Design and Characterization of a Soft Electroactive Adaptive Structure for Legged Robotic Motion

Legged robotics exhibit mobility over complex terrains that overcomes many of the challenges experienced with traditional wheeled robots. This includes the ability to traverse rough terrain, climb obstacles, and in some robotic platforms, even scale walls. It is known from bio-locomotion research that humans and other animals adjust the stiffness of their muscles to accommodate differences in the terrain. Methods to implement changes in the passive mechanical stiffness on a legged robotic platform have included geometric changes to the leg configuration, complex mechanical linkages and gears, or thermally induced modulus changes in polymers. Each of these cases are limited in their dynamic response and efficiency. As an alternative, we have developed a leg module that changes its stiffness by application of an electric field. This is achieved by applying a large voltage to the dielectric elastomer VHB. Previous studies have demonstrated up to a 92% stiffness reduction. The goal of this work is to identify the electromechanical dynamic responses of those elements to understand limits in adaptability from abrupt changes in terrain. We quantify the structural dynamic behavior and electromechanical limits governing rapid stiffness changes in our legged VHB module. Structural vibration characterization is presented to illustrate transient dynamic changes when the VHB material is exposed to a step input voltage change. The results are analyzed and compared to the system dynamics required for the iSprawl legged robot.