Multiple Unit Consisting

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Summary: Multiple Unit Consisting allows the modeler to faithfully replicate prototype operations by creating a consist of several locomotives to haul a train. This has the effect of creating one large higher horsepower locomotive controlled by one engineer. With Digital Command Control, a Multiple Unit Consist can be easily created and operated from one throttle.

Video

See the Video.

CPR Operations on the Big Hill, 1890

Note: Before creating a consist, be sure to match up your loco speeds.

Consisting Overview

Power exits Lower Spiral, passing under its train.

Terminology

There are a number of terms used with consisting. There are the "official" terms the NMRA uses, and those employed by the manufacturers. Unfortunately, the two don't mix well.

NMRA DCC Terminology

See the NMRA website for the RP 9.2.1 Extended Packet Formats for more details.

Terms

  • A Consist is a group of multifunction decoders linked together, such as several Diesel-Electric locomotives in a Multiple Unit lashup.
  • Consist Address: The address to which several linked multifunction decoders will respond. For example, the consist address is 100, and that address controls multifunction decoder addresses 1234, 5678 and 90.
    • Consist Addresses range from 1 to 127, usually beginning at 127 ($7F) and decrementing as consists are created.
    • If the address is greater than or equal to 128 ($80), the consist will be running in reverse.[1]
  • Consist Control Instruction: A subset of instructions used to send commands to a consist. Used to assemble or dismantle a consist.
  • Basic Consisting: An early form where all decoders in the consist share the same address.[2]
  • Universal Consisting; Command Station Based: The command station builds and manages a list of locomotives which are part of a consist. When a command is sent, the command station sends a packet to each unit in the lashup. This consist is not portable, when the locomotives are moved to another layout the consist ceases to exist. Once back on home rails, they are again a consist.
    • This method will work with a small number of locomotives. On a large layout with multiple locomotives consisted, network latency becomes an issue, and erratic operations result due to the volume of packets that must be transmitted.
    • Sometimes called "the old way" or "brute force" consisting.
    • A variation on Universal Consisting is Throttle Based Consisting. This variant relies on the throttle to build and maintain the consist. Employed by third party wireless throttles which cannot access the throttle bus protocols and commands in the same manner a native throttle can.
  • Advanced Consisting; Decoder Based: All locomotives share a common address assigned by the command station. The consist address is stored in the multifunction decoder's (CV19). The command station will set CV19 using Ops Mode[3] for all the locomotives in the lash-up. It is in the Primary Address space, beginning at 127. The command station will decrement that address as new consists are created. The original Primary and Extended Addresses are not altered (CV 1, 17/18). The command station can economise on bandwidth by sending one packet for all the units in the consist. It may be possible to address individual units for the purpose of sending a function command. The lash-up is portable from layout to layout, since the information needed is stored onboard the locomotives.
    • If a locomotive will not respond to its address, it may have been part of a consist that was not cleared. Setting CV19 to zero will clear the consist address.
  • Unified Consisting: The consisting method is a mixture of Basic and Advanced Consisting. Only Digitrax and NCE support these under the term Nested Consisting.
  • Nested Consist: A consist within a larger consist.

Comparison of NMRA Consisting Terminology with Manufacturer Terms

Alternate Terminology for Basic and Advanced Consisting
DCCWiki.com
Manufacturer Basic Consisting Advanced Consisting
NCE Old Style[4] Advanced
Digitrax Basic/UniVersal Advanced
Lenz Double Traction (DTR) Multiple Traction (MTR)
Easy DCC Standard Advanced
Zimo Double Header
MRC Universal[5] Advanced

Consisting with Digital Command Control

CP westbound at the same location, approximately mile 69 Thompson Sub east of Spences Bridge, BC, Canada in November 1984

There are three ways of creating a consist with Digital Command Control. Each consisting method has its advantages and disadvantages. Not all methods are supported by all systems - check your documentation if you aren't sure what you can do with your equipment!

  1. Basic / Decoder Based: All multifunction decoders in the consist have the same Primary or Extended address.
  2. Advanced: All multifunction decoders in the consist have the consist address stored in CV 19, while retaining their Primary or Extended Address.
  3. Universal / Command Station: The command station manages the individual locomotives in the consist.[6]

Another method which is beginning to appear is Throttle Based Consisting. This relies on the throttle creating and managing the consist, instead of the command station. Usually found on third party wireless throttles.

Basic Consisting, Decoder Based

This is the simplest method of creating a consist. Simply program all the locomotives you want to run together with the same address. This can be done with a Primary or Extended address. The locomotives must all be facing the same direction for this to work, as direction of travel is determined by their orientation. If it is planned to operate locomotives as a permanent consist, such as an A-B-A set, the NDOT must be set accordingly.

Its advantage is only using one address in the command station. The command station will see all the locomotives with the same address as a single locomotive, and they will all respond to all commands in unison. All locomotives in a basic consist will respond to function commands at the consist address. The command station sees the basic consist as a single locomotive. This requires reprogramming a locomotive's decoder to change consists.

If the consists were created with a Primary address (1-127), there may be issues operating as a consist on another layout. There will be conflicts if the primary address is also used by another locomotive which is not part of the consist.

  1. An analog (non-decoder equipped) locomotive cannot be part of a Basic Consist.
  2. Decoder Based Consisting is easy to use and understand: All multifunction decoders in the consist have the same address.
  3. The operator cannot control individual locomotive functions such as the horn, bell, and lighting, as all the decoders will act on the command.

Creating a Decoder Based Consist

Once the locomotives for the consist are chosen and tuned to match each other, place all the selected locomotives individually on your programming track and set the desired address for the consist. All locomotives will now have the same address. Doing each locomotive individually avoids overloading the Program Track output, which may cause erratic results.

Remember, if the consist is separated, all the locomotives will still respond to that address unless reprogrammed to new addresses.

Advanced Consisting

Also known as Decoder Assisted Consisting, uses a temporary secondary address (in CV 19) to group locomotives together without changing the Primary Address. The locomotives keep track of the consisting information. If creating a consist manually, avoid using an address which is already in use by another locomotive which is not part of the consist. Removing a locomotive from the consist without clearing the consist information in CV19 will result in an orphan locomotive which responds to the consist address.[7]

If the locomotives are taken to another layout the consist will still function, as it is stored onboard the locomotives. Correct orientation and sequence are important.

The consist will use a single address in the command station. It is limited to a Primary Address. There may be address conflicts when operating as a consist on another layout.

Advanced Consisting is done by using ops mode programming to change configuration variable 19 to set the address and normal direction of movement. This also requires reprogramming the decoder to change the consist, but some systems do this transparently to the user. Some decoders will allow you to specify what functions will respond to commands addressed at the consist address. Creating and breaking the consist are handled by the command station using specific commands sent to the decoders.

This method was given the name Advanced Consisting to reflect that its possibilities were much more advanced than that of Basic Consisting, as the Primary or Extended addresses were not altered, and individual control of each locomotive in the consist is possible. This implementation of consisting was considered to be a better choice than relying on the command station to create and manage consists.

The command station sees the consist as a single locomotive:

  1. The consist address is stored onboard the multifunction decoder
  2. The consist address is a Primary Address (see below)
  3. Some command stations may include the ability to easily create an Advanced Consist within their software
  4. The consist is portable because of this
  5. The operator can control any locomotive's function operation from its specific address
  6. CV 21 (F1–F8) and 22 (FL, F9–F12) can set the functions available on any locomotive in the consist
  7. An analog locomotive cannot be part of an advanced consist
  8. Advanced Consists operate in 28 speed step mode
Additional Features
Main article: Mutiple Unit Consisting/Consist Configuration Variables

While part of an Advanced Consist, a locomotive cannot respond to function commands sent to the consist address[8]. There are two optional CVs, 21 and 22, which can enhance consist operations in this mode. Acceleration and deceleration also can be further adjusted using CVs 23 and 24, which are optional.

For control of functions, CV21 and 22 are used. CV 21 is responsible for F1 to F8. CV 22 controls lighting effects (FL) and functions F9-F12. Acceleration (CV 23]]) and Deceleration (CV 24) can be fine-tuned by adding their value to those in CVs 3 and 4. CV23 and 24 can contain positive or negative values. These CVs must be programmed prior to the locomotive being using as part of a consist. Most DCC systems do not do this automatically, the user is required to manually program these CVs.

Since CV 23 and 24 are optional, their method of implementation can vary. The NMRA DCC Standard does not require them to be active during consisting. Some multifunction decoders may activate CV 23 and 24 in an Advanced Consist, others may not. They may need to be activated by setting another CV. In other cases, the decoder may ignore the sign of the values in CV 23 and 24, only adding a positive value to CVs 3 and 4.

Address Space Conflicts

Advanced Consisting uses an address in the Primary Address space. If Primary Addresses are in use for Multifunction Decoders, it is possible to have a consist address sharing the same address as a vehicle on the layout. In this situation the locomotive with that address and the consist will move in concert. It will be necessary to re-assign the consist to an address which does not create a conflict. See the manuals for the DCC system for details.

EPF Consisting

Extended Packet Format is another term for Advanced Consisting, where consist information is stored in each decoder. Locomotives can be added or removed in any orientation. All locomotives in the consist must be equipped with decoders supporting this feature, which allows a consist that is "transportable" from one DCC layout to another, but ensure the locos are on the track in the same order and orientation when they were programmed to avoid unexpected results. Most decoders today should be compatible with the Extended Packet Format.

Notes about CV19

CV 19 is used to consist the locomotives by writing a common address for the consist.

CV 19 can be altered in one of three ways:

  1. Using Service Mode (programming track), either manually or by the use of a computer
  2. Manually using Operations Mode
  3. By the Command Station

The command station can use specific Consist Control commands to configure the decoder. See Digital Packet article for more detail.

If a locomotive was part of an advanced consist, clearing CV19 (by writing a value of zero to it) removes it from the consist.[9]

Addressing Modes

Decoder Assisted Consisting

See Advanced Consisting above.

Main article: Multiple Unit Consisting/Decoder-Assisted Consisting has additional details on this consisting method.

Universal / Command Station Consisting

All the bookkeeping chores for the consist are performed by the command station. With this method of consisting, no changes to the programming of the multifunction decoders are made. Each locomotive in the consist is a separate entity in the command station, so the size of the consist is limited to the capacity of the command station. Analog locomotives may be a part of one consist - all analog locomotives on the track will respond to the same commands, so you can't run them in different consists.

Digitrax calls their implementation of command station consisting UniVersal Consisting (Yes, with a capital "V" in the middle).

Consists may be stacked, making up consists within consists. Locomotive functions can still be individually controlled without affecting other locomotives in the consist. The command station sees the consist as individual locomotives, sending each locomotive its own speed and direction commands.

  1. The lead locomotive's address is also known as the Top Address.
  2. The functions are only acted on by the top address, or lead locomotive.
  3. Functions on the other locomotives can be controlled directly from their address
  4. Since the command station does the housekeeping for the consist, there will be memory or software-imposed limits on the number of consists.

Other Implementations of Universal Consisting

The following systems allow any address can be used, with the exception of Address 00.
  • Lenz
    • Double Header (DTR)
      • Two locomotive limit
  • NCE
    • Old Style
      • Eight locomotive maximum
  • EasyDCC
    • Standard Consist
      • Eight locomotive maximum
Digitrax UniVersal Consisting

With UniVersal Consisting, the consist responds to commands sent to the Top Locomotive (Address). The top locomotive does not have to be the lead engine, nor does it even have to exist. The consist is managed by the command station. An analog locomotive can be included in the consist. UniVersal Consisting Allows:

  • Any address to be used, including Address 00.
  • Number of consists is limited by the number of slots.

Summary

Summary of Consisting Methods
DCCWiki.com
Consist Type Decoder Based Notes
Basic Yes All multifunction decoders have the same address
Advanced Consist information stored in CV19
Universal / Command Station No Managed by Command station
UniVersal Managed by Command station, Digitrax Only

Throttle Based Consisting

Throttle Based Consisting is a new method often found with third party wireless throttles. These throttles will connect to the throttle network using a WiFi connection.

In this instance, Command Station Consisting such as Digitrax's UniVersal Consists are handled within the wireless throttle. This method was chosen due to the proprietary nature of LocoNet. Design of the throttle's software allows the throttle to be used on multiple throttle networks without the requirement of having to make configuration changes to the throttle any time it is connected to a new network. In addition, it permits the throttle's software designers to side step multiple protocols and network languages to make this feature work, including licencing issues surrounding proprietary technologies.

DecoderPro

DecoderPro offers a number of options when setting up a consist, depending on the multifunction decoder installed. The image below is for an ESU LokSound 5 multifunction decoder

Setting up a consist with DecoderPro



Best Use of Each Consisting Method


  • Basic Consisting is best used when command station slots or limited memory capabilities are at a premium (because of either command station limitations or large numbers of trains to be run) or locomotives are always run together (such as A-B-B-A sets for long passenger trains). Since you are programming the primary address for these locomotives, it is best done on a separate programming track rather than on the layout where you might accidentally reprogram ALL the locomotives on the layout.
  • Advanced Consisting can be used in the same circumstances as Basic Consisting, but can be done on the main layout using operations mode programming since you select the individual locomotive before programming it. The consist address is limited to short addresses, so this might be an undesirable restriction if you want to use the train number as the address. Some DCC systems have ways of controlling the Advanced Consist using a long address.
  • Universal or Command Station Consisting is the most convenient method which requires the most system resources. This can be an issue if your command station has limited memory available or a large number of consists are in use.
    • Digitrax Example: An entry level Digitrax Zephyr command station is limited to 10 slots and for operators wishing to run four trains with three locomotives each, that's a total of 12 slots using this method - it's not going to work. You'll have to use one of the other consisting methods for at least one of the trains. Also see Dispatch[10].
    • NCE Example: NCE command stations do not have slots and as such does not require the user to be aware of them. There is no requirement to dispatch a locomotive. NCE's Entry Level system is limited to two engines per consist with a maximum system limit of 12 unique engine addresses in use simultaneously. Therefore, the NCE entry level system can run up to a maximum of six consists of two locomotives each. The only way it could run four trains with three locomotive each would be by using Advanced Consisting.
  • You can mix and match consisting methods:
    • Digitrax Entry Level Example: If you have three locomotives running together as a basic consist (one slot), three running together as an advanced consist (one slot), and four running together in a command station consist (four slots), you can create another advanced consist bringing all 10 locomotives together, and it will use no more than six slots.
    • NCE Entry Level Example: It could run the same setup as Digitrax, the only exception being that a given engine cannot be used in more than one consist at the same time. So, you cannot do the last step of create another advanced consist using the previous locomotives. However, you could run 10 more locomotives in an advanced consist if those 10 locomotives were not part of any consist.
An analog locomotive can be part of command station consist if it is supported by the DCC system, but it cannot be part of a basic or advanced consist which rely on the installed decoder to determine the consist.
Digitrax UniVersal Command Station Consisting
Main article: Multiple Unit Consisting/Digitrax Advanced Consisting

The greatest advantage of the command station consists as implemented by Digitrax is its flexibility. It is not difficult to add (or delete) locomotives or groups of locomotives to a consist, making assembly of long trains with multiple mid-train helpers effortless (common on N-Trak layouts) or to add/remove helpers to get a long train up a steep grade. It is important to remember though that while it is still using one slot per locomotive with this method – and the most capable system from Digitrax has 120[11][12] slots available, command station consisting is not suitable to use on large layouts where you are expecting more than 20 or more operators at a time.

The TOP locomotive is the address controlled by the righthand throttle on an Advanced Throttle (DT200/300/400/500/602). When this address is Dispatched, the entire consist is Dispatched.

NCE Consisting

The advantage of Advanced Consisting as implemented by NCE is its flexibility. NCE utilizes a hybrid of Advanced and Command Station consisting, where the consist address is in the multifunction decoder's CV19, and the command station maintains a table of aliases for managing the consists. It is very strightfoward to add and delete locomotives or groups of locomotives to a consist (nesting), making it effortless to assemble long trains with multiple mid-train helpers or adding helpers to assist a long train on a steep grade.

Depending on the NCE system chosen, you can control from 16 to 127 unique advanced consists. There is no limitation on the number of engines within a given advanced consist. The NCE command station has the ability to control a given consist using the lead locomotive's address regardless if it is a long or short address.

Specifically, if the locomotive has a long address, that long address is used to control the consist (an Alias). In other words, use the engine number like you would normally if the engine was not part of a consist. Unique to NCE is the ability to dynamically redefine the leading locomotive consist without turning the engines around. Select the last engine of the existing consist and instantly it becomes the lead engine of the same consist. Included in this change is both train direction and function control (headlight and sounds). The advantage becomes obvious when running a train down a stub branch which has no turning facilities. It goes forward down the stub branch line to the end and leaves going forward in the opposite direction. This action follows the prototype, where the crew would relocate to the front engine.

A nested consist is constructed using Command Station consisting to manage multiple Advanced Consists and/or a mix of individual locomotives and an advanced consist. A maximum of four pre-defined advanced consists may be combined into a temporary single consist. Hence, you can temporarily add a helper consist to a train with a lead consist, climb the grade using one throttle, subsequently break the nest consist into their original individual consists. Afterwards, the helper consist goes down the hill to await the next train.

NCE also has a consist browser which allows management of all of the advanced consists by:

  1. Viewing the locomotives in a specific advanced consist and
  2. Editing consists
NCE Consisting Notes
Main article: Multiple Unit Consisting/NCE Consisting Notes

Videos

There are several videos available through the Videos page:

Consisting with SoundTraxx Decoders: More on consisting methods.

NMRAx

ABCs of Consisting

The DCC Guy

A Quick Video about Consisting

Soundtraxx prepared a short and simple video demonstrating various types of consists:

There are several ways to use consisting, so how do you choose the best type for you? We will explain each type of consisting and its pros and cons in this video.

Notes

Nested Consist

Nested Consist describes two consists which have been merged into one, such as helper/pusher locomotives, allowing control from a single throttle. When they are no longer needed, the consist can be split into its component parts, such as the helpers disconnecting from the train and returning to the bottom of the grade to await the next train. Your manuals should explain how this is done.

Unified Consist is another term for this method of consisting.


Speed Matching

Main article: Speed Matching Locomotives

An important task before creating a consist is to ensure that all locomotives within a consist run the same speed. If you don't do this, some locos will run significantly faster than others. This will result in tug-of-war between locos, or a push/pull between the locos. This is hard on the couplers, as well as the locomotives themselves. This can also lead to derailments.

The goal: With the same throttle setting, each locomotive travels at the same speed (or the same distance at the same time). Think of method as distance/time matching rather than speed matching.

Also read the article on Back-EMF for more details.

Read your documentation for the decoder as well, as it may have advice on speed matching, plus CVs needed. CV29 enables the speed table, if available.

See Also

References

  1. CV19, Bit 7 set to one: Reverse direction
  2. Basic Consisting can use any valid primary or extended address.
  3. Ops Mode allows the command station to send specific commands to a specific decoder address.
  4. NCE may also use the term Forced in their manuals.
  5. Universal Consisting may be called Old Style in some MRC manuals
  6. Universal Consisting is sometimes called the Brute Force or Old Way of consisting.
  7. This is a common problem, where a locomotive will not respond to its address. If it won't respond after being removed from an advanced consist, the problem is that the consist address (CV19) wasn't cleared when the command station broke up the consist.
  8. Only the Top Address will respond to a function command.
  9. If the address in CV19 is greater than 127, the locomotive is running in reverse.
  10. The DCS51 and DCS52 versions of the Zephyr increase the available slots to 22.
  11. The DCS240+ offers an additional 280 expanded slots accessible by the DT402 R2, DT500, and DT602 throttles only.
  12. JMRI does not support the Expanded Slots.