" or "minus" - I'm just using those terms to illustrate the point.)

 

Phil (Harlequin) has it correct. I have (well buried at lower level as part storage access) this set up with auto-reverser, but even more complicated with further branch line & storage loops access. This has been running without issue for over 10 years now.

Only thing to watch is ensure reverser feed section  is as long the lonest train (in my case 7car HST with power units both ends).

 

Dave

[Chimer]

I see where some people are coming from, but think it's getting over complicated.  For DC, providing there are no other crossovers, For trains turning back around the loop, surely all that's needed is to set the points, ensure one (DC) controller is off, and use the other one to drive the train, just like on any other basic train set where you have 2 concentric circles connected by a crossover.  Providing the red and black (to use David's colours on page 1) rails are the correct way around, there should be no issue.  You could probably even get around needing any sort of common return and use individual controllers by using isolating fishplates on each end of the black rails that form the circle (ie just before the points) and use a simple three-way switch to select controller 1 < off > controller 2 depending whether you were running trains around the main line or the loop.  

 

I just can't imagine the sort of sizeable layout the OP is envisaging wouldn't have at least one crossover between the up and down lines somewhere.  And as soon as you've got that, in DC, you've effectively got a reversing loop and the associated polarity problem.

 

Chris