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I have motorized the Constitution Chase train by putting a PF train motor into the coal car. I disassembled the rest of the cars, down to the car bed, and let my kids build whatever train cars they want. This, plus a few cars from a City train let me run a train with the engine (which is a dummy), the motorized coal car, two short cars with fixed wheel trucks and two long cars with turning wheel trucks.

The problem is that sometimes this train works really well and other times it just cannot stay on the tracks at all.

The tracks are laid out on a carpeted floor, but I always put the train in the same place and it usually runs fine. But today's layout was just unworkable and I had to disassemble it and start over. The second layout works and I'm not sure what the difference is. The train rolls along and then whoops, the front wheels of the engine are turned, and the whole things falls down.

The layout itself is designed to withstand the perturbations of the train. This is accomplished by using a single piece of flex track every 1/4 turn and wherever there is a switch. This helps keep the track from shaking loose, as nothing is typically attached anywhere, except for the snap-together action of the track pieces.

Today I tried to settle down a particularly bad stretch of track by mounting it on some 10x20 bricks but that didn't really solve the problems.

Is there a way to reliably run the train on a carpet base? Or even to just improve the reliability over what I have now, which seems somewhat random.

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  • I'm no train head, but I suspect the best solution is a piece of plywood big enough to accommodate your layout.
    – gev
    Commented Nov 2, 2014 at 5:20
  • So, is the problem that the train is coming off the track, or the track is coming apart? I'm not sure what you mean by "...the whole things falls down." Also, what happens if you don't have the flex track?
    – Nick2253
    Commented Nov 3, 2014 at 1:17
  • :) Yes, I'm sure if I were to build on a table or wooden floor or some other more structurally sound surface it'd work better. But I lack the space for such a surface, so I was hoping for a bricks-only solution.
    – Mr. Shiny and New 安宇
    Commented Nov 3, 2014 at 14:58
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    @Nick2253 What happens is that the front wheels of the locomotive derail, and on that locomotive they are constructed in such a way that the entire wheel truck can turn and sway significantly. Once the wheels are off, it's a matter of seconds before the locomotive falls over. The track stays together, primarily because it has so many flex pieces here and there to provide some tolerance to the flexing that occurs. The thing is, most of the time the flex track works just fine, even long stretches of flex track aren't an issue.
    – Mr. Shiny and New 安宇
    Commented Nov 3, 2014 at 15:01
  • I'm wondering if the flex track is causing more problems than it fixes. If you allow the track to move with any vibration from the train, sure, the track may not come apart, but that means that the track is also no longer dampening the vibrations from the train, which could be allowing the train to jump the track. Non-sequitur: maybe you need to add some more weight above the front axle. Try something like: bricklink.com/catalogItem.asp?P=73090b
    – Nick2253
    Commented Nov 3, 2014 at 15:26

2 Answers 2

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One thing I would say from my model train experience is that shunting (pushing) is more likely to derail a train than pulling, especially at speed.

There are a few factors that influence this in models more than we see in "real life":

  1. The force is usually transferred via the couplings rather than buffers. This means there is more chance that the force will be applied at the wrong angle, forcing the leading elements off the track
  2. The elements are too light. In real "multiple unit" trains where the driving force is at the rear of the train, the front elements are still very heavy, which mitigates the effects of force distribution somewhat - if you can add more weight to the Locomotive build then you may have more success.

A simple confirmation of this would be to remove the Locomotive from the train and see if you get the same derailments?

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    Yes, taking the locomotive off the track did help with that troublesome layout. But the same locomotive works fine at other times. I have a weighted 2x6x2 brick from an old fishing boat, I'll see if I can work it into the design.
    – Mr. Shiny and New 安宇
    Commented Nov 3, 2014 at 14:58
  • Hmm, and it's not like a standard loco where you could flip the tender and loco around due to the massive cow-catcher...
    – Zhaph - Ben Duguid ♦
    Commented Nov 3, 2014 at 15:03
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    I think your observation about the coupler applying force at the wrong angle is probably correct. I may have to bite the bullet and just rebuild the entire locomotive, but until now I never realized how tricky it was to make it work reliably. It would probably be easier to have my floor redone with hardwood instead of carpet.
    – Mr. Shiny and New 安宇
    Commented Nov 3, 2014 at 15:14
  • Yes, that seems to be the considered opinion among other model train geeks - more so with the standard Hornby couplers where they are basically fairly thin loops pushing against each other ;)
    – Zhaph - Ben Duguid ♦
    Commented Nov 3, 2014 at 15:16
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I've taken apart, and rebuilt, my layout a few times and come to the following conclusion. It seems that the locomotive is extremely sensitive to any curve or gap in the tracks. The front wheels are attached via a technic pin, and essentially float under the front of the boiler, but the pin only really allows for lateral movement and not vertical. Thus, when the tender pushes the locomotive, if there is anything that causes the rear of the locomotive to drop slightly or be twisted, the front wheels will lift and the train falls off the tracks.

The problem is worse, but not limited to, the flexible track. Sometimes a simple curve is sufficient, and the switch tracks are also problematic.

I tried putting a boat weight inside the boiler, This makes the locomotive heavier but doesn't really apply much force on the front wheels, and it means the center of gravity of the locomotive is not well placed for taking corners.

The other change I've made is to how the IR sensor is mounted in the locomotive. I rebuilt the roof of the cab so that the sensor pokes up out the top of the roof. I also re-routed the wires between the tender and the locomotive so that they are coming out the bottom of the tender, just above the coupler, and go under the sensor. I also pack them tightly into the locomotive so that there is no slack. This prevents the wires from pushing against the locomotive, which was causing at least a few derailments.

Finally, I removed as much flex track as possible, and put 2x4 plates on the track to hold the layout together.

The result is that the train runs acceptably well as long as nobody separates the tender from the locomotive.

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