By Roland Piquepaille
It's not always easy to explore small buildings in dangerous areas and even more difficult to see what might be hidden in a cave or a tunnel. In this short article, the MIT Technology Review describes the results obtained by Swiss researchers with a small robotic aircraft. It only weighs 30 grams for a 80-centimeter wingspan and can flow inside a building for about 4 minutes. With its two 1-gram cameras, a gyroscope, and a small microcontroller onboard, it can detect walls and automatically avoid collisions. The team is now working on even smaller versions of these flying robots which will be used for search-and-rescue, reconnaissance, and inspection applications. Read more...Before going further, let's look at the robotic platforms (Credit for images and legends: Jean-Christophe Zufferey and Dario Floreano, Laboratory of Intelligent Systems, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland).
[The picture above shows] two Khepera robots, the left one equipped for obstacle avoidance (steering) and the right one for lateral wall following (corresponding to altitude control in the case of a flying robot). Gyroscopes for yaw rotation detection are visible on the top turrets, just below the 1D cameras (one-dimensional array of pixels).
[Note for those of you who are not airplane engineers: according to this Aerospace Science and Technology Dictionary from NASA, "yaw" is "the rotational or oscillatory movement of an aircraft, rocket, or the like about a vertical axis" or "the amount of this movement, ie, the angle of yaw."]
[This second picture shows the] 30-gram indoor slow-flyer equipped with a yaw gyroscope and two horizontal 1D cameras pointing at 45° off the longitudinal axis of the aircraft. This plane flies around 2m/s and features a minimum turning radius of approximately 1.3m. The energy source is provided by a 310mAh Lithium-polymer battery. Overall power consumption is around 2W.
Here is how the flying robot operates according to Technology Review.
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.
An 80-centimeter wingspan might still be too large for small environments, so the researchers are working on smaller versions.
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.
The results obtained with this robotic aircraft were presented during the 2005 International Conference on Robotics and Automation (ICRA 2005), which was held on April 18-22, 2005, in Barcelona, Spain.
The technical paper was named "Toward 30-gram Autonomous Indoor Aircraft: Vision-based Obstacle Avoidance and Altitude Control" and here is a link to this paper (PDF format, 6 pages, 672 KB). The above images were extracted from this paper.
And for even more information, here is a link to the project home page at the Laboratory of Intelligent Systems of EPFL, "Bio-inspired Vision-based Flying Robots," where you'll find more pictures and even video clips.
Sources: Corie Lok, Technology Review, September 2005; and various web sites
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