DOI: 10.5061/dryad.3bk3j9ktv
title: Data from: A rapid-response soft end effector inspired by the hummingbird beak

description: Biology is a wellspring of inspiration in engineering design. This paper
 delves into the application of elastic instabilities-commonly used in
 biological systems to facilitate swift movement as a power-amplification
 mechanism for soft robots. Specifically, inspired by the nonlinear
 mechanics of the hummingbird beak and shedding further light on it, we
 design, build, and test a novel, rapid-response, soft end effector. The
 hummingbird beak embodies the capacity for swift movement, achieving
 closure in less than 10 ms. Previous work demonstrated that rapid movement
 is achieved through snap-through deformations, induced by muscular
 actuation of the beak's root. Using nonlinear finite element
 simulations coupled with continuation algorithms, we unveil a
 representative portion of the equilibrium manifold of the beak-inspired
 structure. The exploration involves the application of a sequence of
 rotations as exerted by the hummingbird muscles. Specific emphasis is
 placed on pinpointing and tailoring the position along the manifold of the
 saddle-node bifurcation at which the onset of elastic instability triggers
 dynamic snap-through. We show the critical importance of the intermediate
 rotation input in the sequence, as it results in the accumulation of
 elastic energy that is then explosively released as kinetic energy upon
 snap-through. Informed by our numerical studies, we conduct experimental
 testing on a prototype end effector fabricated using a compliant material
 (thermoplastic polyurethane). The experimental results support the trends
 observed in the numerical simulations and demonstrate the effectiveness of
 the bio-inspired design. Specifically, we measure the energy transferred
 by the soft end effector to a pendulum, varying the input levels in the
 sequence of prescribed rotations. Additionally, we demonstrate a potential
 robotic application in scenarios demanding explosive action. From a
 mechanics perspective, our work sheds light on how pre-stress fields can
 enable swift movement in soft robotic systems with the potential to
 facilitate high input-to-output energy efficiency.
description: This document outlines how the data in this repository is structured. The
 software required to run the files in the repository is: * Matlab *  MP4
 player (for instance, VLC media player) The folders in the repository are
 structured as follows. 1. The folder "Figures" contains the
 Matlab plots that have been used for the figures in the paper. All Matlab
 .fig files can be opened with Matlab and the curves copied then elsewhere.
 The data from each of the figures can also be extracted from the plots by
 accessing the object fields directly. See the Mathworks help pages for
 more details. For example, see here:
 [https://uk.mathworks.com/matlabcentral/answers/2951-extracting-data-series-from-fig-file](https://uk.mathworks.com/matlabcentral/answers/2951-extracting-data-series-from-fig-file) 2. The folder "Video" contains the videos shot during the test or made based on the continuous photos taken during the test. The formats of the videos are '.mp4' and '.m4v'. The folder contains two additional folders: i) MechanicalTestingFEVerification: the vidoes show the mechanical testing on the sensitivity study of pre-rotation on the response of the beak structure. The folder contains six additional folders: a) Pre-Rotation0.25: Videos for the pre-rotation being 0.25. b) Pre-Rotation0.3: Videos for the pre-rotation being 0.3. c) Pre-Rotation0.35: Videos for the pre-rotation being 0.35. d) Pre-Rotation0.4: Videos for the pre-rotation being 0.4. e) Pre-Rotation0.45: Videos for the pre-rotation being 0.45. f) Pre-Rotation0.5: Videos for the pre-rotation being 0.5. ii) BallThrower: the vidoes shows the beak-inspired catapult. 3. The folder 'stl' folder contains the `.stl' file for the beak model we used in the study. Jiajia Shen, Martin Garrad, Qicheng Zhang, Vico Chun Hei Wong, Alberto Pirrera, Rainer M. J. Groh