As small legged robots for search and rescue are deployed in collapsed buildings with unstructured terrain and steep drop-offs, they run the risk of flipping over and becoming incapacitated. A single degree of freedom low-mass tail is added to a 77.5 g, 18 cm long VelociRoACH legged robot with protective shell, which gives it the capability to dynamically self-right. Quasi-static analysis of terrestrial self-righting gives design requirements for the tail actuator. Dynamic simulation predicts that terrestrial self-righting is slower than aerial self-righting with a massive tail, but can be achieved without adding significant mass away from the base of leg support. Open-loop experiments on terrain with varying friction and roughness show that VelociRoACH can dynamically self-right using tail contact in as little time as 256 ms. Finally, an autonomous self-righting experiment on an obstacle with multiple step drops demonstrates that the robot can detect inversion and rapidly self-right while walking on challenging terrain.
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