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

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.

A biologically inspired micro-vehicle capable of aerial and terrestrial locomotion

“…Using a single drive motor, the 9 cm long robot has run at 10 body lengths per second, and can easily run over 3.5 cm tall obstacles -higher than its body. The more recently developed iSprawl [32] also uses single motor propulsion and benefits from abstracted biological principles. It has run even faster, 15 body lengths per second, although its obstacle climbing ability is more restricted because of the relatively small range of motion of its feet.…”

Biologically Inspired Robots

“…To date, the two fastest types of legged robot seem to be robots of the Sprawl series and RHex (Figure 1). The Sprawl robots, hexapods based on the biomechanics of cockroaches, have been specifically designed to include compliant features in their six legs (Bailey et al, 2001;Cham et al, 2002;Dordevic et al, 2005;Kim et al, 2006). Recent versions can move at about 2.3 m/sec.…”

STAR, a sprawl tuned autonomous robot

“…Their low weight and cost allow their deployment in large numbers, independently or in swarms, to cover a large work area and increase the odds that some of the robots will succeed in performing a specific task. Some existing examples of comparable robots can crawl at more than 5 (and up to 15) body lengths per second, such as Mini-Whegs [10], Dyna-RoACH [4], DASH [1], iSprawl [6], OctoRoACH [11], RHex [3], and Sprawlita [2]. Since it is difficult to implement active leg joints at this scale, a key challenge in developing a high speed and highly maneuverable miniature crawler is the design of passive mechanical elements which contribute to the stability of the robot during locomotion, similar to insects [8] [5].…”