Droning On: Choosing a Flight Controller

do4 The flight controller is the nerve center of a drone. Drone flight control systems are many and varied. From GPS enabled autopilot systems flown via two way telemetry links to basic stabilization systems using hobby grade radio control hardware, there is an open source project for you.

Modern drone flight controllers can trace their roots back to R/C helicopters. Historically, R/C planes were controlled directly by the pilot’s radio. Helicopters added a new wrinkle to the mix: tail rotors. Helicopters use their tail (or anti-torque) rotor to counteract the torque of the main rotor attempting to spin the entire helicopter’s body. It all works great when the helicopter is hovering, but what about when the pilot throttles up to fly out? As the pilot throttles up, the torque increases, which causes the entire helicopter to do a pirouette or two, until the torque levels out again. The effect has caused more than one beginner pilot to come nose to nose with their R/C heli.

The solution to this problem was gyroscopes, heavy brass spinning weights that tilted in response to the helicopter’s motion. A hall effect sensor would detect that tilt and command the tail rotor to counteract the helicopter’s rotation. As the years wore on, mechanical gyros were replaced by solid state MEMS gyros. Microcontrollers entered the picture and brought with them advanced processing techniques. Heading hold gyros were then introduced. Whereas older “rate only” gyros would drift, weathervane, and wiggle, heading hold gyros would lock down the helicopter’s nose until the pilot commanded a turn. These single axis flight controllers were quickly adopted by the R/C helicopter community.

Today’s flight control systems have many sensors available to them – GPS, barometric pressure sensors, airspeed sensors, the list goes on. The major contributors to the flight calculations are still the gyros, coupled with accelerometers. As the name implies, accelerometers measure acceleration – be it due to gravity, a high G turn, or stopping force. Accelerometers aren’t enough though – An accelerometer in free fall will measure 0 G’s. Turning forces will confuse a system trying to operate solely on accelerometer data. That’s where gyros come in. Gyros measure rate of rotation about an axis. Just as our helicopter example above covered yaw, gyros can be used to measure pitch and roll of an aircraft. A great comparison of gyros and accelerometers is presented in this video from InvenSense.

Stay with us after the break for a tour of available flight controllers and what each adds to the mix. [Read more...]

Awesome little UAV flies 1 km

After going to an SMD soldering workshop at the Stuttgart hackerspace ShackSpace, [Corvus] decided to be an over achiever and build a flight controller for his very own unmanned aerial vehicle.

The airplane itself is a regular store-bought foam contraption, and not terribly interesting in and of itself. Autonomous flight piques some interest, though. A custom flight controller PCB was designed and built by [Corvus] to work alongside a tiny STM32 Linux board. These two boards, combined with the OpenPilot project allow the plane to keep altitude, bearing, speed, and position in check autonomously. Telemetry between the ground station and vehicle is handled by UAVTalk and a ThinkPad.

In the video after the break, [Corvus] piloted the plane up to altitude, then directed it to fly 500 meters North and turn around. The result was an autonomous flight of over one kilometer. The next stage of the project is implementing some SLAM applications with optical path finding and obstacle avoidance.

[Read more...]