Caterpillars are able to crawl across a wide variety of surfaces, they can move in any orientation, and they're highly flexible – all traits that would also make for good soft-bodied robots. With that in mind, scientists have recently taken an interesting approach to analyzing just how the creatures move.
Ordinarily, when tracking the gait of an animal, optical markers can be placed on points of articulation such as the knees or ankles. Those markers are subsequently followed by a motion-tracking camera. Caterpillars lack joints, however, so how do you track them?
Working with Prof. Barry Trimmer, Tufts University postdoctoral researcher Guy Levy decided to trying stitching a series of tiny retroreflective markers directly onto the cuticle (outer skin layer) of a tobacco hornworm caterpillar (Manduca sexta). He did so as it was anaesthetized. A total of six markers were attached – one at either end of the body, and one above each of four "prolegs" on one side of the creature's body.
The idea was that commercially-available Vicon motion-tracking cameras would be able to detect those markers, and thus ascertain the caterpillar's movement patterns. Unfortunately, though, the animal's shiny cuticle kept the reflective markers from adequately standing out for the camera.
Levy and Trimmer proceeded to replace those markers with minuscule LEDs – seen above – which emit infrared light. Each of the LEDs measures just 0.3 x 0.3 mm (a larger version was unsuccessfully tried first), and are electrically linked to a power source using thin interconnecting strands of copper wire.
When the caterpillar was placed on a rotating circular treadmill, the setup allowed its movements to be finely tracked using an array of five computer-connected Vicon cameras. It is now hoped that the technology could ultimately lead to bioinspired systems of locomotion for soft-bodied robots, or similar technologies.
Levy will be presenting the research later this month in Tampa, Florida, at the meeting of the Society for Integrative and Comparative Biology.
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