For Star Wars: The Force Awakens, they built a (multiple?) practical BB-8 prop. They brought it to D23 last year, where they showed it rolling around, doing the basic movement you see BB-8 doing in the film. But in the film, we see BB-8 having compartments containing tools they deploy as needed. Were these compartments part of the practical BB-8 prop, did they have specialized BB-8s that were used in these scenes, or were these parts of the film accomplished using some kind of SFX in post-production?
How much of the film was accomplished via the practical BB-8 prop?