Parallel stiffness in a bounding quadruped with flexible spine

Legged locomotion involves periodic negative and positive work, which usually results in high power consumption. Improvement of the energy efficiency is possible by using energy storage elements to reversibly store the negative work performed during a walking or running cycle. While series elastics with high impedance (high gear ratio) actuators are widely used, we investigate the application of parallel stiffness with highly backdriveable actuators. We specifically show that the use of parallel springs in a bounding quadruped with a flexible spine can lower power consumption by over 50%.