A few years ago, engineers at Cornell were rejoicing when their Ranger robot set an unofficial world record by walking for 5.6 miles without stopping. Since then, the 22-pound bot has only built up its endurance, to the point where it can now chug along for a full 40.5 miles without a single battery recharge, or an ounce of human assistance. The Ranger pulled off the feat last week, when it completed nearly 308 laps around the university's Barton Hall running track, over the course of more than 30 hours. Engineers say that their b
