Finally.

The weather was nice enough yesterday to try autotuning outside. The battery held out for about a minute each of pitch and roll tuning and long enough to write the results to EEPROM to dump out at home. I ended up with PIDs that seem to work great for my Q4 as defaults in the code. It flies just about as well as I remember the stock firmware behaving, which given my untrained thumbs is like saying Apple earbuds sound as good as $30k Sennheiser Orpheus headphones. It even works with the original remote.

There's still work to be done: change PID tuning TX channel to something less destructive, more code cleanups (most importantly pull from victzh's latest commit), better documentation, test unlock procedure on a new Q4.