Thanks for your reply. I think driving the film directly with a drum (with rubber rings to press against the film) would be the best solution for me. From what I can tell from pictures, it seems that the Roundshot 220VR and also the Voyageur cameras use this method. What I am not sure of is if they also drive the take up spool -I wouldn't think the film would wind up tightly any other way but I may be wrong. Which brings me to driving the spool at a suitable speed so that the film will wind up smoothly, but not so much as to force the film to slip past the transport drum, or to cause the drum to rotate faster.
Incidentally, I am using two motors in order to separate the camera rotation from the film transport, with the camera body mounted on a short rail to allow variable positioning relative to the rotation axis, so I can use different lenses and compensate for the varying entrance pupil location and focus distance.