VGN 2-10-10-2 - my 2014 challenge

[Sumpter250]

One question I have is whether the motor for the front unit, turning inside the boiler with the front unit, will have enough clearance to allow the loco to make any kind of reasonable curve. That would be worth a check, maybe making a full-size mockup in cardboard or whatever.

If you look at the drawing again, the motor in the boiler, for the front unit, is connected to a drive shaft, mounted in the cylinder supports of the rear engine's cylinders. the only thing that moves with the front engine is the drive shaft (cup and ball)
to the front engine's geared driver axle.
My 3' gauge outside frame 2-4-4-2, uses the same drive system but with only one motor ( actually mounted in the tender ), and it has been basically trouble free for over twenty years. ( I cured the "dirty wheel electrical pickup problem" by hauling a track cleaning car, (( box car with a weighted pad under )) to keep the rails clean )