John,
There's really not a single answer. The Faulhaber gearhead motors shown are really nice but not as powerful as say a large Pittman. I've done quite a few locos with a single motor but I did an RSD for a friend with two motors because of the weight. A single motor wouldn't have been powerful enough.
After that I wondered if I could fit two of the gearhead motors into a RC shell so the whole thing was kind of an experiment. I also installed ball bearings to the axle journals and Delrin wiper mounts and phosphor wipers all around. Everything beyond the gearhead is setup for a 1:1 ratio so everything turns far slower than other drives. This greatly reduces vibration, noise, wear, etc. Also, every shaft turns in ball bearings.
I'm in the process of doing another but it will be standard O Scale.
Hope this answers your questions.
Jay
