Sunday, October 05, 2008

Braking in digital and how my expectations have gone up again

Several Web sites deal with approaches to how to make digital trains stop in front of a red signal. It seems a need that was implemented trivially simple in analog times (isolated section before signal; red signal removes power from section; no power, train stops), somehow fell under table when we entered the digital world. While it is now possible to run multiple locomotives independently on the same section of track, stopping them in some automated fashion at the right place as needed is surprisingly hard.

The standard solution (and most similar to the old analog way) is to use a little module that generates a brake signal in an isolated section. The implementation details vary from system to system, but they all share the property that you have no control over the locomotive until the signal is set to green. At list the loco lights stay on, and the loco decelerates in a somewhat controlled fashion before the signal, which is much better than the analog way. The cost of the brake modules, which can run as high as $40 per module and signal, is steep, too.

Other solutions that track locos with IR or RFID, are even more expensive.

Making matters worse is how most decoders implement the deceleration part: If the brake signal is detected, the decoder gradually reduces the speed by one speed step every 1/nth of a second. This means a locomotive of an express passenger train going full speed needs a longer distance to stop than a slow local freight train. In order to reliably stop both kinds of trains, one needs to size the brake section long enough for the express train to make a stop in front of the red signal. ... Which means the local freight will stop much farther away from the signal, when in reality I want both to slow down and stop before the signal, or even slow down from the advance signal until the "engineer" can "see" the main signal, then creep to the main signal, and stop only if it's still red once we get really close. This is exactly what real trains do to avoid the hassle of first stopping several hundred tons of steel to a dead stop, just to get it going again a minute later.

Yes, given that digital control should be able to give me this behavior, my expectations have gone up ... again.

The only way this actually can work is with using computer control for the trains not under manual operator control. While it's a lot of fun to really "drive" a train around a larger layout manually and do all the right moves, sounds, etc. at the right time, my layout is neither big enough to provide for long train running, nor do I have the space (or interested people) to actually keep traffic up.

The next best thing is to have a set of trains run on a (pseudo) schedule, and control a few of them manually. E.g. swapping out cars from a freight train, run a passenger local, or even switching work in the yard along with deliveries to local industries. This is fun, but I still want the feeling of a busy railroad with train meets, and background traffic, that I enjoyed with my fathers layout as a boy, and not have only one train operating at any one time.

There is actually software that implements the kind of train behavior and control I'm looking for with minimal amount of detection points. Railware substitutes detection points around signals with precisely measured distances of track, and calibrated locomotives. Since the software knows at any point in time how fast a loco is going, and keeps track of occupancy state of the various sections, it can deduce at what location of track a train is, and make them stop within centimeters from arbitrary points on the layout, ... e.g. just before a red signal.

Now that my expectations have gone up, I want the signals to show red behind a train. I want trains to stop properly at that signal. I want to be able to see traffic happening on my layout without me doing anything ... Well, ok, not so sure about that one. I want switches lined as needed. But at the same time I also want to be able to intervene manually at any point in time, and most importantly, I don't want to sit in front of a screen.

There. I said it. And just created yet another money sink.

Yes, I actually don't want to control my switches and signals from a screen. I stare at a screen long enough during my day job. I want the tactile feedback of buttons, switches and knobs to run my trains, not using a mouse.

Some visual feedback about the state of what the computer thinks what train is where and where it's going will still be needed, so there will need to be a screen somewhere. I'm dreaming of a self-built digital enabled control table.
Alternatively, I control switches and signals the old analog way (still using a control table, but not nearly as slick), but then I can also say Goodbye to most of what I wrote in the previous paragraph.

Time to pull out plans of the layout again, and figure out what I need where, and how much it's going to cost me to do all this... Then take a deep breath put it back in the drawer and concentrate on building the coffee table for the living room first...

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