Gravity defying Robotic Insect

Winged flight, or simply fly-by-wire? (Image: South West News Service / Rex Features)

CREATING a free-flying robotic insect is the dearest wish of many an engineer because such a machine would have great potential in surveillance and in seeking out trapped people in search-and-rescue situations. But a curious effect might upset their plans.

Last year, a team at Harvard University released a video demonstration of a robotic fly they had developed, showing it flapping its wings and levitating up a pair of guide wires.

Fly by Wires

But Michele Milano of Arizona State University in Tempe wondered whether the wing motion was entirely responsible for giving the robot lift, or whether some other force was involved. "The video showed that the guide wires were vibrating significantly when the wings beat," he told New Scientist.

Lift without Wings

To find out if these vibrations played a role in the fly's upward motion, his team built a vibrating model "insect" with no wings. The balsa-wood contraption consisted of a motor with an off-centre weight on its spindle that produced vibrations, and four metal tubes through which vertical guide wires were threaded (see Diagram). When they set the motor running, the team discovered that the model moved up the wires despite having no wings. They've dubbed it the "flying brick".

Traveling waves

The researchers suspect that the vibrating motor sets off traveling waves in the guide wires, rather like those produced by plucking guitar strings. Each vibration cycle produces a kink in the wires above the model, which forces the model to travel upwards.

Movements of up to 5 centimetres were seen, depending on the wires' tension and the diameters of both the wires and the tubular connectors. The greatest "flight" effect was achieved when the vibration frequency matched the resonant frequency of the wires (IEEE Transactions in Robotics, vol 25, p 426).