Tehachapi, BC

[ednadolski]

Mostly it's a tongue-in-cheek comment on the fact that I have designed a complicated configuration of loops under the main loop.

I'll try to refrain from making any references to "backed up" traffic.... oops, I just did... oh well... 

Coincidentally, Jim Kelly's column this month (Sep MR) has a story about a train breaking loose from its locos in an enclosed helix on his Tehachapi pike.

Yah, IIRC he blames the crash on truck-mounted couplers.  But how's this for a helix test:

Around and around it goes...

Ed

[robert3985]

I don't think it's necessarily a mutually exclusive thing--that a helix that's not entirely visible is also difficult to access. Perhaps just a cloth drape velcroed across the front (or something along those lines) would be relatively aesthetic, yet offer more than adequate accessibility.

+1

[ednadolski]

Aha, here is the helix test I was looking for (nice work CK!):

Design observation: that lead-out at the bottom is *really* important!   Even tho there is an S-curve, if that train were heading into an uphill grade, and/or some further curvatures, that kind of test could have some undesirable results.

Ed

[GaryHinshaw]

My IKEA benchwork kit showed up yesterday:



All the parts needed to make the helix support shown in grey in this drawing:



Every piece has a slightly different length and mitre - hopefully they all fit...   In the drawing, the black track connects to the storage yard shown earlier and the brown track is the mainline between Bakersfield and Edison, which makes one loop to gain elevation so that Edison will clear the storage yard beneath it.  The Mojave staging helix will rise directly above this loop to join the upper deck.  At the bottom of the helix, you can either proceed directly to the storage yard, or join the Edison-Bakersfield line at the crossover to enable continuous running via the Bakersfield balloon track.

I got the black benchwork and roadbed installed last weekend, but I'll hold off on further pictures until the construction mess is cleaned up. 

-gfh

P.S. Thanks for the helix feedback.  Hopefully the arrangement I have at the bottom will accommodate the occasional runaway!

[C855B]

My IKEA benchwork kit showed up yesterday:

...

Where's the little Allen wrench?

 

[RSWController]

Looking good.

[GaryHinshaw]

Where's the little Allen wrench?

 

[ednadolski]

Where's the little Allen wrench?

I found it stuck in the back tire of my car the other day.... 

Ed

[GaryHinshaw]

The lower-level roadbed for the Vortex™ is now in place and I am ready to lay track (photos to follow).  However, before I install feeders, I must come to grips with my plans for auto-reverse sections.  I have a year-old thread in the DCC section with some ideas, but I thought I would post my final plans here instead of dredging that one up again.  Here is the schematic stripped down to the essentials, and my current plans for reversing sections (A and B, shown in red):



Some key points about traffic flow:
* The Bakersfield staging yard is an 8-track balloon which crudely mimics Kern Junction where UP and BNSF split onto their separate lines and terminals.  UP trains would arrive/depart from the top side and BNSF from the bottom (but every track connects in the balloon).

* The stub-end storage yard connects to both Bakersfield staging and to Mojave staging (not shown, but where the S is).  Traffic will be busy in and out of Bakersfield for both the normal mainline trains and for transfer jobs between the 3 yards, so I need to be wary of having trains spanning both ends of any reversing section.

* In the old thread I had a scheme for one reversing section that would have been about 18' long (greater than the longest likely train), but it required the two crossovers, 1 and 2, to be reversed L⟷R and that turns out not to support the traffic flow I have in mind.  The crossovers shown above allow 1) transfer jobs between storage and Bakersfield to enter/leave either side of Bakersfield and 2) SB trains taking the cutoff back to the NB main to achieve right-hand running for the remaining 10-12' run into Bakersfield.

I think the plan above with 2 short reversing sections meets all of my needs with respect to traffic flow.  The two sections would each be about 3' in length: longer than my longest MU'd lash-up, but short enough that no other train will be bridging the other end of the section at the same time.  It would also work fine with rear DPU's.

As far as I can tell, the only sacrifice I make with this plan is that I can't easily support lighted passenger trains that would span either reversing section, but I really have no interest in such trains.  If I were to make these sections longer to avoid that issue, I increase the risk that heavy freight traffic bridges both ends due to operator error, a much more likely scenario.  Am I missing any other obvious pros or cons with this scheme?  Have I missed any obvious shorts?...  For reference, the line between A and B is about 10' long.

Thanks for looking.  Progress photos coming soon.

[jagged ben]

Hmmm... 
I think that rolling stock with metal wheels could still cause problems for your short reversing sections.  Some testing might be in order.  Remember the shorts occur directly through the wheels, and therefore do not actually require lighted passenger cars or DPUs or any other power consumption.

I still think than an X-block or two could be your friend.

[Coxy]

I agree with Jagged Ben. Metal wheels may cause intermittent problems with short reversing sections on occasions when both ends of the reversing section are simultaneously bridged to the adjacent track by metal wheels. In that moment, the reverser flips to neutralize the the short, in doing so creates a short at the other end of the reversing block. The unit would switch polarity of the reversing block back and forth with a short present continuously at one end or the other. The effect would be worst if a train was stopped.

No metal wheels, no problem.

If you do plan to use metal wheels, the safe and most reliable solution is to ensure that all trains fit entirely into individual reversing sections and only one train at a time is permitted to occupy the reversing section. The overall design objective is always the same - that both ends of the reversing section will never be simultaneously shorted with adjacent tracks having opposite polarity from one another.

We'd need to know the block lengths and block boundaries on your schematic to propose alternate reversing blocks that operate that way.

[GaryHinshaw]

I was worried about metal wheels too, but then I re-read this post.  I don't think the explanation in that post is correct: as long as one metal wheel bridges a polarity gap across one rail, you have a short.  But there is still potential truth to the statement that metal freight car wheels don't cause a problem because the time span over which a wheel bridges a gap is very short compared to a loco.  Is there a particular time constant in the reversing circuitry that tries to distinguish these cases?

I'll post a more detailed schematic of the section in question.

[Coxy]

Timing will be important. It may be that you rarely see problems and that works for you. You could build as planned and see if you can generate a short. However, if you want to be assured there'll never be a problem with shorts at the reverse blocks, you'll have to structure things to make sure it cant happen in normal operations.

[ednadolski]

I don't think the explanation in that post is correct: as long as one metal wheel bridges a polarity gap across one rail, you have a short.  But there is still potential truth to the statement that metal freight car wheels don't cause a problem because the time span over which a wheel bridges a gap is very short compared to a loco.

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

[GaryHinshaw]

You can always put a short length (0.020" or so) of styrene or other insulator in the gap. 

Brilliantly simple!  That solves it.  Maybe I should get some of that rubber rail the N Scale Kits uses for their welded rail train.

So, as an aside, I have been following the Kato FEF hoopla and will probably end up getting a UP excursion train...   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?

Thanks gents!