Return loop technology?

[plord]

I am in a real space bind and the only way I can make it work is a fold-down return loop that merely sends the train back onto the same track it came on. My question is, does this require a switch at the point where the loop comes back to the track or is there some form a always open connection. (Am I explaining this right?)

[MisterBeasley]

There are two things to deal with here, one mechanical, the other electrical. You can set up a "slip switch" which will normally send you in one direction, but if you approach from the wrong side, it's forgiving enough to slide over and let you through. Alternately (and I think preferably) you can use a detection circuit to sense the the train and use that to throw the switch the right way.

The other problem is electrical, because as you come back around, you will be reversing the polarity of the track. For DCC, this requires a "reverser" circuit that handles the problem automatically. For DC, you need to flip the polarity of the main track, either manually or once again with something automatic. You will not have this problem with 3-rail O-gauge, by the way.

[stokesda]

I believe you'll have to use a switch/turnout, unless you want to have two parallel tracks (less complicated electrical-wise), or you want to use a gantlet main line, which is basically two overlapping sets of parallel tracks on the same ties (heres' an example: http://image03.webshots.com/3/0/83/44/21408344mgAUFPpzaa_ph.jpg).

Update: Oh, wait... maybe you meant an electrical switch? If you have a reversing loop, you have to isolate both rails at both ends of the loop, so you end up with a totally isolated section of track inside the loop itself. If you are using DC, the wiring to the loop and the wiring that controls your loco's direction (fwd/rev) are wired to a DPDT toggle switch. When the loco enters the loop, you flip the switch, which reverses the polarity of the rails. Normally, this would make the train suddenly reverse direction, but since your loco's fwd/rev switch is also on the same DPDT switch, the loco's direction is reversed at the same time... so the rail polarity is reversed, but the train continues to move in the same direction. When it exits the loop, it will be facing the "wrong way" on the main tracks, but since the fwd/rev switch has already been flipped (via the DPDT toggle), it's continues back the way it came.... At least, I think that's how it works... Hopefully that made sense [%-)]

DCC works similarly, but as MisterBeasley explained, there's other weird stuff going on there that I'm not familiar with, because I don't use DCC (yet).

[chateauricher]

QUOTE: Originally posted by stokesda
http://image03.webshots.com/3/0/83/44/21408344mgAUFPpzaa_ph.jpg

Your link doesn't work. [:(]

Something to do with not having permission to access it. [:(]

[stokesda]

QUOTE: Originally posted by chateauricher

QUOTE: Originally posted by stokesda
http://image03.webshots.com/3/0/83/44/21408344mgAUFPpzaa_ph.jpg

Your link doesn't work. [:(]

Something to do with not having permission to access it. [:(]

Hmmm... Actually, it's not even my picture... I just Googled it to try to find an example. Apparently the website has some kind of anti-hot linking device.

Try this one instead:

http://www.probertencyclopaedia.com ... Type in the word "gantlet" in the search window.

[plord]

To all who replied, thanks. Now I have to digest this. Back to wiring 101. Fortunately I have a while before I actually have to commit myself to design. I will do my homework.