A Flapped Paddle-Fin for Improving Underwater Propulsive Efficiency of Oscillatory Actuation

Simha, Ashutosh; Gkliva, Roza; Kotta, Ülle; Kruusmaa, Maarja

doi:10.1109/lra.2020.2975747

Cited by 15 publications

(9 citation statements)

References 33 publications

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“…Animals including insects [7,17], turtles [8,18], otters [9], and salamanders [19] have been a source of inspiration for amphibious robots. Arthropods, such as crabs and lobsters, have many desirable traits that can improve the way robots can traverse in sandy environments.…”

Section: Introductionmentioning

confidence: 99%

Dactyls and inward gripping stance for amphibious crab-like robots on sand

2021

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Sandy beaches are areas that challenge robots of all sizes, especially smaller scale robots. Sand can hinder locomotion and waves apply hydrodynamic forces which can displace, reorient, or even invert the robot. Crab-like legs and gaits are well suited for this environment and could be used as inspiration for an improved design of robots operating in this terrain. Tapered, curved feet (similar to crab dactyl shape) paired with a distributed inward gripping method are hypothesized to enable better anchoring in sand to resist hydrodynamic forces. This work demonstrates that crab-like legs can withstand vertical forces that are larger than the body weight (e.g. in submerged sand, the force required to lift the robot can be up to 138% of the robot weight). Such legs help the robot hold its place against hydrodynamic forces imparted by waves (e.g. compared to displacement of 42.7 mm with the original feet, crab-like feet reduced displacement to 1.6 mm in lab wave tests). These feet are compatible with walking on sandy and rocky terrain (tested at three speeds: slow, medium, and fast), albeit at reduced speeds from traditional feet. This work shows potential for future robots to utilize tapered and curved feet to traverse challenging surf zone terrain where biological crabs thrive.

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Section: Introductionmentioning

confidence: 99%

Dactyls and inward gripping stance for amphibious crab-like robots on sand

2021

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“…The efficiency metric η, shows that this actuator performs worse than previous prototypes designed exclusively for aquatic locomotion [38], [39], mainly due to reduced force generation. While further optimization of the actuator's morphology, motion planning and control can improve this metric, we recognize that the reduced performance is a tradeoff that enables locomotion in terrestrial conditions.…”

Section: Resultsmentioning

confidence: 93%

Soft Fluidic Actuator for Locomotion in Multi-Phase Environments

Gkliva

Kruusmaa

2022

IEEE Robot. Autom. Lett.

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This letter presents the design, development, and experimental assessment of a soft fluidic actuator that can enable locomotion in a variety of aquatic and terrestrial environments. Most actuation strategies for amphibious locomotion rely on rigid, fast moving components to generate thrust and tractive forces. Our prototype, comprising soft materials, and relying on simple motion planning and control strategies, demonstrates two gaits, that we employ for locomotion in two vastly different scenarios, underwater swimming and moving on granular terrain with varying levels of water content. By adjusting its internal pressure, the actuator dynamically varies its stiffness and shape, and transitions between wheel and soft paddle form. Experimental results of locomotion in controlled laboratory conditions serve as proof-of-concept for the proposed actuator's efficacy. Using two different motion patterns and control schemes, we show that this prototype achieves both thrust and tractive forces.

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“…[45] Another key characteristics of the paddle was twenty passive flaps to further reduce the drag during recovery stroke; 12 pieces and 8 pieces were integrated onto SP and SL, respectively (Figure 2c,d). Although such passive flap was already proposed in ref., [25,26,29] the integrated design of passive flaps, flexural joints, and sliding-based variable stiffness mechanism into a single paddle was firstly proposed in this work. The functionality of flexural joints and passive flaps are explored in Section 3.1.…”

Section: Design and Working Principlementioning

confidence: 99%

“…Whereas, inhibiting the anterior side deformation is required during power stroke to maintain large surface areas of the propulsors. Although this drag-powered rowing was studied in many previous works, [8,10,12,21,22,[25][26][27][28][29][30] only handful of robots had employed stiffness-adjustable propulsors in aquatic rowing. [12,21,22] Due to the tethered power cables, however, the robot was unable to perform free swimming in underwater.…”

Section: Introductionmentioning

confidence: 99%

“…First, a novel stiffness-adjustable paddle cascaded with dozens of passive flaps for aquatic rowing is developed. Although three main components of the proposed paddle 1) sliding laminatebased variable stiffness, [24,32] 2) film flexural joint with mechanical stopper; [8] and 3) passive flap for extra drag reduction during recovery stroke) [25,26,29] were already addressed from previous studies, this article newly introduced the fabrication method of integrating all these components into a monolithic structure. Secondly, a non-tethered swimming robot propelled by a bilateral pair of paddles is developed to demonstrate the advantage of stiffness change in frequency-varying swimming.…”

Section: Introductionmentioning

confidence: 99%

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Development of a Stiffness‐Adjustable Articulated Paddle and its Application to a Swimming Robot

Kwak

Choi

Bae

2023

Advanced Intelligent Systems

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Stiffness of a swimming appendage is the key mediator between thrust generated and its beating frequency. Due to the advantageous role of flexible propulsors, they are widely adopted in previous swimming robots. As an optimal propulsor, stiffness is highly dependent on its beating frequency, and stiffness modulation is crucial when a robot is swimming with multiple beating frequencies. Herein, a novel swimming paddle that can switch two different stiffness states by sliding a laminate inside and its application to a swimming robot is studied. This paddle has 8 articulated joints and 20 passive flaps to achieve drag asymmetry with minimum control effort. A semiempirical model to estimate the stiffness change in good accuracy is also studied. The thrust modulation caused by stiffness change is comprehensively studied by varying frequency and range of motion. In addition, a nontethered swimming robot propelled by a bilateral pair of paddles is developed to investigate when and how the stiffness adjustment is useful. There is a threshold frequency dividing two regimes where one stiffness excels the other stiffness with respect to cost of transport. Finally, it is shown that the paddle thickness is closely related to the necessity of stiffness change mechanism.

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A Flapped Paddle-Fin for Improving Underwater Propulsive Efficiency of Oscillatory Actuation

Cited by 15 publications

References 33 publications

Dactyls and inward gripping stance for amphibious crab-like robots on sand

Dactyls and inward gripping stance for amphibious crab-like robots on sand

Soft Fluidic Actuator for Locomotion in Multi-Phase Environments

Development of a Stiffness‐Adjustable Articulated Paddle and its Application to a Swimming Robot

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