The "Optical Flow" of Insects Provides a Path to Accelerometer-Free Autonomous Micro Drones
Investigating how insects known down from up may have led to a breakthrough in micro drone stabilization technology.
Researchers at the Delft University of Technology and Aix-Marseille University have investigated how insects can tell which is up — in order to develop a drone that can do the same without the need for an accelerometer.
"Attitude control is an essential flight capability," the team explains of the heart of its work. "Whereas flying robots commonly rely on accelerometers for estimating attitude, flying insects lack an unambiguous sense of gravity. Despite the established role of several sense organs in attitude stabilization, the dependence of flying insects on an internal gravity direction estimate remains unclear."
Insects aren't blessed with unlimited senses, which gave the team somewhere to being with its research. They soon discounted several possibilities: the insects' legs can feel the impact of gravity while pushing against the ground but not in the air, ruling out the sense of touch; flight involves acceleration in multiple directions with forces that greatly exceed that of gravity, so that's no help; and organs capable of operating in a similar way to gyroscopes can help with stabilization but not provide absolute angle of attitude.
Finally, the team decided it may be related to optical flow, the perception of movement relative to the environment, when combined with a model that predicts how the insect should move. In testing, the researchers found that such an approach provided the direction of gravity almost every time — except for what they call "rare and specific" edge cases, such as when the insect is completely immobile.
The concept was the applied to an insect-inspired drone with flapping wings. While the drone was moving, it proved able to determine up from down without difficulty — and during the periods when it was still enough to forget which way is up, the resulting instability resulted in enough motion to remind it again. In operation, the drone appears to oscillate slightly — in a manner the team found "reminiscent of insect flight."
While the research may have suggested a path for understanding the sense of gravity in insects, it also has the potential to assist with autonomous drone projects too — reducing the payload of ultra-compact micro drones by removing the need to fit an accelerometer.
The team's work has been published in the journal Nature under open-access terms.
Main article image courtesy of Christophe De Wagter/TU Delft.