Life finds a way

As I was watching a train pass the other night, I noticed something odd about one of the cover hoppers: There was something fuzzy on the front end. It turned out to be a plant of some kind. While it looked like a tree, I suppose it could also have been a vine like Kudzu (the train was in Alabama).

A few more cars passed, and there were more plants. I guess those cars had been sitting for quite a while. If they were trees, it would appear they had been growing for about 6-12 months. This could be an interesting thing to model.

Unfortunately, I don't have a picture.

Flashlight

If you use a Digitrax DT-400-series throttle, did you know you've got a flashlight? Simply hold down the Power button in the lower left-hand corner and the white LED will turn on and stay on while the button is pressed.

One caution: This will switch the throttle to the power control screen. If you press "+" or "-" the system will cycle through power modes or turn off. To return to "normal", press the "Func" button on the top row.

Staging Yard

The club layout design called for an upper staging yard over a lower one. Building the upper staging yard posed a few problems, chief of which was figuring out how to support the track.

Since a good bit of the upper yard would be over the lower yard, it would be difficult to bring supports down to the lower roadbed without possibly impacting trains. One easy solution to that is to take a track out to get room for a support. It worked out that by cutting the upper yard roadbed larger than needed, the place where a track had to be removed was a shorter track. The shorter track was approximately the same length as a switch, and the switch to that track could be removed as well. So, it turns out that we don't lose any storage space at all and gain a switch that can be used elsewhere!

The upper yard is temporarily supported by threaded rod. This has the advantage of being easily adjustable and once the nuts and washers are properly tightened, reasonably permanent. Once the yard is properly leveled (or acceptably out of level--a downhill pitch won't bother a staging yard), it's possible to put in more traditional supports where possible.

The problem with threaded rod is that it has to stick up above the roadbed to secure to the roadbed. This makes running track in that area impossible. Solutions such as T-nuts or threaded inserts are available, but threaded rod only lends support to a small area. A wood riser type of support will support a much larger area.

Now for the difficult parts: There's limited access for a screwdriver, so how are the supports going to be changed over to wood? Can we add support and provide a solid barrier to prevent trains from going off the end and hitting the stairs?

Problems and solutions like this are part of what make model railroading fun.

Plaster Substrate

In one area, paper towel was glued to the foam and Masonite (hardboard) roadbed to bridge the gap between the two. The paper towel was then covered with plaster and painted. Everything was ok, until it came time to scenic the track near the area. Wetting the scenery put a lot of water on that part of the layout, and the paper towels buckled and warped, taking the plaster with them.

The area has been repaired with plaster mesh tape and a layer of plaster pushed in to the tape. Hopefully, this will hold up better, as the scenery on the track above is not finished.

Applications

In the last few posts, the various uses and usage of a test light was discussed. To wrap up the series, we'll cover a couple uses that might not be obvious.

When installing block detection, it is sometimes useful to have a way to trip the detector without messing with a train. As long as the test light draws more current than the block detector needs to trip, it will trip the detector. Simply place the test light leads across the rails so the light lights.

Need to temporarily connect two rails? (i.e. To test if making a connection will fix the problem.) Simply connect the test light straight through just like it was a wire. The light may glow a little bit, but power will pass through. As more current is drawn, the light will glow brighter. (This is simply connecting a light bulb in series.)

There are likely many more non-obvious uses for the test light, but these are two I've found most useful. Additional uses can be suggested in the comments.

Reversing section diagnosis with a test light

Previously, the basic operation of a test light was discussed. In this post, the use of a test light will be employed to diagnose issues with a reversing section.

DCC reversing sections are placed between two sections of fixed-phase track. The phases are opposed, so a short would occur without the autoreverser. The autoreverser works by sensing a short and flipping phases to correct the problem. As long as this works, operators don't notice a thing. When this fails, trains will often work correctly until the crossing between the opposed fixed-phase track and the reversing section.

The test light can be used to indicate which phase the rails are connected to at the moment. Connect the test light to one rail in the fixed section and one rail in the reversing section. If the light lights, you know the rail is the opposite phase of the one connected to the test light. If the light doesn't light, it's probably a good idea to check the other rail just to make sure the connection is good.

To test the reverser, a momentary short must be created. If the test light you're using has a long probe, it can be used to bridge the rails to create a short. At this point, the reverser should flip polarity (check by repeating the test above.) Sometimes the reverser flips multiple times, or faster reversers (such as the PSX-AR) may see the short for too long and not change polarity. If this happens, another way to trip the reverser is to use the test light to bridge an insulating gap. A test light with a long probe can be used to bridge the gap.

If the reverser does not trip, start looking for the trouble in the end that's working fine. Most likely, something is closing or bridging the gap.

If needed, power can be strategically removed to help isolate the trouble area. By disconnecting power to the fixed section, then looking for current to flow from the reversing section to the fixed section, the rail that contains the short can be located. For example, if the test light is connected to Rail A and Rail B in the reversing section it should light. Keeping one end of the test light in the reversing section, move the other out into the fixed section. If the light lights, that rail is receiving power from somewhere.

Once the operation of a test light is understood, it can be a very useful tool in troubleshooting. Troubleshooting can be described as the process of eliminating what works properly in order to reveal what does not. The test light is an excellent tool for doing just that.

Checking phasing with the test light

One of the most important requirements of a multi-block layout is that the phasing (or polarity) is correct. Trains will short at block boundaries if this is not correct. In a multiple booster configuration, it is essential that each booster's output properly matches up with the adjacent blocks. Use of a test light can ensure this is the case.

The test light leads do not have to be connected to one booster for the light to work. This means the light will work across booster boundaries, which will be the basis of checking for proper phasing.

To check for proper phasing, connect the light across the rails in the same block. The light should light. Next, move one connection over to the other side of the gap to the same rail. Again, the light should light. If the light does not light, move the connection over to the other rail. If the light lights, that means the phasing is incorrect and the wires will need to be swapped.

Test Light

One of the most useful diagnostic tools is a simple test light. The test light I use most often has an alligator clip on one end and a light bulb and long sharp metal probe on the other. It looks similar to the ones here: http://www.harborfreight.com/3-piece-circuit-tester-set-94130.html (It likely came out of that set.)

The test light lights when a circuit has been completed. That usually occurs when one side of the light is connected to Rail A and the other to Rail B. The test light requires voltage to be present for operation, but with DCC this is no problem. With DC, power to the block must be on and the throttle set high enough to turn on the light. If either side is not connected to the rail or connected to rails of the same polarity, the light will not turn on.

Locomotives run under the same conditions that make a test light light. Just as a locomotive will move with the rails at any polarity, the test light will light with the rails at any polarity. Conversely, the test light will not light under conditions where the locomotive will not run, so it's safe to assume that if the light is lit a locomotive will run. (A DCC locomotive at speed step 0 is still technically running. The decoder is receiving power and interpreting commands.)

The test light works according to this truth table: (This doesn't represent all the options, just the important ones.)

Probe A | Probe B       | Result

--------------------------------

Rail A  | Not connected | Dark

Rail A  | Rail B        | Lit

Rail A  | Rail A        | Dark

Note where the probe lights when connected to different rails, but does not light when connected to the same rail.

Armed with this information, consider the following scenario: Trains can run on a section of straight track until they reach a specific point, then stop dead. How do you diagnose where this happens with a test light, and determine what rail the issue is in?

Insulated Rail Joiner

On a piece of track rarely used, there's an insulated rail joiner. It does not look like its needed any longer, perhaps it was back in the DC days. No reason to tear up existing track to get to an insulated joiner that's not bothering anything, in fact, I often advocate installing more insulated joiners than you need and wiring around them.

But here's the thing: the rail joiner has melted. It looks like someone tried to attach a feeder to the rails at that point and solder to a plastic rail joiner!

It's really not that bad

I subscribe to the theory that every rail should be soldered to something--either another rail or a feeder. Others say a feeder every 10' is good enough, while others report having gotten away with feeding an entire layout with one pair of feeders.

The game changes as soon as you paint the rails or glue ballast. The paint or glue works its way in between the rail and joiner, and turns an electrically conductive connection into an insulating one. This might not be a 100% insulating connection, but it often is enough to stop trains.

Now there's an insulating connection and the ballast has been laid or the rails painted. Fixing the connection requires either scraping some paint off the rails or drilling through ballast. The easiest repair is to drop a feeder at that point, so now there's a hole for the feeder and a bright shiny spot on the rails. Might as well do it before you start.

Compared to repairs and time that must be spent doing diagnosis, dropping a feeder to every rail is really not that bad.