The robot, called Atlas and made by Boston Dynamics, is competing in the DARPA Robotics Contest, organized by the U.S. Defense Advanced Research Projects Agency. Over the weekend, robots of varying shape and design, all controlled remotely, attempt challenges meant to test the limits of artificial sensing, manipulation, and agility. Each task is inspired by work that could help stem a leak at a stricken nuclear power plant. The jobs are seemingly simple, but not for robots. In one, the machines must get across a pile of rubble; in another they have to climb a tall ladder.