Providing straight DC to L/R switches in reversing loops

Which MTH switches are they and are they Non-derailing???

Marty

Jerry:

Regardless of the brand of switch, the type of mechanical activator, or the type of electricity (AC or DC) (fixed or variable) you decide to use, the concept is the same.

There is a wiring method that will ensure that the switch will always direct a train into the loop on either the straight ("normal" in real railway terms) or the diverging ("reverse" in real terms) choice.

The simple way, using one insulated rail section ("IRS") per switch, assumes that you will be using a short train and that the train will always/usually be the same length.  It also assumes that the mainline track section is longer than the length of the typical train, and that the loop is longer than a typical train.  

Trains that are too long will louse up this scheme. So, these assumptions are, in turn, based upon the assumption that you wish to create a constantly-running, or demonstration type of layout.  I have a similar scheme on a short subway line. The train always enters a stub station on the right-hand track, waits a few seconds, and then departs over a crossover track, to leave the station on the opposite track.

Visualizing a "dog-bone" track layout, you place an IRS at each end, on the mainline track. The IRS at the left end controls the switch at the right end, and vice versa. The momentary electrical pulse from the IRS at the left end is wired to the terminal at the opposite (right end) switch that happens to be the non-derail terminal on that switch, for traffic normally entering the curve part of the switch.

See if you can visualize this sequence: A train is heading from right to left, on the mainline section of the dog-bone. When the locomotive and cars roll over the IRS at the left end, the switch at the right end, way back behind the train, flips to the curved position.  The train goes around the left loop (we have not discussed the wiring for that in detail yet) and heads back towards the right end loop. It gets there and is directed into the loop through the curved choice of the switch. The train continues around the loop and the non-derail feature now senses the train coming out the straight part of the switch and sets it correctly for the straight path.

The sequence is repeated for the loop at the left end by the action of the train passing over the IRS at the right end of the layout. And around and around she goes...

The clever guys here who design and build electronic circuits will now chime in and tell you how to create a small inexpensive circuit board (called a "one-shot") that will accept the first pulse, and ignore subsequent pulses, to prevent the switch motor from buzzing and clicking unnecessarily after the switch is thrown by the locomotive of the passing train.  I will hand it over to them now...

Jerry:

As I understand what you are asking - you want a train to run the loop (enter the loop through the turnout in one direction and exit the loop through the turnout in the opposite direction without having to use the switch control). Caveat - I know next to nothing about MTH track. With that said AC or DC power to the turnout won't really matter. However if you want to use DC from an AC source simply place a rectifying diode like a 1N4001 in line with the power wire to the turnout. Wire the turnout in the normal way per instructions.

This is just an idea - If it is possible to use isolated track to control the MTH turnout then you can place the track far enough inside the loop so the whole train consist goes through the turnout in one direction then another isolated track on the main line far enough down the line so that the train consist again clears the turnout. The isolated track on the main line could be uses to control both turnouts at each end loop.

Hopefully someone who knows MTH track can chime in and say whether or not the above would work.

Joe

Well the MTH O-31 manual itself suggests you can use DC.  I'd try the following, derived from Figure 9 in the manual.

Remove the jumper that straddles the right 2 screw terminals.  Then apply DC power as shown.

Stan,

Thanks for the info. It is crystal clear.

Jerry T