iSprawl

Sprawl is the youngest and fastest sibling of Autonomous version of Sprawl robot family. Professor Kim joined BDML at the end of this Office of Naval Research (ONR) project and designed iSprawl for the first creation at Stanford. Sprawl robots are designed by inspiration based on study of cockroaches.

Whereas other sprawl robots utilize pneumatic system, iSprawl is equipped with battery and electric motor and power transmission system that convert rotary motion to reciprocal leg thrust. What most makes iSprawl unique is push-pull cable transmission system. Since Sprawl family turn its orientation by rotation of their leg with respect to hip joint, power transmission path is not fixed. Which is frequent problem in legged robot with centered engine.

Usage of steel cable as pulling transmission is very common as you can find very easily in bicycle brake and car throttle. iSprawl's cables, however, thrust and pull the legs in high speed (up to 17Hz) without significant energy loss. This enables
iSprawl's light and fast movement of legs leading to fast locomotion up to 15 body-lengths/sec(2.3m/s).

The predecessor of iSprawl, the first sprawl robot that operates with autonomous power uses hydraulic power transmission system. The idea was to explore hydaulic power transmission to distribute power to the legs. The tubes contain water and the system works like hydraulic brakes on a car, with a single master piston and slave pistons at each leg. Aqua Sprawl is assembled in a bathtub to prevent air bubbles.

After many design iterations, including remachining the original Sprawlita pistons to put in double seals to handle negative pressure on the return stroke, a version of Aqua Sprawl was produced that ran fairly well. Although Aqua Sprawl ran reasonably well, there is a fundamental limitation to the achievable speed because while retracting the pistons, only atmospheric pressure is available. On the other hand, this could be a good design for underwater use.