‘Splain it To Me…


Throughout our listings we will sometimes use terminology which may be unclear or downright mysterious. This can be especially challenging if you are new to the HO railroading hobby. Or perhaps you want to buy a gift for an experienced modeler, but don’t want to get something that might not work as you hoped. Understanding the language can help you avoid such mistakes.

Accordingly, we have gathered together here in one place our plain language explanations of the terms that may otherwise confound you.

And, if you can’t find the answer you need here -or have any other questions– feel free to click the email link below to ask anything your heart desires.

Use the menu at left, or just browse through the material below. Click “Exit” when you’re done -and you’ll be right back where you started.

DCC – The Executive Summary

Until about 15 years ago, model trains were powered by “direct current” -the same stuff that comes from flashlight batteries. A “transformer” or power pack converted house current (AC) into DC, and fed it to the tracks. The amount of power being fed was controlled by the throttle (speed knob) on the power pack. No power -train doesn’t move. Full power: train may fly off at a curve and land in your neighbor’s outdoor grill. And so, the amount of power applied to the track is what ran the train slow or fast.

Sounds easy enough -until you put more than one loco on the track. They can’t be controlled independently because they both are controlled by whatever power is applied to the track. One throttle is powering 2 loco’s with exact same power setting at the same time. And even though they both get the same amount of juice, one loco will go faster because it has a different motor in it, or maybe they’ll run in opposite directions. Bottom line: it is a hassle. The solution is to put gaps in the rails so you have basically two isolated portions of track -and get a separate power pack for each section. But that gets complicated -and expensive.

But these days, there’s a way to get around the problems of plain vanilla DC. Apply FULL power to the track ALL THE TIME, and THEN put little micro-chips (called “decoders”) in each loco that control how much power the loco will use and which direction it will go. Talk to the decoders by sending commands to them through the rails. Give each decoder its own unique “address,” so that ONLY the commands sent out to that address will control the loco where the decoder is located. Thus, decoder #1 won’t respond to commands sent to decoder #2; and #2 won’t do what you command #1 to do. This is like a set of remote control garage doors; each one has its own address, so the remote for door #1 won’t open door #2, and vice-versa. Simple concept. BRILLIANT concept, in fact.

NOW you can have 2 or 50 locos on the same track, and as long as each has a decoder with a unique address, you can run each of them independently of the other, just as you could separately control garage doors. The power pack (“command unit”) itself has a an array of buttons sort of like a push-button phone -that’s how you select an address. So, you punch in “301” to get loco 301 going, then punch in “401” to start loco 401 -and meanwhile, 301 just keeps doing the last thing you told it to do. And, as long as you’ve got decoders for each of the locos, why not use more decoders to throw switches and do other things on the layout as well? Exactly -you use “stationery decoders” for those tasks -and they get their power from the rails, too -same as the locos.

This is all very well and good -but what about the existing investment people already HAVE in plain DC operations? The answer is to retrofit existing DC locos with decoders, so they will now run on a DCC powered layout. And as a matter of fact, most DCC systems will allow you to run ONE (just one) DC loco while you also run DCC equipped locos at the same time.

But what about the old style DC transformers -will they work with DCC equipped loco’s? The answer is, “well, maybe.” Some DCC power packs will allow a regular DC transformer to be “slaved” to the DCC unit so it can control one train. But generally, your old DC transformer can’t be deployed to run DCC trains because it has no way to “talk” to the decoders. It CAN however, be used a source of power for other things -such as lighting or small DC motors which run accessories -like a merry-go-round or a crane.

The wiring for DC and DCC is basically identical -two wires go to each of two rails; and so, you can usually swap out a DC transformer with DCC equipment, hook up the existing wiring -and everything should work.

There’s more to it than that -but now you have the basic idea. Search the ‘net for model railroad DCC -and start your research.

Converting Older Athearn Locomotives to DCC
One particular brand of quality locomotive has perhaps outsold all others: Athearn. Consequently, when DCC became widely deployed by modelers, many wanted to upgrade their “old reliables” to DCC control. Digitrax, an early and highly regarded producer of DCC systems, therefore made up a special kit for easy upgrading of the Athearn, which uses the same basic arrangement of motor and electrical connections inside most of their locomotives.

The kit consists of a special harness with clip-on connectors to the motor and light in the locomotive. It is easy and quick work – even I have done it.

Follow this link to the Digitrax instructions where you can see for yourself.

DCC Equipped and DCC Ready
A DCC “Equipped” loco refers to any locomotive which already has a DCC decoder installed in it. You need add nothing more to make it DCC (assuming, of course, you already have the layout itself operating on DCC. (What is DCC?)

But a DCC “Ready” locomotive is one that requires you to install a chip -usually by simply plugging one into a socket already provided. This is about the same as putting batteries in a TV remote or changing a light bulb. You WILL, however, need to know if the socket is for an 8 or 9 pin decoder. Sometimes there are 2 sockets, so either decoder will fit. At left, the 9 pin socket is in the center, the eight pin is to the left of it. Then, you need to decide on what functions you want, in addition to the basic control of lights, direction and speed. Sound, for example, is a possible option.

Track Code
Track code, such as “code 100” or “code 83” (sometimes just C100 or C83) refers to the height of the rails as measured from the ties on which they rest to the top of the rail -where the wheels roll. The higher the number, the higher the rail. And it’s not just a number, either: it refers literally to the height. So, a C100 track has rail that is 100/1000ths of an inch tall, which is to say, 10/100th’s, which is to say 1/10th of an inch tall. Code 83 is 83/1000th’s of an inch -in other words, 17/1000ths shorter than code 100.

You could say that code 100 is 1/10th of an inch, and code 83 is 1/8.3rd of an inch. C100 and C83 account for most HO scale track, followed by C70 (7/10th’s) and C55 (5.5/10th’s). To model a really prototypical railroad, you might use C100 on the mainlines, C83 in the secondary lines and yards, and C70 on lightly used sidings. Or, you might use the combo of 83, then 70, then 55. Or you might say, “Let the devil take it, I’m sticking with C100 or C83 everywhere!”

Relative to the real thing, code 83 is more prototypical. But C100 is often deployed because it has a bit more heft, more muscle than the others. And the truth is, its darn hard to tell, when you look at a layout. If you use 2 or more codes, can you join one to the other? You betcha you can. And yes, the car wheels will fall, or bump up, from one to the other. To avoid this, shim up the lower rail so the tops of both are even.

How? Well, that’s a subject of debate, but here’s the quick and dirty way that I do it: Slide your rail joiner on the taller rail in the usual manner. Then, FLATTEN the exposed part of the joiner with a pair of pliars, so it takes on the appearance of a tongue sticking out from the higher rail. NOW, butt the two rails together, with the shorter one sitting on top of the tongue of the rail joiner that’s attached to the higher one. If one rail is higher than the other, file the tongue, or file the rail, to get a good match. When you’ve got them matched, top to top, secure them to keep them in position (tape often works for this) and solder the lower rail to the tongue on which it is resting. Badda-bing!

Obviously, there’s less fuss if you are going from one code to the next higher or lower code; 100 to 83, for example. But if you’re going from 100 to 70, that’s a drop of 30%! Try to use a transition code in between, if possible. If not possible, then you may need to put a flattened half piece of joiner on top of the other flattened section to get the lift you need. Another approach is to skip the joiners completely, and simply shim up the lower track (ties, rails, all of it) to the higher rail. Secure everything, and solder the rails together. In this approach, you’ll need to put a shim UNDER the ties of the lower track to support it. But, not to worry, the real railroads deal with this problem all the time. Think they’re going to use expensive mainline rail on secondary routes and sidings? I DON’T THINK SO! That said, the change from one height to another occurs where traffic will be slow -it ain’t happenin’ in the middle of the high speed main lines, OK?

Bottom line: the fact that you’ve committed to a particular code does NOT mean that you can never use anything else. Indeed, you can. And, if realism is your goal, you probably should.

Wheel “Codes”
While all properly constructed wheel sets (a set is two wheels joined by an axle) will be the same distance apart, the shapes of the wheels themselves may vary from one model to another according to manufacturer preference. But a more important factor is modeling “era,” because the standards of manufacturing are much different today than they were 20 years or more ago. In fact, the problem was a lack of standards which most manufacturers would follow. Today, the “standard” design of an HO scale wheel is based on “RP-25.” The “RP” part means “Recommended Practice,” and the number “25” simply designates the number assigned to the recommended design of wheels. The organization which oversees all this is the NMRA (web site: www.nmra.org). Thus, if you hear or read about “RP25” wheels, you know they conform to the NMRA’s recommended practice.

All that aside, just what IS the RP25 design of wheels? They look like this:

On the left is an approximation of the RP25 wheel contour -this is the way most wheels are made today. On the right is a somewhat exaggerated contour of a wheel that could well have been made as late as the 1970’s and beyond. As you can see, the flange is thinner and plunges much deeper than the RP25 design. The thinking was that the shape would keep the wheels on the rails, and make cars and locomotives more forgiving of sketchy trackwork.

But, there’s a problem here when you put those old style wheels on modern code 83 track. That flange will ride so low that it will actually bump along the top of the retainers (tie plates) that hold the rail onto the ties. In your mind’s eye, put a piece of rail in the above diagram and you’ll see the issue. The wheels might be called “code 100” wheels although of course they were not so named. Its just that code 100 track matched with the deep wheel flanges was thought to be a good combination for reliable operation.

What this means for you as a consumer is that if you buy vintage rail cars (a perfectly fine idea) and your layout uses code 83 track, you may see (and HEAR) some rough running -perhaps even derailments! The solution is easy enough: replace the wheel sets! Many of the vintage models are really excellent reproductions of the real thing in terms of paint work and detail and they therefore may be an economical source of stock for operational upgrades -new wheels and couplers, most often.

It may be difficult to discern which kinds of wheel you have when you look at any given model -everything is small, measured in 1000th’s of an inch. In fact, you may be better able to feel the old style wheels, because the flange has an edge almost like a blade -a pizza cutter wheel.

Whereas the point rails move, nothing else does. After crossing the point rails, the train moving from left to right (west to east) rides the “closure rails” for a short distance before hitting the “frog.” Think of the closure rails as “closing the deal” set up by the point rails. If you’ll look closely, you’ll see the point rails are actually straight, or pretty much so, whereas the closure rails take on the geometry of either the through or diverging rails. Regardless of through or diverging, we reach a spot where there must be a break in the rail to allow wheels to pass. This is the “frog”:

The frog is so named because it has the appearance of the “frog” of a horse’s hoof, by the way. Anyway, as you can see, the flanges of the train wheels will be trapped in channels that match up with the path determined by the point rails. But there is a void -right in the middle of the frog- where a flange could actually go the wrong way. That problem is overcome by the “guard rail” on the outside rail which traps the opposite wheel to the rail along the intended path and so pulls the wheel in the frog in the proper direction, so it neither wanders along the wrong path NOR hits the point at the end of the frog itself. The real railroad uses guard rails, as well, for an extra measure of safety, but momentum of the heavy cars is usually enough to keep everything headed the way it is supposed to. Take a moment to look at the turn out diagram and you’ll see how all this works.

The turnout pictured above is a left hand (LH) turnout, because the diverging route goes to the left as you look into the turn out from the points. Turn outs can be left, right, or “Wye,” meaning two diverging routes, left and right -no straight through. And they can be “3 way,” meaning left, right and straight through.

Which brings us to turn out “numbering.” Numbering is simply a way of designating how quickly the diverging track moves away from the through track; that is, how extreme the angle of departure is.

However, the measurement is not expressed as an angle, but rather as a ratio. Figure 1, above, shows where the measurement is taken -right after the frog. Figure 2 shows what is being compared to get the ratio. The “run” refers to a distance along the rail of the through track which connects to the frog. The “rise” is the separation between that rail and the rail on the diverging track, which also runs from the frog. (These two are called the “inside” rails).

To make this simple, let’s suppose you “run” 10 inches along the through rail from the frog and make a mark on the rail at that point. You then take the measurement (the “rise”), at a right angle (as #2 shows) across to the diverging rail. Let’s say the rise turns out to be 2 inches at that point. The ratio is 2 to 10, which reduces to 1 to 5. The turn out is therefore a “number 5.”

It may be easier simply to find a place where the distance between the two rails is one unit of measure (such as a single half-inch division on a ruler ). Locate that spot by laying a ruler across the two rails, at a right angle to the through rail. Slide the ruler along the through rail toward the frog until a single unit of measurement is the exact separation between the two rails. Your “rise” is one (1) of those units. Mark the through rail at that spot. THEN, measure the distance along the through rail back to the frog to get your “run.” Suppose it is 4 of those units. The ratio is 1 to 4. You’ve got a number 4 turn out.

(In actual practice, it usually works better with centimeters or quarter-inch divisions, because bigger units may actually hit a point beyond the end of the turn out diverging rail. If you look at the turn out diagram, you’ll see the diverging rail isn’t very long.)

What this all means is that the more gentle the slope, the higher the number, because you’ll need more “run” to get the same “rise.” You see this illustrated in figures 3, 4 and 5 above, in which the rise is constant, but the run gets longer with each illustration because the slope gets more gentle with each.

Bottom line: higher numbers mean gentler slopes and smoother operation because the train has more track to use on the diverging route. The very same thing you would face in your car: a gentle fork in the road is easier and safer than turning on a right angle a downtown intersection.

If you’re perceptive and observant, you will realize that what I have just told you is not exactly true, physically, because track curvature (radius) also is part of the equation. We’ve been working in straight lines and right angles when, in reality, the diverging rail does curve ever so slightly. And the degree of that curve will obviously impact train behavior as it trundles through the turn out. Turn out numbering is really a “convention,” an agreed upon method to express the severity of separation between the diverging and through routes. But, now you know what it is, and how its calculated, and you know why bigger numbers are better.

See that circle? Red touches blue -and THAT’s a problem! Your track rails are really just the same thing as the wires in an extension cord. In fact, that’s EXACTLY how they work. You could just as well touch the opposite wheels on your loco with the wires coming from your power pac or controller -forget about the rails- and the loco’s motor would run. But what would happen if you took the two wires in an extension cord that was plugged in -and touched one to the other? ZAP! That’s what would happen. A short circuit! As you can see in the above diagram, the problem happens at the frog. So, let’s take another look at the frog:

Track Radius

The radius of any circle is the distance from the center of the circle to the outside edge. The center of any circle is always half way across the circle, measuring across the widest part of the circle from one side, right through the center, to the other side. Therefore, the radius is one-half of the distance across the circle. If you had a circle that was 30 inches across, from one side to the other, the radius would be exactly half that distance, or 15 inches!

Suppose the circle is a railroad track that made a 30″ circle. The radius would be one-half that amount -15 inches. And so, if you have curved sections of track that are specified as 15″ radius, it means that if you connected enough of these 15 inch radius sections of track together, you’d end up with a 30″ wide circle.

The smaller the radius of the track sections, the smaller the circle they will make. Which is to say that each piece of track must have a sharper and sharper curve in order to make a smaller and smaller circle. Likewise, the larger radius track sections will make larger circles, and the curves will be more gentle. In HO model railroading, the standard radius sections are 15, 18, and 22 inches, which in turn would make circles that are 30, 36 and 44 inches across.

So what? Well, the “so-what” part is this: the smaller (tighter) the radius, the more difficult it is for the cars, and the locomotive in particular, to make it around the turns. You know the problem from driving your car. Its easier to keep the car lined up on a gentle curve than on a sharp one. And this gets to be a real challenge if you’re driving a big truck -that’s pulling a long trailer. Which is exactly what’s going on with the train -a big loco pulling a string of many “trailers”. And, therefore, modelers prefer to use the largest radius they can, in general.

Bear in mid that the steering tires on your car can swivel sharply side to side to make a turn. But on a locomotive, there is NO steering. The wheels follow the track. But quite often, the wheels are in sets of four or six (two or three axles mounted in a carriage -called a “truck”). The entire carriage may rotate to follow a curve -but the wheels themselves do NOT -they are always pointing straight ahead.  Therefore a small loco with fewer wheels will get through tight radius curves easier than a loco with more wheels.

The situation becomes complicated when the radius changes along a curve. If the changes happen suddenly, the train will want to jump the track.

There’s a lot more to it, of course, and if you’d like to learn more then follow this Getting Radical about Radius link for more information. It will open in a new separate window -just close it when you’re done. But for now, you know that in general, higher numbers are better -and you know why.

In railroad modeling -and on the real railroad- the word “truck” doesn’t refer to a self-propelled wheeled vehicle for hauling freight or material -like a pickup truck or an 18 wheeler. Rather, it refers to the framework in which the wheels or a locomotive or rail car are mounted. The wheels ride in trucks, and the trucks are attached to the locomotive or rail car.

Model railroad locomotives and cars use two kinds of trucks. One of them holds the wheels, and nothing else -a regular truck- as seen at upper left. Cars with regular trucks have the couplers mounted to the body of the car itself.

The other is a “Talgo” truck, pictured below it. This one has a tongue attached to it, with a coupler mounted on the end of the tongue. With Talgo trucks, the coupler and truck are a single unit.

Couplers mounted on Talgo trucks stay centered over the track because as the truck turns to follow a curve, the coupler turns with it. The advantage is that the pulling force along the entire train stays centered over the tracks, and therefore there is less chance of a derailment compared to couplers mounted directly on the car body. This is especially true on tight curves. For this reason, Talgos are often used for youthful modelers whose emphasis is on activity as opposed to completely realistic modeling.

Couplers mounted on the body of a car, unlike the Talgo mounts, are not following the curvature of the track -rather, they’re lined up with the end of the cars attached to them -and the ends are facing at an angle away from the center the track when moving through a curve. Consequently, cars are being nudged slightly away from the center of the track.

But Talgo couplers don’t behave as well when being pushed (when a train is running in reverse, for example) because all the pushing force is absorbed by the trucks -not the cars themselves, and the likelihood of a derailment increases, compared to couplers mounted directly on the car body. This is so because the pushing force is NOT centered. On the other hand, trains are usually running slowly when being pushed, and usually on level terrain -such as a yard or siding, and the slower action and level travel reduces chances of derailment.

Which should YOU use? The single biggest factor is track geometry. If there are a lot of tight curves, going up and down slopes and changing direction, the Talgo mounted couplers will probably “snake” through the curves more reliably, when being pulled. On the real railroad (in the United States, anyway) couplers are always mounted to the body of the car -not the trucks. So, if dead-on realism is the goal, you’ll shy away from Talgo. A frequent exception is passenger cars and certain freight cars, whose length alone makes them tough to drag reliably through tight curves; for them, Talgo is often the only real answer.

Coupler Types
Looking at HO model railroading as it stands now, there are basically two kinds of couplers in common use: the “horn and hook,” which appears on the left in the photo and the “knuckle” which is to the right of it.

If you are familiar with the appearance of a real-world coupler, you will immediately perceive that the knuckle at right is the more realistic of the two. And you can also see how they got their names.

Historically, there had always been a problem in making couplers which were BOTH realistic AND operationally convenient and reliable. The horn and hook was “as good as it got” for many years, until the Kadee Company introduced its version of a knuckle coupler. The Kadee folks, ever mindful of their own economic fortunes, wisely patented their design. Accordingly, until sometime about the turn of the century, when the patent ran out, Kadee was the only widely available alternative to horn and hook.

But when the patent DID run out, all kinds of KD “knock-offs” were introduced under a variety of names. It wasn’t long before there were “shoot-out” tests among the competitors, and in a nutshell, Kadee won by a wide margin because their couplers could pull POUNDS of weight around a track before falling apart -not just a few ounces. But that’s not to say all the others should be written off, and since the initial tests, the others have been substantially improved.

So, the REAL question is, “Which brand is RIGHT for ME?” The answer truly is, “It depends.” And what it depends on is the kind of rail modeling you are doing. If you basically are deploying a layout as a pleasing diorama that captures a certain look and serves as a diversion for you and friends or family, I lean toward “not” Kadee because of the cost. But if you are modeling realistic operations in which reliability approaching perfection is essential -such as a public exhibits- then Kadee is a very rational choice.

Another factor is standardization. While all knuckle couplers work on the same principles generally, using just ONE kind for all cars will work the best. That said, many modelers are buying new rolling stock, selling old, and refining their rosters over time. Does it make sense to undertake the expense of the reputed best coupler upgrade for an item which you may no longer use in the near future? That’s something for YOU to decide. All that said, among the closest competitors to the Kadee is the Mchenry product. Athearn, a well regarded maker of cars and locomotives, in fact, has standardized on it. The E-Z Mate product from Bachmann is essentially a carbon-copy of the McHenry, made by Bachmann under license from McHenry.

To my mind, therefore, the E-Z Mate is a good, cost-effective alternative to the Kadee, which is why I deploy them for the locos and rolling stock I offer for sale on Ebay and elsewhere. The “Mark II” series is the particular version I prefer, because it incorporates a special coil spring retainer that helps keep the knuckle return spring (visible in above photo) from escaping. That tiny spring is the dickens to replace, so anything that prevents it from flying away is an advantage.

Finally, I have standardized on the E-Z Mate because I really don’t know about my customer’s modeling preferences and the situation in which rolling stock that I sell will be deployed. If the layout is operated by youngsters, for example, the exposure of a costly Kadee product might not be a good idea. On the other hand, the experienced and devoted modeler is likely to make all kinds of customizations to the product I sell -couplers included and I have no way of knowing the customer’s preference.

Below is a simplified diagram of a knuckle coupler. The various mounting heights of the knuckle on the shank are selected so that the knuckle will be at the correct height above the track, and matched to couplers on other cars. Thus, an “underset” knuckle will ride higher off the track than a medium or overset knuckle.

Installing Couplers
Most couplers fit into a “pocket” with a lid on top and a pin mounted in the bottom of the box. A hole in the shank of the coupler fits the pin and rotates around it, allowing the coupler to swing left and right so it can engage and disengage other couplers. But the actual process of replacing or installing new couplers can be like building a house of cards -one wrong move and everything falls all over the place. Very irritating.

We’ve prepared an illustrated tutorial that will help you get started. Click this Coupler Installation link to see it.

Turnouts (“Switches”)

Few pieces of equipment are as confusing to the new-comer -and even the experienced modeler- as “switches.” Whereas most objects in the hobby world of railroading take the same names as the the same things in the real world, that’s not the case with switches, so let’s cover that little discrepancy, first. In the hobby world, “switches” are called “turn outs.” Why? Because in the hobby world, we not only have switches, meaning track, but we also have switches meaning the electrical things you push, throw or otherwise move to turn electricity on and off -like switches to turn lights on, switches to turn track power on, and, yes, switches to switch the switches. See the problem? On the other hand, if you call the switches (the rail kind) “turn outs,” then everyone knows what you’re talking about, as in, “switch the turnout,” which would mean to throw the electrical switch to activate the turn out.

With that detail out of the way, let’s take a look at the parts of a turn out.

As you’ll note, the idea of a turn out is to make the train go one way, or another way. Assuming the train is approaching from the left of the picture (“west,” they call it) and it stays straight, it is said to go on the “through route.” Otherwise, if is going to be turned away from the through route, it will diverge from it -it will take the “diverging route.” If it is coming from the right (east) on either the through or diverging route, it might be said to be moving “against the points.” The points are the exposed ends of the “point rails” you see above left. Those rails can slide back and forth to maintain a “through” path or a “diverging” path. If you move “against” them, it means simply that point rails are not lined up to match the incoming path of the train coming into the turn out from the right (the east).

This is not always a problem, because the wheels of the train can push the point rails into a position to match its approach. UNLESS the point rails are held firmly in place by some kind of mechanism, such as the device that “throws” the rails via the throw arm. The real railroads anticipate this problem, sometimes, by setting up their turnouts so the point rails can move if a train approaches “against” them.

And by the way, you’ll notice the point rails are kind of like blades, with very skinny ends. Those fit into pockets that have been carved out of the inside of the stock rails, so they kit snugly and take on the shape of a regular rail.

The reason for NOT allowing this to occur on a model layout is that without a firm “closure” against either “stock” rail, the motion of a train coming through can move the rails slightly, so that they end up somewhere in between the stock rails -going nowhere, so to speak. That’s NOT a problem for traffic traveling against them -because the train wheels will simply push the point rails to match the direction of travel -as we explained above. HOWEVER, loose point rails are a very bad problem for trains moving toward the points, in this case coming from the west (left). Look at the picture above and you’ll see a disaster waiting to happen because the point rails are in fact BETWEEN the stock rails -not closed against either one. Therefore, for an east-bound (left to right) locomotive, one wheel on the train will take the diverging route, and the other will take the through route. You can do one, or you can do the other -but you can’t do BOTH at the same time. Train wrecks. Let’s look at some other features of the turn out:

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