Do they have to be small? Geometrically you'd think that they could be a reasonable fraction of the wheel diameter without clashing. The roller width is the limiting dimension because that defines how close to the wheel axle the edge of the roller can get - would thin, large diameter rollers work?
Yeah that’s true, instead of small diameter wide rollers, you could have large diameter narrow rollers, like for example bicycle wheels or scooter wheels. Actually you could even use tracks for the rollers, which might be an interesting innovation. That would increase friction and reduce battery life, but there may be some advantages. Of course it would be very complex mechanically!
But something made with scooter wheels could be used to navigate around a city for example. That might be interesting.
