Improved Performance on Moving-Mass Hopping Robots with Parallel Elasticity
This addresses the problem of improving performance and efficiency in robotic hopping for applications like legged robotics, though it is incremental as it builds on prior single-spring designs.
The paper tackled the challenge of robotic hopping by adding a parallel spring to a moving-mass robot, resulting in 2.5x better energy efficiency, 40% less peak actuator force, and stable hopping without controllers, with experimental hop heights up to 40cm.
Robotic Hopping is challenging from the perspective of both modeling the dynamics as well as the mechanical design due to the short period of ground contact in which to actuate on the world. Previous work has demonstrated stable hopping on a moving-mass robot, wherein a single spring was utilized below the body of the robot. This paper finds that the addition of a spring in parallel to the actuator greatly improves the performance of moving mass hopping robots. This is demonstrated through the design of a novel one-dimensional hopping robot. For this robot, a rigorous trajectory optimization method is developed using hybrid systems models with experimentally tuned parameters. Simulation results are used to study the effects of a parallel spring on energetic efficiency, stability and hopping effort. We find that the double-spring model had 2.5x better energy efficiency than the single-spring model, and was able to hop using 40% less peak force from the actuator. Furthermore, the double-spring model produces stable hopping without the need for stabilizing controllers. These concepts are demonstrated experimentally on a novel hopping robot, wherein hop heights up to 40cm were achieved.