Coordinated Robot Swarm Inspired by Snails

close up eye level view of a snail with a dark background

Innovation: Academia

The Chinese University of Hong Kong

Image: Victor Grabarczyk / Unsplash / Free non-commercial use

Modify Position

Many resources that living systems require for survival and reproduction constantly change in quantity, quality, and location. The same is true of the threats that face living systems. As a result, living systems have strategies to maintain access to shifting resources and to avoid changing threats by adjusting their location or orientation. Some living systems modify their position by moving from one location to another. For those that can’t change location, such as trees, they modify position by shifting in place. An example of an organism that does both is the chameleon. This creature can move from place to place to find food or escape predators. But it also can stay in one place and rotate its eyes to provide a 360-degree view so that it can hunt without frightening its prey.

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Navigate Over Land

Organisms that navigate over land must avoid obstacles and find their way from one point to another. Because land lies at the interface of the ground and air, these organisms have the opportunity to use signals transmitted through both the ground or air, rather than relying on one potential source. To take advantage of this opportunity, these organisms must have strategies attuned to diverse signals, which may travel through multiple media. An example of an organism that navigates over land is a desert ant in Tunisia that senses smells from two different directions at once, forming a “mental map” of its surroundings.

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Optimize Shape/Materials

Resources are limited and the simple act of retaining them requires resources, especially energy. Living systems must constantly balance the value of resources obtained with the costs of resources expended; failure to do so can result in death or prevent reproduction. Living systems therefore optimize, rather than maximize, resource use. Optimizing shape ultimately optimizes materials and energy. An example of such optimization can be seen in the dolphin’s body shape. It’s streamlined to reduce drag in the water due to an optimal ratio of length to diameter, as well as features on its surface that lie flat, reducing turbulence.

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Physically Assemble Structure

Living systems use physical materials to create structures to serve as protection, insulation, and other purposes. These structures can be internal (within or attached to the system itself), such as cell membranes, shells, and fur. They can also be external (detached), such as nests, burrows, cocoons, or webs. Because physical materials are limited and the energy required to gather and create new structures is costly, living systems must use both conservatively. Therefore, they optimize the structures’ size, weight, and density. For example, weaver birds use two types of vegetation to create their nests: strong, a few stiff fibers and numerous thin fibers. Combined, they make a strong, yet flexible, nest. An example of an internal structure is a bird’s bone. The bone is comprised of a mineral matrix assembled to create strong cross-supports and a tubular outer surface filled with air to minimize weight.

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Attach Temporarily

Living systems must sometimes, temporarily, stay in one place, climb or otherwise move around, or hold things together. This entails attaching temporarily with the ability to release, which minimizes energy and material use. Some living systems repeatedly attach, detach, and reattach for an extended time, such as over their lifetimes. Despite being temporary, these attachments must withstand physical and other forces until they have achieved their purpose. Therefore, living systems have adapted attachment mechanisms optimized for the amount of time or number of times they must be used. An example is the gecko, which climbs walls by attaching its toes for less than a second. Other examples include insects that attach their eggs to a leaf until they hatch, and insects whose wings temporarily attach during flight but separate after landing.

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Domed robots mimic snail locomotion and suction capabilities to move separately and join together.

Benefits

All-terrain mobility
Obstacle crossing
Reconfigurable robotic structures

Applications

Search and rescue
Environmental monitoring
Infrastructure maintenance

The Challenge

Robotic swarms, designed to perform various tasks in controlled indoor environments, frequently encounter significant limitations when deployed in outdoor, unstructured settings. Traditional designs typically rely on rigid, predefined formations and connections that lack the flexibility to adapt to unpredictable and varied terrain. Furthermore, the stability of these systems is often compromised due to the freeform connections between individual units, making them less effective in environments that demand robustness and adaptability.

In addition to physical limitations, most terrestrial robotic swarms are not designed for dynamic reconfiguration under real-world conditions, limiting their usability across different scenarios. This results in a decreased efficiency and a reduced range of tasks that such systems can handle effectively.

An illustration of snail robots moving across urban ruins.

This illustration showcases the operational versatility of the snail-inspired robots: Individually, a single robot is capable of navigating diverse outdoor terrains and scaling metal structures for surveillance tasks. In collaboration, the robots adeptly handle complex landscapes including stepped, trench-filled, and other difficult terrains. Together, they can also configure into collective structures, such as robotic arms, to manipulate objects effectively.

Innovation Details

The snail-inspired robotic swarm system revolutionizes terrestrial robotics by incorporating unique dual-mode connection mechanisms based on the biological traits of land snails. This approach enhances both adaptability and robustness, allowing for seamless operation in diverse and challenging environments.

To the versatile locomotion of snails, the system utilizes a free mode where robots are equipped with magnet-embedded tracks. These tracks provide freeform mobility, enabling the robots to adapt dynamically to their surroundings. This mode is optimized for tasks that require high maneuverability and rapid response times.

For situations that demand enhanced stability, such as navigating over rough terrain or in adverse weather conditions, the robots switch to strong mode. This mode employs vacuum suckers combined with directional stalks, which mimic the adhesive properties of a snail’s foot. This design allows for robust, secure connections between individual robots, significantly enhancing the swarm’s overall stability and resilience.

The dual-mode capability ensures that the robotic swarm can switch between high-speed, agile movements and strong, stable configurations as needed. This adaptability is critical for a wide range of applications, from environmental monitoring and agriculture to search and rescue operations.

Images comparing snail robots to the organisms that inspired their creation.

Image: Zhao, D., Luo, H., Tu, Y. et al. / Nature Communications /

a) Morphological evolution from a snail to a snail robot. b) Snails outdoors may climb onto another snail’s shell for various reasons. Inspired by this, snail robots can also interconnect with each other. c) Comparative illustration of snail foot adhesion and snail robot connection mechanism under varying external forces. (Zhao, D., Luo, H., Tu, Y. et al.)

Biological Model

Snails manage to thrive across a variety of terrains, from dry land to moist habitats, using their unique biological features.

Land snails are equipped with a muscular foot that contains glandular tissues capable of secreting mucus. This mucus plays a critical role in motion and adhesion, allowing snails to adhere to multiple surfaces—even those that are vertical or upside down. The secret lies in the texture and chemical properties of the mucus, which can be modified depending on the environmental conditions, such as surface texture and moisture levels.

The foot’s structure also features complex muscular movements that facilitate locomotion while maintaining stability and grip through various terrains. This dual capability of motion and adhesion inspired the robotic swarm’s two-mode connection mechanism: the free mode for mobility and the strong mode for enhanced stability and adhesion.

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Mucus Aids Movement

Pulmonate

The mucus produced by terrestrial slugs aids movement due to its viscoelastic nature.

over a dozen white limpets of varying sizes adhere to the side of a black rock

Biological Strategy

Tiny Mollusk Makes Adjustable Glue

Limpets

The foot of a limpet varies how tightly it attaches to tidal zone surfaces by changing its mucus composition and muscle action.

References

“The bionic design approach for the hybrid connection system demonstrates the substantial value of biomimicry in robotics. Not only does it provide a model for enhancing the stability and flexibility of freeform terrestrial robot swarms, but it also suggests a promising avenue for future research in developing connection mechanisms and strategies inspired by other elements of nature.”

Journal article

Snail-inspired robotic swarms: a hybrid connector drives collective adaptation in unstructured outdoor environments.

Nature Communications | April 29, 2024 | Zhao, D., Luo, H., Tu, Y. et al.

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