There are some things Mark Hamill said in his interview, and there are some things he DIDN'T say.
He didn't say it was remote control.
He didn't say it moved under its own power.
He did say- They let me play around with it. [Laughs] I was running it all around at the creature shop up in Pinewood.
I spent weeks chasing down every bit of information on this thing before I started building.
It is my belief that the BB-8 that was in the teaser trailer was indeed a physical prop. I believe it was shot against a green screen, and the model had a long pole that extended out behind it, and came into it from the opposite side of the camera, like a ten-foot pole with a right angle that entered the backside of the prop. The head turning was controlled by cables. It would have been pushed alongside a traveling camera dolly, then the background was added later.
There would be several different models for different scenes. Each round panel has a different design, the designs are actually outlines to opening compartments. The droid is said to carry a light saber, tools and some personal items- a self-propelled valet of sorts.
The round dots that are all over the outside is where a self-defense protruding spike system comes out, similar to a puffer fish. I think this little guy (most sites call it a 'she') is going to be the comic relief and the conduit for connecting the other characters, like R2 and C3PO were in the earlier films.
Just my 2 cents.
Kurt