Tunable Leg Stiffness in a Monopedal Hopper for Energy-Efficient Vertical Hopping Across Varying Ground Profiles

TL;DR

HASTA (Hopper with Adjustable Stiffness for Terrain Adaption) is a vertical hopping robot that tunes its leg stiffness in real time to hop as high as possible on different ground conditions — softer legs win on soft, damped ground; stiffer legs win on hard ground.

Key contributions:

• A monopedal hopper with real-time tunable leg stiffness, built on pneumatic tunable-stiffness bellows actuators driven by a central tendon.
• A ground emulator that physically reproduces pairs of ground stiffness and damping conditions for repeatable locomotion experiments.
• Experiments and simulations identifying the optimal leg stiffness for each ground profile, validating that tunable stiffness enhances energy-efficient locomotion in dynamic environments.

Demo

Learn more

Hardware design, fabrication details, and the electronic system architecture are documented on the project page.

BibTeX

@misc{chen2025tunablelegstiffnessmonopedal,
  title={Tunable Leg Stiffness in a Monopedal Hopper for Energy-Efficient Vertical Hopping Across Varying Ground Profiles},
  author={Rongqian Chen and Jun Kwon and Kefan Wu and Wei-Hsi Chen},
  year={2025},
  eprint={2508.02873},
  archivePrefix={arXiv},
  primaryClass={cs.RO},
  url={https://arxiv.org/abs/2508.02873},
}