MR announces new coupler from JTC

[jagged ben]

I think you missed my point.  There should be slack action.  (I'm going to delete the non-slinky part because now I realize it's a complete distraction for so many of you.)

It should be a round post in an oval hole.

[ednadolski]

It should be a round post in an oval hole.

Would that still work?  Seems to me, the round post is needed in a split-shank design, to keep the top/bottom halves aligned and pivoting correctly.

Perhaps there would be enough play between two mated couplers, to give the impression of some slack action.  That would differ from the TSC, where the two joined couplers have almost zero play, and behave more like a drawbar.

Slack action is prototypical, slinky is not.   That said, these will be pretty small parts and it will be a substantial challenge just to make them work reliably.  No functional model coupler can ever be 'perfect' (sorry to use another loaded word), so JMHO limited slack action seems like a reasonable trade-off.

Ed

[ednadolski]

While maybe not a conventional straight whisker, it is not a MTL-type compression coil spring either.  To me that spring is more like extended whisker than coil.  That is why I called it  a "single whisker-type" spring. It's all in the semantics I guess.

Wouldn't that be a (micro) torsion spring?   Basically, with a single winding.

https://www.leespring.com/micro-springs
https://www.leespring.com/torsion-springs
https://www.amazon.com/small-torsion-spring-Industrial-Scientific/s?k=small+torsion+spring&rh=n%3A16310091

Ed

[learmoia]

If you lengthened the pivot hole slightly of the VRK coupler you should get the realistic slack action your looking for..

~Ian

[Ike the BN Freak]

Wouldn't the play in the tolerances of the coupler head/knuckle give slack also? I doubt the coupler head will be as tight as a prototype coupler.

[Sokramiketes]

The tight coupling of a MTL TSC sorta helps it stay together well despite the smaller head.  So remember if we move toward a smaller head and try to keep the same floppy nature, performance will suffer. 

Couplers are still hard. 

[peteski]

Wouldn't that be a (micro) torsion spring?   Basically, with a single winding.

https://www.leespring.com/micro-springs
https://www.leespring.com/torsion-springs
https://www.amazon.com/small-torsion-spring-Industrial-Scientific/s?k=small+torsion+spring&rh=n%3A16310091

Ed

Sounds good to me.

[learmoia]

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~Ian

[turbowhiz]

I’ve posted on slack before so I won’t completely repeat myself:
https://www.therailwire.net/forum/index.php?topic=54237.msg744535#msg744535

It’s very clearly evident based on the picture that the VRK coupler will have some slack in the knuckle, so that should satisfy a desire for slack without needing to add more of it elsewhere, which will definitely lead to more problems.

Draft gear movement, which honestly is where any visible “slack” exists in the prototype especially in N scale terms, you have your perfect model for that in the existent MTL design. And we all know how that turns out! (SLINKY to be super explicit). Physics doesn’t scale.

Excess free play in the pivot post (or knuckle) will lead to “wiggle jiggle” in some circumstances. I noticed this effect in my development process when I had subtly too much (like  ~.004”) free play in my own boxes. It takes the right circumstances to occur, but its noticeable when it does.

In this designer’s opinion slack is very much a bad thing in small scale model trains. The TSC and my own N-Possible scale head couplers DO have slack in the head, but not much. Technically an overscale amount.  Things operate (and I mean operate, switching, not just roundy-round) SO much better with low slack couplers. Physics doesn’t scale, so your trains will operate much more prototypically in appearance (No “wiggle jiggle”… technical term. Not to be confused with “Slinky”) and more importantly in a mechanically reliable fashion without intentionally adding slack. Everything is a tradeoff, nothing is ever 100% perfect, but on balance I’m strongly in the “slack is bad” camp.

Couplers are hard!

[thomasjmdavis]

I am not an expert on cushioned underframes, but my understanding is that when a train has a large number of cars so equipped, a lot of what we view as "slack" is the expansion and compression of the cushioned underframes as the train accelerates or decelerates.  Which cannot be simulated by the coupler (and it strikes me as unreasonable to ask that coupler manufacturers simulate it), although I suppose someday a clever model designer will come up with an N scale underframe with a shock absorber of some description built in, that will allow for that 6 or 8 scale inch compression, and add another $15 to the cost of a freight car.

[ednadolski]

... I suppose someday a clever model designer will come up with an N scale underframe with a shock absorber of some description built in, that will allow for that 6 or 8 scale inch compression, and add another $15 to the cost of a freight car.

To me this sounds like a sure recipe for the slinky effect, so no need to wait for 'someday', or pay more for it.

Scale models cannot simulate the potential/kinetec energy, momentum, inertia, friction, etc. of an actual train.  If our models could be as free-rolling as the prototype, then we surely would also need scale brakes to apply/release, every time we tried to spot or pick up a car.  Those are all just a starting point for where the physics does not scale.

"Realism" in models reaches a point of diminishing return.  Otherwise we just could try to get a job working on a real railroad somewhere. 

Ed

Aside: all that being said, it would be way cool if our models could have an audio simulation of the couplers 'groaning' as the 'slack' runs in and out.

[ednadolski]

Couplers are hard!

Yes, as evidenced by the fact that model trains have been around for decades and still do not have a generally accepted solution that works for most cases.

Just to raise the bar:  @turbowhiz  do you think your design could work as a scale-sized (or close) coupler in N scale, and/or as a Z scale coupler?

Ed

[turbowhiz]

I am not an expert on cushioned underframes, but my understanding is that when a train has a large number of cars so equipped, a lot of what we view as "slack" is the expansion and compression of the cushioned underframes as the train accelerates or decelerates.  Which cannot be simulated by the coupler (and it strikes me as unreasonable to ask that coupler manufacturers simulate it), although I suppose someday a clever model designer will come up with an N scale underframe with a shock absorber of some description built in, that will allow for that 6 or 8 scale inch compression, and add another $15 to the cost of a freight car.

Here is a great image that sums up how the prototype works:



A functional version of a sliding sill cushioned underframe has been modelled in HO scale by Kadee. Its cool, and is a great way to understand how the prototype actually works, but its utility in a model is non-existent. Technically would be possible to do in N scale too, but its not going to show any “slack” action unto itself.

Modern car cushioning devices seem to be very much of the end of car style. See my previous post about that; But in effect it won’t scale well.

[jagged ben]

Would that still work?  Seems to me, the round post is needed in a split-shank design, to keep the top/bottom halves aligned and pivoting correctly.

Every existing split shank design has some other design element between the shanks to keep them aligned (with I guess the exception of the TSC, which has no slack).  Accumate and Kato have an additional pin and slot between the shanks.  MT has the trip pin.  Anyway if the axis of the oval is aligned in the direction of travel I don't see how it would affect the pivoting. 

Perhaps there would be enough play between two mated couplers, to give the impression of some slack action. 

This play is why my locomotive lashups come apart when one loco has a very momentary issue with track pickup.   I absolutely despise this approach.  Please give me knuckles that stay closed when shoving, as tight as reasonably possible like the prototype, and put a tiny bit of slack in the draft gear (I'm not asking for much).   

[jagged ben]

...

Excess free play in the pivot post (or knuckle) will lead to “wiggle jiggle” in some circumstances. I noticed this effect in my development process when I had subtly too much (like  ~.004”) free play in my own boxes. It takes the right circumstances to occur, but its noticeable when it does.

I have no idea what you mean by "wiggle jiggle" and whether it's something I would care about.  Curious if you can describe it better or show a video.

In this designer’s opinion slack is very much a bad thing in small scale model trains. The TSC and my own N-Possible scale head couplers DO have slack in the head, but not much. Technically an overscale amount.  Things operate (and I mean operate, switching, not just roundy-round) SO much better with low slack couplers. Physics doesn’t scale, so your trains will operate much more prototypically in appearance (No “wiggle jiggle”… technical term. Not to be confused with “Slinky”) and more importantly in a mechanically reliable fashion without intentionally adding slack. Everything is a tradeoff, nothing is ever 100% perfect, but on balance I’m strongly in the “slack is bad” camp.

I may be in the minority but I would like to run 40 car trains with DPUs pushing the rear quarter to third.  I'm pretty sure if there isn't at least an inch or so of slack in the train that's going to cause problems on a curve somewhere.    1" over 40 cars works out to about 0.0125" of slack per coupler (0.025" per car) minimum.  Just kinda guessing here, maybe it doesn't have to be that much.  But if there isn't enough slack for that to work I'm not personally likely to be a convert to a different coupler, FWIW. 

Couplers are hard!

Fair.