While wheels or treads are easier to design and control, multi-legged robots, in particular, could traverse far more complex terrains with greater robustness and maneuverability, making them valuable for various exploratory and autonomous applications. In regard to implementing legs, animals, and insects, in particular, provide excellent models for legged locomotion over difficult terrains.
Now, researchers are studying real and robotic insects to better understand how they sense forces in their limbs while walking. The research could provide new insights into insects’ biomechanics and neural dynamics and inform new applications for large-legged robots.
The team studied the role of force sensors in walking insects because these sensors are critical for successful locomotion. Called Campaniform sensilla (CS), these sensors are a class of mechanoreceptors found in the limbs of insects that respond to local stress and strain within the animal’s cuticle – providing important information for controlling locomotion. Similar force receptors exist in mammals suggesting that understanding the role of these force sensors in insects may also provide new insights into their functions in vertebrates such as humans.
The benefits of building robotic models over computer models include more realistic modeling of friction between moving parts and the inclusion of delays to send neural signals. Robotic limbs are even better than animal models as they can record the sending and receiving of every single signal and resulting mechanical actions.
“Walking is an inherently mechanical task, so understanding the neural control of walking requires simultaneously investigating mechanics and neural control,” says Dr. Szczecinski, an assistant professor in the Department of Mechanical and Aerospace Engineering in the Statler College of Engineering and Mineral Resources at West Virginia University, USA. “Properly functioning walking robots can serve as prototypes for machines that could help people farm in extreme terrains, explore other planets, or walk through forests to monitor their health.”
Dr. Szczecinski has two main research robots. The first is a biomimetic hexapod robot with legs designed based on the Common fruit fly, Drosophila melanogaster. It enabled the team to capture a complete picture of how campaniform sensilla monitors forces while walking. The other one is a single-legged robot, which allows for a simplified simulation of the sensory experience of one insect leg while walking.
Researchers also explore the role of CS in real insects by isolating their limbs and monitoring sensory pathways with electrodes when different forces are applied. These recorded sensory signals are then used to develop models for the robotic legs.
“By recording their response to many different signals, we can paint a clearer picture of how they convert forces into neural activity,” says Dr Szczecinski. “We use many different stimuli because the CS are highly dynamic and are always adapting to the applied forces.”
The team found strong correlations between their real insects and robotic counterparts through their research. “We find that for every insect species we check, our model is equally well equipped to describe the way the CS turn forces into neural activity,” says Dr Szczecinski. “This suggests that each species’ organs are broadly functioning in the same way.”