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Open AccessArticle

Control strategies of gecko’s toe in response to reduced gravity

1
Special Robot Research Center, Hefei CSG Smart Robot Technology Co., Ltd., Hefei 230088, China
2
Special Robot Research Center, CSG Smart Science & Technology Co., Ltd., Shanghai 201619, China
3
Institute of Bio-inspired Structure and Surface Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
4
Department Functional Morphology and Biomechanics, Zoological Institute of the University of Kiel, Kiel 24118, Germany
*
Author to whom correspondence should be addressed.
Appl. Sci. 2020, 10(7), 2257; https://doi.org/10.3390/app10072257
Received: 7 March 2020 / Revised: 24 March 2020 / Accepted: 24 March 2020 / Published: 26 March 2020
Shear-induced adhesion is one of the key properties for the gecko moving safely and quickly in a three-dimensional environment. The control strategies of such locomotion strongly relying on adhesion are still not well understood. In this study, we measured foot alignment and three-dimensional reaction forces of the single toes of the Tokay gecko running on the ground freely (gravity condition) and running in a situation where the gravity force was counterbalanced (reduced gravity condition). The forelimb rotated from the outward position to the front-facing position and the hindlimb rotated from the outward position to the rear-facing position, when running with balanced force, which indicated that the adhesive system was employed behaviorally through the modulation of the foot alignment. The toe was compressed and pulled in the gravity condition, but it was tensed and pulled in the reduced gravity condition. There was an approximately linear relationship between peak normal forces and the corresponding shear forces in both the reduced gravity condition (FN = −0.40FS − 0.008) and the gravity condition (FN = 2.70FS − 0.12). The footpad was compressed and pushed in the gravity condition, whereas it was tensed and pulled in the reduced gravity condition. There was an approximately linear relationship between peak normal forces and the corresponding shear forces in both the reduced gravity condition (FN = −0.39FS − 0.001) and in the gravity condition (FN = −2.80FS − 0.08). The shear-induced adhesion of the gecko footpad is controlled by the coupling of the normal force and shear forces: that is why in this system adhesion was shear-sensitive and friction was load-sensitive. Our measurements of single toe reaction forces also show that geckos control their footpad attachment using ‘toe rolling-in and gripping’ motion in both gravity and reduced gravity conditions. View Full-Text
Keywords: control strategies; reduced gravity; adhesion; reaction forces control strategies; reduced gravity; adhesion; reaction forces
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Wang, Z.; Gorb, S.N.; Dai, Z. Control strategies of gecko’s toe in response to reduced gravity. Appl. Sci. 2020, 10, 2257.

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