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[jagged ben]

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First, gap the rails close to the turnout.  Then replace the manual DPDT switch with a DPDT relay. Power the relay's coil through the switch machine contacts in such a way that the polarity of the reverse loop will match the route selected by the turnout.  That way the loop will always match the polarity of the selected route.  I hope that this makes sense.
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Note that a Tortoise IS a DPDT relay.  It's possible to use it without a separate relay. 

Of course this still only works in DCC.

I'd also point out that if this is only going to be a one train layout it might make more sense to switch the polarity of the mainline, not the loop.

[peteski]

Note that a Tortoise IS a DPDT relay.  It's possible to use it without a separate relay. 

Of course this still only works in DCC.

I'm aware of the DPDT contacts on the Tortoise but often one set is already uses for powering the frog or for signaling.

As far as working with DC, the DPDT relay solution I provided will seamlesly work with DC too (assuming that upon exiting the loop you stop the train to throw the switch  and you also flip the throttle's direction switch). 

[jagged ben]

I'm aware of the DPDT contacts on the Tortoise but often one set is already uses for powering the frog or for signaling.

 

In your scenario, if you're using a turnout that requires switching the frog power... you don't need to gap the frog!!!!  In can be electrically continuous with the entire inner rail of the loop.  Indicators could be easily done.  Actually the fact that the Tortoise will momentarily lose any connection is a bigger probelm though, if you don't want the train to stop.

As far as working with DC, the DPDT relay solution I provided will seamlesly work with DC too (assuming that upon exiting the loop you stop the train to throw the switch  and you also flip the throttle's direction switch). 

Yeah but c'mon, that's hardly 'seamless' having to stop the train.  Also forward and reverse on the throttle shouldn't change.  Like I said above, if it's a one cab layout, it makes more sense to switch the main and not the reverse, with the caveat that you always have to take the reverse in the same direction.  The right way to do this, as we all know, is to reverse both segments of track.  It would be possible to make that 'seamless' somehow, I'm sure.  Or you can just use an Altas Controller.   

[peteski]

 

In your scenario, if you're using a turnout that requires switching the frog power... you don't need to gap the frog!!!!  In can be electrically continuous with the entire inner rail of the loop.  Indicators could be easily done. 

What about the outside rail? What powers it?

[John]

I didn't realize the MRC Tech III was a DCC system.   

_{I would add: if I wanted to throw lots of switches to run trains, I  wouldn't go DCC in the first place.}

The MRC isn't DCC .. I didn't feel like photoshoping out the MRC .. just imagine a DB150

Also, I merely offered Phil a quick and cheap solution .. that he could replace later on ..  we don't always have to over engineer model railroading .. 

[jagged ben]

What about the outside rail? What powers it?

The other Tortoise contact.

If you want an indicator for the turnout you can do that with directional bi-color LEDs wired in series with the turnout motor.  You don't need to use the Tortoise contacts for that if you just want a simple indicator light.

However...as mentioned...the train will stop momentarily while the tortoise throws, so in the end you win with the relay, at least for DCC.   

I do like the idea for a simple reverse loop.  Heck, under the right circumstances one could use it for an entire portion of a balloon staging yard instead of an AR.

[jagged ben]

The MRC isn't DCC .. I didn't feel like photoshoping out the MRC .. just imagine a DB150

Also, I merely offered Phil a quick and cheap solution .. that he could replace later on ..  we don't always have to over engineer model railroading .. 

Fair enough.  (The Tech III really is kinda confusing though...)

[Philip H]

Also, I merely offered Phil a quick and cheap solution .. that he could replace later on ..  we don't always have to over engineer model railroading .. 

And believe me I appreciate it. I managed to save a toggle or two, and a fellow a$$hat has proffered a couple ARs to try at a reasonable rate. So I pretty sure once I get my loop built (!) I'm good either way.