Creating a biologically accurate spider robot to study active vibration sensing

Orb-weaving spiders rely on vibration sensors in their leg joints to sense vibrations on their webs to detect prey. Spiders often crouch their legs during prey sensing, likely a form of active sensing. It is difficult to measure vibrations in the presence of such motions in the biological system. To gain insight, we use robophysical modeling to study how leg crouching affects vibration sensing of the orb-weaver U. diversus. Previously as a first step, we used a greatly simplified spider robot constrained by traditional manufacturing. It only had four legs, its body and legs morphology did not well represent the spider’s, and the range of motion of leg crouching was much smaller than the spider’s. Here, to improve our robophysical modeling’s biological accuracy, we used advanced manufacturing to create a new spider robot. It has a body and eight legs whose exoskeletons are 3-D printed and morphologically more accurate. Each leg has four joints that together well approximate the range of motions of spider legs. Variable joint stiffness was achieved by silicone molding with adjustable material composition and cross-sectional geometry. Inside the body exoskeleton a motor actuated the legs via a tendon-driven system, achieving leg crouching with a range of motion similar to the spider’s. Accelerometers on leg joints recorded vibrations. With this robophysical model, we will systematically study how spiders localize prey, functional differences between legs, and how different joints contribute to sensing.