The Role of Leg Differentiation in Hexapedal Running

Designing a robot that can autonomously traverse a variety of terrain types is difficult. For this reason, one may refer to nature for inspiration and produce robots that mimic biological organisms. EduBot is one such device, a hexapedal robot that resembles a cockroach. Building a robot that mimics a living creature offers numerous advantages, including design efficiency and locomotive stability. In addition, mathematical models that describe animal walking and running can be applied to the device, so an entire existing body of analysis can be used to characterize the robot’s movement; this saves time and increases intuitive understanding. One such model, the spring-loaded inverted pendulum (or SLIP) model for animal running, has been successfully applied to EduBot’s forward motion. However, like many animals, EduBot deviates from this model in that it exhibits a rolling motion about its forward axis. The goal of the current research is to describe this motion with a simple model and use the model to motivate modifications to the robot that will eliminate the roll. To characterize the roll, we measure the ground reaction forces from each of the robot’s legs with a force plate and use a video-based motion capture system to record the robot’s trajectory through space. We show that the maximum roll appears to decrease as the middle legs are made stiffer, which matches the prediction from the model.