The overlap between viable diesel locomotives, owing to the development of the first high-speed diesel engines from around 1930, and the era of small rigid framed driving wheels was short. The first diesel shunting locomotives were of C or 0-6-0 wheel arrangement, as they were neither heavy enough nor fast enough to need the pony trucks. These low-powered shunting locomotives could also make do with a single traction motor. More powerful mainline locomotives used multiple traction motors, one per axle. This was mostly due to the locomotive's generator being able to produce DC current, thus allowing simpler and more controllable DC motors to be used. These could easily be made in the smaller diameters needed for per-axle use, rather than the large diameter many-pole AC motors. As diesel locomotives developed, the per-axle traction motor design became ubiquitous, with 1′Co1′ and 1′Do1′ designs in early years, later with bogies as Bo′Bo′, then Co′Co′ and heavier designs. A rare exception was the Armstrong Whitworth locomotive of 1929 for the of Argentina. This used a single transmission and jackshaft drive from one end, with coupling rods. The locomotive was unsuccessful, owing to problems with the transmission and lay unused for several years before being scrapped in 1943. The 1′Co1′ wheel arrangement was similar, except that the wheels were driven by separate traction motors for each axle, rather than them being coupled together. As each axle was driven, there was no longer a need for the coupling rod connection between them. This independence would in time raise the issue of wheelslip, starting with a single axle, but that was not an issue for the early locomotives, with their low ratios of power to adhesive weight. Diesel-electric locomotives used the 1′Co1′ arrangement with separate traction motors, rather than the coupled 1′C1′. This was because these were some decades later than the first electrics, by which time traction motor technology had developed. Also the generators on board the locomotive could generate DC, rather than AC. Control of DC was more sophisticated by this time and there was no need for the traction motors to be the large diameter that the 1900 AC electrics had required. The first British mainline diesel locomotive, Armstrong Whitworth's 800 bhp locomotive built for the LNER in 1933, was of this type. This locomotive was unsuccessful and scrapped after only a few years, in 1937.