Two N Scale Turbo Trains, 50 Years Apart

[Dwight in Toronto]

This pic simply shows the 2-wheel truck attached to the coach bulkhead:



In this pic, I’ve started roughing out a vestibule cover, which I hope to be able to snap-fit, by pushing from the top down, to cover the bogie assembly:



Here is a trial fit showing the tube on the bogie inserted into the hole in the bulkhead.  In this pic I’ve also fashioned and crudely shaped a vestibule cover, having closely followed the dimensions and contours of the Rapido design, shown just to the left:

[Dwight in Toronto]

@peteski  - thanks for commenting.  Peter, you are SO absolutely spot-on with your observations regarding how both Rapido and Bachmann managed to keep the 2-wheel trucks aligned properly on the track.  I recognized this issue right from the get-go, and I realize that my preliminary design is indeed susceptible to the bogie “crabbing” that you allude to. 

Nevertheless, I decided to proceed with my experimental approach, accepting that I will try to cross that bridge when I get to it.  And it may certainly turn out that when I DO get to that bridge (which will be soon), I may well never find a way to cross it, and it will be back to the drawing board.  And maybe you and the fellas here will have some ideas?

Anyway, for now, here’s where I’m currently at … I opened up the rear end of a second coach, fashioned another bulkhead insert, and managed to get the first two trial coaches connected:



Although I haven’t tried pulling the two coaches with a locomotive, I already know that the bogie is going to free-wheel and “crab” around.  So, I’m at that bridge!   I’m away for a few days, and will be mulling over possibilities … and I will always welcome thoughts and suggestions from my RW peers.  In the meantime, thanks for following. 

[peteski]

Why not retain Bachmann's original double-pivot design but just rebuild it (shorten the coupling arms, or move the bulkheads farther into the car) so the cars can be coupled closer, and also add a diapghram?

[Point353]

Both of my Bachmann TurboTrain models have run fine - without any modifications - once I did the following:
1) adjust the mounting screws for the single-axle trucks, as necessary, so that the trucks pivot freely.
2) lubricate the pins on the single-axle trucks, onto which the adjacent cars couple, with Labelle #106 grease.
3) inside the rear/unpowered power dome car, grease the slots in which the two-axle truck pivots so that it doesn't bind. 

[wm3798]

With the ends of the coaches open, the temptation to add lighting, and perhaps a bus wire to pull pick up from the "dummy" power car might be to much to resist.... A little interior detailing could be a necessity if you light them up.

Looking forward to the test results from the mechanical department, though.

Lee

[Dwight in Toronto]

With the ends of the coaches open, the temptation to add lighting, and perhaps a bus wire to pull pick up from the "dummy" power car might be to much to resist.... A little interior detailing could be a necessity if you light them up.

Looking forward to the test results from the mechanical department, though.

Lee

Hey Lee, it was nice to have met you in Altoona, and I enjoyed our short chat about the DKS vintage layout. 

I admit that I DID dwell on the possibility of adding LED’s to the coaches, but decided that I already had my hands full with figuring out an alternative way of coupling the cars with single-axle bogies.

Having puzzled over how to prevent the “crabbing” problem, I’m giving this approach a try:



I finally found a use for all those springs that were in the old Rapido-style couplers!  In this pic, the springs have been recessed into bore holes and retained with a tiny drop of epoxy.  Once the glue sets, I’ll make two small styrene blocks to affix to the platform, butted up against the face of each spring.

At this point, I have no idea if this is going to work.  But in my mind’s eye, I can see either spring compressing just enough as the coaches traverse a curve, and then pushing the vestibule back into a “the straight-&-narrow” parallel orientation once out of the bend.

Fingers crossed!

[peteski]

I don't see any physical connections between those springs and the free-swiveling single-axle, single-pivot-point bogie, so I'm not sure how they will reduce the crabbing.  The single axle bogie will still be able to go askew. All the springs will do is to keep adjacent cars under tension.
 I still think the Bachmann's original dual-point pivot was an elegant solution.

Another alternative (which is possible due to the loose tolerances and short car lengths) would be to permanently attach the bogie to one of the cars, and just connect the next car to the pivot. The axle will always stay aligned with the single car and will likely not even be noticeable that it doesn't perfectly follow the curves in the track.

[Dwight in Toronto]

Peter - the key items missing in the photo are the two “blocks” that I refer to in my explanation.  Apologies for not being clear enough.  Once the epoxy sets up and has a firm grip on the springs in the bulkhead, I’m going to fashion two small styrene blocks, or curbs, and will solvent-weld them to the vestibule platform such that they butt up against/contact the front face of each spring. 

Does that help?  I hope to get the next steps done by this evening, and will post another pic then.

I agree that the Bachmann coupling approach was simple and workable. But this project just kinda sprung up suddenly - I was looking for another styrene scratchbuild to further my skills, and this bit of fun seemed to comply.  The old Bachmann set was sitting abandoned for 40-odd years, so I figured nothing ventured nothing gained. 

I have toyed with the thought of rigidly attaching the vestibules to one end of each coach, but will save that as a fallback option should all else fail.

Although not nearly as exotic of an endeavour as many of the projects we see here, I can say that a myriad of tools and techniques have been called into play thusfar, and it keeps me thinking.  If it ends up being an exercise in futility, no problem … I’ll have learned more stuff, and will have had fun doing it.  Thanks for following along, and partaking in the thinking!

[peteski]

Yes, if the blocks are added to the bogie platform and another pair of springs is also present in the adjacent car, that could be a workable solution.

[wm3798]

Clever use of stuff that's laying around all of our workbenches...

It was fun meeting you too.  Thanks for venturing South of the Border!
Lee

[Dwight in Toronto]

The experimentation continued, and I’m happy to report that the idea of using two old rapido coupler springs to prevent single axle bogie ‘crabbing’ worked like a charm.

Here’s a closeup showing the two small styrene blocks positioned and cemented in place, such that they are just touching the face of the springs when the coaches are in parallel alignment on a straight section of track.  The trailing coach is connected by pushing the “C” clamp over the styrene post in the centre of the vestibule.  The vestibule cover is off to the side, for clarity.




Here’s an overhead view on a section of 15” radius Unitrak, showing slight compression of the inside spring:




And a wrap-up shot showing the vestibule cover in place:




Manually dragging the coupled cars between curved and straight track verifies that the springs gently push the bogie back into the desired ‘at rest’ parallel orientation.  I would have to make a short video to demonstrate, but not really necessary for this crowd!

So, proof-of-concept is a “go” … now I just have to make 3 more coupler/vestibule assemblies.

Before doing that, I might turn my attention to refurbishing the old Bachmann mechanism, and get it working smoothly on DC.  I might try my hand at making the locomotive’s single axle bogie into a track-powered pickup configuration for more consistent and reliable motor operation.  And so a new round of brainstorming and try-&-see scratchbuilding begins!

[peteski]

LOL!  I thought you were going to use 4 springs (2 in the end of each car to equalize the forces.)

If the bogie is free swiveling I guess I don't understand what forces it to twist. When on a curve does the bogie platform push against the end of the spring-less car?

[Dwight in Toronto]

Peter - I too thought that I might have to resort to 4 springs, but was hoping that just the 2 would work.  Luckily, it did.  I was worried that 4 springs would impose excessive force, with an increased liklihood of derailments, so seeing it work with only 2 springs was bonus!

And you know what - I’m not sure what is forcing the bogie to twist.  Because it is indeed free swiveling, you would think that the two springs would be striving to keep it parallel with the coaches while traversing a curve.  I was expecting it to behave similarly to that fall-back scenario we proposed where the vestibule could be firmly attached to, say, the leading coach, with only the trailing coach allowed to swivel.  But that’s not what happened.

And you may be right about the bogie platform contacting the bulkhead in the springless car.  But I think that the coaches would need to be on a sharper curve than the 15” radius I’ve been using in order to come into hard contact.  I’ll have to pay closer attention to that when I get back to it.  But hey, good thinking … (man, you’re good!).

[peteski]

I'm enjoying watching your experiments.  Never too old to learn something new. 

[Dwight in Toronto]

I’ve briefly turned my attention to exploring how I might configure one of the single axle trucks for track power pickup. 

The original Bachmann design solely relies on a piddly two axle/4wheel gear-driven bogie located at the front end of a single powered cab.  If I can pick up power with the rear wheelset, it would be located roughly 4” rearward of the driven mechanism, and would provide a desperately needed additional source of voltage to help ensure continuity through turnouts etc.

Some time ago, I had purchased a handful of small wheel-wiper assemblies made by ESU.  As shown in the following pic, these things are somewhat dimensionally compatible with the single axle truck.  Here, I’ve unsoldered two of the wipers from the pc board, just to see what I might have available, material-wise, to play with.  Note that the copper wipers already have a small dimple embossed in the ends:




In this next pic, I’m showing a couple of possibilities. 

First, the tweezers on the right are crudely holding one of the copper wheel wipers in a position where the dimple is located over the point where the sharp axle tip gets inserted (I have no idea at present how I would affix the wiper to the delrin bogie).

Second, the 2-axle truck is from an Athearn bi-level Bombardier commuter coach (yeah, those cringe-worthy abominations!).  As it happens, the wheelsets in these things consist of half axles within friction-fit tubes … nice for track power isolation.  Unfortunately, the Athearn wheels don’t have pointy axle ends.

Thirdly, I thought maybe I could cut a Rapido wheelset in half, and then insert the axles into the Athearn ‘joiner tube’.  Again, unfortunately, the axles are different diameters … 0.058”/1.48mm for the Rapido, and only 0.046”/1.17mm for the Athearn.  Maybe I can find some other tubing or some such thing to fit over the Rapido axle.




Funny how these projects often seem to be one baby step forward, then two steps back!