Self-Deploying Robot Wings Inspired by the Ladybird Beetle

Innovation: Academia

Seoul National University

2020

Image: Jean Beaufort / Needpix / Public Domain - No restrictions

Modify Size/Shape/Mass/Volume

Many living systems alter their physical properties, such as size, shape, mass, or volume. These modifications occur in response to the living system’s needs and/or changing environmental conditions. For example, they may do this to move more efficiently, escape predators, recover from damage, or for many other reasons. These modifications require appropriate response rates and levels. Modifying any of these properties requires materials to enable such changes, cues to make the changes, and mechanisms to control them. An example is the porcupine fish, which protects itself from predators by taking sips of water or air to inflate its body and to erect spines embedded in its skin.

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Prevent Fatigue

When materials that comprise living systems are subjected to repeated loads, they can weaken over time. This is called fatigue and it can lead to cracks and eventually failure. However, fatigue doesn’t occur just anywhere on a material; the cracks usually start in areas subjected to elevated local stresses. Therefore, living systems often employ shapes, materials, and/or smooth transitions to decrease the potential for fatigue. An example of using shape is found in brown algae, an intertidal seaweed. Rather than being bent by the constant flow forces of waves and currents, its shape causes it to be pulled. This reduces stress by roughly 800 times compared to another species that bends with the flow, ultimately reducing structural fatigue.

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Prevent Deformation

When a living system undergoes compression, tension, shear, bending, or twisting, its internal inter-molecular forces can often resist these forces and even change shape temporarily, returning to the original shape when the forces stop. However, if the force is too strong or lasts too long, permanent deformation or structural failure can occur, resulting in death. Therefore, living systems have strategies to resist deformation or help ensure limited deformation. For example, bones have thin crystals and proteinaceous fibers that provide strength and flexibility, protecting them from forces that would otherwise cause deformation on a daily basis.

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Prevent Buckling

When a living system undergoes compression to the extent that it causes structural damage, it results in buckling. For example, if a person pushes down on the top or the side of a paper cup, the cup’s wall will eventually give way, or buckle. Although a living system could add material to strengthen a structure, this requires expending precious energy. Instead, it must use energy and materials conservatively to avoid buckling, strengthening structures through careful placement of materials to resist, absorb, or deflect compressive forces. For example, instead of one long, tubular stem, some plants like bamboo have stronger nodes scattered along their stems. When compressed, these nodes keep the round stems from taking on an oval shape that weakens the structure and could result in buckling.

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Manage Mechanical Wear

A living system is subject to mechanical wear when two parts rub against each other or when the living system comes in contact with abrasive components in its environment, such as sand or coral. Some abrasive components are a constant force, such as finger joints moving, while others occur infrequently, such as a sand storm moving across a desert. Living systems protect from mechanical wear using strategies appropriate to the level and frequency of the source, such as having abrasion-resistant surfaces, replaceable parts, or lubricants. For example, human joints like shoulders and knees move against each other all day, every day. To protect from mechanical wear, a lubricant reduces friction between the cartilage and the joint.

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Winged jump-gliding robot from Seoul National University utilizes a curved vein shape that allows for self-locking.

Benefits

Increased energy efficiency
Increased performance

Applications

Aviation
Robotics

The Challenge

Jump-gliding is a specific locomotion style for robots that combines gliding and jumping movements and can increase energy efficiency and travel distance. To do this, the wings should be foldable, rapidly deployable, and resilient under aerodynamic forces. Traditional jump-gliding robots use linkages, springs, and actuators in their wings, which usually make the robot heavy and bulky, hindering their overall locomotion performance. Additionally, these wings cannot be rapidly deployed, making them unusable in certain high intensity situations.

Innovation Details

The robot was inspired by the wings of the ladybird beetle. It has a compact and lightweight wing system that is self-deployable due to a single curved joint, similar to how a tape measure is able to keep its shape. This joint stores elastic energy until released to sustain flight. The lightweight design allows the robot to travel farther, but is still sturdy enough not to buckle under large aerodynamic forces.

Illustration of ladybug-inspired origami. Photo: Baek et al./Seoul National University.

Biological Model

Ladybird beetles have deployable wings that are carefully folded beneath a stiff outer barrier. The shape of the wing joints allow the wings to rapidly spring free when needed, usually within 0.1 seconds. The wings are also very resilient and sturdy, preventing them from folding or buckling when flapping at a high frequency. The secret to these wings is a unique tape-spring-shaped vein. When a ladybird beetle folds its wings, the vein deforms, allowing elastic energy to be stored inside it. This stored energy allows the wings to be quickly and easily deployed, and also allows it to lock in place without the need for additional components.