Ian Connellan
If you’ve watched a butterfly fluttering around your garden, you’ll know that flying insects have evolved efficient strategies for navigating around their natural environments.
Yet it’s these traits that make studying them in an experimental setting difficult. They’re generally very small, and they fly and manoeuvre at relatively high speeds. Studies have, until now, been limited to observation of tethered or hovering flights, or restricted flights in confined laboratory chambers.
But research just published in Science Robotics rather changes the game. A French engineering team led by Rémi Pannequin, from the Université de Lorraine, has built a remarkable mini-lab to closely study insect flight.
The fast-moving lab – dubbed “lab-on-cables” – bears some resemblance to the cable-operated “spidercams” that are commonly seen in sports stadia. It consists of high-speed cameras mounted on a cube-shaped frame suspended on cables and it can follow tiny, speedy bugs in three dimensions as they fly.
The lab has provided Pannequin and his colleagues with close-up observations of the flight motion of the two-centimetre-long black cutworm moth (Agrotis ipsilon), leading to a greater understanding of the insect’s flight.
Flying insects employ various strategies in mastering flight that would be useful to replicate in robotics, and it’s hoped that learning more about these strategies has the potential to inform the design of faster and more agile flying robots.
The thing to overcome is the difficulty tracking insects in flight because of their speed and size.
Past experiments have featured insects tethered to a fixed point and provided with pollen sources – such as flowers – to encourage hovering. Insects have also been loaded with miniature flight-recording devices. These approaches yielded limited success because they restrained the free-flying capabilities of the insects.
Seeking to overcome these limitations, Pannequin developed the rapidly moving, cable-suspended lab that allows the target insect to move freely within an open space without encumbrance to slow or hamper its speed.
A program that anticipates the insect’s flight patterns and future directions controls the motion of the lab-on-cables, while minimising tracking errors using real-time data on the relative positions of both the insect and the lab frame.
The researchers first validated the performance of the lab-on-cables in simulated experiments using the previously recorded fruit fly, mosquito, and moth flight trajectories. They then ran flight tests with 32 black cutworm moths flying freely at speeds of up to three meters per second. High-speed cameras directly mounted on the lab frame collected a plethora of visual data as the lab moved automatically with the insect.
The researchers extracted flight kinematics data by analysing the recorded video with 3D computer graphics software, enabling them to separate features such as wingbeat frequency, wing-flapping angles, and the position and rotation of the insect’s body and wings.
Additional on-board sensors could be used in future prototypes to assess chemically controlled flight behavior, the authors say.
Credit: Pannequin et al., Sci Robot. 5, eabb2890 (2020)