Page 15 - November December 2016
P. 15

 What is DCC and Why is it Valuable?
Model railroad operation, and the expectations of the operators, has changed over the years since we abandoned keys for electricity. We've always wanted to see the trains run, and in those early days, that’s all they did, with an occasional, sometimes more than occasional, prod required to keep them moving. As time moved on, our expectations changed: we wanted our trains to move realistically and reliably, and we wanted to be able to operate them, rather than just see them go by. Then we wanted to be able have lights that stayed on when the train stopped, and, even better, lights that we could turn off when they weren't appropriate. And we want them to sound like the real thing, as well as move like it. Over the years, there have been many solutions to these challenges. The most prevalent of these solutions is DCC.
DCC is a different way to control your trains, with a significant difference over conventional DC. With DC, you actually control whatever locomotive, or locomotives, are sitting on the track connected to the controller. You'll have a control panel for your railway that you use to direct the power from the controller to specific pieces of track, so that you can isolate the locomotives you don't want to move. And with more control panel complexity, you can run more than one locomotive simultaneously, so long as they are in different track sections. If they're in the same track section, they move together, which can be a bit limiting. In effect, you're not really driving the trains themselves, just what happens to be on the track. You also have no control over anything else on the loco; all you can do is adjust speed and direction. There’s also the issue that there is one controller for all the locomotives, a one-size-fits-all solution, regardless of the characteristics of the motor, gearbox or wheel diameter of each loco, and what that loco does on the layout.
Keith Webb and Mick Moignard enjoying digital operations on Mike Tricker’s HO B&O layout. Photo: Mike Tricker
DCC reverses all that. It places the control of each locomotive inside the locomotive, it wires the entire layout as a single power block (ok, as we'll see later, that's a little utopian a concept), and thus frees you from all the artificial constraints that DC control and operation suffers from. By placing the control inside the locomotive, it more easily opens up the possibility of doing more with the electrons available in the loco than just driving the motor and wheels. You can do things such as having lights, controllable lights, in locomotives, and also in cars. You can do fancy things with those lights, too such as flashing strobes, rotating beacon simulations, flickering fireboxes and many
more. Or harness those electrons into animations, such as operating pantographs. And of course, add sound.
D for Digital
The D bit of DCC is the word Digital. The first C is Command, the second, Control. Which, together, means that we are Controlling our locomotives by sending Commands to them, Digitally. And not just locomotives. We can also operate points, signals, grade crossing lights and barriers with the DCC system. Indeed, pretty much anything that is electrically operated or controlled on the layout - and beyond - can be managed by or through the DCC system.
Much of it is standardized, so components from different manufacturers will work together in harmony. The standards are owned and managed by the NMRA. They cover the format and timings of track packets, various decoder wiring and plug formats, and some of the Configuration Variables that are used to define mobile decoder behaviour, and the new LCC capability. We’ll introduce you to these terms more completely later in these articles.
Historically, DCC was invented and defined by Bernt Lenz, he of the Lenz company. The original work was done under contract for the Arnold and Marklin companies. After a while, they discontinued work with Lenz, but Lenz continued to work on their inventions. In the early 1990s Stan Ames looked at Lenz’s work and proposed it to the NMRA as a future control system. The NMRA looked at both Lenz’s work and an offering from Keller, and decided that the Lenz digital ideas offered the greater potential. The NMRA then licensed and extended it to become the DCC that we have today. As we'll see, the standards cover the key parts of DCC, but in such a way that the various manufacturers have quite a lot of space and freedom to innovate and compete. Innovation and competition means that DCC components are by and large decently priced, and that we continually see new products and ideas appearing and being delivered such that they are easy to incorporate as and when they deliver value to us. An example of this is the rise in the use of model aircraft servos for point and signal operation, controllable from existing DCC systems with no change to those systems.
Freedom
All of that spells Freedom. Freedom to operate realistically as well as watch the trains go by; freedom from having the one-size-fits-all controller. Freedom from a lot of the layout wiring that a conventional cab-control and block switches regime forces upon us. Freedom from the need to have such a control panel, too. With most DCC systems, you also get a hand-held walkround controller than can be unplugged and replugged without the trains stopping, giving the freedom to run the trains from anywhere around the layout, or, even, with the addition of the internet, from somewhere else entirely if you wanted to. As it will run multiple locos at once, you can easily manage double- headers and multi-loco lashups. Indeed, you can individually move the locos to get them coupled up to each other and the train, then simply - a few button presses, operate them as though they were a single loco; what's called Consisting. Tail-end helpers, too. And, because all of this is standardized, you get a great deal of freedom from being locked in to one manufacturers gear.
Some Technobabble
The core of DCC, and a major part of the standard, is the electrical signal on the track. This is a specialised high-frequency - around 8khz - square-wave AC signal of somewhere between 12 and 16 volts, on all of the track in the layout, all the time. The digital signal is carried by frequency-modulating that 8Kz signal in a precisely defined manner.
 




















































































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