"...camber of the rail bed (ie banking) would help zero out the centrifugal forces on a trail going around a bend...calibrated for a specific speed..."

Yes, but that's not part of this question. I think that's so the railroad riders don't get champagne splashed on their evening finery. Or whatever.

"...flanges ARE necessary to provide second order nudges..."

Not really, although they're sorta like a parking brake. Good for emergencies, and also critical for when you're not moving. If the flanges were responsible for keeping the train on the tracks, they'd be worn off in several hundred miles. And you'd hear the training coming a looooong distance off.

"...rotation of the motor-generator set is not central to the riddle..."

Right. I said that. It's totally irrelevant.

The first given clue is that the two wheels on an axle are rigidly mounted to the axle. However one wheel turns, so turns the other wheel.

The second clue, which Nappy never asked for, is equally critical -- the wheels are slightly tapered. The larger diameter is toward the center of the vehicle (and the flange). The smaller diameter is toward the outside.

Cogitate.