The Biomimetics & Dextrous Manipulation Laboratory at Stanford University has come up with what they call the 'Perching Project'. It's trying to produce a series of MAV's (micro aerial vehicles) for reconnaissance and surveillance. The vision of the designer is stated thus:
A flock of small, unmanned air vehicles flies quietly into a city, maneuvering among the buildings. They communicate as they search for places to land, not on streets or flat rooftops but on the sides of buildings and under the eaves, where they can cling, bat or insect-like, in safety and obscurity. Upon identifying landing sites, each flier turns toward a wall, executes an intentional stall and, as it begins to fall, attaches itself using feet equipped with miniature spines that engage small asperities on the surface. Using its propeller in combination with its limbs, the flier can creep along the wall and reorient for a better view. With opposed pairs of spines, the flier clings tenaciously to resist gusts of wind and ride out inclement weather. The fliers stay attached for hours or days, consuming little power and emitting no sound as they monitor the area. When finished, they launch themselves with a jump and become airborne again, ready for their next mission.
Ares reports on the project:
Stanford's testbed is a Flatana RC aeroplane with a powerful electric motor (giving an aerobatic capability that comes in handy), Paparazzi autopilot, three-axis inertial sensors, and an ultrasound sensor to detect the wall. The jointed landing legs have a foam "hip", short balsa/carbon "femur" and long carbonfiber "tibia". Each of the feet has five microspines, or "toes".
On sensing the wall, the aircraft pitches up to reduce speed and shuts down the motor to protect the propeller. The highly compliant, highly damped suspension both absorbs the remaining kinetic energy and directs the forces to the feet to engage the microspines on small bumps or pits in the brick, concrete, stucco or wood, allowing the aircraft to cling to the vertical surface.
To take off, the microspines are retracted electrically, the aircraft drops, the motor starts and it hovers briefly before transitioning to forward flight.
For a more efficient MAV with lower thrust-to-weight ratio, Stanford is looking at using a pigeon-inspired jump maneuver to get the aircraft off the wall and airborne.
Work is already being done on MAVs that can land and crawl on horizontal surfaces, but Stanford wants to develop the capablity to maneuver on sloped and vertical surfaces to reposition the vehicle. An example of a flying/crawling MAV is the Micro Air-Land Vehicle (MALV) developed by the University of Florida by equipping its hand-launched micro-UAV with "Whegs" (wheeled legs) developed by Case Western Reserve University.
The way ahead is shown by the SpinyBot developed by Stanford and now under development by Boston Dynamics as the RiSE climbing robot, which has six legs tipped by micro-claws.
There's more at the link.
The video below shows how the MAV works, including a fascinating close-up look at its 'toes' that grip the wall upon landing.
It's a very interesting development . . . also a bit creepy. In the not too distant future, if one sees what one thinks is an insect settling on a wall nearby, it might not be an insect at all - it might be relaying audio and video data back to a controller!