multi train loop

Dennis, as you describe it, your problem seems to be the same as Gus deGuilo had a while back. Here is what I recommended to him:

You will need 7 DPDT relays. It doesn't matter whether AC or DC, as long as you have a suitable power supply for them.

Each siding has two control rails, one at each end, and a stop section with an isolated center rail at the end where the locomotive will stop. The control rail at that end is arranged so that it is bridged before the locomotive stops. The control rail at the other, entrance, end is cleared by the end of the train and not bridged when the train stops.

There are two relays for each siding. The first is an "arming" relay which is operated by the control rail when the train enters the siding. It has a latching contact, which bypasses the control rail to ground when the relay operates. The other contact on the arming relay is in series between the "power" relay's coil and the other control rail. So, if the arming relay is latched by the time the locomotive reaches the end of the siding, the power relay will operate, even though the train is past the first control rail. The power relay controls track power to the stop section of the next train to run. It also has a latching contact that takes over from the control rail when the relay operates.

The other ends of all six relay coils are connected to the appropriate supply voltage, except that the arming relays' coils are connected through a normally closed contact on a seventh "reset" relay. The reset relay is operated by a control rail somewhere in the section of main line that all the trains pass through.

The two switches for each siding are of the non-derailing type, with the coils within the pair connected together, so that when one switch throws automatically, the other matches it. This way, the switches are always lined to return the train whence it came.

Here is the scenario. A train leaves its siding. As it exits, it throws the trailing-point switch so as not to derail. The corresponding switch at the other end throws at the same time, insuring that the train will be routed back onto the same track. As the train passes the common section of track, it operates the reset relay, which releases all the arming relays. This in turn releases all the power relays.

As the train re-enters its siding, it operates that siding's arming relay, which latches. Then, as it reaches the other end of the siding, it operates the siding's power relay, which has been enabled by the arming relay. This supplies power to the stop section for the next train. An instant later the first train comes fully onto its stop section, and stops. Then the cycle repeats with the second train, and so on.

thanks Bob, I knew you would have the answer.
Dennis

Dennis,

How long is this loop going to be? To contain train length sidings for three trains + some track in between it must be quite large. Just curious.

John, I have a space 12 x 18 set aside, so I can do plenty with it. Plus, with a little rebel ingenuity, I can make it loop over itself for even more trackage. I am getting the final plans together now.
Dennis

Dennis, I got to thinking about coordinating the turnouts. Depending on how you lay out the sidings, they may need a little more attention.

If the arrangement is symmetrical, for example, with track B being the main line, track A on the left, and track C on the right, with the track-C turnouts both outside the track-A turnouts, there is no problem. But, if one track-C turnout is between the track-A turnouts and one outside, train C could pass through only one turnout when departing and leave one turnout lined wrong when it returns.

Fortunately, the fix for this kind of problem is dirt simple: Just add extra control rails as needed at any exit to line any other turnouts needed for a correct return.

Thanks Bob,
I was thinking about how to do this as I have the RR-tracks program and am in the process of designing it this weekend. I will let you know and maybe we can post some photos so that others can pick up on it. Thanks for your advice.
Dennis

The problem with trying to do this just with relays is that the sequencing will lose its memory when power is cut. If all 3 trains are in the siding,which one will go first.? As an old pinball mechanic I can give you an easier solution. It is called a rotary or step switch. It is composed of a coil and a latching mechanism which rachets up one click each time the coil is powered. Normally the coils is 24 or 28 VAC. Some are for continuous operation and some can only be powered a few seconds on each activation. Then there is a disc or wiper blade with contacts where you can wire an individual circuit. The disc travels in a circle where the cycle repeats itself. It can have from 3 to as many as 20 or more different contact or positions before repeating. In a pinball machine for example it can be used to light up bulbs counting one to ten. With the usage of IC chips these mechanisms have fell out of favor but are still around as surplus. I could probably salvage one out of some scrap machines I still have.

For your application you would need an insulated center rail in each siding where the train stops, lenth woud be maximum train lenth plus train stopping distance. You would also need an insulated outside rail at the end of the block,lenth would be maximum stopping distance.To each of these you would activated a 24v SPDT relay. Wire the contacts of the three relays in series so that when all three are energized by block occupancy, it advances the rotary switch one click.

Lets say for our example you have a 10 position rotary switch. You wire this so that in any of the 10 positions it activates only one of 3, DPDT relays,each of which controls blocks A,B,and C. Only one relay can be activated at a time as limited by the step switch. One set of contacts of the block relay can power on the insulated center rail to the block,while the other set of contacts can throw the turnouts in the proper direction. You can hook the sequence anyway you like. Example ABCBCBABCB,then the step switch repeats.

Each time the blocks are occupied by 3 trains,the step switch will advance one notch,stopping the train that just pulled in and starting the next train selected on the step switch.

For more realistic operation you could install an interval timer which totally cuts off the track power each time 3 trains enter the blocks.,so all the trains wait a while. You could also trigger a station announcement sound board. You could then stage a couple of start relays for a soft start of the trains,blocking some of the initial voltage with diodes in series. On my layout for example as the train starts there are 8 relay staging steps,gradually increasing the voltage and working the bell and whistle. Not only does this allow for more realistic operation but it saves wear and tear on the engine and components.

The problem with automating turnouts is that the system is only as good as the turnouts. If you have a derailment the system keeps running and you have a mess,pretty much like real train. This may be a little too prototypical for you.

Dale Hz

Thanks for the imput Dale. I will be putting the layout together next month and need to get all this down on paper before build time.
Dennis

Of course you could also just install a pushbutton to momentarily power whichever track you want to go first.

If you use a stepping switch, keep in mind that these come in two flavors, front-acting and back-acting. Front-acting switches move when the coil is energized. Examples are e-units and telephone Strowger and minor switches. Back acting switches move when the coil is de-energized. Most other telephone-type switches--what the British call "uniselectors"--work this way. For Dale's scheme, you need a front-acting switch (or some sort of pulse-generation circuit). I'm not familiar with pinball machines, for which front-acting switches may be standard.

I don't see why the stop block needs to be much longer than the locomotive. In fact, for passenger trains, I would think that you would want any lighted cars to stay lit.

I think it would be simpler to use an existing non-derailing feature to line the turnouts. Even if you would have to add this feature, and even an extra control rail for the worst-case turnout arrangement that I described, I think it would still be simpler. (Note that more than one extra relay contact would be needed to line the multiple turnouts to get out of and back into some of the tracks.)

When power is cut to the loco,different locos have different coasting characeristics. postwar stuff actually coasts farther as they free wheel. Dual rollered passenger cars can jump the center pin if you attemt to leave them lighted,repowering the locomotive. You could get around this problem by leaving 3 to 5 volts in the block and using LED lighting in the passenger cars. Of course the train would take longer to stop. If you have the room this is good thing.

Most pinball step switches are forward acting. 28 VAC coils except for Bally which are 56 VAC. The former will work on 20 VAC. Some are spring loaded,going to an end point and then reset by a cancel solenoid. Others are just circular.Some are simple while others have multiple wipers and contacts which can do very complex multi function switching. The contacts only handle small current loads so relays must be used in conjuntion if powering heavy loads.Step switches went out of fashion in the late 70s with pinballs.Gottlieb was the last company to use them as they were slow to adopt modern technology. It cost them their leadership in the market.

Dale Hz

Dale, I don't understand what you mean by "leaving 3 to 5 volts in the block and using LED lighting". Unless you also intend to regulate the LED current, this would seem to dim the lights substantially. But you could power the lamps or LEDs through diodes in series with the individual pickups, which would prevent any pass-through of track voltage.

On the other hand, tenders, baggage cars, and express cars could probably provide enough of a dark zone at the front end of the train to take care of any likely coasting.

Bob

I guess you could isolate the pickup rollers but that would defeat the purpose of the double rollers,which keeping on the lights over turnouts and crossovers. Engines vary greatly in coasting distance. A dual rollered passenger car behind the engine could simply repower the block through the 22 gauge pickup wire.
With an automated block system,like I use on my layout if the train overruns the block there is risk of collision.

You could run the center rail stop block wire to the relay contact common, run the transformer power to the NO contact and run the transformer power through a resistor or diode array then hook it to the NC contact leaving 5 volts to the track. The problem with this is that it increases stopping distance. On my layout I allow 40 inches stopping distance,the lenth of an Atlas track,and this barely stops some locos. So for critical block stops I pull the plug. On non critical stops such as station stops I leave 5 volts.

On my automated tracks I leave the transformer at full throttle,18 volts and I use a diode array (a string of 6 amp, 18 pair) and relays as the throttle. The diodes reduce 18 volts to about 5 volts at the end of the array. As the train starts a set of 9 relays close one by one increasing the throttle allowing small voltage increments also turning the bell on and off. The first 6 diodes in the string are not cross connected so you can unbalance the sine wave to accomplish this. Top speed is 14 volts as the first 6 diodes are left in reserve to blow the whistle.

I light my passenger cars with LEDs by installing an LM350T voltage regulator circuit. I set the voltage at a little over 3 volts,the forward current of the diodes used. The LEDs can be wired in parallel without individual dropping resistors. For diodes I use either 150 MA 10mm daylight or white with a 140 degree view angle or I use 20 ma with a 20 degree view angle. The latter I install foil on the car ceiling to reflect and diffuse the light. If 5 volts are left on the track the LEDs should stay lit unless the engine motor hogs too much current. I have been working on some outside projects in the nice weather so I am still perfecting this.

Sorry I did not get back sooner,I had trouble registering.

Dale Hz

Dale, short of regulating the LEDs as you do, it is still not very difficult to wire double pickups to a single set of lamps or LEDs so that they cannot power the train across the gap, yet still keep the lights on over breaks in the center rail.  The trick is to rectify the track voltage, then combine the DC to power all the lamps.  This can be done half-wave or full-wave.  For half-wave, all that you need is a single diode in series with each pickup.  The RMS voltage will be reduced by about 30 percent.  If you don't want to exploit this to increase lamp life, you can substitute lower-voltage lamps.  For full-wave, two bridge rectifiers will do the job, although, since the diodes on the return side are doubled, the circuit could be built up from 6 individual diodes, not 8.  The RMS voltage remains virtually unchanged.

However, if you are rectifying the lighting voltage anyway, you might as well put in a capacitor, which is what I do.  This does a better job of eliminating flicker, which can still happen with two pickups.  In fact, I have removed the second pickup on some MTH cars that had particularly stiff ones, just to get easier rolling.  A capacitor big enough to power the lamps through the gaps will raise the voltage by about 40 percent.