Motion capture based on multi-camera is widely used in the quantification of animal locomotor behaviors and this is one of the main research methods to reveal the physical laws of animal locomotion and to inspire the design and realization of bionic robot. It has been found that the multi-camera layout patterns greatly affect the effect of motion capture. Due to the researches for animals of diverse species, determining the most appropriate layout patterns to achieve excellent capture performance remains an unresolved challenge. To improve the capturing accuracy, this investigation focuses on the method of multi-camera layout as a motion capture system for diverse animals with significant differences in outward appearance characteristics and locomotor behaviors. The demand boundaries of motion capture are determined according to the appearance types (shapes and space volume) and the behavior characteristics of the animals, resulting in the matching principle of the typical multi-camera layout patterns (arch, annular and half-annular) with diverse animals. The results of the calibration experiments show that the average standard deviation rate (ASDR) of multi-camera system in the half-annular layout patterns (0.52%) is apparently smaller than that of the other two patterns, while its intersecting volume is the largest among the three patterns. The ASDR at different depths of field in a half-annular layout demonstrate that the greater depth of field is conducive to improving the precision of the motion capture system. Laboratory experiments of the motion capture for small animals (geckos and spiders) employed the multi-camera system locked in the 3-D force measuring platform in a half-annular layout pattern indicate that the ASDR of them could reach less than 3.8% and their capturing deviation rate (ACDR) are respectively 3.43% and 1.74%. In this report, the correlations between the motion capture demand boundaries of small animals and the characteristics of the multi-camera layout patterns were determined to advance the motion capture experimental technology for all kinds of small animals, which can provide effective support for the understanding of animal locomotion.

Understanding how animals avoid overturning and rolling in motion to maintain movement stability and to accommodate their habitat and the mechanisms of movement in these habitats is a matter of concern. Gecko climbs a more inclined substrate by lowering the speed; meanwhile, the duty factor is increased with the increase of the incline angle, indicating that the gecko switches the diagonal gait when climbing on the shallow inclines to the triangular gait when on the inverted surface. The overturning impulse moment is increased with an increase of the incline angle. On inclines larger than 90°, the positive and negative overturning impulse moments are increased significantly and show obvious differences. The maximum value of rolling impulse moment on the surface at 180° can reach 15 times that of the minimum value on the surface at 90°, and the positive and negative rolling impulse moments at the inclined surface of 120–180° have obvious differences. The above results show that on shallow inclines, the low centre of mass and the flat posture of the gecko can effectively improve locomotion stability; simultaneously, through the timely conversion of the limb function, the overturning/rolling impulse moments are low, which greatly reduces the probability of overturning/rolling during locomotion. However, on inverted inclines, the gecko takes full advantage of the flexibility of body and limbs to delay the occurrence of rolling and overturning, and actively cooperates with the adjustment of the gait, using the alternating change of gait to avoid overturning and rolling.

Geckos can climb freely on various types of surfaces using their flexible and adhesive toes. Gecko-inspired robots are capable of climbing on different surface conditions and have shown many important applications. Nonetheless, due to poor flexibility of toes the movements of gecko-inspired robots are restricted to flat surfaces. To improve the flexibility, by utilizing design technique of soft actuator and incorporating the characteristics of a real gecko's toe, the design of new bionic soft toes is proposed. The abilities of this bionic toe are verified using modelling and two soft toes are manufactured. One is Type A toe having varied semi-circle cross-sections as the feature of real gecko toe and the other is Type B toe with a constant semi-circle cross-section. The bending behaviors of the bionic toes subjected to a range of hydraulic pressure are also experimentally studied. It demonstrated that both toes can perform similarly large bending angles for the adduction (attachment) and abduction (detachment) motions. In comparisons, Type B toe exhibits larger output force, which is ascribed to the fact that at proximal section of Type B corresponds to larger volume for bearing fluid. Both toes can not only provide sufficient adhesion, but can be quickly detached with low peeling forces. Finally, different curved surfaces are used to further justify the applicability of these bionic toes. In particular, the flexible toes developed also have the advantages of low cost, lightweight, and simple control, which is desirable for wall-climbing robots.

Climbing behavior is a superior motion skill that animals have evolved to obtain a more beneficial position in complex natural environments. Compared to animals, current bionic climbing robots are less agile, stable, and energy-efficient. Further, they locomote at a low speed and have poor adaptation to the substrate. One of the key elements that can improve their locomotion efficiency is the active and flexible feet or toes observed in climbing animals. Inspired by the active attachment–detachment behavior of geckos, a hybrid pneumatic–electric-driven climbing robot with active attachment–detachment bionic flexible feet (toes) was developed. Although the introduction of bionic flexible toes can effectively improve the robot’s adaptability to the environment, it also poses control challenges, specifically, the realization of attachment–detachment behavior by the mechanics of the feet, the realization of hybrid drive control with different response characteristics, and the interlimb collaboration and limb–foot coordination with a hysteresis effect. Through the analysis of geckos’ limbs and foot kinematic behavior during climbing, rhythmic attachment–detachment strategies and coordination behavior between toes and limbs at different inclines were identified. To enable the robot to achieve similar foot attachment–detachment behavior for climbing ability enhancement, we propose a modular neural control framework comprising a central pattern generator module, a post-processing central pattern generation module, a hysteresis delay line module, and an actuator signal conditioning module. Among them, the hysteresis adaptation module helps the bionic flexible toes to achieve variable phase relationships with the motorized joint, thus enabling proper limb-to-foot coordination and interlimb collaboration. The experiments demonstrated that the robot with neural control achieved proper coordination, resulting in a foot with a 285% larger adhesion area than that of a conventional algorithm. In addition, in the plane/arc climbing scenario, the robot with coordination behavior increased by as much as 150%, compared to the incoordinated one owing to its higher adhesion reliability.

Background: Geckos are endowed with the extraordinary capacity to move quickly in various environments; they benefit from efficient control for the complex footpads. Research on the locomotor behavior and contact status in the attachment–detachment (A-D) cycle of the footpads for diverse challenges is linked to the revelation of regulatory strategy. At present, there is a lack of systematic research for the A-D cycle, which limits the understanding of the adhesive locomotion mechanism.Methods: The A-D cycle that facilitates the level and up–down locomotion on inclined and vertical surfaces of Gekko gecko was investigated to clarify the locomotion postures and durations in the release, swing, contact, and adhesion stages, respectively. This reveals the relationship between the structure and function of the attachment devices, and its regulation when faced with changing locomotion demands.Results: Despite changes in climbing demands, gecko foot locomotion posture (angle extremes and changing trends) in the swing stage, the posture (bending angle: fore 41°, hind 51°) and contact time ratio (7.42%) in the contact stage remain unchanged, which is in contrast with the adjustable postures in the stance phase. Furthermore, the variation range of the forefoot locomotion posture is larger than that of the hindfoot, and the forefoot angle changing trend is opposite to that of the hindfoot, indicating that the combination of anatomical structure and functional demands results in the differentiation in the adaptation mode of the A-D cycle for the fore- and hindfoot. Conclusions: Gecko’s fore- and hindfoot have evolved different structures to undertake differential functions. The function (adhesion) for various locomotion demands relates to footpad deployment in the stance phase but is unaffected by the regulations (postures and durations) in the swing and contact stages. The results demonstrate that the unified adaptation strategy reduces the diversity and complexity of the control. It advances the understanding of the adhesive locomotion mechanism, reflects the structural evolution and adaptation strategy of attachment devices for functional requirements and provides biological inspiration for effective design and control of adhesion robots.