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Abstract
A body in motion tends to stay in motion but is often slowed by friction. Here we investigate the friction experienced by centimeter-sized bodies sliding on water. We show that their motion is dominated by skin friction due to the boundary layer that forms in the fluid beneath the body. We develop a simple model that considers the boundary layer as quasi-steady, and is able to capture the experimental behaviour for a range of body sizes, masses, shapes and fluid viscosities. Furthermore, we demonstrate that friction can be reduced by modification of the body's shape or bottom topography. Our results are significant for understanding natural and artificial bodies moving at the air-water interface, and can inform the design of aerial-aquatic microrobots for environmental exploration and monitoring.
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Affiliation(s)
- Giuseppe Pucci
- Brown University, School of Engineering, 184 Hope St., Providence, (RI), United States
| | - Ian Ho
- Brown University, School of Engineering, 184 Hope St., Providence, (RI), United States
| | - Daniel M Harris
- Brown University, School of Engineering, 184 Hope St., Providence, (RI), United States.
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Chen Y, Doshi N, Goldberg B, Wang H, Wood RJ. Controllable water surface to underwater transition through electrowetting in a hybrid terrestrial-aquatic microrobot. Nat Commun 2018; 9:2495. [PMID: 29950597 PMCID: PMC6021446 DOI: 10.1038/s41467-018-04855-9] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2018] [Accepted: 05/25/2018] [Indexed: 11/09/2022] Open
Abstract
Several animal species demonstrate remarkable locomotive capabilities on land, on water, and under water. A hybrid terrestrial-aquatic robot with similar capabilities requires multimodal locomotive strategies that reconcile the constraints imposed by the different environments. Here we report the development of a 1.6 g quadrupedal microrobot that can walk on land, swim on water, and transition between the two. This robot utilizes a combination of surface tension and buoyancy to support its weight and generates differential drag using passive flaps to swim forward and turn. Electrowetting is used to break the water surface and transition into water by reducing the contact angle, and subsequently inducing spontaneous wetting. Finally, several design modifications help the robot overcome surface tension and climb a modest incline to transition back onto land. Our results show that microrobots can demonstrate unique locomotive capabilities by leveraging their small size, mesoscale fabrication methods, and surface effects.
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Affiliation(s)
- Yufeng Chen
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA.
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA, 02138, USA.
| | - Neel Doshi
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA, 02138, USA
| | - Benjamin Goldberg
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA, 02138, USA
| | - Hongqiang Wang
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA, 02138, USA
| | - Robert J Wood
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA.
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA, 02138, USA.
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Ortega-Jimenez VM, von Rabenau L, Dudley R. Escape jumping by three age-classes of water striders from smooth, wavy and bubbling water surfaces. J Exp Biol 2017; 220:2809-2815. [PMID: 28546506 DOI: 10.1242/jeb.157172] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Accepted: 05/19/2017] [Indexed: 11/20/2022]
Abstract
Surface roughness is a ubiquitous phenomenon in both oceanic and terrestrial waters. For insects that live at the air-water interface, such as water striders, non-linear and multi-scale perturbations produce dynamic surface deformations which may impair locomotion. We studied escape jumps of adults, juveniles and first-instar larvae of the water strider Aquarius remigis on smooth, wave-dominated and bubble-dominated water surfaces. Effects of substrate on takeoff jumps were substantial, with significant reductions in takeoff angles, peak translational speeds, attained heights and power expenditure on more perturbed water surfaces. Age effects were similarly pronounced, with the first-instar larvae experiencing the greatest degradation in performance; age-by-treatment effects were also significant for many kinematic variables. Although commonplace in nature, perturbed water surfaces thus have significant and age-dependent effects on water strider locomotion, and on behavior more generally of surface-dwelling insects.
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Affiliation(s)
| | - Lisa von Rabenau
- Department of Mechanical Engineering, University of California, Berkeley, CA 94720, USA
| | - Robert Dudley
- Department of Integrative Biology, University of California, Berkeley, CA 94720, USA.,Smithsonian Tropical Research Institute, Balboa, Republic of Panama
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Yan JH, Zhang XB, Zhao J, Liu GF, Cai HG, Pan QM. A miniature surface tension-driven robot using spatially elliptical moving legs to mimic a water strider's locomotion. BIOINSPIRATION & BIOMIMETICS 2015; 10:046016. [PMID: 26241519 DOI: 10.1088/1748-3190/10/4/046016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The highly agile and efficient water-surface locomotion of the water strider has stimulated substantial interest in biomimetic research. In this paper, we propose a new miniature surface tension-driven robot inspired by the water strider. A key feature of this robot is that its actuating leg possesses an ellipse-like spatial trajectory similar to that of a water strider by using a cam-link mechanism. Simplified models are presented to discuss the leg-water interactions as well as critical conditions for a leg penetrating the water surface, and simulations are performed on the robot's dynamic properties. The final fabricated robot weighs about 3.9 g, and can freely and stably walk on water at different gaits. The maximum forward and turning speeds of the robot are measured as 16 cm s(-1) and 23°/s, respectively. Furthermore, a similarity analysis with Bond number and Weber number demonstrates that the locomotion of this robot is quite analogous to that of a real water strider: the surface tension force dominates the lifting force and plays a major role in the propulsion force. This miniature surface tension-driven robot might have potential applications in many areas such as water quality monitoring and aquatic search and rescue.
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Affiliation(s)
- J H Yan
- State Key Laboratory of Robotics and System, Harbin Institute of Technology, Harbin 150080, People's Republic of China
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