In the twilight years of steam, some railroads, most notably PRR, became interested in the concept of duplex drive locomotives. A duplex locomotive has a single rigid frame and one set of drivers, yet has four cylinders like an articulated locomotive would.
A single Q1, number 6130, was constructed in 1942 as a prototype duplex drive freight engine. It originally received streamlining in the form of a nose cone and sheet metal covering the piping and valve gear along the sides, perhaps to associate it with PRR's flagship high-speed passenger locomotive, the S1. This streamlining made maintaining the engine more difficult and was soon removed. Also unusual on this engine were the 77 inch drive wheels, more suited to a passenger locomotive.
The Q1 proved that duplex drive could be used on freight locomtoves, but it was not, itself, a successful engine. The primary problem came from the location of the rear cylinders near the firebox. This caused additional wear and tear on these cylinders. 6130 was taken out of service in 1946 and scrapped several years later, a very short service life for any locomotive.
The concept of a duplex drive freight locomotive was carried on in the Q2, a similar engine in general, but sporting smaller drive wheels, and a 4-4-6-4 wheel arrangement with more conventionally-placed cylinders. The Q2 is generally regarded as the most powerful non-articulated locomotive.
My model of the Q1 features Big Ben Bricks' new XL steam drivers, owing to the prototype's 77 inch drivers. It is powered by 3 Power Functions Medium motors, and all of the PF gear is in the engine, itself. Despite its substantial size (especially length) it is fully capable of navigating tight curves and switches.
Hopefully more pictures will follow in the near future, but for now these will have to do until I get back from Brickworld. Come see me (and the Q1!) this week in Chicago.