A big, hairy spider scurries across the floor of your room, you get up to remove it with a glass cup and piece of paper (since you love nature). But once you get closer to the little arachnid, its robotic like legs begin working overtime as it runs and hides under your bed. Besides the haunting dreams that you will be having tonight, ever wonder why small spiders scurry away from you rapidly in any direction when you get close to them? Well there bodies rely on hydrostatic pressure in their skeleton. If a single leg was to be punctured or lost, they risk losing pressure in their entire body and deflating. Some species have valves or sphincters to help prevent a catastrophic lose of hemolymph. The spider’s leg extension is achieved by hydraulic pressure generated in the cephalothorax. The hemolymph flows into the legs from the cephalothorax into spaces between all the soft tissues inside a leg. Thus volume inside joints and legs increase, leading to extension.
Spiders do have muscles to flex their limbs inward, they use hydraulic pressure to extend them outward. That is why when you finally “remove the blessed life from one of gods creatures” aka, there legs flexor muscles curl up in towards there abdomen since the hydraulic system has been shut off.
Different research groups have mimicked the hydraulic mechanism of spider biology to come up with creative designs for unique problems and solutions. Like, a research team at the Fraunhofer Institure for Manufacturing Engineering and Automation has developed a spider robot to track and sense information deemed too dangerous for humans.
“As a real spider would, our robot keeps four legs on the ground at all times while the other four turn and ready themselves for the next step. With its long extremities, the spider has a range of ways to get around. Some models can even jump. This is possible using hydraulically operated bellows drives that serve as joints and keep limbs mobile.”
Another remarkable engineer, from the UK, created a giant-mantis robot with hydraulic legs. The original design of the robot was used for entertainment purposes, it was meant to be cool, insect-like and fun. The machine did arise the interests of mining companies, and marine research organisations.
The downside to spider hydraulic mechanism (which all exoskeleton animal species experience) is that the spider cannot grow very big. The mechanism has a hard time supporting large animals or objects. But consider the scaling principles of this semi-hydraulic locomotive apparatus in spiders may help to better localize its limits by understanding the design criteria and support convergence of the design of small hydraulically driven machines or robots. There could be cheap, light weight robots used to look inside pipes, or through small crevices that a conventional wheel robot would have trouble navigating. Its up to the engineer or designer to figure out the degree of sophistication needed to mimic the biological examples.