Natural patent with potential for robotics: Bionics researchers have documented an astonishing function of the tail of a gecko species: The reptiles use the appendage like a fifth leg to avoid bouncing off tree trunks after gliding jumps despite a hard landing. In order to clarify the function, the scientists transferred the concept to a robot and thus also showed possibilities for technical use.
They can even run on the ceiling with their sturdy feet: Geckos are famous for their acrobatic climbing skills. But the small reptiles have other abilities that are of interest to researchers who are concerned with the transfer of natural patents to robotic systems. For years, the fringed-tailed house geckos (Hemidactylus platyurus) in focus. Their ability to run over the surface of water without sinking has already been investigated, and researchers are also interested in their ability to jump confidently from tree to tree while gliding. The latter was now the focus of the team around Ardian Jusufi from the Max Planck Institute for Intelligent Systems in Stuttgart.
As the scientists report, the fringed-tailed house geckos mainly use the air to escape predators in a flash. On many of these rescue jumps, the gecko still accelerates on landing – it almost slams onto the vertical target surface. Surprisingly, despite the hard impact, the animals can hold on to the trunk without falling. This ability aroused the interest of the researchers and so they investigated the process in a wildlife reserve in the rainforests of Singapore using high-speed cameras.
Anti-fall function of the tail
The analyzes of the recordings showed that the geckos often hit the vertical surfaces at a speed of over 21 kilometers per hour. They cushion the impact by bending their torso backwards by up to 100 degrees. As a result, the front feet lose their grip – but the animals manage to keep their back legs on the trunk. It became apparent that the tail made this possible: it functions as in the fifth leg and ensures that the energy of the impact is diverted with a stabilizing effect. This explanation supported observations that geckos that had lost their tails in the course of life often fell after jumping, report Jusufi and his colleagues.
However, in order to document the function of the attachment more precisely, the bionics went to the laboratory workshop: They built a physical model of a gecko in order to better understand the forces to which the animal is exposed. In addition to front and rear feet with Velcro material, your gecko robot has a flexible torso to which a tail can be attached and removed again. When the front feet hit a vertical felt material surface, a control system created a curving movement – just like the natural models. This also activates a motor that pulls an artificial tendon and thus presses the tail against the vertical landing surface.
Potential for robotics
The researchers examined the performance of the gecko robot with tails of different lengths through throwing experiments and also recorded the forces that occurred during the landings. It was shown that the effect of the tail significantly reduces the force that pulls the hind feet away from the surface. The smaller it is, the easier it is for the robot to hold on. Without a tail or with a reduced length, the forces on the hind feet become too great – the robot loses its grip, bounces off and falls, the experiments showed.
These results thus confirmed that the tail plays a decisive role in the stable landing of the geckos. “This discovery has important implications for our understanding of tails as multifunctional appendages in animals,” says Jusufi. Up until now it was assumed that in geckos they mainly serve to stabilize the hold while running fast on walls. Now it turns out that they also use the tail to improve the success of landings during their jumps, ”Jusufi sums up.
For the bionicists, in addition to the biological significance of the results, the technical focus is now of course also in the focus: They form a basis for the technical use of the gecko concept, as first author Robert Siddall from the Max Planck Institute for Intelligent Systems finally emphasizes: “The Nature offers many unexpected, elegant solutions to technical problems – this use of the tail is a wonderful example of this. Landing from flight is technically difficult and we hope that our findings will lead to new solutions for the mobility of robots, ”said Siddall.
Source: Max Planck Institute for Intelligent Systems, University of California, Berkeley, specialist article: Communications Biology, doi: 10.1038 / s42003-021-02378-6