Watch the skies
Psssst, wanna get high with the Pi (in complete compliance with local aviation laws of course)?
So far we’ve managed to keep our feet/wheels/ caterpillar tracks on the ground, but we think we should finish our robotic journey with a brief foray into the world of drones.
Keeping a drone in the air is a complicated business. Each motor has to be able to respond as close to instantly to changes in orientation. These are detected by a three-axis accelerometer. Other instrumentation is required, too: gyroscopes, servos, and of course motors to keep the propellers turning and generate lift. A vanilla Linux Kernel isn’t built to respond within such operational deadlines as this, so it’s common for drones to run a real-time OS (RTOS) such as NuttX, or indeed a proprietary OS. The Linux kernel can be tweaked to get closer to such response times though. The PREEMPT_ RT patchset is probably the most popular way to achieve this. This patchset, having gone for a long time without funding, is now part of the RTL Collaborative Project, an industry-sponsored initiative under the Linux Foundation. See https://wiki.linuxfoundation.org/ realtime/rtl/start for more information.
Erle Robotics ( http://erlerobotics.com) makes the Erle Brain: small Linux computers capable of fulfilling all the functions required to keep a drone in the air. They include all the sensors and expansion ports you could imagine. Erle also makes the PXFMini, a hat for the Raspberry Pi that uses Dronecode’s APM Flight stack. Dronecode is an open source platform that’s fast becoming an industry standard. The stack consists of the PX4 autopilot, the Mavlink communication protocol, QgroundControl software and runs on a huge variety of hardware. Read more at www.dronecode.org.
Even if drone makers often would rather have some other OS flying their aircraft, it doesn’t preclude having a separate Linux machine on board. This may even be advantageous, since it enables all of that machine’s resources to be devoted entirely to fun tasks, perhaps 360 degree photography via a gimbal-mounted camera.
It feels like we’ve barely scratched the surface of Pi robotics. PiBorg founder Timothy Freeburn tells us he’s “working on Pi-based robots for mining simulations with a big Australian mining company, robots for aircraft intake and exhaust duct inspection, and robots for pipeline inspection. The list is growing rapidly!”
He also points us in the direction of some of his favourite community projects: Pi In The Sky, The Big Hack, and Liam Kennedy’s ISS-Above (see http://issabove.com/iss-above-and-the-raspberry-pi). Thanks Tim. And thank you, dear reader. Now off you pop and build something amazing!