Existing film scanner patent (2013, Canada)

Another consideration is the capstan material, and the tension required on the film to hold traction. If the capstan is the made of the same material as the o-ring, I would agree that more surface requires less force (and tension) which would be preferable.

One aspect where the O-ring may have an advantage is the flexible nature of the material configuration (the O instead of the solid), which may then require less tension over the capstan, but I do not know if that would be the case.

One successful example of stop-motion capstan is the Gugusse Roller built, which uses a large capstan (a skate silicone wheel).

I am doing an iteration of the snailscan, using an aluminum silicone encoder wheel as capstan / driven directly by a geared-stepper.