Robots Based on Arthropod Design
Posted February 1, 1998
A cockroach scurries into a crevice. A walking stick creeps slowly up to its prey and pounces. A crab scuttles quickly into a tide pool. Scientists would like their
mechanical robots to be as nimble and well balanced as these arthropods. A robot with such precise balance would be useful for investigations in dangerous areas such as toxic waste sites,
and for exploring difficult terrain such as craters on the moon and Mars. Military applications include crablike robots that could hunt for mines on beaches.
Insects, arachnids, and crustaceans have specialized organs in their legs that detect tiny deformations, or strains, in their exoskeletons. In mathematical terms,
strain is the ratio of the change in the length of an object to its original length. In man-made machines, such as bathroom scales, strain gauges consist of metal foil or flexible semiconductors.
When a person steps on the scale, a mechanical beam is distorted. A strain gauge attached to the beam transforms the beam's deformation into an electrical signal. This signal is displayed
as a readout of pounds or kilograms on a digital scale. In the same way, arthropods have strain gauge organs in their legs that measure strain and help regulate walking movements.
By studying the strain gauges of arthropods, scientists hope to be able to manufacture more effective strain gauges and more agile robots. Spiders, crabs, and insects
bear these sense organs just below the exoskeleton or cuticle, mainly on the legs. Each organ is attached to a sensory nerve, which is deformed as the animal moves. Strain gauge organs
are as sensitive to displacement as the receptors in the human ear are to sound.
Studies of spiders show that strain gauge organs control and direct movement. Spiders are disoriented when strain gauge organs near leg joints are destroyed. Tropical
wandering spiders are nocturnal hunters. When they have successfully captured prey, such as a fly, in a certain area, they remember the spot and return to it to look for more prey. Tropical
wandering spiders without strain organs in their legs attempting to return to the capture site start off by walking in the wrong direction. They do not correct their direction, and thus
they miss their targets. Control spiders with intact strain organs find their prey even when their eyes are covered. Strain gauge organs clearly play a role in helping spiders remember
locations in a process that is not yet clearly understood.
Zill, Sasha N. and Ernst-August Seyfarth. "Exoskeletal Sensors for Walking," Scientific American, July 1996, pp. 86-90.