That real-time controller still needs the IMU sensors, which is maybe what GP was responding to. (Your iPhone could have an additional set of them, but the ones on the phone don't do any good to the real-time subsystem.)
Oh, I got an accelerometer card for that. It's very small and cheap, there are also cards that contain a gyro + barometer. So if the phone ones are not real-time enough cheap options exist.
