"Until you start to do acrobatics, I'd stick with the PID controller. That really is sufficient for most other applications. Some of the lack of responsiveness may be due to small communication delays caused by Android (assuming you are using the…"

"Great work! I've done something similar here so, if you have any questions about my work feel free to ask.
 
FYI, in case you haven't encountered it yet, heat may start to give you troubles with the barometer. Since phones tend not to dissipate heat…"