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Skins with asymmetric kirigami scales and soft spikes are integrated to the surface of a base self‐burrowing robot, which consists of a soft one‐segment extending actuator. Friction anisotropy is observed at the interfaces between the burrowing robots and different granular materials. Its effects on the pulling resistance and burrowing characteristics are studied. The results demonstrate that the development of friction and friction anisotropy is affected by the characteristics of the granular material, the asymmetric skins, and the relative size of the asymmetric features to the granular particles. Robots with scales or spikes aligned along the upward direction burrow faster than those aligned against the upward direction, especially in relatively coarser granular materials. Particle image velocimetry analysis on the particle displacement fields around the actuator reveals the complexity of dry granular material interactions with soft robots, implying that aligned scales or spikes can impact the distribution of friction preferentially, opening up many possibilities for thoughtful material and geometry‐based manipulation of friction in the design and optimization of future soft burrowing robots for more versatile locomotion capabilities.
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Fundamentals of burrowing in soft animals and robots
Creating burrows through natural soils and sediments is a problem that evolution has solved numerous times, yet burrowing locomotion is challenging for biomimetic robots. As for every type of locomotion, forward thrust must overcome resistance forces. In burrowing, these forces will depend on the sediment mechanical properties that can vary with grain size and packing density, water saturation, organic matter and depth. The burrower typically cannot change these environmental properties, but can employ common strategies to move through a range of sediments. Here we propose four challenges for burrowers to solve. First, the burrower has to create space in a solid substrate, overcoming resistance by e.g., excavation, fracture, compression, or fluidization. Second, the burrower needs to locomote into the confined space . A compliant body helps fit into the possibly irregular space, but reaching the new space requires non-rigid kinematics such as longitudinal extension through peristalsis, unbending, or eversion. Third, to generate the required thrust to overcome resistance, the burrower needs to anchor within the burrow . Anchoring can be achieved through anisotropic friction or radial expansion, or both. Fourth, the burrower must sense and navigate to adapt the burrow shape to avoid or access different parts of the environment. Our hope is that by breaking the complexity of burrowing into these component challenges, engineers will be better able to learn from biology, since animal performance tends to exceed that of their robotic counterparts. Since body size strongly affects space creation, scaling may be a limiting factor for burrowing robotics, which are typically built at larger scales. Small robots are becoming increasingly feasible, and larger robots with non-biologically-inspired anteriors (or that traverse pre-existing tunnels) can benefit from a deeper understanding of the breadth of biological solutions in current literature and to be explored by continued research.
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- Award ID(s):
- 2047330
- PAR ID:
- 10412045
- Date Published:
- Journal Name:
- Frontiers in Robotics and AI
- Volume:
- 10
- ISSN:
- 2296-9144
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3389/frobt.2023.1057876
