20. Feb, 2017

Mimicking nature: bat teaches drones how to fly and navigate

Nature is full of mysteries. We still know little of starling murmurations with their ever-changing formations,  or how bats manage to navigate through dense thickets without crashing into each other. Think also of the smooth interactive arm movements of the octopus (see Blog 4 Sept 2016) or the complex flying and navigational skills that birds and bats have developed in millions year of evolution. It is not a surprise that robot engineers became fascinated by the amazing refinement of these animal skills and attempted to mimic their behavior  in their machines. Animal intelligence is of a different order than human intelligence. But surpassing in many respects the adaptive skills of Homo Sapiens, traditionally  considered as 'the marvel of Gods creation'  or -stated differently- as the species on top of cognitive evolution.  

Flight dynamics Current flying robots or drones are noisy, energy  in-efficient and can also  collide into objects or people.  Aeropace engineers  of  unmanned aerial systems now believe  that insight into the way a bird or bat move their wings or how they navigate, can help them to build  safer and more efficient flying robots.  Especially  bats have  long fascinated  both biologists and engineers with their unrivaled agility and wings that have the capability of changing shape. Bats are the only flying mammals capably of flying by wing movements. Research using high speed film of bats flying in the laboratory and mathematical analyses of their flight patterns has now  revealed some of the mysteries of their flight mechanism.  This involves several different types of joints that interlock the bones and muscles to one another, creating a musculoskeletal system that is capable of movement in more than 40 rotational directions. Its like  a human hand with long fingers with a built in wing. The bat can  change the form of its wings independently from another to make  abrupt  changes  in direction. It can also squeeze it wings against the side of its body during an upward wing beat, saving  about 35% of energy as compared with birds.

Some engineers  have  even managed  to build a robot  that  mimics the flight of bat. A recent example is Bat Bot, a self-contained robotic bat developed by researchers at Caltech and the University of Illinois at Urbana-Champaign (UIUC)*. Bat Bot  is shaped like a bat,  has a  one-foot wingspan  but weights only 93 grams. It alters the shape of it swing by flexing, extending, and twisting at its shoulders, elbows, wrists, and legs. Bat Bots creators also gave their creature special wings: an ultra-thin silicone-based membrane that simulates stretchable, thin bat wings. So instead of a drone with four spinning rotors that may damage the environment and itself, aerial  bat-inspired robots have the potential to be safer and more energy efficient than traditional drones, because their flexible wings amplify the motion of the robot’s actuator.

Navigation A different kind of  bat-like robot was recently developed at Virgina Tech. This model however was not inspired by the bat's wing movements but its refined navigational ability, in particular its echolocation system. A bat can tell how big an insect is based on the intensity of the echo. A smaller object will reflect less of the sound wave, and so will produce a less intense echo. It can also sense in which direction its prey is moving based on the pitch of the echo. If the insect is moving away from the bat, the returning echo will have a lower pitch than the original sound, while the echo from an insect moving toward the bat will have a higher pitch. This difference is due to the Doppler effect.

Learning how bats navigate through dense thickets without crashing into each other could also help unmanned aircraft designers create better vehicles. Bats use echolocation to obtain  an  spatial map of the  environment, by emitting  ultrasonic  squeeky sounds with  their mouth. The frequency of a sonar pulse changes when it reflects off an object, like a tree, a moth, or another bat. The echos are then received by their large ear and transmitted to the brain.  The sounds do not interfere with the bats hearing because they are tranformed to other frequencies,  not detectable by their hearing system but only by their brain. A very special  bat is the greater horseshoe bat (Rhinolophus ferrumequinum; see left picture above). Horseshoe bats  use their nose to produce sounds. Their flappy noseleaves make them what sonar experts call “dynamic emitters.” As the walls of these nasal megaphones deform, they alter the sounds that the bats produce. Similarly, horseshoe bats also can shift the shape of their ears at the extremely fast rate of within one-tenth of a second, allowing them to filter incoming sounds according to their needs. This in turn allows the bat to fly with incredible  speed through dense woods and bushes, avoiding every obstacle. Engineers at Virginia Tech have been observing the movements of the horsehoe bat  in the hope of achieving bat-quality sonar that could one day guide drones**. Using high-speed video, ultrasonic microphones, and laser Doppler, Mueller and his team studied the motion of the bats’ ears and noseleaves.  Based on that data, they built a digital 3D model of the bats’ noses and ears, then turned that model into a real-world prototype (see right picture above). Four motors control the rubber noseleaves and ears, and Mueller says ''they move almost as quickly as the real thing''.