Tehachapi, BC

[Scottl]

I feel a bit dense here, but how does the styrene filler permanently prevent bridging?  If it wears down a little, then the problem could return, no?

[ednadolski]

I feel a bit dense here, but how does the styrene filler permanently prevent bridging?  If it wears down a little, then the problem could return, no?

I should think it would take quite a while to wear to that point (but what do I know any more?).   AFAIK people have been doing that sort of thing for frog gaps and such for a long time.  Anyways I suppose one could always replace it, or make the gap longer, if it really becomes an issue.  Or build it with an insulated rail joiner in the first place.

Ed

[jagged ben]

You can always put a short length (0.020" or so) of styrene or other insulator in the gap.  That will make it impossible for a single wheel to simultaneously contact both rails that may be at opposite 'polarity'.  The locos still will trigger the reversing detector.

Ed

Yeah, that's actually a great solution.  I agree with the number 0.020" as well.

And it will take a very long time for it to wear down in N scale.  We have some filled gaps like that on our club layout that have been there 20 years and are still functionally at the same height as the rail.

[Coxy]

+1

[GaryHinshaw]

Since I don't own a single passenger car as of now, I don't know how the pickup generally works; are the wheels in a truck typically tied together electrically?

Partially answering my own question here: I have some of the new Kato auto racks with the goofy trucks that pick up power from the track (lord only knows why...).  In any case, the contact strips do join the two wheels on the truck, so this would cause a problem for the proposed short-block solution.  I will no doubt alter or replace the trucks & couplers on those cars when I add weight to them (seriously, what was Kato thinking to make these so light?   )  so we're still a go, but it does give me pause that virtually any passenger train would have to be modified, or have special operating restrictions.

Before committing 100% to the short-block solution, let's revisit some of the alternatives explored in the old DCC thread.  The following schematics show two proposals, the "long-block" solution:


and the "medium-block" solution:


In the long-block scheme, the salmon-coloured section between crossovers 1 and 2 joins A and B into one long reversing section, longer than the longest freight train.  But this only satisfies the long-block criteria as long as a train remains on Track 1 (top main) while traversing the block.  Any train taking either crossover encounters a short block which is basically no better than the above short-block proposal.  If I add roughly the same length of Track 2 into the block I solve the crossover problem, except for the route UP/Bakersfield ⟷ storage.  I could also add the connector track down to storage into the block, but the distance between crossover 2 and the storage yard throat is only 12', shorter than the longest freight train...  (This is the track I'm ready to lay permanently, hence the timeliness of the matter).

In the medium-block proposal, the two blocks are longer than the longest passenger train (I think I can swing that).  But having both main lines in a block means that I have to carefully manage traffic on the two mains.  For example, I couldn't have trains enter and leave the yard at the same time on tracks 1 and 2 without very careful management.   I really don't want the yardmaster to have that kind of responsibility.  I could place the burden on the signalling system, but that is a ways off, and still prone to human error. 

Another option is for block A to be 7' long on Track 1 (and limit passenger trains to 7'), then make the entire Bakersfield yard a reversing section.  But that still has the problem that trains can't enter and leave the yard simultaneously on Tracks 1 and 2.

Now you see why I crave a short-block solution.  The only disadvantage to it that I see is the "passenger train problem" but the operating restrictions for freight are quite minimal, even with rear helpers.  If nothing else, this has been an interesting design problem to think through.

Thanks again for your feedback.

[Coxy]

For discussion purposes, below is one possible solution to the long reverse block solution. The key concept is that one or more reversing sections will always fully accommodate the maximum length train before it re-enters a normal block which is the key to ensuring zero reverse block shorts.

Operationally, trains would have to hold clear of the boundaries between occupied reversing and normal blocks and only enter a reversing block if it is unoccupied. As long as this condition is satisfied, trains could traverse any route on the schematic without any fear of show-stopping shorts.

Bakersfield yard throats and tracks are all normal blocks. Trains may happily enter and exit both ends of the Bakersfield yard simultaneously. If needed, trains may even access the same Bakersfield track simultaneously from both ends without risking shorts.



Life's full of compromises. The possible downside to this plan is that throughput is lower than desired. For example it may be desirable to have trains move more assertively through the plant to facilitate faster relocation of trains between storage and staging. It may also be desirable to have trains stop at locations other than reverse block boundaries as shown, that are better for operators due to track visibility or access. If so, the reverse block arrangement can be carved up in to progressively smaller reversing sections (at the cost of additional reversing modules) which allow trains to move closer to the various junction points in the schematic per the schematic below.

The schematic below shows each reversing block subdivided to allow trains to hold at the crossovers and junction points. A single train could occupy multiple reversing sections in the plan below without fear of creating a short. The same overall constraint applies that if a reversing block is occupied, a short may be created if another train enters that reversing block from a normal block. However, given the way the reverse block boundaries line up with typical control point boundaries, that should not be a problem.



So the basic trade-off appears to be operational considerations (hold points and throughput) vs. cost of additional reverser units.

[Sokramiketes]

Not only is a single Kato passenger truck's axles connected electrically, but both trucks will be connected when you install either car lighting or want to drive a rear marker light on the passenger special.  Now the styrene gap needs to be 85' long!

Did I miss in the narrative why you can't flip polarity on the end loops themselves, and leave everything in between alone?  You really want the polarity of both the E and W mainlines to be the same on the rest of the layout so you aren't farting around with every crossover between the two.

[GaryHinshaw]

Not only is a single Kato passenger truck's axles connected electrically, but both trucks will be connected when you install either car lighting or want to drive a rear marker light on the passenger special.  Now the styrene gap needs to be 85' long!

I figured as much...  Thanks.

Did I miss in the narrative why you can't flip polarity on the end loops themselves, and leave everything in between alone?

Yes.  In addition to the yard, the connector track from the end of the SB main back to the NB main is a reverse section.  Also, if I make the yard a reverse section, I still have issues with trains simultaneously entering on Track 2 and leaving on Track 1, no?

Coxy, thanks for your proposals.  Your 2-block scheme is similar to one in the old DCC thread.  At the time, it raised a question that I never found the answer to: what happens when you have two adjoining independent reversing sections?  If they start off with the opposite polarity, why don't the two reversers duke it out in an infinite loop of simultaneous polarity switching?  This may be an unlikely scenario, but not a forbidden one, as far as I can tell.   

[ednadolski]

Not only is a single Kato passenger truck's axles connected electrically, but both trucks will be connected when you install either car lighting or want to drive a rear marker light on the passenger special.  Now the styrene gap needs to be 85' long!

How is that different than any loco with all-wheel pickup (ie, most locos)?   Longer gaps are not needed for those.


Ed

[Bendtracker1]

Not only is a single Kato passenger truck's axles connected electrically, but both trucks will be connected when you install either car lighting or want to drive a rear marker light on the passenger special.  Now the styrene gap needs to be 85' long!

Mike, Not sure if you mistyped your statement or not, but regardless, whether you have car lighting or a drum head installed makes no difference in the KATO passenger cars.

There are two strips that run from the front to the rear of each car that connects the front AND the rear trucks together electrically.   When the lights are installed, they just make contact with those two strips.
Or at least the older cars are made that way.

[Sokramiketes]

How is that different than any loco with all-wheel pickup (ie, most locos)?   Longer gaps are not needed for those.


Ed

Even the .020" gap isn't needed then, right? 

With the short block you're assuming that all the engines fit in the reversing section before it triggers again.  Having a train full of engines would be the same issue as running passenger trains, where the whole train doesn't fit in the reversing section.  And that's what I thought you were trying to solve with the .020" gap so metal wheelsets didn't trigger the reverser, while the reversing section was full with the end of the train still crossing the gap.

[Sokramiketes]

Mike, Not sure if you mistyped your statement or not, but regardless, whether you have car lighting or a drum head installed makes no difference in the KATO passenger cars.

There are two strips that run from the front to the rear of each car that connects the front AND the rear trucks together electrically.   When the lights are installed, they just make contact with those two strips.
Or at least the older cars are made that way.

Yes the strips are in the car to start, but could be removed to isolate the trucks.  I was just bringing up the point two steps later when you want to go back and use the pick-ups for lighting, you're going to want both trucks picking up power, and then have an 85' long jumper.  So the .020" gap solution is not really a solution.

[C855B]

Yes the strips are in the car to start, but could be removed to isolate the trucks.  I was just bringing up the point two steps later when you want to go back and use the pick-ups for lighting, you're going to want both trucks picking up power, and then have an 85' long jumper.  So the .020" gap solution is not really a solution.

Well, if it was seriously an issue you could cut the strips in half and have each truck independently feed a bridge rectifier, the output of which would then feed the lighting circuit. Yeah, PITA, but solves the problem. Or forget Kato's lighting kits, pull the wheel wipers so even a single truck doesn't bridge the gap and use Rapido's Easy-Peasy setup. There are ways around it.

[ednadolski]

Having a train full of engines would be the same issue as running passenger trains, where the whole train doesn't fit in the reversing section.  And that's what I thought you were trying to solve with the .020" gap so metal wheelsets didn't trigger the reverser, while the reversing section was full with the end of the train still crossing the gap.

Oh I thought the concern was about the metal wheel bridging the gap, which even if it does not trigger the reverser still could cause arcing (even if you may not see it, it's not a desirable thing).

Long trains with trailing DPUs are also a concern if the reversing section is too short.  Will the passenger trains be as long as the freight trains?  On Tehachapi I thought they would generally not be quite that long.

Ed

[C855B]

My concern is not so much being able to contain an entire train in a reversing district, but having two or more trains entering or exiting a reversing section, each needing to adjust the polarity for their routing. I have an uncomfortable feeling given this discussion I will need 4X more reversers for the GC&W than I originally thought. Plan execution is a long way away, but, still... ugh.