A team of engineers from Harvard University under the leadership of James Weaver have created a robot whose structure and movement mechanisms resemble those in sea hedgehogs. On its surface are tubes resembling the legs of sea seals, allowing the robot to cling to the surface, as well as artificial analogues of needles, with which it can use push off and turn.
Sea urchins use an unusual mechanism for movement. Their main organs of movement are ambulacral-legs. They are heavily elongated tubes with a wider suction cup at the end. To move hedgehogs pump water into their legs and thus, increase their length. After contact with the surface, the leg is attached to it due to the release of the adhesive substance. If the leg needs to be unattached from the surface, the substance dissolves with another enzyme. In addition, if necessary, the sea urchin can push itself with needles.
For this, they created a robot equipped with artificial analogues of the legs and needles of sea urchins. As a basis, they took the structure of young sea urchins, which mainly differs in the branched shape of needles. The robot is made in the form of a hemisphere, assembled from five equal segments. In each of the segments, two needles are installed, one of which has a branched shape, and the second is more smooth. The needle is mounted on a base of three inflatable elements, which, when pressure is applied, elongate and cause the needle to turn in one direction or another.
In addition to needles, one hollow corrugated leg consisting of an elastomer is installed in each segment. At the end of the leg is a magnet, and it is installed in such a way that it is initially located inside, and when the threshold pressure is reached, it is pushed out. Engineers used magnets as an alternative to chemical bonding to the surface. However, this imposes a limitation on the robot: it can only move on ferromagnetic surfaces.
To control the needles and legs in the robot, there are two pumps working with air or water, as well as eight valves. Five of them are used to individually control each leg, and the remaining three are connected to one of the three inflated elements of the needles, so all the needles in the robot move simultaneously.
Engineers conducted experiments and compared the speed of movement of the robot with real hedgehogs. The diameter of the robot’s hemispheric body is 23 centimetres. In one cycle of motion, ten seconds long, it is able to move six centimetres. This corresponds to 0.027 body lengths per second, which is about nine times less than that of real young sea urchins.
Last year, Japanese engineers created a 32-legs robotic stand, each of which can independently lengthen and push the robot in the right direction. This allows the robot to instantly change direction and move in any direction with the same efficiency.