Lashup Comparison, Pros and Cons; DCS and Legacy

I have been playing with lashups quite a bit lately and have come up with things I like and dislike about both DCS and Legacy lashups. I wanted to share these so that others can chime in and add their own observations and experiences. This is not intended to to stir up an orange vs purple debate. I am sure there are many members who are exclusive proponents of one camp or the other. But I would like to hear what others have found and what you like and dislike about each system. Please lets keep it constructive. So here goes: (Note this is a control system topic and could have gone into either DCS or TMCC/Legacy category. So I just picked one, it does not mean it is the favorite or the best!)

There are some fundamental differences between lashups with the two systems; here is a brief comparison with some of my pros and cons for each. Both work well and are quite reliable.

DCS

Arguably building an AA or ABA lashup is easier with DCS than with Legacy. PS-2 and PS-3 multi-unit diesels are inter-connected by 10 pin tether cords (similar to steamers) that are positioned just underneath the couplers and plug in from unit to unit. (Note 1) They are somewhat visible however, which some find objectionable. The tether carries signals between the units, smoke unit, coupler, and lighting signals, etc. Powered B or trailing A units are typically equipped with “slave” boards that respond to commands from the lead unit to control its motors, smoke unit, lights, etc. Some sets are AA; one powered, one dummy. Others are ABA sets with two powered A units, and a dummy B. Some sets have addon dummy B units available separately which will tether right in with the base set and run together just fine. (Note 2) All lead A units are intended to run cab forward while trailing A units run cab backward, which is how most roads ran MU’d AA units.

When connected together all units automatically behave as one unit and answer to the lead A unit address and commands. Very easy to “build” a lashup with this system, and they cannot get “out of sync”. It can be a bit tricky to plug the tether cords in from unit to unit though; it is a two-handed job and takes some getting used to. One good way is to lay the units end to end on their sides on a protective surface. Then plug in the tethers and lift them onto the track as one. Once assembled it is best to leave tethered units connected and parked on the layout if you can.

Tethers can also be a major headache if you have a multi-unit derailment or other problem in a hard to access area of the layout. There is often no good way to get the tethers disconnected and it's impossible to lift more than 2 connected units out without help. Good luck with the rescue!

Most often 3 unit Premier sets have both A units powered and a B unit dummy. You can run the full ABA set or just the AA units. If preferred you can also run the AB units together without the trailing powered A unit, but if the rear coupler on the B unit is fixed only, it obviously will not uncouple. Typically RK sets are one powered unit and either one or two dummies.

A lashup of dissimilar (untethered) diesels is basically done by assigning separate engines to a Train name, as is a steam lashup. Assemble the lashup per instructions using the DCS handheld or engine manual, and give the lashup a unique recognizable name. Note if you put power to a previously dead block where a lashup is parked, the engines won’t see a watchdog signal of course, and will startup in conventional. No worries; when you push DCS Startup the lashup will work properly.

Legacy/TMCC

With Legacy and TMCC each AA or ABA diesel unit is a separate entity with no electrical inter-connection between. Each has its own power rollers, motors, independent lighting, couplers, smoke units etc. Unless a unit is completely non-functional (like B units), each will have separate command electronics including a radio board, motherboard, RCMC, sound board, etc, Higher end sets will often have smoke units in each unit, electro-couplers on both ends, directional headlights, markers, MARS, cab lights, etc. Lower priced sets have less features. Some sets have addon B units sold separately, which may be dummy, powered, or have Railsounds or Superbass sound systems.

There are a couple of ways you can lash these units up. Simplest way is to assign the same ID number to each unit. Then all units will start up and operate as one, connected or not. All will make smoke, sound, etc simultaneously on command, as equipped. Easy peasy. But a problem arises with the couplers since all will respond to either the F or R coupler command.

For instance if the trailing A unit is non-powered but has electro-couplers on both ends, activating the Rear coupler while moving will disconnect and leave the trailing unit. Likewise a B unit rear electro-coupler will open when R is pushed, which will disconnect the trailing A unit if present. (Not a problem if there is no trailing A unit of course!) This can be avoided though if the B unit has a switch to disable the rear coupler when there is a trailing A unit; most newer B units do. And it’s a non-issue for an AA lashup if each unit has electro-couplers only on the nose.

Another potential issue with using the same ID number is some sets come with the trailing A unit configured to run nose end forward, same as the lead unit (common with early Legacy) This means both headlights/cablights will be on in forward, both backup lights in reverse. When you open the Front coupler, again the trailing unit will disconnect and be left behind if unpowered. Not great.

A better but more complex way to lash these units up is to assign different ID numbers to each, and build a Train. (Use a couple of unique digits from each unit’s road number) Follow the Cab2 guidance to assemble your lashup, or page 60 on of the Legacy manual. Basically you assign a Train number, push Info, then the Build softkey. Start with the lead unit, then add the intermediate unit(s), then finally the trailing unit. With each you can choose which direction it will run with the push of the Dir softkey. When done push the Set softkey and the units will program, which takes several seconds. You will hear whistle sounds, then the engine startup sounds, and you are good to go. Address the Train ID number and they should all behave as one. Engine sounds will be heard from all units as equipped; whistle only from the lead unit. Directional lighting, markers, cab lights etc should alternate from lead to trailing unit depending on direction. All smoke units should turn on and off on command. TMCC lashups follow slightly different keystrokes to program, but they behave similarly. A lashup of separate steam engines is built the same way. Refer to the manual.

A Few Caveats: Note that with multi-unit diesels in a Legacy/TMCC lashup, if you remove one or two units the remaining lashup will still work fine. The Cab2 does not seem to care that one or more units are missing. Also note that an engine programmed in a lashup can supposedly be part of another lashup at the same time. And any engine in a lashup can also be operated separately by addressing its unique Engine ID number. Pretty handy. Occasionally an engine in a lashup will miss a command, get out of sync and fight the other engines, or not move at all. When this happens simply power the track down, wait 10-15 seconds, then power up and address the lashup, and all should be well once again. If this doesn’t fix it, delete the train and rebuild it.

Note that when a Legacy lashup is programmed the information is stored in the Cab 2 handheld. This means the lashup will only operate with a Cab 2; and not with any TMCC or Cab1L handhelds.

Also note that when you shut down a Legacy/TMCC lashup and leave the track powered, the sounds will be dead if you address it again. You must power the track down, then re-power it and address the Train for the sounds to function. This behavior applies to separate engines as well of course.

Note 1: PS-1 sets used 4 pin connectors with the receptacle at the front of each trailing unit. PS-2/3 sets use 10 pin connectors and the receptacle is on the rear of each unit, while the tether cord is at the front of each trailing unit.

Note 2: If an MTH AA or ABA set has been upgraded from PS-1 by installing a full Diesel Upgrade Kit in both powered units, they should be lashed up as separate PS-2/3 engines. No tethering is required between any units in this case.

Rod