Duncan W. Haldane and Jonathan E. Clark
Department of Mechanical Engineering
Florida A&M University - Florida State University College of Engineering
2525 Pottsdamer Street
Tallahassee, Florida 32310
Biomechanical studies have shown that animals modify their leg stiffness to adapt to changes in their running environment. A recent empirical study investigating the performance of mechanically variable stiffness legs on a dynamic hexapedal robotic platform, Edubot, has shown that optimal performance was measurably increased by adaptively modulating the leg stiffness. While effective, the resulting mechanism was too heavy, complex, and fragile for extended field operation.
The aim of this study is to develop an electrically activated variable stiffness leg for Edubot using a class of polymeric smart materials called shape memory polymers. Shape Memory Polymers (SMPs) experience a several order of magnitude drop in modulus as they approach their glass transition temperature. By fabricating a composite using a SMP as the resin matrix, a shape memory polymer composite is formed. A shape memory polymer composite (SMPC) developed in this manner should be capable of sustaining the high bending loads required of a locomotion appendage. By modulating the leg stiffness, the robot will then be capable of adaptation to variations in terrain and payload.
We present a design for a variable stiffness leg that utilizes a polymeric smart material to modify the leg compliance without any external mechanism. In section 2 the styrene-based shape memory polymer material used in the legs design is described and characterized. The design of and fabrication of the robot legs using this material are detailed in section 3, and the experimental testing of the legs is reported in section 4. Section 5 describes the results and directions for future work.