7j43k Early on in this topic, I suggested the OP define his term: "accordianning" He hasn't yet. And, as I noted earlier, it is open to interpretation. We have all been guessing about what he means, some with more self-assurance than others. I'm kind of tired of guessing. I've got other things to do. Ed
Early on in this topic, I suggested the OP define his term: "accordianning"
He hasn't yet. And, as I noted earlier, it is open to interpretation. We have all been guessing about what he means, some with more self-assurance than others.
I'm kind of tired of guessing. I've got other things to do.
Ed
jjdamnit ... If the train moves too fast the plank will slam down on the downward side. If the train moves slowly this downward motion can be better controlled. When the entire train passes over the summit now all the couplers are under compression. Just like the teeter-totter example, if the train over the summit runs too fast the compressive forces of the summiting cars will slam the couplers together causing uncoupling or derailments due to what you describe as "accordioing". ...
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If the train moves too fast the plank will slam down on the downward side. If the train moves slowly this downward motion can be better controlled.
When the entire train passes over the summit now all the couplers are under compression.
Just like the teeter-totter example, if the train over the summit runs too fast the compressive forces of the summiting cars will slam the couplers together causing uncoupling or derailments due to what you describe as "accordioing".
Our models should come close to mimicking this phenomenon, and do much of the time. However, there's that problem with rolling resistance that several of us have alluded to, and that varies between cars, and this resistance makes the problem of accordianing all but unsolvable unless the operator learns how to shove up all the slack using a rear-end pusher to keep the train moving smoothly along its entire length, regardless of wether it's up hills or down them.
The steepest grade on mine is a tad over 1%. I've never had a problem.
Sometimes I park the train (20 cars at the max) on that slope to do switching operations. When I start it again, I start out in creeper speed, and you can hear the slack as the train starts to move.
Mike.
My You Tube
Hello all,
As a train crests a given summit the couplers downhill from the locomotive(s) are under tension.
When each car passes over the summit the now downhill couplers (on the other side of the summit) are under compression while the remaining uphill couplers are still under tension.
The key for the engineer is to account for this tension and compression change along the length of the entire train as it passes over the sumit.
As the entire train moves over the summit think of running the train over a teeter-totter.
At some point the trains weight will move the plank over the fulcrum to a point of equilibrium.
Then the weight of the train will begin to move the plank downward.
The solution is to be more proactive in your throttle movements OR use a trailing locomotive, MU'ed to the lead units, to control the transition of tension to compression forces on the couplers as the train passes over the summit.
Hope this helps.
Post Script: As a prototypical train moves over a summit you can hear the couplers move from tension to compression.
"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"
Hey! It is a matter of train control. The big railroads have the same issues.
They can apply train-line brakes, you cannot. If you have a caboose, you can apply brakes from the rear of the train, ditto if you have distributed poer on your consists. With a DCC loco on thae back that is a gimmee. For a Caboose you can simulate with axel wipers , and even light up the caboose in the bargain.
ROAR
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Here there be cats. LIONS with CAMERAS
rbturner....the problem can be 90% fixed by removing the slop (longitudinal slack in the motor or work assembly) by using thrust washers either on the motor armature or anyplace else that you can find excess fore and aft movement in any of the drive line....
Thanks for your reply, Randy. I knew that I'd left something out of mine, but simply couldn't remember what it was.
Wayne
Arto Last night I gave the accordianing portion of the train a little push forward to "tighten up" the slack and surprisinly the cars stopped accordianing.
Last night I gave the accordianing portion of the train a little push forward to "tighten up" the slack and surprisinly the cars stopped accordianing.
(As a reminder, we're talking about a downhill grade, here.)
If you can push the rear of the train forward and eliminate the problem, that says to me that the train isn't doing that same thing by itself. It is needing help from you.
It seems to me that, on a grade, the train would naturally "compress" by itself. Which it apparently isn't doing. By itself.
That gets me thinking that there's too much friction at various places in the train. Different cars would then hang up a bit until they were joggled forward.
To find out if my theory of too-much-friction is correct, try placing each of the cars singly on the grade. Do not shove them downhill. Do your best to just place each one gently, and see if each and every one "wants" to roll down.
What happens?
Oh, yeah. Just fer fun. And information. How about finding out "exactly" how steep the grade-of-interest is. Can't hurt. And maybe, for even more fun, you can check the grade at several locations, just to see to what extent it varies. If any.
Thanks for all the answers guys!
More details: The trains in question are 20-25 box car long. All are equipped with body mounted Kadee and upgraded metal wheels.
I didn't have this problem with longer trains (40+ cars). I think the longer trains were long enoungh to create enough drag on the total train before the back half was actually going downhill. I've since realized I don't need to run trains that long on my layout for effect, but now the accordianing occurs.
It's also not a locomotive problem. The locos are running very smooth & I can't observe any jogging regardless of the accordianing of cars behind them.
Since I've spent all the time and money replacing original couplers with Kadee I'm not too keen on ditching those for non-operational ones even though I never use them that way. Even if I did - someone mentioned play in the shank - I think this will still be an issue.
After all the comments, and giving this some more thought, I think I'll try installing wheels with a slightly longer axle in the caboose, using an axle that's just a little bit longer - enough to give a little more rolling resistance against the bearing & see how that works.
If slack action is the problem, take comfort in the fact that it is very prototypical. Real trains surge back and forth and part of the art of train handling is managing slack. Cabooses were hazardous because of all the whiplash in their ride. Pity the conductor or brakeman who is thrown into a wall or sharp object by a sudden thrust.
BATMAN I can run a forty car freight all day without incident, however, if I park the same train on a long downgrade for a week, when I run it again, as soon as it hits the flat it will come apart in several places. I still haven't figured that one out.
I can run a forty car freight all day without incident, however, if I park the same train on a long downgrade for a week, when I run it again, as soon as it hits the flat it will come apart in several places. I still haven't figured that one out.
I suspect this is due to some manufacturers couplers developing a memory, in this case being pushed open by compression. That is why some people will only use Kadee couplers.
Peter
I think a little experimenting is in order. First I would put lighter cars at the rear of the train and see if that helps. Our little rail cars are not equipped with brakes so that is a problem. Just drive a truck and trailer and see what happens when the trailer brakes are not up to snuff.
A mid train Loco may very well help with the situation as it will relieve some of the compression that is going on. You didn't say how many cars you are talking about.
Brent
"All of the world's problems are the result of the difference between how we think and how the world works."
If I understand the problem, the loco is surging ahead then slowing down and then surging ahead again.
If this is true, the problem can be 90% fixed by removing the slop (longitudinal slack in the motor or work assembly) by using thrust washers either on the motor armature or anyplace else that you can find excess fore and aft movement in any of the drive line.
Once this excess movement is taken care of your down hill surging will be gone.
One easy way to minimize the slack action is to put high rolling resistance trucks on your cabooses, or friction wipers on the trucks if you don't have some that don't roll well. Just be careful, as that may increase the possibility of stringlining.
If you don't use cabooses, then the only thing to do is put less free rolling trucks on everything. That will severely reduce the number of cars your locos can haul, and will also increase the possibility of stringlining.
Mark P.
Website: http://www.thecbandqinwyoming.comVideos: https://www.youtube.com/user/mabrunton
It sounds to me as if the OP is referring to the run-in of slack when the train is going downhill: the train is going slowly, the slack runs in, pushing the locomotive and the train slows. The locomotive continues to run, stretching slack somewhat at the front of the train, and when the total train is again in motion, the slack once again runs-in, repeating the problem. This is related to the way our locomotives are geared, where the wheels cannot make the gears or motor turn faster, even though they can intermittently push the locomotive faster on a downgrade.
I've noticed that there can be a "sweet spot" in the speed that won't cause this effect, but it varies with different locomotives, different grades, and, of course, with different trains.
I think the first response has it correctly. There are several places where friction plays a part, but the main ones are in the coupler shanks against the coupler box openings, coupler shank eyelets against the top/bottom cover of the box, or maybe against a shim or washer, and the various eases with which axles roll in their journals in the trucks.
Aside from some variability in the actual total weight of the cars in a consist, they're all on the same grade. Even if the grade were perfectly laid on a steady ramp, no track issues, the couplers and rolling resistances from car-to-car will mean that one car will want to roll freely and keep up steadily to the locomotive/tender, while the next one, two, three, or four might be stickier in the coupler shanks and in the way their axles spin. When left behind several couplers as the engine takes up the slack, the jerked slower cars must quickly get in motion, and their combined weight with all those that get jerked behind them at the same time means there's a lot of weight crashing into the free rolling cars up front. Or a combination of all that, onesies and twosies, sometimes larger groups, all putting on brakes or wanting to roll freely.
If you were to get a pusher on the back and adjust it's throttle setting to bunch up all the slack from the rear of the consist, I bet this would all go away. Of course, you'd up the risk of a derailment as the lighter cars want to get lifted up and out of the gauge, but that's another topic.
Now that RailPro's decoders can be controlled by the RailPro hand controller or a standard DCC hand controller, you might want to check them out. I have been using them for about a year in my consisted engines and I love them. By running an engine in the middle of the train, there is no accordion effect.
The engines play follow-the-leader and automatically speed match themselves.
I would definitely recommend using RailPro's hand controller though.
I am not sure whether you are describing an oscillating event or simple compression. More info could be useful.
But.
There will always be slack (easy back and forth motion) in coupler connections. It's not noticeable going uphill because the train is stretched out by gravity. Going downhill, it will compress for the same reason. As the slope of the grade lessens, the gravity effect does, also. There will likely be points where the slack is not eliminated, and you can get oscillations.
In the above, the irritating effect is lessened by having less slack in the couplings. The only way I know to do that is to convert to either dummy or Sergent couplers.
Also, sometimes the oscillation is triggered by the locomotive(s) themselves. I've got an ABA set of diesels that does a little bit of jelly-wobble just running together on a flat straight. Needs work. Either in the couplings, or by adding DCC and fiddling with various settings.
Arto What's a good way to stop longer trains from accordianing when going down mild grades ( <2% ) at slow speeds? I guess a better question would be why is it doing this? I spent a LOT of time getting my trackage/grades perfectly smooth/level.
What's a good way to stop longer trains from accordianing when going down mild grades ( <2% ) at slow speeds?
I guess a better question would be why is it doing this? I spent a LOT of time getting my trackage/grades perfectly smooth/level.