Automatic Operation

Automatic operation makes for interesting model railroads.  The passing of a train is enhanced by automation and the casual viewer is always amazed by the action.  Automatic operation requires:

  • Detection of a approaching train
  • Operation of the device
  • Detection of a passing train

Perhaps the simplest automated device in Z-Scale is the 8992 Crossing Gate:

Grade crossing accidents are serious business, and even in my brief railroad operations career, I was involved in an accident at a grade crossing.  I was fortunate enough to be in the lofty confines of the cab of a Seaboard GP-40, which was leading a train of three other Geeps and a train of 80 or so cars, when we collided with a truck loaded with live chickens. 

After the initial meeting at the grade crossing, our train rolled and generally crunched up this truck for perhaps 1/2 mile before we came to a grinding stop. My immediate view from the locomotive’s cab was that of poultry pandemonium, with thousands of alarmed hens running about the countryside. More than a few met their doom that day, and not all necessarily as result of the collision. Many of the survivors were spirited away in the trunks of automobiles, collected by passersby who were interested in inexpensive dining that evening.  It is humorous in retrospect, but that truck could have easily been loaded with gasoline and I would have likely been incinerated.

So, every grade crossing closure is cause for celebration in the railroad’s legal department, and the operating department, too. But, railroads continue to have crossings at grade with highways, and the grade crossing gates are a continuing part of the railroad landscape.  And, the Märklin gate has all of the necessary features.  The 8992 crossing gate consists of two identical sections that represent a railroad crossing.

Each crossing gate has internal light bulbs and a solenoid which operates the gate itself. When power is applied to the gate, the lights come on and the solenoid pulls the gate to the down position.  When the electricity is turned off, the lights go out and a spring pulls the gate back upward. The solenoids in the 8992 crossing gate are designed to operate for longer periods than the solenoids in the relays and turnouts.

It can literally be operated with a 72740 Control Box, but at some point, your finger is going to get tired.  There is an easier way to have the train operate the gates when it approaches.  Central to this process are Circuit Tracks; there are three of them, one for the 8520 radius, one for the 8530 radius and one for straight track.

 Curved circuit track (above) and straight circuit track (left)

   The circuit tracks have a small treadle which is located in the center of the track. When a locomotive passes over the circuit track, the treadle is pushed over enough to momentarily close a circuit, acting like a momentary push button.

Note that a train passing over the circuit track in the opposite direction will also momentarily close a another circuit.  In this way, when a train passes over a circuit track, it can be used to operate a solenoid. In most cases, the solenoids will be inside either the 8945 or 8947 relays, but it can also be used with the solenoids in turnouts and in the 8940 semaphore.

It is important to note that this action must be momentary, for if the treadle of the circuit track is held down by a stopped train (for instance), the effect is the same as if holding a turnout control button down.  Heat will build up and the solenoid will burn out.

The circuit track gives you a powerful tool toward layout automation.

Because the 8992 crossing gate requires constant power when in operation, and because the circuit tracks only operate momentarily, you need to add the 8945 relay.  The circuit track activates the solenoid in the relay, which in turn operates the crossing gate.

The circuit tracks can be either straight or curved, and should ideally be placed at a distance from the gates which is about the same as your longest train.  As the train approaches the automatic gates, it activates the relay via the action of the circuit track. The gates close and the train passes over the crossing.  As the locomotive passes over the second circuit track, it activates the relay again, this time turning the gates off.  This action works in both directions. If you have more than one track, you will need a relay and pair of circuit tracks for each track. In this way, two trains can be passing the crossing at the same time. When the first one clears the crossing, the gates will still stay down until the second train has cleared. You may also want to connect a 72720 momentary control box to the relays as a backup control of the relay which operates the gates.

The instruction sheet with the 8992 includes a wiring diagram.

Automatic Train Control with Signals

As mentioned in in the Signals section, it is possible to control train movement with color light signals & relays. By adding the circuit tracks, you can now have trains controlling themselves. At the heart of this is the basic signal & relay combination, with the individual circuit tracks operating the relays (or semaphores). One circuit track is located just beyond the signal, with a second one located further down the railroad line.  As the signal passes an individual signal, it activates the signal’s relay, turning that signal red.  Any train following will approach that red signal and come to a stop.  Once the first train has gone far enough, it passes over another circuit track which turns the previous signal to green, allowing a following train to resume. Once it passes that signal, the signal turns red again, and any following train stops until the earlier train has gone far enough.

The Noch “Cortina” layout features three signals on its inner loop, enough to support two trains following each other. In practice, the location of the circuit track which turns a particular signal green should be long enough to give the passing train a “head start”.  In the case of the Cortina layout, a train passing a particular signal turns that signal red and the previous signal to green.  Here is a diagram from the 0290 track plan book:

From the left; the circuit track which turns the signal red (note, the track number used is an earlier part number), the 8588 isolation track, the signal itself, some straight track and then the next 8588 isolation track which defines the control segment of the signal. To the right is the relay which operates this particular signal, with one blue activating wire connected to the circuit track; the other blue activating wire goes to another circuit track in another part of the layout. 

The circuit tracks can also activate relays for turning station platform lights on and off, operating turnouts and such.  One example is in the automation of a reverse loop.  The reverse loop is a problem with two rail trains.

This problem can be addressed by using the 8993 reverse loop set.

 The 8993 requires manually changing the direction switch on the transformer each time the train passes through the loop.

One way to solve this problem is to automate it:

In this illustration, a single circuit track operates both the loop’s turnout and also the 8947 reversing relay.  In this way, the layout operators’ attention is not disturbed by the mundane operation of the reverse loop.

This page is just an overview of what automation can do for your model railroad experience. It is anticipated that future developments with command control and computer interfacing will improve things further.

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