You'll notice that there are 3 sets of tracks (that is if you click on the image and get a larger copy of it). The end points are each a station. There are 3 other stations in between. The center station will be between the middle set of switches. The other two are in between the center station and the end points.
The tracks are labeled Track 1, Track 2, and Track 3 from top to bottom. The extreme left of the diagram is "west" and the extreme right of the diagram is "east". Tracks 1 and 3 are the "local" tracks... the ones that have station platforms next to them. Track 2 is the "express" tracks, and these are the tracks that the express train will mostly run on.
The express train (Bachmann Amtrak Acela) will service the terminals on each end, and the center station. It will skip the lesser stations between the center and terminal stations. The local train will stop at every station.
The other components of the diagram are the pink dots and the green boxes. The pink dots represent IR sensors. The green boxes represent stationary decoders (Digitrax DS64). The diagram needs to be updated, as I believe I can do with only 3 of these rather than 4, but that is for another post.
A typical starting position will be as follows... the local will be on Track 1 in the east terminal. The express will be on Track 2 in the east terminal. The trains will depart heading west (not sure which one goes first, this will be a variable that I will control programmatically). The local will travel to the first station and stop. The computer will sense the IR detector at that station and command the local to slow down and stop. After some period of time, it will continue on moving west.
Meanwhile, the express will move west and stay on Track 2 bypassing the first station. As the trains approach the center station, they will trigger the IR detectors in front of the turnouts. If the local gets there first, the turnouts will be set to closed and it will be cleared into the center station. If the express then triggers the detector on Track 2, then it will be commanded to stop and wait for the local.
If the express gets there first, the local will be commanded to stop after tripping the detector on Track 1. Either way, the first train then moves onto Track 1 at the center station, and after a time, moves on. The computer will know which train it allowed onto that track, so it will set the turnouts appropriately, to either allow the local to continue on Track 1, or move the express back to Track 2.
There is no contention at the next station and so the action begins as the trains begin to approach the west terminal. In this case, I want to move the local from Track 1 to Track 3, crossing Track 2. Right now, that is set up two pairs of turnouts, one to move it from Track 1 to Track 2, and then another to move it from Track 2 to Track 3. This is to position the local onto Track 3 for it's eastward leg after stopping at the west terminal.
I could probably use a crossing and get away with 2 of the 4 turnouts. I may consider doing this, as it would save some money, but it will lower the flexibility of the layout as there would be no way to get a train on Track 1 or 3 to Track 2, except at the center station. I'll noodle that.
Anyway, I need sensors to make sure that the trains do not collide and right now that is drawn as detectors that operate similarly to the above - who ever gets there first has right of way. Once the trains move into the west station, there are 2 more IR detectors to sense the end of the tracks and stop the train in the station.
The eastward operation functions as a mirror to the westward run. I leave it as an exercise to the reader to see how that run would work, given how long this post is already.
Any comments on what I'm doing here in terms of detection and control are certainly welcome. Expect future posts on the questions of IR detectors vs. Block detection (and why I'm planning on going the IR route) and for the relative merits of turnout position sensing and whether or not I really need that. One thing is for sure, it gets complicated really fast, even on a fairly straightforward and simple layout like this!
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