The Crossbow MNAV
autopilot system is a pricey (starting at $1,500) package of sensor and GPS hardware that has received a lot of attention in the amateur UAV world because Crossbow, to its credit, open sourced the autopilot software
. This has provided a useful learning tool for all of us writing our own autopilots, since the source code shows examples of everything from Kalman filtering to crosstrack waypoint following.
Curtis Olson, best known as the creator of the open-source FlightGear
flight simulator, has done the best work of building on the Crossbow code. He's recently released the source code
to his Microgear autopilot
, which uses the Crossbow IMU hardware and replaces the Crossbow processor unit, known as Stargate, with a much more powerful Gumstix Linux single-board computer
. He's also released the groundstation software (shown), which naturally works with FlightGear. He describes the project well here.
This is a little out of our league at DIY Drones, both in price and complexity, but for those you who want to go deeper on autopilot theory, a browse through Curtis's source code is very instructive. He's written it in C++ and done a pretty good job with comments, so it's not too hard to parse. The Kalman filter is still a little over my head, but I thought the waypoint handling was very clear.
If you're interested in learning more about the Crossbow (often known as Xbow) hardware and software, Tony Truong Giang Le has some good tutorials here and here.