# Reverse loop in a reverse loop



## Cal Trask (Jun 18, 2019)

Is this even possible? I think I can make it work in DC, but would it be easier in DCC? Would like to know before I get too far in construction.


----------



## DonR (Oct 18, 2012)

Yes, you can make it work with DCC. You would need
2 reverse loop controllers. You would simply isolate
the track connecting the high loop to the lower. That
section would be powered from your main track bus.
Be sure that both loops are longer than your longest
lighted passenger train, or train with lighted caboose.

Don


----------



## Shdwdrgn (Dec 23, 2014)

You should make it more challenging by connecting the reverse loops with a full wye (allowing access from either direction). I'm only half joking, it would improve the access the the second loop, but would require at least a third reverse-loop controller?

Which raises another question... this business of making your reverse loops longer than your train, how does that work with a wye where each leg is relatively short?


----------



## mesenteria (Oct 29, 2015)

Shdwdrgn said:


> ... this business of making your reverse loops longer than your train, ...


In some cases, it may be absolutely essential, but only if the gaps are two and are directly transverse (directly across from each other relative to the track's axis). 

If you make two sets of gaps at the ends of each leg of the loop, and separate them by the length of the longest wheelbase that will be picking up power from the rails, you can run trains longer than the length of the loop. See Digital Specialties' instructions on wiring the PSX series of reversers.


----------



## Shdwdrgn (Dec 23, 2014)

Would that then require a separate reverse-loop controller for the gap at each end of the loop?


----------



## DonR (Oct 18, 2012)

Mesenteria

Couldn't find the suggested instructions. Could you
provide a link? Just how are
these 'gaps' powered, by what source? 

The way many of use use a 'wye' only a loco and
perhaps another car or two transit it, thus no problem.
You could also lengthen the 'wye' 'isolated' section beyond
the turnouts at each end if it was in a main line. Might
have to do some additional insulated joiners.

Don


----------



## gregc (Apr 25, 2015)

mesenteria said:


> In some cases, it may be absolutely essential, but only if the gaps are two and are directly transverse (directly across from each other relative to the track's axis).


of course there are two gaps, one in each rail and since the polarity of the rails across a single gap are opposite, a short occurs if just on gap is bridged by a metal wheel.

i agree a train can be longer than the loop, but with issues.



Shdwdrgn said:


> Which raises another question... this business of making your reverse loops longer than your train, how does that work with a wye where each leg is relatively short?


a wye is intended to reverse just a loco, not an entire train



Shdwdrgn said:


> Would that then require a separate reverse-loop controller for the gap at each end of the loop?


a reverser is required for each loop where a short can occur. 

The mainline power connection of the reverser for the 2nd loop would be connected to the loop track of the first loop (adjacent to the mainline)


----------



## mesenteria (Oct 29, 2015)

DonR said:


> Mesenteria
> 
> Couldn't find the suggested instructions. Could you
> provide a link? Just how are
> ...



Don, it's on page 7, in rubric:

https://dccspecialties.com/products/pdf/man_psxar.pdf


----------



## mesenteria (Oct 29, 2015)

gregc said:


> of course there are two gaps, one in each rail and since the polarity of the rails across a single gap are opposite, a short occurs if just on gap is bridged by a metal wheel...


I may not have been very clear. Yes, there must be two gaps at each end of a wye-leg or of a loop, one on each rail. However, it isn't necessary to have a train shorter than the leg or loop unless there are only those two gaps, one on each rail. As the instruction I linked to in the previous post suggests, you don't have to limit yourself to trains that fit into a loop between the gaps if you are willing to cut an additional pair close to them, but spaced apart enough that the longest metal frame/truck mated to metal wheelsets will fit between those gaps. 

Some locomotives may not like that arrangement, particularly if they are short in the power pickup wheel base. An SW-7 type, for example, might stall...probably will. But, even my little P2K 0-6-0, with its power pickup tender, was able to get over my double gaps on my last layout, they being spaced about 2.5" apart. It also got across my Fast Tracks insulated frog/non-powered frog #8 turnouts.


----------



## gregc (Apr 25, 2015)

mesenteria said:


> you don't have to limit yourself to trains that fit into a loop between the gaps if you are willing to cut an additional pair close to them, but spaced apart enough that the longest metal frame/truck mated to metal wheelsets will fit between those gaps.



if i understand this, there is a isolated unpowered section of track between 4 gaps at each end of the reverse loop. short enough for a loco (e.g. 0-6-0) to span but long enough that an all metal truck cannot bridge. hence, only a loco could bridge both the mainline and reverse section and trip an auto reverser.

if you don't have all metal trucks, can the unpowered isolated section be shorter (e.g. 1/4")?

of course this doesn't apply for the types of reverse loops shown in the drawing, both the loco and caboose of a train can't both occupy the turnout.


----------



## cv_acr (Oct 28, 2011)

gregc said:


> a wye is intended to reverse just a loco, not an entire train


That's not necessarily true. There's enough junctions that have wyes to connect in both directions. Or major stub terminals.


----------



## mesenteria (Oct 29, 2015)

cv_acr said:


> That's not necessarily true. There's enough junctions that have wyes to connect in both directions. Or major stub terminals.


Yes. The UP's FEF routinely turns the entire consist on a wye someplace, can't remember where, and Winnipeg's Prairie Dog Central does the same a few miles north of the city. Yet, in some places, the tail is only 250 feet long or so. Spences Bridge in south-central British Columbia had such a tail until CP removed the facility about 10 years ago now.


----------



## mesenteria (Oct 29, 2015)

gregc said:


> ...
> if you don't have all metal trucks, can the unpowered isolated section be shorter (e.g. 1/4")?
> 
> ...



That I don't know, but why would you want the double set of gaps if you have no worries over metal trucks? All you need to do is to prevent metal tires, any of them, from bridging the gaps and causing a short, but there's where the PSX goes to work. So, you can still have a train that doesn't fit within the single leg, the reversible tail, or the reversed loop. You just need to be wary of two metal tires bridging their proximal gaps at the same time, so stagger them a bit. That's also what the instruction suggests. This only needs to be about a three or four mm stagger, not half an inch or anything like that.


----------



## gregc (Apr 25, 2015)

mesenteria said:


> That I don't know, but why would you want the double set of gaps if you have no worries over metal trucks?


i don't thinks it's been made clear why you want a short isolated unpowered section of track.





mesenteria said:


> You just need to be wary of two metal tires bridging their proximal gaps at the same time, so stagger them a bit.
> 
> That's also what the instruction suggests. This only needs to be about a three or four mm stagger, not half an inch or anything like that.


i don't believe there is any issue with the same wheel simultaneously bridging the pair of gaps(?). The short is no worse if there are actually two shorts in parallel. 

So I don't understand the need to stagger the gaps. Can you explain?


----------

