Author Topic: Buffer locking  (Read 6366 times)

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Offline 454

Re: Buffer locking
« Reply #15 on: Oct 16 2013 13:43 »
It's not just under braking Tim, a long loose coupled train on a down grade hitting a curve will do it. The rear wagons want to over-run. We don't have the luxury of being able to pin brakes down or have a frantic guard winding on his handbrake on a 20T brake van when he is anticipating such an obstacle ahead. We just have to know the limits of our rolling stock & motive power on our home tracks & away at GTG's.

Dave
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Offline Andy B

Re: Buffer locking
« Reply #16 on: Oct 16 2013 15:23 »
....... or have a frantic guard winding on his handbrake on a 20T brake van when he is anticipating such an obstacle ahead.

Dave - I'm disappointed in you! ;)
As one of our remote control / servo experts, surely you can knock together a servo-operated brake mechanism under a brake van that can apply the brakes as required.  Just needs some extra weight and high-friction wheels so the wheels don't just slide on all the oil dribbled all over the track by those messy steam locos ...........  ;D
Andy

Offline 454

Re: Buffer locking
« Reply #17 on: Oct 16 2013 16:06 »
Andy, there was an embarrassing moment at Barry when I had the privilege of controlling Brian Torr's Brit with his 3 Pullmans in tow. When I cut the steam on the regulator two thirds the way down the long straight the whole lot kept careering on into the curve, the slowing down was not evident & my heart missed a beat. Got visions of swapping my Brit for his Brit as a post crash scenario. It was at this point I wish there had been a retro-braking parachute system to deploy like on Victor tankers. No such luck, it made it around the curve though. Such was the quality of the Barry track & the skill of the laying  crew.

Just wish there was a simple solution. Have given this a bit of thought in the past.

The problem with a lot of weight in a rear vehicle to bear down on the tracks to give adhesion is that the lighter vehicles in the train during normal running will want to take a short cut along the chord of most curves, at least that is how I imagine it to be in my mind. So when the servo controlled brake is applied it amplifies the effect & makes this more likely, with consequences.

There should be plenty of space in most G3 brake vans for an on-board Rx commonly bound to the loco receiver to act on the brake using a spare variable stick channel on the loco Tx.  This brake would be a friction band around a disc mounted on one or both axles.  It would have to be carefully designed not to snatch but to be progressively applied in a proportional but not violent ( emergency stop) application.

Alternatively, fit an electric motor in the brake van & there is one really versatile vehicle.

I remember brake vans rolling down the colliery exchange sidings near my childhood home where the colliery branch met the main line. The brake van could be seen rolling on it's own under control of the guard then gently rolling into the rear of the next outbound coal train.

Q) When would this versatility be useful to braking?
A) Put the brake van in reverse when braking required.

If upgrades are encountered then one has the perfect banking assister.

If it lacks effectiveness then fit traction tyres.

Don't ask me about sand squirting on track to counter the mess left behind by dirty oily steamers I'm not listening.

Dave
454
454

Offline MikeWilliams

Re: Buffer locking
« Reply #18 on: Oct 16 2013 18:55 »
In the 1950s a friend of mine Jim Richards built a pair of GWR Toads in 7mm with the largest and heaviest flywheel he could fit into it, friction driven from the flanges of one wheelset.  The idea was that when braking the van would make the couplings slacken and wagons buffer up in a prototypical manner.  I never saw it in action, though I did see it demonstrated during fly shunting and it was fascinating to watch - no electronics in those days!  He was a good friend of W.S.Norris whose railway hosted one of the vans on long trains with no problem at all.

That was 7mm indoors, not Gauge 3 in the garden, so the dynamics may be quite different, but ever since seeing it I've wanted to build one myself - even a basic test frame, to see how it performs.

Mike

Offline John Candy

Re: Buffer locking
« Reply #19 on: Oct 16 2013 19:23 »
In the BR tests, the problem was that the leading wagons had their buffers fully compressed and the wagons were forced upwards and then buffer lock occurred.
Combinations of down grade and fierce brake applications by heavy diesel locos exacerbated the problem.

In G3 buffer lock situations, is it the result of "over-ride" or lateral displacement?

I doubt buffers become fully compressed unless springs are exceptionally weak.

Does it occur only on curved track or does it happen on straight sections?

John.

My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline AllWight

Re: Buffer locking
« Reply #20 on: Oct 16 2013 19:37 »
It can happen on straight track if there is sufficient movement in the track. This is usually in sidings where the shunted tries to get a 12 coach train into a 10 coach siding and the buffer stops end up 120' further down.

Mark

Offline John Candy

Re: Buffer locking
« Reply #21 on: Oct 16 2013 19:49 »
Mark,

My post refers to trains braking in forward motion, not shunting.

Regards,
John.
My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline 454

Re: Buffer locking
« Reply #22 on: Oct 16 2013 20:02 »
At different GTG's I have witnessed a bogie carriage buffers rise over adjacent coach buffers on straights & on bends. Could be a unique facet of a particular vehicle. My bet is that it is a combination of over ride & lateral displacement. Could be worn bogie pivots, causing rocking or swaying. Your guesses are as good as mine.

A possible solution to buffer locking would be a piece of transparent plastic across each pair of buffers to act as a shield. Transparent so that it does not detract visually for appearances sake. The dimensions could be adjusted to eliminate the possibility of rising & lateral locking.

Has anyone tried this?

Dave
454

Offline John Candy

Re: Buffer locking
« Reply #23 on: Oct 17 2013 07:03 »
If I were at home, I would draw and scan this suggestion for a new coupling but do not have access to scanner, so a description will have to suffice.

1) Imagine a screw coupling stretched to its limit in a horizontal plane.
2) Remove the screw section from between the "eyes".
3) Replace with a telescopic arrangement whereby a spring is retained within a tube and a rod acts as a piston/plunger (the piston having an enlarged crown which is restrained by a constriction in the "bore" tube at the limit of extension).
4) The spring and piston/plunger are soldered to the coupling's "eyes" at either end.
5) To prevent the coupling eyes lifting out of the draw hooks under compression, a loop is soldered to the coupling eyes (not the draw hooks) at an outward facing angle (45 degrees).

Explanation of operation.
The coupling "eyes" of the original screw coupling are fixed rigidly to either end of the telescopic arrangement (i.e. so the coupling does not droop and is maintained in a horizontal position).
The loop (under compression situation) prevents the eyes being forced upwards out of the draw hooks.
The spring is there to act purely as a "damper" against "hunting" in normal forward motion (not to hold the coupling in an extended position or to resist compression under braking conditions).
The telescopic movement is limited under compression, so as to retain sufficient spacing to prevent buffer locking.

Does that sound as though it would work?
Whether it could be economically mass-produced is another matter!

John.
My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline MikeWilliams

Re: Buffer locking
« Reply #24 on: Oct 17 2013 07:37 »
Dave,

Your suggested clear plastic and similar arrangements were common in the smaller scales 40 years ago but other ways were found to reduce the problem (thin wire, larger heads, reduce slop etc).  The bar needs to be loose so that each buffer head can rotate relative to it, such as when one buffer only is compressed on a curve.

John's idea sounds interesting, though I'm not clear how the loop works.  Ted implies that such a device is already use by G1MRA, so does anyone have experience of it?  or a photo?

Coming back to Andy's question and the start of this thread.  Who has actually experienced buffer locking in Gauge 3 and what were the specific causes?  His "forensic analysis"?

Mike

Offline John Candy

Re: Buffer locking
« Reply #25 on: Oct 17 2013 07:55 »
Mike,

The loop would be (rigidly) soldered to the removeable coupling link, at an angle, such that it slots beneath the draw hook and prevents the coupling link being pushed upwards out of the draw hook.

Whether the actual link would benefit from being sprung (or would suffice as a rigid rod) is debatable but would possibly prevent "hunting".

John.
My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline IanT

Re: Buffer locking
« Reply #26 on: Oct 17 2013 10:56 »
I am not sure which device Ted is referring to but several ideas have been put forward by G1MRA Members over the years. One is to solder a length of wire between the buffers for instance.

The one I like best (for carriages) was for two pieces of brass strip, with a pivot through the centre to hold them together. The top piece has two holes in each end which slip over the hooks of each carriage. The bottom piece has a step at each end, designed to slide under the body of the hook, that holds the top piece in place. To use, the two parts are swivelled at 90deg to each other and the carriages are hooked up via the top piece. The bottom piece is then twisted back to lock everything in place.

They are therefore simply made, do not involve any modification to stock and can be used as and when required.

For anyone interested the idea was originated by Ulli Holtmann and appeared in the G1MRA Journal of Summer 2001. It was reprinted in "Modelling in Gauge 1 - Book 4: Coaching Stock". Incidentally, G1MRA publish four of these books that are essentially a collection of articles from the Journal over the years (Electric Locos, Steam Locos, Wagon Stock & Carriage Stock). They are not only very good reading but the majority of the ideas given will scale very easily up to G3. Recommended reading (and Christmas is fast approaching - so maybe some hints to herself would be useful!)

Regards,

IanT
Nothing's ever Easy - At least the first time around.

Offline Peaky 556

Re: Buffer locking
« Reply #27 on: Oct 17 2013 13:11 »
I'm scratching my head over all this agonising, so will forward my views, albeit theoretical only and from a purist aspect at this early stage in my modelling career, at the risk of upsetting a lot of people!

 Buffers were there for 'buffering' on early stuff (3-link & screw link couplings)

 So why try and cut them out of the process with rigid or outwardly sprung links, etc?

 If the stock rides up and over then there is a problem with buffer height or slackness of bogie pivots etc, or the stock is too light to keep it down on the track, or you are driving dangerously;

 Don't brake so hard, keep it all realistic with changes of speed;

 Keep speeds realistic, don't forget that a fast walking pace (4 mph) equates to 90!

 Live within the limitations of the track and stock you are pulling, drive accordingly, it is more fun!;

 Keep it looking realistic with buffers close or touching;

 Use sprung buffers only, and softly sprung at that;

 On downgrades with long goods trains then the driver would have kept the speeds low, so don't charge down them and expect to brake successfully before the next curve!  Anyone who has towed a heavy road trailer will know that;

 If buffer lock occurs when propelling then it is because the curves are unrealistically tight, or some sloppiness problems as above, so then the big hand from the sky is necessary.  C'est la vie.

 ::) Tim


Offline AllWight

Re: Buffer locking
« Reply #28 on: Oct 17 2013 16:31 »
I am going to refer to the fleischmann couplings where on the straight track the couplings would close up tight and open up on the curve. The way it was done was to have a V shape plate floating in a larger V shape plate the first plate has the coupling attached. More upto date now Hornby and Bachmann have a similar arrangement where in a fixed rake a solid bar replaces the individual couplings and maintains a safe secure distance apart from each coach. Propelling and hauling through a 1st radius crossover at speed is entirely possible so theoretically it should be possible in the larger scales. Another company that makes the couplings to fit to your 00 stock is "Keen Couplings". Maybe a bigger version could be made up on a 3d printer to work in a fixed rake of coaches in G3.

Mark

Offline blagdon

Re: Buffer locking
« Reply #29 on: Oct 17 2013 22:47 »
Tim (Peaky 556), I could not have put it better! I think its called Ministry of the (what happens when you cut yourself)-ing Obvious. This is why I test newly laid trackwork after laying by using a loco to shunt stock over it; if needs be up comes the track, head scratched, problem re-examined, track re-laid until problem solved.

 Ian the Gauge '3' Pirate