Weighing in at a diminutive 54 grams, the VelociRoACH can zip across a surface at an impressive 4.9 meters per second making it the fastest legged robot of its size. The creature, developed by Duncan W. Haldane and Ronald S. Fearing at UC Berkeley's Biomimetic Millisystems Lab, uses the mobility booster of an increase in stride cycles per second as the key to its speed. In other words, it is faster because it takes more steps. Created from 3D printed parts, the only reason for the ceiling on the speed is the fact that the robot begins to fly apart, but as the composite materials used in printing improve in strength, there's no reason to believe it won't get even faster. Read more about the robotic device here: http://3dprint.com/68119/uc-berkeley-fast-cockroach/
Below is a photo of the fastest robot: