Controlling Tensegrity Robots through Evolution using Friction based Actuation

Traditional robotic structures have limitations in planetary exploration as their rigid structural joints are prone to damage in new and rough terrains. In contrast, robots based on tensegrity structures, composed of rods and tensile cables, offer a highly robust, lightweight, and energy efficient solution over traditional robots. In addition, tensegrity robots can be highly configurable by rearranging their topology of rods, cables, and motors. However, these highly configurable tensegrity robots pose a significant challenge for locomotion due to their complexity. This study investigates a control pattern for successful locomotion in tensegrity robots through an evolutionary algorithm. A twelve-rod hardware model is rapidly prototyped to utilize a new actuation method based on friction. A web-based physics simulation is created to model the twelve-rod tensegrity ball structure. Squarewaves are used as control policies for the actuators of the tensegrity structure. Monte Carlo trials are run to find the most successful number of amplitudes for the square-wave control policy. From the trials’ results, an evolutionary algorithm is implemented to find the most optimized solution for locomotion of the twelve-rod tensegrity structure. The software pattern coupled with the new friction based actuation method can serve as the basis for highly efficient tensegrity robots in space exploration. Keywords— Robotics, Tensegrity, Evolutionary Algorithm, Machine Learning, NASA Introduction Tensegrity robots are a new field of robotics that diverge from the traditional sense of robotics. Traditional robotics relies on robots composed of rigid joints. Tensegrity structures, on the other hand, are composed of pure tension and compression elements as shown in Fig. 1 [12]. The lack of lever arms makes tensegrity structures resistant to force magnification in joints or other points of failure. The goal of these structures is to take part in low-cost planetary exploration [1]. In this task, tensegrities have numerous benefits to offer over traditional robots: • Highly Reconfigurable: Topology of rods, cables, and motors can be changed to add new functionality. • Light-weight: The structures are made of tubes/rods and cables/elastic lines. • Energy efficient: Dynamic movement of the tensegrity structure results in efficient locomotion. • Scalability: Composed of rods, cables, and actuators, the tensegrity structure can be scaled up in size without a significant cost difference. • Ease of Deployment: The shock absorbent structure allows for a smoother landing on planetary missions. • Robust to failure: The inherent tension network distributes harmful external forces to reduce the structural damage.