I'm starting a discussion specifically related to the FY31AP, to share experiences with this new autopilot/stabilization system. I am new to Feiyu Tech products, and I hope that others with more experience will join in. Hopefully my noob perspective will be helpful to others who are starting out.
I'm doing this one step at a time...
Installation: I installed the FY31AP and its GPS module on a Bormatec Maja UAV, with the FY31AP and the GPS both sitting on the surface of the fuselage, and the wiring connecting to the receiver (Hitec Optima 9) inside the fuselage. This provided easy access to the AP unit for initial setup and testing. The wiring is straight forward using the supplied connectors. The AP receives power from the receiver through the signal input connections. No other power supply to the AP is required. There is a cable that can be used as an extension for a USB connection, which could be handy if the AP is installed in a less accessible area, but I did not need to use it.
Initial Tx setup: I used the two 3-position switches on the Hitec Aurora 9 to select flight modes through channels 5 and 6. Channel 5 selects for Normal Flight, Stabilized Flight, and Waypoint Navigation. Channel 6 selects for Normal Flight, Return to Home, and Circle Current Point (these are my terms, which makes most sense to me). To fly the plane without signal modification from the AP, both switches must be in the Normal Flight positions. When Stabilized Flight is selected, the flight path is still controlled by the pilot, but the attitude is stabilized against change that was not commanded by the pilot. Waypoint Navigation, Return to Home, and Circle Current Point are all fully autonomous flight modes, requiring no pilot input.
Test flight 1: I took off in Normal Flight mode. As expected, the plane did nothing unusual. After gaining some altitude, I switched to Stabilized Flight, and all hell broke loose... The plane flew straight for a moment, then banked, first slowly, but the bank rate rapidly increased, flipping the plane onto its back. Fighting the roll with the sticks was unmanageable. I tested this a few times, going between Normal Flight and Stabilized Flight, with consistent results. I landed, and discovered that the direction of aileron reaction when in Stabilized Flight was reversed. I should have checked this before the first flight (duh!).
Test flight 2: I corrected the aileron reaction direction by turning the aileron gain/direction control to the same deflection, but the opposite angle, and I took off again. This time there were no issues with the stabilization. It was very effective, making the plane extremely docile in the air. I had to use much more stick input than normal to execute turns. It felt a little like steering a ship. There was no oscillation in the flight path. The gains as set at the factory were spot on for the Maja. After going back and forth between stabilized and normal flight many times I landed to install a fresh battery.
Test flight 3: This time I explored the autonomous flight modes. After gaining altitude I selected Circle Current Point. The plane immediately went into a left bank and started a gradual left turn, and just continued to fly in a large circle at what looked like about 150 feet. I took over control and flew a distance away, then selected Return to Home, and the plane immediately turned around and headed back. After reaching the point where it was initially switched on, it entered into a large circular pattern. I repeated this several times, from various distances and directions. It worked flawlessly every time.
So far I am immensely impressed with the FY31AP. The next steps will include uploading waypoints using the GCS, and autonomous flight to a series of waypoints. That will be followed by installing FPV using the Hornet OSD. Finally, I intend to hook up an Xbee data radio for real-time autopilot control and flight path monitoring via a laptop PC.