General practice I

General practice I follow.....

Power Zones - straight

Auto Reverse Zones - specified by manufacturer, 1/4" if nothing stated in the instructions

Both power and reverse zones must be isolated from the adjoining zone. Two reverse zones should not be next to each other unless specified in the instructions and the proper CV settings.

Really? (Pls state source)

"Generally Accepted"? Really? Please state source...

(I feel a "specific application, matching specific locomotive pickup configuration"
rumour-which-becomes-legend issue afoot???)

Happy Modelling,
Prof Klyzlr 

I've never heard it is

I've never heard it is generally accepted to stagger gaps.  Quite the opposite rather.  

The only time I heard that you should stagger things

Is when forming flex track into curves, you should try to stagger where the ends of the rails line up in placing rail joiners, primarily so you can avoid having a kink form.  Don't recall anything about staggering electrical gaps. 

Janet N.

@Prof

A quick Google search (okay, I had to say this) shows several articles for reverser sections (dccconcepts, tony's trains, etc) advising the (slight) staggering when using a reverser circuit in loops to avoid a single wheelset bridging both gaps at the same time causing a short instead of the reverser being able to figure out to adjust the polarity. The chance is very small and only if both rails are cut at the exact spot, but we are dealing with people who are into track details like that

Gaps

Perhaps I mis-spoke about this? Maybe it was something that stuck in my mind when I was laying all the track in my helix structure? Or maybe it was something I read when I was looking up reversing zones recently? Maybe it was some suggestion to avoid a very direct joint alignment when doing reverse sections? I just can't remember now.

It doesn't seem to make sense, does it?

The reason I was asking is that I want to cut across both rails in the single track portion of my stone arch viaduct to provide for 2 different power districts. I was thinking the tracks would best stay in alignment if they were firmly glued down to their cork roadbed, AND the cut was angular across the 2 rails.

Here is where I was hoping to make that break in the rail. The single rail going down to the left would become part of one of either two power districts of the lower deck. The portion to the right of that break including the wye turnout and a short length of the double mainlines entering that 'tunnel to the helix' would become part of the power district dedicated to the helix.

aah Yaron, you found it. I

aah Yaron, you found it. I thought I recall reading something like that. So it was in a reversing discussion.

Touche

Dear Yaron,

I walked straight into that one... Touche

That said, I had done the similar research, and largely found it applied-to reported-in situations where either:

- the most-commonly-used locos were steam with "RH pickup on loco, LH pickup on tender",
(IE the gap-offset was related to pickup-footprint-offset)

And/Or

- where poor "short detection" HW/SW-algorithm within the Reversing Unit lead to rapid "flip-flopping" of state,
(a kind of "switch bounce" issue within the detection system, which should be solved in-the-unit, rather than being "patched over" at the track-gaps...
...IE smells of "Using a Tactical Solution to fix a Strategic Error",
which becomes promulgated as "generally accepted knowledge"...)

Personally, with gaps around 0.020"
(about the width of a Dremel cut-off disk, and perfectly filled with a slip of styrene),
I've yet to have any such issue, running everything from Trackmobiles, thru SD40-2s, to LH/RH-pickup'd Mallets...

Happy Modelling,
Aim to Diagnose and Define Root-Cause accurately,
Prof Klyzlr

PS if "Reverser gaps must be staggered", how do such units handle Turntables,
IE where it is essentially-impossible-by-application to stagger the gaps?

No to Staggered Gaps

So to answer my question I should NOT stagger any of my insulation joints,...either between two PSX power districts, nor between a PSX and PAS-AR zones??
 

Something like my 1/4"-1/2" stagger would be totally NO??

Reversers and Turntables

Prof,

Yeah, that was an easy shot in front of an empty goal. I knew you'd get it and handle it in good jest.

Reversing units and turntables: I totally agree with your questioning this logic, because especially in turntables the tolerances are extremely close to the "perfect storm" of being able to "short both rail gaps at the exact time preventing reversing units from functioning and shorting instead". With LHS-RHS pickup offset equipment, the gap is inherently offset, so no problems should ever be seen with thiose. But servicing a turntable's polarity with locomotives using all wheel pickup would have to be a reversing units worst nightmare!

I guess this discussion brings up more questions than answers.

Do we have any PSX-AR, Digitrax, NCE, TCS, Digikeijs, or any other DCC hardware vendors reading this thread that could shed some electrical engineering light and insights on this matter?

Have seen it bother ways

Good evening,

I have see both applications work with out any issues.  My one suggestion is to cut the gaps at least a 1/4 inch wide and epoxy into the gap plastic strips shaped to match the rail profile.  This will prevent metal wheels from causing any unwanted shorts.  

Good luck with your layout.

Andy H

Minooka, IL

Yaron, I think this issue is why..............

.......a dual frog juicer is the preferred method for turntables than reversing units.

Peter

LH/RH pickup VS rail gaps

Dear Yaron,

Au Contraire, with colloquially-grouped-together "dual-channel" Reversing units, 
(and the below is "as observed in field", unfortunately I don't have enough data to map specific units <> specific internal modes-of-operation)

- some of them wait for both rails to "detect a short"
(think "stereo"
Dual-Input AND --> Output state)

- some of them wait for either rail to "detect a short"
(Ganged detection,
Dual Input OR --> Output state)

- some of them independently detect short-conditions
(think "dual mono"
2x Single Independent Input --> Output state )

- Some will flip the output-state of both rails when either of the 2x "Short detected" Input rails are triggered
(IE "IN --> Linked-State Toggle Output"), 

- Some will set the output-state of both rails 
(IE "Explicit Out/Inverted-Out" output pair, as opposed to state-relative "toggle current state")

- Some will flip the output-state of one-rail-only when that particular rail detects a short
(2x Single-Input ---> Respective Single Output "dual mono").

This combination/variety of Input/Output conditions and mapping means that an AWP loco like a GP or SD
(IE both Detected Rails are triggered near-simultaneously, 
and there is a clear, continuous, unambiguous "reversing section/static-polarity section" condition that the Reversing section can "harmonise to"),

will generally trigger as-expected ,
(assuming a solid wheel/rail pickup condition, 
and the reverser unit not suffering a "too-short switch debounce" condition)

..whereas a "LH/RH" loco like a steam loco+tender can plausibly
- trigger the Nth Rail to flip (loco wheels pickup-footprint span gap)
- while the Sth rail does not (tender wheels not-yet spanned gap)
- AND Motor is spanning Nth-Reversing-Rail + Sth-Static-State-Rail
(trace the signal path)

and when the tender-wheels do end up spanning the gap,
intermittent pick-up + detection "switch bounce" timing pays havok....

..there is a reason why many of the Reversing Units have adjustable Current-detection and "switching-time" variables...

Happy Modelling,
Aim to separate "general hearsay" from properly-diagnosed application-specific conditions,
Prof Klyzlr

PS NB that many of the above conditions can be due to the User mis-selecting/mis-configuring/mis-wiring a "multi-channel" polarity-switching circuit for a given specific task....
...simply "using a 2-channel unit" is not-necessarily the same as using
a proper 2x Input-detected PLUS 2x Output-ganged "Turntable Reverser",
esp if the "detection-timing"/switch-bounce system is skittish...)

Permutations...

Argh, Prof! Why can't these implementations be easy for once, right? Totally forgot that you could have all those different permutations of solving this reversing problem each with their own pros and cons... Ugh.

The headaches will stop eventually... (pass the beer)

(Prof passes @yaron a beer...)

"we've all been there..."

Happy Modelling,
Aiming to engage brain, instead of blindly abdicating responsibility to a "magic bullet" circuitry or software solution,
Prof Klyzlr

PS knowing what you/I do about sw logic and circuitry,
you can see why I hear the OP statement-promulgated as "everyone knows",
and feel a touch of Julius Sumner-Miller kicking in...
 

Used to be that the

Used to be that the instructions for the Digital Specialties PSX-AR advised to stagger the joints by a few mm transversely, and to cut dual sets of gaps just a bit more separated than the distance between the nadirs of the outboard wheels in any truck of following rolling stock that might pick up lighting power, as an example.

Lets do some reading...

Dear MRHers,

From the PSX-AR Manual
https://tonystrains.com/download/PSXAR_install_manual_RevO_for_website.pdf

Page 11

NOTE that there is no actual justification given for the " staggered 1/8" gap " reccomendation,
(IE "we reccomend 1/8" gap, and this is the technical/physics/electrical reason why")

but it is interesting that the very-next statement is that "Perfectly aligned gaps may reduce the current needed...to reverse properly"

Apart from the obvious config-step that this may require settng the "Trip Current" to match the "reduced trip current", this would seem to suggest that "perfectly aligned gaps" might actually be a Good Thing?
(Lower Trip Current = more-reliable triggering,
bordering on "nuisance tripping" if not tuned-for during initial config...)

Moving on...

Here we clarify another of the "incomplete generalisations".

The intro qualification is

"...- IF the train is longer than the entire reversing block/section
(and)
IF the train has metal wheels..."

which sets the specific conditions in which "double-gapping each end of the reversing section" would be relevant/appropriate...
(Not "Thou shalt" or "It's generally accepted",
but explicitly "under these specific conditions")

...and if we think about it for, say, 10 seconds,
the most common Real-world application for a "train length" reversing section,
IE a balloon/reversing loop

kinda makes it darn near impossible to have a train which "exceeds the reversing section",
as exceeding the balloon-loop length means the train will be hitting-its-own-caboose as it tries to traverse the turnout and re-enter the mainline...
(IE you actually want a "showstopper electrical condition" to occur,
because it's the clear-and-present warning before you have a far-more-terminal physical collision/derailment issue!)

Now, I'll readily admit that there may well be an application-situation that isn't explicitly addressed above, which may require a "dbl-gapped" implementation,
(If you've got one on your layout, then by-all-means, step up to the microphone   ),

but I would hope that we all aim for "implementations which match the application/situation, based on evidence" rather than "generalised accepted" situation-agnostic advice...

Happy Modelling,
Aim to Improve,
Prof Klyzlr

Staggered gaps as a best practice

Again, Specific-application info dressed as Universal Advice...

Dear MRHers,

Hmmm....
(per Bruce P's "DCC Impulses" article linked above)

Sooo, reading between the lines, what Bruce P is highlighting is a Trigger/Switching-Timing Race Condition in ??? Specific Reversing Units ??? where:

- The unit "sees a short"/trigger

- Presumably begins switching/toggling the state of the Output Rails

- but BEFORE the Output has (fully?) changed-state
(IE the time-window could be 0.00x seconds for "solid state switched" units,
or 0.x seconds for "relay/mechanical switched" units),

a "second short/trigger" is seen/detected

- creating an "ambiguous"/"double-triggered" scenario

Now, per the earlier posts in this thread, hopefully it is clear that:

- Poor Design, Choice, or Implementation of "auto-reverser" unit could create the conditions that Bruce P is concerned about
(Specifically, units which do NOT use a proper "Ganged-Output" or explicit "Out + Inverted-Out" output switching stage,
and/or are actually 2x independent-channel "Dual Mono" units forced to work "in tandem",
while not having any "understanding or interlocking" between the channel states...).

- Simple adjustment of either Trigger-Threshold (short-circuit current detection level)
and/or Trigger--> Output Switchover Time (length of time the short must be present before output switches)
as available for User-Adjustment on better-designed units will solve these concerns for either "offset" or "perfectly-aligned" gap-situations...

- Locos with AWP mechs and pickup footprints measured in multiple-inches (think any contemporary multi-trucked locomotive model)
should not provoke such issues, as they create a "clear, unambiguous short-condition measured in seconds",
(front truck on Reversing section, while rear truck still sits on static-state rails
= clear "bonding" between the polarities),

which should be more-than-enough for any "Auto-reverser" unit
(even the poorly-designed or implemented-ones)
to get a Very Clear indication of what state each/both Output Rails should be in.

NOTE! having "Offset gaps" does NOT enable "the 2nd short/trigger input condition" to pass un-affected,
Rather, it allows the Switched-Output rails to achieve a congruent and stable-state relative to the adjacent static rails before the "2nd gap is bridged", and thus no actual "2nd short-circuit condition" actually occurs...

Upshot, while I have utmost respect for Bruce P and his wealth of DCC experience.
I've yet to see a justification for "Generally Accepted/Best Practise use of offset gaps" 
which isn't simply a "tactical field patch" over a "strategic failure" in the reverser-unit design, 
unit selection-for-purpose, or in-situ user configuration...

Happy Modelling,
Aim to Improve,
Prof Klyzlr

What I took notice of in one

What I took notice of in one of those articles that JoeF referenced,
https://s3-us-west-2.amazonaws.com/mrhpub.com/2015-01-jan/online/index.html?page=58

Biggest argument against staggered gaps

Short reversing sections

One situation where a short reversing section may occur is in a Wye that does not lead to dead-ends on any of its legs. If, for example, benchwork forms a 'T' and a single-track Wye is laid at the junction, with mainline extending from the wye in all 3 directions, any leg of the wye between turnouts is likely to be shorter than a train passing through the wye. 

Even a wye used for reversing an engine and another car together might, if the radii are sufficiently tight, have no sides longer than the engine+car.

Wye (is it so?)

Dear EW, MRHers,

Good Catch EW, must admit I hadn't thought of Wyes. However, again, this files neatly under "do your layout design research, and choose/implement the appropriate solution".

As Joe mentioned, locos have known linear lengths and pickup-footprints. The "reversing section" needs to be sized to suit, and in the case of MU consists, very likely means it's better to think in terms of a "Y" shaped reversing section (IE includes one of the 3 turnouts which form the Wye), rather than trying to encapsulate an uber-shorty-reversing section between (any) one pair of the Wye's turnouts.

As far as "metal wheelsets" go, perfectly-aligned styrene-filled 0.020" gaps mean that no single-wheelset
(EG the individual wheelset on a freight car)

can span both the "Static State" rails and the "Reversing section" rails at the same time.
they will have a period when they are riding/contacting solely on-top-of the styrene insulated gaps,
(a single wheetset with actual circular wheels has a "contact footprint" measuring in 0.00x" ),
and thus cannot cause a "double-trigger" or "timing race condition" within the Reversing Unit.
 

Where a Truck (a rolling assembly with 2-or-more metal wheelsets, think a freight car truck),
hits said "perfectly-aligned, styrene-filled 0.020" gaps", there is no Wheelset<> wheelset path, 
and thus each individual wheelset follows the principle above.
(whether said car is coupled ahead or behind of a loco as it traverses a "short encapsulated Wye revesering section" is irrelevant).

Where a Truck does have wheelset<> wheelset conductive paths measuring 1" - 2" long in "pickup footprint"
(EG an all-wheel pickup truck as found under Passenger cars,
ST "Soundcar equipped" cars and similar "sound-equipped reefers",
Ring Engineering "FRED" equipped cars, et al)

then yes, certainly having one of these following a loco thru such a "short reversing section" could well cause an un-expected "loco is exiting, while coupled/trailing sneak-path powered-car is entering" situation...
(Loco pickup-footprint is spanning one-end of the reversing section,
while powered-car pickup-footprint is simultaneously spanning the other-end ...)

This makes complete sense when you rationally "talk it out, out-loud",
but is the kind of "scenario-specific gotcha" that is not the reverser-unit's fault,
would not be fixed by "staggering the gaps", 
and is likely to "fly under the radar" until that one time when....
...I mean, it's a Car, not a Loco, you just don't naturally think about Cars as being electrically-significant...

Where a Car has multiple all-wheel-pickup trucks, with a pickup-footprint measured in 3" - 12" long in HO
(EG Passenger cars,
ST "Soundcar equipped" cars and similar "sound-equipped reefers", et al)

then it really should be considered under the same "long linear pickup footprint" headspace as we think about locos... Running a multi-F-unit-powered passenger train with all-cars-lit thru a "encapsulated shorty wye reversing section" is an arguable "perfect storm" recipe for disaster... which again, staggered-gaps simply will not do anything to assist...

...and the "dbl-gapping" technique, as noted in the PSX-AR doc, becomes problematic-in-practise,
as the "dbl-gap unpowered/ISO section length" at each end of the proper "reversing section" would need to approach> 1/2 the pickup-footprint length of the trailing "powered unit" 
(loco, lit passenger car, sound-equipped reefer, whatever),
in order to truly "trap" and solve the issue....

..and then we're talking about consciously creating multi-inch long sections of "dead rail" ,
(which is inherrently contrary to the very wheel/rail powered ethos the system is based upon),

to avoid a "reversing circuit shorting condition",
which really should have been resolved with proper before-we-even-picked-up-the-gap-cutting-Dremel analysis of the situation, in the first place....

Seriously, none of the conditions noted are insurmountable,
and virtually all can be eliminated-from-consideration from the outset,
if only we "do our complete-layout-design homework" well-before we pick up a Dremel or soldering iron....

Happy Modelling,
Aim to Improve,
Prof Klyzlr

Doing Our Homwork

That is what I was trying to do by starting this subject thread BEFORE I cut those insulation joints.

Seems like we have valid viewpoints from at least 2 actually experienced persons?