A Self-Righting Mechanism for Autonomous Robots Inspired by Click Beetles (Elateridae)

Nature’s Inspirations

Many biological systems, including arthropods and plants, have evolved power amplified mechanisms to achieve extremely high accelerations when locomoting, striking, or projecting body elements. As no muscle can generate such fast motions, these systems use a combination of latches and bio-mechanical springs to store energy slowly and release it very quickly. Click beetles have evolved a clicking mechanism based on power amplification principles. When the body is unconstrained, the clicking motion may result in a legless jump. They initiate the movement by flexing and bracing their body (see Figure bellow). Thanks to a mechanical latch situated in the beetle’s thoracic hinge, this braced position is maintained while the energy is transferred from the muscles to the bio-mechanical springs. Then the latch is disengaged and the stored energy is released almost instantaneously.

Engineering Challenges

Harvesting and releasing energy quickly in a robust and consistent manner is a major challenge for  small robots. Current actuators, specially at small scales, are not able to generate accelerations in the order of magnitude of 102– 107m/s2 and release energy in less than 1 milli-seconds. This limits robots’ agility and adaptability capacities. Enabling robots to achieve high accelerations repeatedly will allow for improved  locomotion autonomy (i.e. ability to traverse unknown and unstructured terrains without external help).

BAM Approach

Our goal is to develop a self-righting mechanism inspired by click beetles. We focus on understanding, modeling and simulating the physics of the jump for beetles across a wide size range, while building prototypes to validate our models.

We have identified the three stages of the jump (pre-jump, take-off and airborne) by looking at the jump of 13+ species of beetles of different sizes and shapes with high speed cameras. We model and simulate the different stages using micro and macro-mechanics and dynamics models and principles.

The jump can be divided into 3 stages: the pre-jump stage, the take-off stage and the airborne stage. During the pre-jump stage, the beetle arches its body and holds this position by latching two conformal exo-skeletal structures, the peg and the mesosternal lip, while storing energy. The beetle starts releasing energy during the take-off while still being in contact with the ground and propels its center of mass upwards. Then, the beetle somersaults in the air during the airborne stage: the overall trajectory follows a ballistics motion while the body units rotate around the center of mass.

 

 

We study the morphology of the click beetle’s hinge to estimate the hinge’s stiffness using CT-scanning and Scanning Electron Microscopy (SEM). Our experimental and modeling results show that the hinge structures (peg and mesosternal lip) act as a mechanical latch. The latch allows for the braced position to be maintained during the energy storage and for the energy to be released through the springs recoil as the hinge unlocks.

 

The peg (1,2) and mesosternal lip (3,4) are two conformal structures in the hinge that latch to maintain the brace position until the elastic energy is store in the bio-mechanical springs.

This project is developed in collaboration with the Materials Tribology Laboratory, the ABC Laboratory (Dr Alleyne, Department of Entomology, University of Illinois at Urbana-Champaign). We are also grateful for the Suarez Lab and the Socha Lab (Virginia Tech) for providing helpful experimental resources and valuable technical discussions.

Publications

O. Bolmin, L. Wei, A. M. Hazel, A. C. Dunn, A. Wissa, M. Alleyne, “Latching of the click beetle (Coleoptera: Elateridae) thoracic hinge enabled by the morphology and mechanics of conformal structures“,

Bolmin, O., C. Duan, L. Urrutia, A. Abdulla, A. Hazel, M. Alleyne, A. Dunn, and A. Wissa, “Pop! Observing and Modeling the Legless Self-righting Jumping Mechanism of Click Beetles,” The 6th International Conference on Biomimetic and Biohybrid Machines 2017, Stanford, CA. DOI: 10.1007/978-3-319-63537-8_4

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