Open-source quadrotor autopilots. (a) Arducopter,
(b) Openpilot, (c) Paparazzi, (d) Pixhawk, (e) Mikrokopter
(photo courtesy of Inkyu-Sa), (f) KKmulticopter, (g) Multiwii
(photo courtesy of Alexandre Dubus), and (h) Aeroquad (photo
courtesy of Ian Johnston).