By far the greatest challenge for robots with legs is staying upright when the going gets rough. A team at the University of Pennsylvania's Kod*lab has a hunch that we don't need extra smarts to make that happen -- just an extra appendage. The upgraded X-RHex Lite (XRL) carries a tail that will swing in the right direction to keep the robot upright if it's caught out by a fall, much like a cat. That's impressive for a nearly 18-pound robot (the previous Tailbot was 0.4 pounds), but we're pretty sure no feline has six springy legs; the XRL can crash to the ground and still get back up like it ain't no thing, which gives it a fudge factor others don't have. We don't know if the hexapod critter will lead to more than further experiments. If there are fewer stuck rovers on future exploration missions, though, we'll know who to thank.