In a short article, New Scientist reports that researchers at Virginia Tech University have developed a tripedal experimental robot. With its three legs, this robot, named STriDER -- short for 'Self-excited Tripedal Dynamic Experimental Robot' -- is actually more stable than 2- or 4-legged robots. As said another researcher, 'It's like a biped with a walking stick.' This robot is intended to deploy sensors and cameras in difficult-to-access areas.
STriDER has been developed under the supervision of Dennis Hong, an assistant professor at Virginia Tech and director of the Robotics and mechanisms Laboratory (RoMeLa). You can see above the various components of this robot. (Credit: Virginia Tech University)
Here is how New Scientist describes STriDER's 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. Although STriDER's body shape is like nothing in nature, its gait is meant to closely mimic the way biological organisms walk. The aim is to minimise the complexity of controlling each limb, and to reduce overall energy use."
You can see on the left a prototype of STriDER, which was 1.8 meters high. Newer versions should be less than 1 meter tall. (Credit: Virginia Tech University) This page about current research projects at RoMeLa gives additional details about STriDER. [It] "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. The simple tripod configuration makes it lightweight, enabling it to be launched to difficult to access areas, and its height makes it ideal for deploying and positioning sensors at high position for surveillance, for example."
For more information, you can read Biologically Inspired Locomotion Strategies: Novel Ground Mobile Robots at RoMeLa, a presentation given at the 3rd International Conference on Ubiquitous Robots and Ambient Intelligence, Seoul, S. Korea, October 15-17, 2006 (PDF format, 6 pages, 5.2 MB).
Here is the conclusion about STriDER. "The simple tripod configuration and tripedal gait of STriDER has many advantages over other legged robots; it has a simple kinematic structure (vs. bipeds, quadrupeds, or hexapods) that prevents conflicts among its legs and between a leg and the body; it is inherently stable (like a camera tripod); it is simple to control (vs. bipeds) 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."
This technical report also explains in details how STriDER walks. The top picture in this post has been extracted from this paper.
Sources: Tom Simonite, New Scientist, September 20, 2007; and various websites
You'll find related stories by following the links below.