NBCUniversal Television Distribution They had to use two actors on a shift system due to the constraints of working within such a small ball.
OK, Abrams didn't make them sit inside the droid during the shoot. Here's how Hader described his job: "J.J. f**king around with this sound effects app on his iPad that was attached to a talk box operated by me. It looked ridiculous but it made BB-8's voice. At first I tried doing a voice, but we all agreed it sounded too human."
Lucasfilm "Damn, we gotta get the fuck out of here! Beep beep, motherfuckers!"
Schwartz's work didn't overlap with Hader's, but he did break down his experience in a little more detail. Essentially, while looking at a fairly final cut of the movie, he and Abrams decided what BB-8 might be saying in those scenes. Whatever words they came up with weren't important, but the cadence and comic timing were. Schwartz isn't sure whether any of that got translated into the beeps and squelches BB-8 used in the film, but he did get to mess around with Abrams and a synthesizer for a few days, so he considers it a success on that basis alone. (So would we, come to think of it.)