Another update - I'm still doing this!
I had spent the summer tweaking the boat and the algorithms, until I was sure I was close to something better in August. Then, as I was making sure everything was working correctly, I turned the board on moments before taking the boat out to watch the circuit catch fire and release the magic blue smoke (see attachment). The post mortem showed that a stalled winch servo overloaded the 6V buck regulator and blew it up. So much for the rest of 2016.
I spent the remainder of the winter building a new circuit, a new boat (I had entombed the internals of the previous in polyurethane foam) and a new algorithm. The new circuit added the new InvenSense MPU 9250, an MPPT solar charger for the LiPo and some general cleanup (including a fuse on the 6V reg).
On the algo side, I ripped out the nonsense that was in there, and dropped in the lovely Arduino PID library for steering control. Maiden voyage this weekend went poorly I thought at first (the boat was zigzagging all over the place), until I realized that I was tuning P and I, but not D (don't ask). Unfortunately I realized that after I left the lake, so I'm hoping that next weekend will be the day it all just works!
We'll see how it goes.
