In my inventory, I give a number to each loco I purchase: the first was “number 1”, the second “number 2”, the third “number 3”, and so on…The doubt is: when I buy a F A/B units, how many new locos I have?. Both have motors inside, as in the real world, but only one has cab; and the B unit, push and pull like the “A”, but only joined with the “A”; so, how many locos did I purchased??? I´ll be grateful for any answer. Bye.
You purchased 2. The B unit can be re-assigned to any other train. You could have an A-B-B unit for example. Or you just might need it with some other engine entirely. It is separate power.
The prototypes didn’t know the answer to this either, at first (from what I’ve read). Some started out by number sets (A/B, A/B/B, etc) with the same number with A,B, and C or some such, some didn’t number B units at all, with the assumption that they would stay attached to the A unit they can with, and serve as one locomotive. I don’t think it was too long before they realized that they had gotten it confused, and that they were indeed separate units, enen if they all did not have cabs. So, Chip is right, but on the other hand, you can count them almost any way you want, and still be right.
I can’t speak for every railroad, but in the case of the Santa Fe: They bought all of their initial FT’s from EMC in 4 unit sets. Since the ATSF was one of the first railroads to dieselize the union contracts were not up to date. The unions stated that there must be a crew (Engineer and fireman) for each operating locomotive (over a certain weight) on a train. I assume this was to prevent a railroad from forcing one man to shovel coal and operate the loco by himself. When diesels first arrived on the scene the unions stuck by their contract. To get around this the ATSF gave their 4 unit sets one number. The four units would be numbered 101L, 101A, 101B, and 101C. The L and the C being A units and the A and B being B units (could they make it any more confusing?). So even though the ATSF knew they had four locos, they numbered the sets as one 4 unit articulated locomotive. The L, A, B, C were not painted on the locos, just the 101. And the 101 was only painted on the A units. This can make it difficult for modeling the ATSF if you have too many F units.
To answer your question… you bought 2 locos.
The ATSF wasn’t the only railroad to follow that practice. The MKT and a few other roads considered their sets to be one locomotive whether they were A-A, A-B, A-B-A, A-B-B-A. On some roads the units were permanantly joined by drawbars (though they were later removed and replaced with couplers).
Even then the Union argued that there were two cabs so they needed two crews. To get around this the Santa Fe ordered a bunch of “B” units, broke up the ABBA sets into ABBB and ABB configurations so there was only one cab in each. Fortunately, the Unions finally saw the light. As I recall the compromise was that they got to keep the “fireman” in exchange for agreeing to only one crew per lash-up.
As for my models, I don’t know either. The Stewart FT AB sets I’ve counted as 1 unit, while the Stewart F3, F7s came in individual boxes so I counted them as individuals. The F9s also came in AB sets and got recorded as a single unit. ? ? ? If you figure it out please let the rest of us know.
I recently bought a 2-10-2 Heavy from Proto. The serial number on that engine was 112. Ergo, it gets cab number 112. Once in a while I would research the engine like WM had a 2-8-8-2 #917 that was pretty close to the Proto model.
Regarding the A-B consists, usually one number is given to both in DCC and the B unit gets the Lights, whistles disabled. That way I can consist an A-A and run any combination of B units by placing them on or off the track.
The Baltimore and Ohio would have the A unit one number and give the same number to it’s B unit with the “X” added.
I think 4 unit sets like ABBA were set up so that they were treated as one big engine that would potentially replace at least two steam engines and thier crews and save the associated costs.
Anyhow, that is how I do it on my line, I do check all my other engine numbers to ensure that my two digit addressing is unique to each one.