Test flying is still the least pleasant phase, even after 6 years of knocking out flying things. The system you put your heart & soul into building is beaten up & usually destroyed before it works.

Physics put up a huge fight. The IR sensor needed more stable power than the battery. The battery had huge troughs. It eventually ran off the Syma's 3.3V power rail with loads of capacitance while the magnetometer ran directly off the battery. The Syma's 3.3V power rail couldn't power any more than the LED.

A place for the LED which is always visible has yet to be found. The trend is to extend it more sideways. Ideally there would be springy wires which could snap it down after takeoff.

For the very slight bank angles encountered, the magnetometer alone seemed to be enough to get heading. The heading still had to be dead on to keep it inside the extremely confined room. It was finally time to write an automatic magnetometer calibrator. Though the calibration is ephemeral, the heading is now dead on when it's perfectly level.

The heading was the 1st of a new type of radio usage. The mag output is sent out the UART, which directly modulates the FSK pin instead of using the radio's FIFO. It would have saved a lot of pain to know the MRF49XA's FSK pin could be directly connected to the UART instead of banging on the FIFO registers, in 2009.

It's still very temperamental. The vision system needs to be right at the limit of its latency. Surprising that altitude is the least demanding direction to stabilize.

Awesome. Could you give some more detail of what and how you do that, please?