I have read an article about harmonic rocking. The premis of it makes sense. You cant go a certian mph over some track sections cause it can rock the cars something feirce right? Well I took a break from sceniking and decided to run a train. First train in a while. i took the sd50 out with a few hoppers and boxcars. I noticed that one of my favorite boxes C&O reefer was rocking like the robin. I then thought about the article. Could this be whats going on?? Has any one else noticed this? I took the box and checked it out. The trucks are tight…the weight in the box is secure…the track is level. I am clueless of what can be done to help out my box. [banghead] Any input or ideas wolud help.
Sometimes this just happens from a rail joint, variation in track gage, out of round wheelset , or it’s Monday after a great weekend. One solution that I remember from my reading is to tighten the mounting on one of the trucks so that it will not swivel at all, making sure that when tightened it is parallel with the rest of the car. This holds the car steady while the othe truck tracks through curves and turnouts.
Good luck with one of lifes mysteries.
If the track is level and you are just coming out of a curve when the rocking begins, perhaps you need to bank the track a bit on the curve. As you round the curve, centrifugal force pulls the cars outward, and this will be more pronounced for taller cars, which are naturally more top-heavy. Then, as you hit the straight, the car quickly straightens up, and if it can rock easily on its truck bearings, it will tip back towards the inside of hte curve, and begin rocking back and forth. The easiest solution is to make sure one truck has very little rocking motion to it. The most likely fault is the bearing with the car base, but if the axle bearings are loose, they can also allow rocking.
I doubt if ‘harmonics’ are the culprit. I would bet on dirty plastic wheels or maybe the trucks are too loose on the bolsters. Contrary to the popular ‘urban modeling myths’, you should be able to tighten ‘both’ trucks down to the point where they do not swivel freely, then back off the screw maybe 1/8th of a turn to get them to swivel free. That, clean metal wheels, and proper weight should produce a good ‘runner’!
When I worked for the Milwaukee there was a timetable instruction for St. Paul Pass over the Bitterroots to the effect that if you couldn’t maintain a certain speed (I think it was 18 MPH) that you had to reduce to 12MPH. The reason being that, when the wheels hit a rail joint they would rock back and forth but at around 15MPH the wheel would hit the second rail joint just at the point it was at the limit of its rocking from the first, then you hit the third at the amplified limit and so forth until you’re in the St. Joe river.
The first thing I’d do with your model problem is put the car up side down on its roof and spin each wheel, observing if you get any pulsing from either a bent axle or, more likely, axle mounted off-center on the wheel.
When I worked for the Milwaukee there was a timetable instruction for St. Paul Pass over the Bitterroots to the effect that if you couldn’t maintain a certain speed (I think it was 18 MPH) that you had to reduce to 12MPH. The reason being that, when the wheels hit a rail joint they would rock back and forth but at around 15MPH the wheel would hit the second rail joint just at the point it was at the limit of its rocking from the first, then you hit the third at the amplified limit and so forth until you’re in the St. Joe river. Loaded grain hoppers were particularly susceptical to this phenomenon. The fishing in the North fork of the St Joe was fabulous due to the grain fed cut throat trout.
The first thing I’d do with your model problem is put the car up side down on its roof and spin each wheel, observing if you get any pulsing from either a bent axle or, more likely, axle mounted off-center on the wheel.
The main reason that I don’t believe that Harmonic rocking is possible in models is that compared to the prototype our carsour much lighter with a lower center of gravity. Most of the weight is also centered low. A real loaded box car is much more top heavy then any model which also in my non scientific mind would make the rocking much more prevlant.
On a related note I might try the two truck mounting methods on my cars and see what works best.
andrew
It would be pretty tough to get harmonic rocking on a model.
Harmonic rocking occurs when the natural frequency of the car matches undulations in one or both rails. When the trucks hit a low spot, the car rocks that direction. As the truck comes back up out of the low spot, the car rocks back, and inertia carries it a little too far to the opposite side, so the car swings back again at it’s natural frequency. If the truck is going into another low spot on that side at the same time, the oscillations build up and you get harmonic rocking. Under just the right circumstances, you can get some pretty severe motions going.
The natural frequency of the car is inversely proportional to it’s mass and inertia. More mass means lower frequency, generally (the rigidity of the mass in question, plus it general shape, also come into play). The mass and inertia of a model freight car is so small that, if it began rocking at its natural frequency, it would “buzz” something like a hummingbird’s wings in flight (don’t ask me for numbers; this is an illustration, not an analysis).
In my experience, rocking in models is usually due to plastic wheels that are not perfectly round. I’ve also had problems with some cars where there was too much play in the trucks - I dealt with this by putting a plastic washer (came with a pack of Kadees) over the bolt before fitting it through the truck and into the car - this combined with the metal wheels seemed effective. Hope this is of help!
try some extra weight and see if it improves it or worsens it. Then try it on a different streach of track, between different wagons.
otherwise, leave it alone for another couple of weeks and see if it does it again lol
[8D]
Would be neat if we could simulate harmonic rocking. I always enjoy seeing the prototypes rock as they cruise by.
Several years ago I read a really interesting article on Santa Fe. I hope I’m remembering it correctly:
During the late 1980s, Locomotive engineers operating SuperFleet FP45s reported an unusual phenomenon with the big cowls on certain fast freight runs. On a long stretch of the 80+ mph line in one of the western states, as the FP45s ran at speeds between 70 and 73 m.p.h, the units rocked violently to the point where engineers became very nervous. Yet, once past that, it was smoother sailing from 75 to 85 mph! [8D] There was quite a bit of debate among the railroad’s brass and track engineering staff as to the cause of the harmonic motion at those particular speeds. Was puzzling, especially since the track and locomotives were so well maintained.
Good point. Even the higher quality axle sets should be checked. Last
On the other hand…haven’t you guys ever noticed prototype freight and even passenger train cars “rocking” from side to side, especially at lower speeds?
I guess I’m weird, but even as a little kid I’ve felt that the rocking and the “clickety-clacking” was cool, especially since it was always in a rythym. I associate it a lot with the rythyms I hear in modern jazz instrumentals.
Only cars that I have rock for some reason is my better car, Atherans. Most are ceap Tyco Bachman and Life Like.
I have one 50 footer that Rocks like Chuck Berry is in it no matter the speed. Ales are ture, well to my eye. Guess I will start start pulling the alxes and replaces them and see what happens.
One sure fire test is to run your train at different speeds. If the rocking persists at all speeds, its a bent axle or wheel as mentioned above. If the rocking occurs at one speed only, it is harmonic. I suppose that you have a bent axle or out of round wheel.
I would probably check for a bent axle/wheel out of round first. If that didn’t work I would make sure the trucks were firmly on the bolster. If that didn’t work I would try replacing one - or both - trucks. If that didn’t work I would probably learn to live with it (I had the fortune - or misfortune whichever is your preference - of seeing Penn Central in its headiest of days - I saw cars rocking so badly that I thought they were going on their side any minute) or I would call in either a good bottle of Chivas Regal or an exorcist.
Spooks find many places to dwell on Model pikes and they can almost drive one to drink. I had an old Atlas RS3 (N-Scale)that ran fine alone but double head it with another one and it picked the point on one particular (leading edge) switch on almost every lap of the layout - no other switches - just that one. And always the same truck and it didn’t matter whether it was running long hood or short hood first or if it was leading or trailing the lashup - onto the ties it would go. I checked the gauging on the wheels several times - no trouble found. Nobody did anything with the switch - after all, nobody else was having any problems.