Train dynamics???(a short story made long)

Discussion in 'FAQs' started by doctorwayne, Oct 30, 2005.

  1. doctorwayne

    doctorwayne Active Member

    I was running some trains today, really just taking a break from rebuilding a couple of Bachmann ten wheelers. I'd also been looking at a couple of threads in the Photo Section, the nicely done ones about the twenty car trains. Now, for my layout, normal train length would be about 12 to 15 cars, mainly limited by passing siding lengths. I decided to run a 20 car train just for the fun of it. I started out with doubleheaded steam, a couple of Bachmann Consolidations. The train length began to grow, and soon I had to add one of my L-3 Mohawks
    (modified Bachmann light USRA Mountain) to the front end. While I normally model the 'thirties, I do have a few diesels on the property for those times I feel like running transition era mid-fifties. As the train length continued to grow, I decided to use some of them, as I don't think it does them much good sitting in the box, so the steamers were switched out.
    I started out with two SW1200RS's (modified and remotored Athearn switchers) sandwiching a ballasted, but otherwise mechanically unmodified Model Power FB-2. the train continued to grow and eventually I had to add two more SW1200RS's, this time on the rear of the train.
    Now normally, when a regular 12 or 15 car train is run, it's double headed due to two long and severe grades (2.5% and 2.8%, both on multiple curves). If the train is especially heavy, (not usually longer, just heavier: I run Athearn two bay hoppers with "live" loads that weigh in at about 8 ounces per car). More than a couple in a train really is noticeable, so I'll add a helper on the rear end. Because the train is short, it's never on more than one grade at a time and usually not spread out over more than two curves, so the pusher works very well.
    The problem with this longer train began on a steep downgrade (about 5% - this track is usually only used for loco break-in or when not-serious-train-nut guests are visiting: the layout is normally operated as point-to-point). Anyway, as the head-end exited the grade, very little of the slack began to run out, since the rear-end was still pushing downgrade. This continued until most of the train was clear of the grade, and since by this time the head-end was wound around a couple of curves, the last 12 or so cars remained seriously bunched up until everything equallized. During this time there were a few minor derailments at the rear of the train caused by the bunched slack. I decided to try another lap of the layout, this time with all of the power on the front end: the FB-2 between the two pairs of switchers. This worked a little better, the odd lightweight car near the front of the train derailing when the slack was really stretched. These were moved further back in the train and posed no more problems. On the short 5% downgrade, there was almost no slack run-in until the last 15 or so cars entered the downgrade, and even then it wasn't excessive.
    I also have three Athearn U33C's, each remotored with two Sagami can motors and each ballasted to about 33 ounces. Since all of my mid-'70's rolling stock has been sold, these orphans almost never get run. I removed the five unit consist, then put two of them on the train and made a trouble-free lap of the layout. With the five unit diesel power on the frontend, maximum current draw of about 1.75 amps occurred on the 2.5% upgrade, as expected, since at the same, time the train was wound around four curves of probably 400 degrees total, although not all in the same direction. The train was made up of a random selection of sixty 40' and 50' cars, varying in weight from 3 1/4 ounces to 7 3/4 ounces and placed at random in the train, except as noted with the few that derailed earlier. A few cars had metal wheels, the rest were plastic, including some early Athearn cars with the original sprung trucks. Rolling qualities varied from excellent (about 8 cars) to poor (5 cars, including 2 bricks disguised as 50' boxcars). Maximum current draw for the two U-boats was about 1 amp, occurring at the same spot. Incidently, the sixth car in the train was an empty Walthers GSC 52' flatcar.
    Both diesel lashups seemed to have quite a bit more power in reserve, especially the U-boats, but I didn't feel like pushing my luck. The long (45') 2.8% grade is on a different line and one of its two horseshoe curves is on a high viaduct, the other on an unscenicked area of open benchwork about 4' to 5' above the concrete floor. Derailments are tolerable, wrecks are not.
    The foregoing exercise confirms my thought that, for me, DCC would be a very useful tool when handling long, heavy trains with a separately controlled rear end pusher. The mere ability to program locomotives to respond similarily is not sufficient to avoid excessive slack run-in and run-out: a separate operator is required. My SW1200RS diesels will run around the layout, separated, neither gaining nor losing ground between themselves. The FB-2, while starting at a higher voltage, will run at normal track speed with the switchers, but because they can't be controlled separately, problems occur. Luckily for me, with normal train lengths, I'll not have to make that conversion, especially since a second operator is seldom available.
    What I'm wondering is there anybody out there using DCC in this way or do you just consist your locos and stick 'em on a train with one operator? Or does anyone know of a way, using regular DC, to run a train with a second operator controlling a rear-end pusher, independent of the head-end? I've thought about using some kind of detectors, maybe activated by the caboose, that would automatically cascade block control down to the pusher, but thinking about that stuff makes my head hurt. That's why the layout right now is all one block, 'cause it's all being run by one blockhead.
    Anyway, thanks to all who've managed to wade through the foregoing. (Hey, I would've posted a sixty car train in the Photo Section, but the camera's not here.)
  2. tillsbury

    tillsbury Member

    Technically that would be feasible, but it'd probably be a whole lot easier to invent DCC from scratch :)... but how come you need more than two locos for a 20-car train anyway? two should pull 20 cars fine up 2-3% surely?
  3. doctorwayne

    doctorwayne Active Member

    Your question got me thinking. (Oh! Oh!) Since the sixty car train was still sitting on the main line, I picked one of my Bachmann 2-8-0's at random, put it on the track and cut the first twenty cars off the train and coupled them to the loco.
    Before I go further, I should explain that when I get a new locomotive, I run it pulling a standard test train, made up of Athearn 2 bay hoppers and a particular Athearn caboose. After testing, I make whatever mechanical improvements I feel necessary, then retest. When I'm satisfied with the performance, I paint and detail the loco as desired, then put it in service.
    Anyway, back to the twenty cars. This loco would not go up the grade (actually 2.66% over 19', comprised of, from bottom to top, 4' straight, 4' curve to the right on a 36" radius, 3' straight, 4' curve to the left on a 36" radius, 4' straight) until I had uncoupled the last eleven cars. I weighed the cars and found that they ranged in weight from 3.25 oz. to 7.0 oz., with an average weight of 5.3 oz. Total train weight was 47.75 oz. The loco experienced more wheel slip than I would normally allow.
    I next assembled a train of twenty standard Athearn boxcars and reefers, with a variety of Athearn trucks and wheels dating from the sixties to the nineties, nothing modified and all weighing in at 3.25 oz. each. The same loco did manage to pull this train up the grade, again with excessive wheelslip. Total train weight was 65 oz.
    Finally, I made up a test train of unmodified Athearn two bay hoppers, this time eschewing the caboose. The hoppers were loaded with loose "coal", each loaded car weighing 8 oz. The test locomotive pulled, again with excessive wheel slip, six cars.
    According to my list showing the tonnage ratings of all my locomotives, this one was rated to pull four loaded hoppers plus a 4 oz. caboose on this grade, with no wheel slip. Actual tests revealed that two of these locos together would pull, with limited wheel slip, nine loads plus the caboose. Since I arbitrarily assign a weight of 70 tons to each car in a test train, including the caboose, I rated all of the Consolidations at 350 tons or five cars each on this hill. Of course, if there are no loaded hoppers in the train, I can get away with a few extra cars. Since normal train size is between 12 and 15 cars, limited by passing siding length, most through freights operate doubleheaded. Way freights and mixed trains are also pulled by these locos, but I also have Moguls and Ten Wheelers available, along with a couple of Mikados. Any of these engines will run in combination with the others, so I can match locomotives to whatever tonnage needs to be moved.
    As a result of all this additional testing, I may have to revisit my policy for weighting freight cars. In the past, I added weight using lead blocks that I had originally cast for use in passenger cars. Most house cars got a 2 oz. block at each end, sometimes in addition to the weight that came with the car. Since the sixty car train showed that unmodified Athearn cars at 3.25 oz. would operate satisfactorily in a train with cars of almost 8 oz., it would seem that a train of cars lighter than the 5.3 oz. average would run well in a train with a few loaded hoppers, at 8 oz., included. When coal moves to the power plant, it does so as a single commodity train, so the loose loads and 8 oz. car weights will be retained, as I enjoy the challenge of moving this potential derailment across the division.
    Thanks for your comments. It's pointed out a deficiency in my operating practice that needs correcting and I might not have noticed it otherwise.

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