N Scale freight cars jerking, how to fix?

[Maletrain]

Another approach to stretching the train out by putting more resistance at the rear end is to use a track cleaning car as the last car.  A pad under the car that rubs on the rails both provides enough drag to keep the couplers stretched out, plus it does the useful job of keeping the tracks clean.  Putting a small fiberboard pad on two posts that slide vertically through holes in the bottom of a car makes a useful track cleaner.  If you don't use cabooses, you can do it with cars that are equipped with Flashing Rear End Devices (FREDs) that will always be the last cars.

[John]

The prototype slinky's

[ednadolski]

As Bryan wrote, a heavier free-rolling car will offend less than a lighter car with high friction rolling qualities. You can see the high friction action as the car is pulled but sticks until the force overcomes the friction and the car suddenly moves until friction takes over again and the whole process recurs over and over.

Starting any car involves overcoming friction and mass, and the energy to do so is stored in the coupler springs, as either tension or compression (depending on direction).  Once the car is moving, the springs want to release that extra energy so they can return to their normal equilibrium state. As the springs release their energy it transfers back to the adjacent cars in the form of a change in momentum (ie, an acceleration or deceleration, again depending on the direction).  As the car momentum changes the energy again transfers back to the springs, and this oscillating cycle is what we see as the pogo effect.

If all factors (friction, speed, etc.) are kept perfectly constant, then the oscillations will eventually dampen out due to transfer losses in the system.  In the real world however this will rarely be achieved, since there are always minute variances in friction, speed, track grade, and such.   And of course, the dynamic behavior becomes increasingly complex as you add more cars, since each one will have its own slight variations in mass, friction, spring constants, etc.

You can change the behaviors by varying mass (weight) of the car(s), and/or the friction (drag springs).   But really all this does is change the precise conditions at which the resonances will occur -- hopefully to a point where it is less objectionable, but in principle the resonance cannot be eliminated as long as there are springs in the system that will store/release energy (which is the principle function of a spring, after all).


Ed

[ednadolski]

The prototype slinky's

To a point, but nothing like our models.   If the prototype were anything like our models, there would be more broken couplers, damaged cargoes, derailments, and injuries/deaths.

(Edit: and the prototype would never add constant drag to freight cars, since it would increase fuel costs and increase the risk of derailments.)

Ed

[peteski]

To a point, but nothing like our models.   If the prototype were anything like our models, there would be more broken couplers, damaged cargoes, derailments, and injuries/deaths.

(Edit: and the prototype would never add constant drag to freight cars, since it would increase fuel costs and increase the risk of derailments.)

Ed

Yhs, we should operate our tiny trains exactly like the 1:1 railroads do because everything scales perfectly, right Ed? 

The "slinky effect" discussions can often get as intense as discussions about politics and religion.    Actually DC vs. DCC, and which DCC system is better can be like that too (but for some reason we have not had any of those discussions for some time.

[ednadolski]

... because everything scales perfectly, right Ed? 

Don't see where I ever said anything like that.  I was just responding to John's post.

Ed

[Doug G.]

I think DC systems without springs are better than DCC systems with springs.



Doug

[jdcolombo]

I've found that using MT1015's (sorry, the McHenry looks awful to me), weighting all my rolling stock to at least 1 oz., and using a pair of axle springs on my cabeese essentially eliminates the slinky effect when pulling trains.  There is still some when doing switching moves, but aside from putting axle springs on every piece of rolling stock (which would severely cut the number of cars my Berkshires could pull), I haven't found a solution for that, and just live with it.

I keep hoping someone will design a functional knuckle coupler closer to scale size (akin to the MT Z-scale coupler) with a "springless" (e.g., maybe leaf spring centering) design to eliminate the slinky effect entirely while also providing a better-looking coupler.  Until then, MT still gets my business for the best combination of operation, looks, and array of mounting options for odd cases (though nearly all rolling stock and engines manufactured since the late 2000's can use a 1015).

I don't know why manufacturers have managed to give us near-prototype detail, fine-scale metal wheels, and operationally flawless engines, and still can't come up with a better-looking and operating coupler.  Is it really that hard?

John C.


 

[ednadolski]

I keep hoping someone will design a functional knuckle coupler closer to scale size (akin to the MT Z-scale coupler) with a "springless" (e.g., maybe leaf spring centering) design to eliminate the slinky effect entirely while also providing a better-looking coupler.

(Pics by @GaryHinshaw)

Ed

[Ike the BN Freak]

Actually DC vs. DCC, and which DCC system is better can be like that too (but for some reason we have not had any of those discussions for some time.

These are all happening over on the Facebook groups

[nkalanaga]

"I don't know why manufacturers have managed to give us near-prototype detail, fine-scale metal wheels, and operationally flawless engines, and still can't come up with a better-looking and operating coupler.  Is it really that hard?"

Yes - as the prototype found out in the late 1800s.  To be widely accepted, any new coupler almost has to be compatible with the existing "standard".  Most model railroaders aren't going to convert all of their equipment to a new coupler just because it looks a little better.  As long as the old ones work, they'll save their money, and time, for things they'd rather have.

If MT could make their Z/Nn3 couplers in styles interchangeable with the various N couplers, they would probably, eventually, become the standard.  The Z couplers will work with the N, but as it is, they only come in one body-mount version, and it requires a mounting hole that doesn't match the common N boxes.  If they were easy to swap, modelers could change a few cars at a time, and it wouldn't be a big hassle.

The prototype had the same arguments when switching from link-and-pin to knuckle couplers, and it took federal regulations to force the holdouts to change.  The European railroads have designed more than one very nice automatic coupler, but the cost and effort of changing was just too much, so they've kept the screw-link couplers for most purposes.

[peteski]

"I don't know why manufacturers have managed to give us near-prototype detail, fine-scale metal wheels, and operationally flawless engines, and still can't come up with a better-looking and operating coupler.  Is it really that hard?"

Yes - as the prototype found out in the late 1800s.  To be widely accepted, any new coupler almost has to be compatible with the existing "standard".  Most model railroaders aren't going to convert all of their equipment to a new coupler just because it looks a little better.  As long as the old ones work, they'll save their money, and time, for things they'd rather have.

If MT could make their Z/Nn3 couplers in styles interchangeable with the various N couplers, they would probably, eventually, become the standard.  The Z couplers will work with the N, but as it is, they only come in one body-mount version, and it requires a mounting hole that doesn't match the common N boxes.  If they were easy to swap, modelers could change a few cars at a time, and it wouldn't be a big hassle.

The prototype had the same arguments when switching from link-and-pin to knuckle couplers, and it took federal regulations to force the holdouts to change.  The European railroads have designed more than one very nice automatic coupler, but the cost and effort of changing was just too much, so they've kept the screw-link couplers for most purposes.

While I do agree with you, on the other hand we have witnessed north American  modelers switch over from Rapido to a totally incompatible knuckle coupler.  I don't think you can still find any US-prototype N scale model produced in the last 5 years (or even longer) with Rapido couplers.

Yet I also suspect that if another, smaller or more prototypical coupler (but incompatible with the current knuckle coupler) was introduced, it would have really hard time finding wide acceptance.

[hminky]

If you think "bobbleheading" looks bad in N-Scale, it is truly dreadful in HOn30.

Use Accumates in that genre, the only reason am building in HOn30.

There are finally couplers that work for HOn30 even though I will burn in Hell for not using MicroTrains.

Harold

[jdcolombo]

While I do agree with you, on the other hand we have witnessed north American  modelers switch over from Rapido to a totally incompatible knuckle coupler.  I don't think you can still find any US-prototype N scale model produced in the last 5 years (or even longer) with Rapido couplers.

Yet I also suspect that if another, smaller or more prototypical coupler (but incompatible with the current knuckle coupler) was introduced, it would have really hard time finding wide acceptance.

Back in the day, it was not uncommon to find cars with a Rapido coupler on one end and an MT on the other - a "conversion" car.  I had a couple such cars while I was converting my fleet to all-MT, all-body-mounts in 1995.  Compatibility would be great, but I don't think it would be necessary as long as the new coupler was (1) significantly better looking; (2) operationally excellent (this is the problem with the MT True-scale - it's not really meant for operational coupling/uncoupling) and (3) could be mounted like a 1015 or use a compatible draft gear box.  I'd be fine with an MT 905-type that would be at the proper height when mounted to an underbody built for a 1015 or could be put in a 1015-compatible draft gear box (like the Atlas Master PS-2 box).  Some folks have already adopted the 905 as their standard coupler, but the problem is mounting it on an engine or car underbody designed for a 1015-like coupler.  For rolling stock, you can use shims, but adapting engine pilots is much more difficult. 

There was a time when no locomotives had DCC - you had to mill and hard wire.  Yet some folks did it.  Then manufacturers shifted to DCC-compatible frames with "drop-in" boards.  THEN, some crazy modelers started putting sound in their N scale diesels and a few years later, lo and behold, we have factory-sound-equipped locos.  If the hobby is going to move forward, someone's got to start the process.  Sometimes the process takes decades, sometimes it is significantly faster. 

John C.

[bbussey]

While I do agree with you, on the other hand we have witnessed north American  modelers switch over from Rapido to a totally incompatible knuckle coupler.  I don't think you can still find any US-prototype N scale model produced in the last 5 years (or even longer) with Rapido couplers.

Yet I also suspect that if another, smaller or more prototypical coupler (but incompatible with the current knuckle coupler) was introduced, it would have really hard time finding wide acceptance.

Yes, the industry migrated from Rapido couplets to MTL-compatible couplers. But it took 30 years for that to happen. The Magne-Matic coupler was patented in 1969. The industry in general didn’t follow suit until Atlas abandoned Rapido couplers in the 1990s. Once Atlas migrated to AccuMate couplers, the remaining manufacturers moved to knuckle couplers that would operate with MTL knuckles.