Wanting to have a oval with a figure eight crossover in the middle

[sagegraqy]

I understand polarity reversal caused from a crossover when four turnouts are added to form a oval.  Seems like the simplest thing to do is isolate the sections of straight track between the turnouts?  I am wondering what is the best way to electrically control these isolated pieces of track?  Would a DCC controller help at all?   what are "loop controllers?

Ray Brooks   raymymail@yahoo.com

[jward]

first of all, some definitions....

a crossover is a configuration of two switches used to cross a train over from one track to another parallel track.

a crossing is a section of track designed to let one track cross another. I suspect this is what you are referring to in your post.

using the crossing and 4 switches to add a figure 8 to an oval means you need to isolate a section of track completely from the rest of the railroad, and use some method to reverse polarity to this section independent of the rest of the railroad. with all forms of control, the insulators on the rails will be in the same locations. but how the isolated section is controlled is different with dc or dcc.


with dcc, control is simplest. you can use an autoreverse circuit to automatically switch polarity when a train enters and leaves the section. with dc, the usual method is to use a dpdt switch to control this polarity manually. dcc autoreversers won't work on dc.

the image below shows where to gap. the red section should be wired as the reversing section.

[jonathan]

Well...

Of all the threads I've seen on this topic, and there have been more than a few, I must say JWard's is the best explanation I've read and actually understood. Thanks for that!

The biggest drawback I see to this design... you will never be able to run more than one small train, in either DC or DCC.  It would be too easy to "pull a Gomez" or burn out a locomotive or power unit with all the polarity switching.  Just a thought. 

I would much rather lay an oval on the outside and a separate figure 8 on the inside.  This gives the same effect with two trains running at once.  Just two cents to keep or toss.

Regards,

Jonathan

[Doneldon]

I understand polarity reversal caused from a crossover when four turnouts are added to form a oval.

Ray-

You actually have a reversing section with only two switches. If you run a straight section on one side of the figure eight you'll run into a short as soon as you enter the straight section after passing through the central crossing the first time. These reversing sections, whether one, to or several, are most easily handled by an automatic reversing module. Yes, you can do it with DPDT switches but automating the process is smoother. It also helps a busy engineer focus on operational tasks which can't be automated. And, last, it's more prototypical. Engineers running trains on a twelve-inches-to-the-foot railroad don't change the polarity of the rails on which they're traveling. (OK. I recognize that there wasn't a track polarity in the first place but you get my point.)
                                                                                                                                                                                       -- D

[Len]

These guys: http://www.azatrax.com/reverse-dogbone-loop.html make an auto-reverse loop module that works with DC, DCC, or AC for the 3-rail crowd.

Len

[Joe Satnik]

Len,

I thought one of the selling points of 3-rail operation was that you didn't ever need to  reverse the 'polarity' (or, more correct for AC: 'phase').

Joe Satnik

[jward]

These guys: http://www.azatrax.com/reverse-dogbone-loop.html make an auto-reverse loop module that works with DC, DCC, or AC for the 3-rail crowd.

Len

Holy Crap! I thought autoreversers were expensive. this is not only expensive, it's unnecessarily complicated as well. It looks like something Rube Goldberg would design.

[Len]

Len,

I thought one of the selling points of 3-rail operation was that you didn't ever need to  reverse the 'polarity' (or, more correct for AC: 'phase').

Joe Satnik

My bad. It's for 2-rail AC, e.g., American Flyer, which does have problems with reverse loops. You're correct, reverse loops aren't a problem for 3-rail.

Len