I'm actually surprised so many people thought the ball droid was CG.

My immediate interpretation of that shot when I first saw it was that JJ was declaring "Look see, I told you, practical effects!"

The way it jittered across the terrain was a dead giveaway to me. A CG droid would have rolled a lot more smoothly.

I imagine it was accomplished in the same way they did the Tire in Rubber. Where they just digitally erased the wires/rig that the prop was guided by.

And no, all the ship shots were definitely all digital.

Edit:

Actually, based on this quote from Mark Hamill:

Mark Hamill said:

They never cease to amaze me with what they’re able to come up with, you know? I said, “How are you ever gonna top R2-D2, the most adorable droid in movie history?” And then they have this new one. I can’t even tell you his name, but you saw it in the trailer. And when they were demonstrating how they did this thing, live on set — because it’s not CGI, that’s a live prop — I was just amazed. They let me play around with it. [Laughs] I was running it all around at the creature shop up in Pinewood. I’m telling you, it’s an absolute delight. And not having thought that I’d ever go back there, to go back into that world, is just – I get the chills. It’s just so much fun.

It sounds like the ball body is actually RC controlled.