A legged robot that breaks on the battlefield is a liability.

But new research into self-healing joints for legged robots could pave the way to a future of autonomous, self-repairing machines.

Legged robots have value for infantry because they allow machines to traverse inclines and rough terrain that’s ill-suited for wheels. In addition, legs can carry robots up ladders and over walls. Its one reason the United States has pursued multiple iterations of robot dogs for military use.

But if a leg breaks in the field, soldiers depending on that robot are left with a handful of unpleasant options.

If the unit has spare parts, they could halt and attempt an in-field repair. If the unit doesn’t the equipment, or doesn’t have time, they can abandon the robot in the hopes that friendly forces will recover it later. Or they can destroy the robot to prevent it from falling into enemy hands, losing not just the ability to carry supplies but spending finite resources wrecking it.

All of this is a knock against legged robots.

But new research, by the University of Tokyo’s JSK Lab and reported by IEEE Spectrum in December, used special joints, liquid metal and heat to let a robot break its leg and then heal.

The design solves two problems at once: by preparing a joint to break, the robot can protect its remaining joints in the fall, and by making the joint that breaks one that can “heal”, the robot is only out of commission for a short time.

“Healing” here is a sort of automated repair. Around the joint is a module of magnets and springs that is designed to separate and then come back together when the joint breaks. The joint is made of an alloy that melts at 122 degrees. The module holds the alloy in place and then melts with internal heaters. The whole process takes about 30 minutes, and leaves a leg weaker than before, but far more functional than if it had just remained broken.

For military planners and designers, the method of a self-healing joint enables robot design that can accompany humans without the risk of becoming a special burden. A little forgiveness in design and automated repair can go a long way to supporting imperfect navigation or climbing systems, especially as the robots are new and there is limited data on which they have been trained.

While the healing takes time, a squad in the field can take a short pause and focus on self-protection while the robot repairs itself. Even if the robot is no longer able to go forward, it could be sent autonomously back to base, essentially walking itself in for repair.

Long-term, automated self-repair is a feature worth exploring in any autonomous systems designed to operate far from humans. The more self-sufficient a robot can be, the more humans can trust it to perform tasks without direct supervision.

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