New layout comments please

[What About The Bee]

@Dukedog.Hi!

You mentioned, at one point, a more extensive fiddle yard on a lower layer, accessed by a helix.  If properly done, you can walk into the center well, as opposed to crawling in.  Why not give that a twirl?

In the end, the only person you must satisfy is yourself.  Please remember that my comments are from the cheap seats far, far in the back of the room.  My comments are intended as food for thought, and only that.

Bee

[Dukedog.]

Hi Bee 

Thank you for your comments they are all taken onboard it is nice to have the benefit of what others have done to aid the facilitation of the outcome.

[Dukedog.]

yet another version

[Dukedog.]

ment to say the gray area is about 600mm boarding

[atom3624]

So overall it's about 3 x 3 metres?  (10' x 10')

[What About The Bee]

Hi Dukedog

I think you will find much greater utility in that fiddle yard.  Very lengthy sidings mean parking longer trains.  

Further, the wells are much more spacious.  It will be easier to work on the layout and much more comfortable to operate.  Plenty of room for grandkids.  Well done!

Earlier in this thread, we discussed reverse loops.   It is quite clear you need 4 auto reversed track blocks, for the four leads to the center double crossover.

 

There is an issue you need to resolve with the current design.  

The two highlighted leads are quite short.  One is ~130 mm (5 inches) whilst the other appears less than 75 mm (3 inches) .  Consider a long steam locomotive with tender pickup, like a 9F.  The power is drawn from the front pickup to the rear pickup.  This can easily exceed the length of your auto reversed leads.

Dead short.  

For the following, we are moving left to right. As the locomotive transitions from the fixed polarity scissors crossover to the auto reversed block, the highlighted auto reversed block flips to match that polarity.  The locomotive continues on, and encounters the transition out of the highlighted zone.  The auto reversed block will flip to match the polarity in that fixed block.

The problem is that if a locomotive can span the auto reversed block  the auto reverser can be required to supply both polarities to both tracks, which occurs when you run the layout as a figure 8.

RULE: Auto reversed blocks must be longer than the longest powered wheelbase of anything you put on it.  

Bee
 

Edited July 13 by What About The Bee
Blick Block

[ntpntpntp]

I would expand on the "rule" above regarding sections with auto-revered polarity:  general wisdom is the section needs to be longer then the entire train not just the loco.  In the case of rolling stock also having metal wheels you can't have the loco exiting one end of the section whilst the tail is still entering as that will confuse the electronics and cause problems.  The same applies to the good old DC reversing loop controlled by a DPDT switch 🙂

[What About The Bee]

Agreed NTP.  I used the 9F as an example only.  Wheelbase extends to rolling stock, for example, lighted carriages.

Bee

Edited July 13 by What About The Bee
"Agreed" instead of "correct"

[What About The Bee]

Hilariously, I forgot that a metal wheel can bridge the gap between an auto-reversed block and a fixed polarity block.

My error!

Bee

 

[Dukedog.]

Thank you all, may have a compleat rethink just just to get longer runs between points and crossovers,  so I will be back with a update soon.

[What About The Bee]

Hi Dukedog

You were so close!! A big part of this hobby is the personal victories and finding the solution.  To conquer the problem on your own.  That's why I held off.

Move crossover A to A.  Move crossover B to B.

Centralize scissors double cross over Sc.  Make auto reversed leads 1, 2, 3 and 4 as long as you can, and likely equal length, to support the longest train through all of them.

There is one further trick we can do, but only if you intend to install keep alive.

Bee

[Dukedog.]

Thanks Bee so yes i intend to fit stay alives  as i go i hope just looking at my final drawing above i have had another thought that i will be looking at 

[Dukedog.]

 

latest incarnation 

Edited July 14 by Dukedog.

[ntpntpntp]

If you could lose those two crossovers in the middle that would remove any reverse-loop / wye formation concerns  🙂

[Dukedog.]

lets try this one

the points on the right and bottom are not fitted yet 

i think this gets close to what i am after, it gives me the option to run a loco and a rake of the main lines and turn the loco around.  I can the turn any loco on any of the loops.

[What About The Bee]

Hi Dukedog 

Wye formations always involve auto-reversers.  Plenty of online resources to show you how to do it.  The same restrictions apply as before.

About that keep alive trick, auto-reversers and metal wheels.  It is offered as a rule that the auto reversed block must be longer than your longest train.  The reason proffered is that a metal wheel will span the gap between the auto reversed block and the fixed polarity block, causing issues.

The trick is really quite simple.  Install a block of dead track (magenta) betwixt the fixed and auto reversed tracks.  The dead block should be on the order of 12 to 18 mm (½ to ¾").  

This means that a metal wheel can never bridge the gap between the auto reversed and fixed polarity track.  Typical rolling stock uses plastic bogies, the metal tires effectively isolated.

So now, we only need concern ourselves with powered stock, locomotives and lighted carriages.  Unpowered carriages and waggons have no affect on the auto reverser.  Only powered stock will span the dead track, causing the auto reverser to swap polarity as needed.  

To obey the now modified rule: In consist, it is the length from the lead axle that draws power to the trailing axle that draws power.  In the case of steam, from the lead axle in the locomotive to the trailing axle in the brake van, should that be lit.  Or to the last carriage that is lit from the track.

This is quite similar to an insulfrog.  There is a tiny section of dead track.  In this case deliberately injected.

The isolation isn't 1 mm or so from an isolating track joiner, rather, it is 12 to 18mm, with two isolating track joiners.

You may require the keep alive to cross the gap.  Deliberately removing power from an axle may halt its forward progress.

THIS DOES NOT WORK FOR DC, obviously.

Bee

[ntpntpntp]

Sorry but all that double-gapping is unnecessary.  Just gap both rails at both ends of the reversible polarity section and stick to the "must be longer than longest train" rule for that section of track.   Works for DC or DCC* , it's the way reverse loops have been done for many decades since the advent of 2-rail track power 🙂 

1) The polarity of the reversible section is switched to match the entry track (either by DPDT switch or by an auto-reverse module when the first metal wheels bridge the gap).
2) The entire train continues into the reversible section.
3) The polarity of the reversible section is swapped to match the exit track via the DPDT switch or by the auto-reverse module as the first metal wheels bridge the exit gaps.  With DC you also have to swap the controller direction.
4) The entire train leaves the reversible section.

* Well, let's say standard auto-reverser modules only work for DCC whereas the good old toggle switch or relay pre-sets the polarity before the train ever reaches the gaps so works for any 2-rail power system.   Aren't Hornby working on an auto-reverser which *can* work with DC, necessary for DC powered HM7000 layouts? 
 

Edited July 15 by ntpntpntp
typo

[What About The Bee]

Hi @ntpntpntp

The major objection to auto reversers is that your longest train must completely fit onto or within the auto reversed block.

This limits the length of a consist. 

For many home layouts, that becomes a short consist.  The problem exists only because of metal wheels.  The trick avoids the metal wheels spanning the gap.  The trick isn't the double isolation, it is the dead track.  This makes the electrical isolation larger, whilst keeping the mechanical isolation short as can be.  The track is there, it just isn't powered.   

I 100% agree that following the time honored rule is easier to obey.  It works for DC and DCC. 

But if you want a longer consist.....

I would like to hear about a technical objection to the solution, if one exists.  Like: metal bogie frames will short it, if non-isolated wheels are used.  

Why did I come to this trick?  I designed a back to back Wye, just like Dukedog's.  I struggled to get anything more than 3 carriages into the auto reversed blocks, when I included other block detecting blocks.  I obeyed the primary rule, found it limiting.  Sure, Hornby's LMR locomotives struggle to pull larger consist, so why do I care?  The LMR double and triple headed; so can I:

https://youtu.be/JJPPQ-4qeGk?si=ciWrdMdlVT7-EaEX

I cannot have back to back Wye if I follow the baseline rule with this consist.  Sticking two tiny dead tracks, one on either side of the auto reversed block permits this consist without fault.  All the Hornby LMR rolling stock uses isolated tires and plastic frames.  Accurascale chaldrons are similarly configured.  So the only concern is the locomotives, IF the trick is utilized.

Bee

[Dukedog.]

I just found this

Part 3: Reverse Loops (gaugemasterretail.com)

[Dukedog.]

 

 

Going on the artical and on  what Bee and ntpntpntp i think this shoul work with just the two rail isolators

or would this be beter

 

ore this one  

Edited July 15 by Dukedog.

[What About The Bee]

Hi Dukedog

Now begins the real exercise!

One way to determine what blocks must be auto reversed and what can avoid this is to color in rails.  Use two colors, say red and green.  

Pick a track, anywhere.  Start with a color, say green.  Color in the green track, everywhere.  How to know?  Green touches green, just go around the layout with green. Now pick up red and color the other track red

Whenever red touches green, you have an issue. 

For points, remember that the frog must be isolated and controlled by your point motor, so when red touches green there, you know to isolate it!  Awesome sauce.

But in a Wye, you will swiftly see that red touches green.  And the previous discussion about auto reverser applies.

Mentally drive your train through every combination, flipping polarity when auto reversed.  Make sure you cover every case.  Keep a record, making sure you never short.  Make the auto reversed block as long as you can.

There is zero substitution for hard work and exhaustive analysis, which fundamentally is up to you.  The work will yield understanding of the principles.  In my view, if you are going to include auto reversers, developing the skill is a requirement.

Up to you lad,  I will certainly check your result, but I expect you to do the work.

Bee

Edited July 15 by What About The Bee
Clarity

[ntpntpntp]

On a normal Wye formation you only need to isolate the trunk of the Y from the two branches.   I would make the entire inner bit of track and siding all the same section and have that as the trackwork which can switch polarity depending on which route out of the wye you choose 🙂  Nice and simple, plenty of length for long trains.

 

I agree with Bee, it's worth learning how to trace round your plan and identify places where you end up back on yourself but facing the other direction - that's a reverse loop,  or where you can leave in two directions onto a main line - that's a Wye.   

In these cases you find the positive rail ends up joining to the negative rail and that's an instant short circuit which requires isolating and then a mechanism to deal with how to set the polarities to match as you drive across. That mechanism can be mechanical - eg. a DPDT toggle switch, a DPDT attached to a point motor - or an electronic DCC auto-reverser which works by detecting that short and flipping the polarity.

I used to run a DCC garden railway (still have the gear but now stored away), and with several amps of power flowing around the trackwork I developed an innate dislike of things like auto-reversers which rely on shorts happening 😞  I feel it's a poor solution to the problem. I much prefer to have the polarity switched and set correctly before anything gets to run over the isolation gaps 🙂

 

Edited July 15 by ntpntpntp

[What About The Bee]

I'm very much in the teach a man how to fish camp.  It is better to learn the skill and let that man develop the result; than to just hand that man the result.

If he just gets the result, he learned to ask someone who knows.  If he develops the result, he learns how to do the task.

Bee

[Dukedog.]

Thank you both i think i will leave it there for now the materials for the base board have started to arrive  the ply is here just waiting on the 2x1 which is due to be ordered with stuff for my garden project to save on delivery so hopefully later this week

[96RAF]

There is a decent Rev Loop guide right here on this forum -