Machine Design

Hannover Fair: Robotic Bird Demonstrates Efficient Flight

The latest development from the Bionic Learning Network laboratories of Festo AG, Esslingen, Germany is the SmartBird, an autonomous, self-propelled biomechatronic bird that, just like its natural model – the herring gull – can take off, fly, and land all on its own. The robot is the result of an R&D project aimed at designing a machine that’s energy efficient and lightweight; uses high-power-density propulsion with high-speed flight controls; and has excellent aerodynamics and maneuverability.

SmartBird video,
Bionic Handling Assistant,

The project has practical benefits, too, according to the company. Combining several electromechanical drives gives Festo engineers insights into industrial hybrid drives. The minimal use of materials and lightweight construction pave the way toward better resource management. And knowledge gained in aerodynamics and flow behavior provides important lessons for improving future generations of pneumatic cylinders and valves.

According to Festo, the wing motion distinguishes SmartBird from previous mechanical flapping-wing constructions. Its wings not only beat up and down but also twist, made possible by an articulated torsional drive.

Each wing consists of a two-part arm spar with an axle bearing on the torso, a trapezoidal joint (used in larger forms on industrial excavators) with a 1:3 amplitude ratio, and a hand-wing spar. The arm wing generates lift, and the hand wing that extends beyond the trapezoidal joint provides propulsion.

Both inner and outer spars resist torsion. When SmartBird lifts its wings, an active-torsion servomotor twists the tips of the hand wings to a positive angle of attack, which changes to a negative angle in a fraction of a wing beat. This sequence of movements streamlines airflow along the wings and converts the power of the flapping wings into thrust.

The battery, engine and transmission, crank mechanism, and control electronics are housed in SmartBird’s torso. The rotor motor linked to a two-stage helical transmission with a 1:45 reduction ratio makes the wings beat up and down. This motor’s three Hall sensors precisely register wing position. A flexible link conveys both flapping and bending forces from the transmission to the hand wing. And the crank mechanism has no dead center, minimizing peak loads to ensure smooth flight.

Also, two electric motors and cables synchronize opposing movements of the head and torso, letting the bird bend aerodynamically and still maintain an even weight distribution. This makes SmartBird agile and maneuverable.

The tail also generates lift, acting as both an elevator controlling pitch and a rudder controlling yaw. When the bird flies straight, the V-configuration of the two flapping wings acts like a conventional aircraft’s vertical stabilizer. To turn, the tail tilts. Rotating the tail about the longitudinal axis produces a yaw moment about the vertical axis.

The on-board controller coordinates flapping and twisting and precisely controls wing torsion as a function of wing position. Two-way ZigBee radio communication conveys data such as wing parameters, battery charge, and power consumption to a ground station. It also handles external pilot commands.

Electronic controls and intelligent monitoring let the bird adjust wing movements in real time during flight and adapt to new situations within a fraction of a second. This ensures efficient flight. SmartBird weighs about 1 lb, has a wingspan of 6.5 ft, and only requires around 23 W of power. Electromechanical efficiency is around 45% and aerodynamic efficiency approaches 80%.

The SmartBird builds on previous Bionic Learning projects, such as the Bionic Handling Assistant, AirRay, and AirPenguin. Possible uses of the technology range from stroke-wing generators in the energy sector to actuators for automation processes.

© 2011 Penton Media, Inc.

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