Flying Robot
Thirty-gram aircraft steers itself

Results: Swiss researchers have built a robotic aircraft with an 80-centimeter wingspan that flew indoors for about four minutes, detecting walls and automatically turning away from them, thanks to two one-gram cameras, a gyroscope, and a small microcontroller onboard.

Why It Matters: Small robots that can operate inside buildings or in tight spaces like caves or tunnels may be useful for search-and-rescue, reconnaissance, and inspection applications. Researchers have previously tested larger flying robots outdoors with fewer obstacles and indoors doing limited maneuvers like landing. Here, Jean-Christophe Zufferey and Dario Floreano of the Swiss Federal Institute of Technology in Lausanne have shown that a smaller aircraft can fly indoors for a relatively long period of time while successfully avoiding collisions.

Methods: The researchers made their aircraft out of carbon-fiber rods, balsa wood, and thin plastic film for the wings and tail. They mounted one video camera on the leading edge of each wing and connected the two cameras to a low-power microcontroller near the front of the aircraft, behind the motorized propeller. The microcontroller grabbed images from the cameras about 20 times per second and calculated how fast obstacles like walls appeared to be moving toward the aircraft. As objects got closer, the cameras saw them as moving faster. The microcontroller recognized a certain threshold speed as an indication that an obstacle was getting too close and sent signals to the rudder to turn the plane about 90 degrees.

However, the side-to-side movements of the plane's nose -- its "yaw" -- also affected the speed at which obstacles appeared to be approaching, confusing the plane's obstacle avoidance system. To counter this effect, the researchers placed a gyroscope behind the propeller that measured its yaw rotation speed. The microcontroller took this data into account when analyzing the camera images.

The researchers tested their obstacle avoidance algorithm on their aircraft in a 256-square-meter arena. The walls of the arena were made of wide vertical strips of black and white cloth to enhance the contrast of the obstacles and make them more visible to the cameras. The researchers controlled the plane's altitude manually with a joystick and a wireless connection.

Next Step: The researchers are working on a 12-gram, 40-centimeter-wingspan aircraft with lighter and smaller electronics so that it can fly in smaller rooms. They are also integrating an automatic altitude-control system into their plane to make it fully autonomous. And they are putting more-sensitive cameras on board, so the plane can detect obstacles that don't have high-contrast coloration.

Source: Zufferey, J.-C., and D. Floreano. 2005. Toward 30-gram autonomous indoor aircraft: vision-based obstacle avoidance and altitude control. Proceedings of the IEEE International Conference on Robotics and Automation 2005, pp. 2605-2610.