STriDER (Self-excited Tripedal Dynamic Experimental Robot) is a novel three-legged walking machine that exploits the concept of actuated passive dynamic locomotion to dynamically walk with high energy efficiency and minimal control. Unlike other passive dynamic walking machines, this unique tripedal locomotion robot is inherently stable with its tripod stance and can change directions while walking.
During a step, two legs act as stance legs while the other acts as a swing leg. The legs are oriented to push the center of gravity outside of the stance legs to initiate a step. As the body of the robot falls forward, the swing leg naturally swings in between the two stance legs and catches the fall. The body also rotates 180 degrees, preventing the legs from tangling up. Once all three legs are in contact with the ground, the robot regains its stability and the posture of the robot is then reset in preparation for the next step. Gaits for changing directions are implemented in a rather interesting way: by changing the sequence of choice of the swing leg, the tripedal gait can move the robot in 60° interval directions for each step.
The simple tripod configuration and tripedal gait of STriDER has many advantages over other legged robots; it has a simple kinematic structure; it is inherently stable (like a camera tripod); it is simple to control as the motion is a simple falling in a predetermined direction and catching its fall; it is energy efficient, exploiting the actuated passive dynamic locomotion concept utilizing its built in dynamics; it is lightweight enabling it to be launched to difficult to access areas; and it is tall making it ideal for deploying and positioning sensors at high position for surveillance, for example.