STriDER or Self-excited Tripedal Dynamic Experimental Robot is a three-legged robot that has a Tripedal gait. The robot exploits gravity to save energy with each step, but it also flips 180 degrees with each step to keep its legs from tangling up. To explain its gait: “To take a step forwards, the robot shifts its weight onto two of its legs, allowing itself to fall forwards away from the third leg. Its body then flips upside-down and the third leg swings up between the other two just in time to catch the ground and return STriDER to a stable tripod stance. To change direction, the robot simply switches its choice of swinging leg.” STriDER is being developed at Virginia Tech, US, and Dennis Hong is the project leader. He says, “STriDER's gait is closer to that of a human walking than most bipedal humanoid robots you see today. This is how we humans walk, we do not actively control our knees, we just let them swing.”

The STriDER Robot boasts of a stable design. The first prototype stands 1.8 meters tall, and the latest version is slightly shorter, at 0.9 meters. Three-legged robots are often seen in video games and sci-fi themes, this is the first time that scientists have incorporated this stance in a robot design. Bipedal robots can move quickly but they have to expend energy just to keep upright when they are not moving therefore a tripod posture is more stable as the joints can be locked.