Biomechanics of gecko locomotion: the patterns of reaction forces on inverted, vertical and horizontal substrates

Abstract

The excellent locomotion ability of geckos on various rough and/or inclined substrates has attracted scientists' attention for centuries. However, the moving ability of gecko-mimicking robots on various inclined surfaces still lags far behind that of geckos, mainly because our understanding of how geckos govern their locomotion is still very poor. To reveal the fundamental mechanism of gecko locomotion and also to facilitate the design of gecko-mimicking robots, we have measured the reaction forces (RFs) acting on each individual foot of moving geckos on inverted, vertical and horizontal substrates (i.e. ceiling, wall and floor), have associated the RFs with locomotion behaviors by using high-speed camera, and have presented the relationships of the force components with patterns of reaction forces (PRFs). Geckos generate different PRF on ceiling, wall and floor, that is, the PRF is determined by the angles between the direction of gravity and the substrate on which geckos move. On the ceiling, geckos produce reversed shear forces acting on the front and hind feet, which pull away from the body in both lateral and fore-aft directions. They use a very large supporting angle from 21° to 24° to reduce the forces acting on their legs and feet. On the floor, geckos lift their bodies using a supporting angle from 76° to 78°, which not only decreases the RFs but also improves their locomotion ability. On the wall, geckos generate a reliable self-locking attachment by using a supporting angle of 14.8°, which is only about half of the critical angle of detachment.

Contribution of friction and adhesion to the reliable attachment of a gecko to smooth inclines

“…The average critical angle of the front foot on a 90° incline is approximately 104° during the movement, similar to the result obtained by Autumn et al [23]. The hindfoot is required to push away or pull towards the substrate in order to provide either a pushing or an adhesion force, respectively, in order to maintain the dynamic stability during movement [18,32], thereby leading to an r h_t value of the foot close to 1. The foot has to withstand a large internal moment during movement.…”

“…This type of frictional adhesion provides a useful means of precisely controlling the adhesive force by controlling the shear force, and enables attachment and detachment to occur using only minute forces [23]. Geckos skilfully utilize this frictional adhesion by controlling the angle of the limb, thereby pulling the foot in such a way to allow a successful climb onto inverted inclines [18]. When the incline is larger than 90°, the h value will be enlarged owing to the effect of gravity, resulting in an increase in β (Fig.…”

Bio-Inspired Adhesive Footpad for Legged Robot Climbing under Reduced Gravity: Multiple Toes Facilitate Stable Attachment

“…Biomechanics of a gecko climbing on a surface reveals the utilization of a particular Yconfiguration in both the first and fifth toes and opposite feet (Figure 2a) [20][21][22][23][24][25][26]. The opposite feet are pulling inward toward the center of mass, generating large in-plane forces to ensure the angle of pulling force vector towards the substrate remains small.…”

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

“…One fundamental property of their adhesive structures that helps to achieve a controlled, energy-efficient adhesion is the directional dependence of their adhesion. Patterns of ground reaction forces show that geckos can control attachment and detachment via shear forces, by pulling their legs towards or pushing their legs away from the body [1,4]. Separate parts of this control system seem to be established at different levels of the hierarchical organization of this adhesive system [5][6][7][8][9][10][11][12][13].…”