reverse loop idea

[aleopardstail]

just chucking this out there so it can be picked apart before I actually build it.

1. Reserving loop, this will normally be driven in a single direction, but may occasionally work the "wrong way"
2. the loop power feed is wired through a DPDT relay, set so the "exit" is the right polarity normally but energising the relay makes it right for "entry" (i.e. reversed)
3. about 2-3" either side of the "entry" isolating break there is a train detection sensor, an infra red beam which is normally "HIGH" output but goes "LOW" output if it sees a train, loco, coach, wagon, whatever cutting the beam which looks up from below at an IR LED above pointing down.
4. both of these sensors feed a NAND gate, this if either or both sensors see a train the output is HIGH, but if neither see one the output is LOW
5. this gate feeds a 555 timer, set for 2-3 seconds, such that if either sensor sees a train the timer is restarted constantly, only clearing 2-3 seconds after nothing is seen - this "smooths" the signal such that gaps between vehicles are ignored, the time set so even a slow moving train provides a constant signal
6. this timer drives (via a driver circuit) the DPDT relay..

so normally the track is set for a train to depart, and it can do so, or come back "wrong way" quite freely. but a train approaching the "entry" isolating joint triggers the relay to reverse the polarity of the neutron flow for it to safely leave, and there needs to be "no train" for a few seconds before it can reset.

thinking being:
there should never be a short circuit condition unless the train is longer than the reversing section (it won't be), and at no point is there a dependency on detecting a short circuit to reverse anything.

benefits: all the circuitry is at one end with all the sensors here so no need to have further sensors at the other end.

[centenary]

Larry Puckett had a nice solution for this using a couple of DCC Concepts components. If you could build similar, it should work. Didnt matter which direction the loco came from, the points were always correctly set and frogs polarity also correct.

https://youtu.be/6qpkbL0Pqwg?si=6wDBZcLDz0zo-3q3

[fourtytwo]

So the distance between the isolated breaks has to be train length + distance traveled in 2-3 seconds I think ?

[Dad-1]

While it's looked down on by many I do use a few Frog Juicers that
rely on sensing the short circuit to operate the rapid polarity switching.

Also the 'train' won't, or shouldn't have any influence, just the locomotive.
Wagons & coaches usually have at least one insulated wheel on any axle set.

My funny little triangle on the Ivor experimental track thread gave a reverse
loop effect, or would have had I been able to make the miniature 'Y' and that
would have been worked by the frog juicers.

What's the problem ?you solution sounds O.K to me ?

Geoff T.

[aleopardstail]

So the distance between the isolated breaks has to be train length + distance traveled in 2-3 seconds I think ?

yes, plus whatever margin is desired on top of that. in practice the loops I have are split into two parts, they could be split into three but this gives an extra 24-36" inches in each allowing some flexibility in stopping positions. also trains will run through here quite slowly.

current experiments show a ~9" 'stop block' (as in the moment a train is seen to enter it speed zero is issued) works quite well

[aleopardstail]

While it's looked down on by many I do use a few Frog Juicers that
rely on sensing the short circuit to operate the rapid polarity switching.

Also the 'train' won't, or shouldn't have any influence, just the locomotive.
Wagons & coaches usually have at least one insulated wheel on any axle set.

My funny little triangle on the Ivor experimental track thread gave a reverse
loop effect, or would have had I been able to make the miniature 'Y' and that
would have been worked by the frog juicers.

What's the problem ?you solution sounds O.K to me ?

Geoff T.

no real problem, just wanted a second brain, well a first one really, to see the idea before I blow something else up

it is likely coaches will get lighting, ditto brake vans at some point, the system I'm working on doesn't need to sense every vehicle to work, but the electrickery means the blocks have to be longer than a train to sop a wheel shorting at both ends at once

the block idea is basically software sees a train entering a section, and marks the section as occupied, regardless of the block sensors the section only clears when the train enters a specific block which is at least a trains length past.

e.g. for the reverse loop to be seen as safe for a train to drive into not only does it have to report as empty, the train that was in it will have to have entered the end block of the next section.

this is for automated running, a human driver can do whatever

[Suzie]

The concept is excellent, and it will work in both directions fine. Just make sure that only one train is in the section!