Locomotion behavior and dynamics of geckos freely moving on the ceiling

To understand the mechanical interactions when geckos move on ceiling and to obtain an inspiration on the controlling strategy of gecko-like robot, we measured the ceiling reaction force (CRF) of freely moving geckos on ceiling substrate by a 3-dimensional force measuring array and simultaneously recorded the locomotion behaviors by a high speed camera. CRF and the preload force (F_P) generated by the geckos were obtained and the functions and the differences between forces generated by fore- and hind- feet were discussed. The results showed that the speed of gecko moving on the ceiling was 0.17–0.48 m/s, all of the fore- and hind-legs pulled toward the body center. When geckos attached on the ceiling incipiently, the feet generated a very small incipient F_P and this fine F_P could bring about enough adhesive normal force and tangential force to make the gecko moving on ceiling safely .The F_P of the fore-feet is larger than that of the hind-feet. The lateral CRF of the fore-feet is almost the same as that of the hind-feet’s. The fore-aft CRF generated by the fore-feet directed to the motion direction and drove their locomotion, but the force generated by the hind-feet directed against the motion direction. The normal CRF of fore- and hind-feet accounted for 73.4% and 60.6% of the body weight respectively. Measurements show that the fore-aft CRF is obviously lager than the lateral and normal CRF and plays a major role in promoting the fore-feet, while the hind-feet of the main role are to provide a smooth movement. The results indicate that due to the differences of the locomotion function of each foot between different surfaces, the gecko can freely move on ceiling surfaces, which inspires the structure designing, gait planning and control developing for gecko-like robot.