iSprawl: Design and Tuning for High-speed Autonomous Open-loop Running

TLDR

The study presents iSprawl, a 0.3‑kg autonomous hexapod capable of running at 15 body‑lengths per second (2.3 m/s), and describes its design features. Its design relies on a tuned set of leg compliances and a lightweight, flexible power‑transmission system that converts high‑speed rotary power into periodic thrust delivered to the rapidly swinging leg tips. iSprawl maintains a nearly constant specific resistance of 1.75 across speeds of 1.25–2.5 m/s and exhibits stable, insect‑like bouncing locomotion with an unusually high stride frequency for its size.

Abstract

We describe the design features that underlie the operation of iSprawl, a small (0.3 kg) autonomous, bio-inspired hexapod that runs at 15 body-lengths/second (2.3 m/s). These features include a tuned set of leg compliances for efficient running and a light and flexible power transmission system. This transmission system permits high speed rotary power to be converted to periodic thrusting and distributed to the tips of the rapidly swinging legs. The specific resistance of iSprawl is approximately constant at 1.75 for speeds between 1.25 m/s and 2.5 m/s. Examination of the trajectory of the center of mass and the ground reaction forces for iSprawl show that it achieves a stable, bouncing locomotion similar to that seen in insects and in previous (slower) bio-inspired robots, but with an unusually high stride frequency for its size.