Functional arm compensation and fault tolerance for a hexapod robot with ipsilateral two-leg failure

Abstract In extreme environments, hexapod robots are highly susceptible to locomotor failure due to leg structure damage or electronic circuit interruptions. Such failures are particularly critical in ipsilateral two-leg loss, where most conventional hexapod designs fail to maintain stability. This paper introduces a hexapod robot platform equipped with a functional arm (FA) and proposes a fault-tolerant strategy based on FA compensation. The FA serves as a task-oriented module under normal conditions and as a compensatory leg during instability caused by leg loss, enabling rapid recovery of stability and walking capacity without complex adjustments to the remaining legs. An optimization algorithm was developed for gait adjustment, using the longitudinal stability margin as the optimization objective with the compensation median angle θ and swing angle α as key parameters. The optimal compensatory positions of the FA were identified for both the ipsilateral middle-hind leg and front-hind leg failure scenarios. Experimental results demonstrate a marked improvement in both walking stability and capability after FA compensation. For both failure modes, the robot’s attitude fluctuations were significantly suppressed, and the stride length was substantially increased, affirming the feasibility and effectiveness of the proposed approach in enhancing the environmental adaptability of multi-legged robots.