Hi!
I believe I did this once before but sure can't replicate it today. I guess I have a Texas sized brain cloud..........
I have a Digitrax system and want to pair two HO E7a units back to back. Without changing the "natural" direction of one, they obviously want to go in opposite directions. Will this correct itself if I MU them, or is there something else I need to do???
When I get the answer I'll get it into my notebook - should have done that before.
Thank you,
Mobilman44
ENJOY !
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central
Take the lead loco put it on the track facing forward and traveling from left to right (could be right to left if you wish). Test it to see if it is moving from left to right.
Take the trailing one put it on the track back to back with the first one. Do not couple it, leave a foot distance, select that engine and make sure it is traveling in reverse from left to right (using the reverse button of your DCC system). Move that trailing loco to the first one, couple it and built your consist in the usual manner.
Jack W.
Exactly right. If both units are moving in the correct physical direction (regardless of throttle indication) then they will move together when the consis is complete. When remvoed from teh consist, they will both operate exactly as before, when forward is indicated on the throttle they will move in teh direction of the cab end.
If you should happen to want to play around with CV19 decoder-assisted consisting, the consist address is 1-127, but if you make the trailing unit CV19 128-254 it will run the opposite direction. So to make consist 10 with the two A units, the one on the head end would get CV19 set to 10, the trailing unit would get CV19 set to 137 (add 127 to the lead unit). Both would run together on address 10, the lead unit running normally and the trailer running 'backwards' Reset CV19 to 0 to clear the consist, and each unit goes back to its own address, running normally.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Thank You!
Obviously I was trying to make something pretty simple into something complicated.
ENJOY,
mobilman44 Thank You! Obviously I was trying to make something pretty simple into something complicated. ENJOY, Mobilman44
See your other question
The answer also doesn't pass on to other DCC systems. I'm slowly learning the Digitraxx way without having one in these forums.
Springfield PA
Hmmm. I've always changed CV29, to get a loco to run the other way.
hobo9941 Hmmm. I've always changed CV29, to get a loco to run the other way.
That's permanent though, until you reprogram CV29. You do not have to do that to get a consist together where some locos run 'forward' and some run 'reverse'
You also don't have to actually make the loco move dwn the track to make sure it's set for the right direction with Digitrax, but it's a good sanity check until you become comfortable with the procedure. You need to indicate direction of travel somehow on any system, either by it previously commanded to run one way or the other or by hitting a button to indicate direction when adding it to the consist. There's know way the system can know which way you set a particular loco on the track.
I personally think this is an awkward work around, not only you have to reprogram CV29 for normal direction of travel when you break the consist, but programming CV involve more actions, steps and key press than the single push of a direction button.
Hi Mobilman -here are some comments that may, or may not, be of use.
You did specify 'MU A/A pairing'. If you are frequently switching out units in your 'consists', the use of the MU operation may indeed be the most convenient. In that case, the remainder below is probably irrelevant.
I tend to use 'consists' of the same 2, 3, or 4 engines together habitually. (Example: Empire Builder p2k F7 A-B-B-A, all powered, all sound.) I find it FAR easier in this case to give them all the same number - such as 363. (This must be done for each individual unit, of course.) That makes it super simple to adjust lights, sound, etc - in ops mode, AND to blow all the horns at once. The four engines all making their engine sounds, or all ringing bells, and especially all four horns at once, gives a VERY good sound, to my ears. It seems to have some spread-out sound, some built-in reverb this way.
Of course, to address and control all locos simultaneously, with one or more NOT heading in the 'normal' direction, the technique of altering bit 0 (makes CV29 odd or even) MUST be used. (Some newer consist technology allows similar operations - seems a bit tedious in my opinion.) Unfortunately, there is a minor glitch in this CV29 procedure, explained later.
In my case, I set all four on the track in the desired direction - separated by 10 inches or so as previously mentioned - and test their direction when powered up. (AFTER setting them all to address 363 or whatever.) Without changing CV29, the A units will go in opposite directions. By turning the B-units end-for-end, you can find an A-B-B combination that will work for the 'forward' direction, without changing CV29. Then if you change CV29 to an odd number in the remaining A-unit, all four will go in the same direction.
For example, the 'normal' value for CV29 is 6 (i.e. bits 1 and 2 on, or 2 + 4). If a main address greater than 127 is to be used (like my 363), then bit 5 (32) must also be on, giving a total for CV29 of 2 + 4 + 32, or 38. This value will move the engine(s) 'forward', i.e., nose is foward direction.
To set one A-unit (or a hood unit) to the reverse direction, you must set bit 0 - this adds '1' to the value in CV29. Thus for addresses below 128, change CV29 to a value of 7. For loco addresses 128 or above, change CV29 to a value of 39. Done.
This works *very well* for my purposes. I never have to fool with 'consists', 'advanced consisting', etc etc. When I do a 'startup' or 'shutdown', all four units cooperate. The same goes for horns, lights, etc. When I increase speed slightly (open the throttle), the sound of all four engines revving up is music to my ears - and especially, control of lights and horns of all four simultaneously.
I simply store them set up this way - remembering which A unit is reversed, or writing a note.
Of course, the locos must be tuned to the same speeds - either by speed tables, or because they are that way from the builder - as is the case with my four p2k F-units. They work very well together.
There are some more tricks one can use with this method, but probably not of interest here.
A ( SOMETIME ) PROBLEM with CV29:
A few days ago, a friend bought some new MRL SD70's, made by MTH. In trying to set them up with CV29, and running back-to-back, as described above, we all learned something - stated in the abbreviated manual provided by MTH (or maybe in Digitrax literature):
"Not all decoders incorporate the NDOT (Normal Direction of Travel) ability in CV29" - or words to that effect.
After many trials, we determined that these MTH units had beautiful sound, neat lighting etc, but absolutely failed to be influenced by the setting of bit 0 (NDOT) in CV29. Of course, it is not possible to read back the values from whatever decoder is in there, either. Both MTH units exhibited the same behavior.
So it is true, and setting the Normal Direction of Travel is *not* incorporated in all decoders, regardless of NMRA standards. So far, MTH are the only locos I've seen that do not include NDOT in their decoders. Perhaps this setup is related to the DCC uncoupling feature in these locos.
It seems MTH is in the process of upgrading their decoders for other reasons, and perhaps NDOT will be included. There seems to be no reference in their accompanying literature as to which company (QSI?) makes their decoders - and precious little information on most other CV's.
So my friend found the solution - for him - was to use the 'consisting' method as described by several folks above - which did work just fine.
That would not be a satisfactory solution for me, but I am probably in the minority.
Dick Chaffer / Bozeman
MISSION ACCOMPLISHED !!!!!
Thanks to all your help, I finally got the two A units linked together - going back to back but in the same direction - and all the individual sound levels adjusted.
They look absolutely beautiful pulling a string of the Walthers IC chocolate/orange cars, and the sound is absolutely awesome in the 11x15 layout room!!!
And, today I ordered a "plethora" of KD 146 long shank whisker couplers, which will allow the string of cars to more reliably be backed up around the two areas of 26 inch curves. As was suggested by someone on the Walthers Passenger Car postings, I'll put a 146 on one end and a 148 (standard length whisker KD) on the other of each car.
I really appreciate all your help, and now I can go back to putting in that scenery interface between the outer edge of the layout and the painted backdrop.
ENJOY !!!!!