The Stick Bug That Taught a Robot to Walk

Meet Twiggy, a stick insect (her nickname is just for our show), and RedMirror, a real six-legged robot from VISTEC in Thailand. Scientists from Tohoku University in Japan and VISTEC used an AI to watch only three or four steps of a stick insect walking. The AI didn't copy those steps. It worked out what the bug was trying to do, like a coach would. The robot then practiced chasing that goal: try, get a score, try again. It learned to walk in about an hour. In computer tests, it crossed bumpy ground it had never seen and kept walking on five legs after one leg was switched off. This week we also talk about why AI works best as a coach, not a copy machine, and our Kid Mission turns you into a Bug Coach.

The wow picture: A skinny twig-like bug takes a few careful steps, and a robot about five times bigger learns from them. Later, one of its six legs is switched off, and it just keeps walking on the other five.

The AI learned from an open dataset showing just 3–4 steps of the stick insect Medauroidea extradentata (2,000 frames covering 18 leg joints).

The method is called adversarial inverse reinforcement learning. The AI works out the insect's goal (its "reward") instead of being told how to move each leg.

Tohoku University says the robot learned to walk in just an hour, and that it learned three times faster than with a standard reward.

When the learned goal was moved to a different robot body, that robot reached a useful walk in 70,000 training steps instead of 200,000 (Interesting Engineering, reporting on the paper).

It was trained only on flat-ground data. On uneven terrain it switched to a more wave-like leg pattern, and its forward speed dropped only slightly.

With one of six legs disabled (simulated damage), it reorganized its remaining legs and shared the load differently to stay stable.

A preliminary test on the physical RedMirror robot showed walking that looked like the simulations.

Quote from Associate Professor Dai Owaki (Tohoku University): "We never told the robot how to walk. We asked what the insect was trying to achieve, and let the robot chase the same thing entirely on its own."

Owaki also said a few steps from one stick insect "were enough to find a principle that works on a machine five times its size."

Possible future use: legged robots that help at disaster sites where wheeled robots can't go.