KB18: Atlas Up & Over Dogbone

This article was last updated on May 8, 2012, 3:23 p.m. | Print Article | Leave Feedback

This Atlas Snap-Track layout appears in the Atlas Model Railroad Company's book "Beginner's Guide to HO Model Railroading". It includes a reversing section which can be controlled with a Digitrax AR1.

DC Control For DC operation, Atlas specified an Atlas Controller (for the reverse loop), two Atlas Selectors (to control eight track segments) and seven controllers for the railroad's turnouts.

DCC Makes Things Simple
With DCC, the wiring of this railroad is considerably simpler. Because each locomotive has a unique address, the section insulated gaps and the two Selectors are not necessary. Likewise, the Controller is replaced with the AR1 autoreversing device, although the double insulating gaps are retained (see below). The track switch controls can be replaced with command control devices, also.

How Much Power Will the Railroad Need?
Your first concern is to select a Digitrax Starter Set which is appropriate. Since this railroad will have only two trains running at any given time, the calculations are fairly simple. A typical H0 locomotive will draw 600 MA when it is in operation. Locomotives sitting idle will also draw power, at the very least, 5 MA for the decoder. If each has LED lights, then it will typically draw 15 MA more; conventional light bulbs will draw 50 MA. If you have lighted passenger cars, these will draw current also; again 15 MA for LED's and 50 MA for light bulbs.

For purposes of estimation, the Up & Over Dogbone will have two trains in operation at any given time. One train will be a freight train with two locomotives and the other train will be a passenger train with one powered locomotive.

The calculation

  • Three locomotives in operation, 600 MA@ = 1800 MA
  • Five passenger cars with LED lights, 15 MA@ = 75 MA

Total power consumption = 1875 MA, or about 1.9 Amps

Which Starter Set?

The Zephyr Xtra (DCS51)
is rated at 3 Amps, which should be sufficient to power this railroad. Likewise, the Zephyr Xtra has twelve "slots", (the limit of locomotive addresses that it can manage at one time).

The planning assumptions are for a total of three locomotives, well within the range of the Zephyr Xtra. Because the Zephyr Xtra is a LocoNet system
, additions to the complete train control system are easy, so detection, signaling, transponding and other featuers can be added as desired.

If your railroad will be using more than the 3.0 Amps available from the Zephyr Xtra (such as locomotives with sound systems), you can add another booster
, connecting it to the Zephyr via LocoNet, connecting to its own power supply and connecting this booster to its own section of railroad.

If you want more than one train operator, you can add remote universal panels such as the UP5
that allow for multiple train operators to plug in their throttles and run trains. Or you can set up or set up for infrared or duplex radio operation.

Turnout (Track Switch) Control

If you want to control the turnouts with your command control system, then you'll need to add stationary decoders . The DS64
controls up to four turnouts, so two DS64s are needed to control all the turnouts on the Up & Over Dogbone. Each DS64 is assigned a unique Board ID, and then the individual turnouts are each programmed to unique addresses so that they can be controlled by the throttles in your system. Turnout control by remote buttons is also available with the DS64.

Power Management

Power management
refers to devices which act as circuit breakers and power distributors on the layout. Power management tools help protect the railroad in the event of a short circuit. These devices also can be used for auto-reversing, a major issue for the Up & Over Dogbone railroad, which has a reverse loop.

Return loops, or "reverse loops" are an issue with all two rail model railroads. When a track turns back on itself, an electrical short circuit is created. That is, when a track turns back upon itself, the rails short out unless you place a pair of insulated joiners at the entrance/exit from the section.

There are several ways to solve this problem on a DC powered model railroad, all of which require changing the track polarity of one segment of the model railroad while a train is in another segment. With DC, you create a defined segment of track which the train occupies while the track polarity is changed on the other segment of track. This segment must be longer than the longest train.

With a DCC model railroad, the solution to the problem is easy. Like the DC model railroad, you first create a defined segment of track which is longer than the longest train. Autoreversing works by comparing the "phase" of the track power & DCC signal between two segments of track. With DCC, the track power is alternating current with the DCC waveform signal. While there is no "+" and "-" as with DC, there is still the need to make sure that when the locomotive passes into another segment of track, the phase of the track power and DCC signal are the same.

Autoreversing electronically compares the two defined sections of track and reverses the phase of the section into which the train is moving to match that of the section that the train is currently operating in. The AR1
is a dedicated automatic reversing unit.

Defining the Reverse Section Area
With an example railroad plan such as the Up & Over Dogbone, the hard work has been done for you already. That is, because the railroad is from a how-to-do-it book, the electrical issues have already been worked out; you simply cook-book your way through the project. In that way, the reverse sections have already been defined. A close examination of the track plan illustration will show you where to put the double insulating gaps, as shown. circled in red, below:

The reversing section is defined by insulated gaps in both rails at the five noted locations.

Here is the reversing section by itself:

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