Today’s groundbreaking entry into the Uncanny Valley is a pair of mechanical, robot legs that are propelled entirely by their own weight: they can walk with a human-like gait without motors or external control. If this sounds too good (or crazy) to be true, watch the first video at the end of the story, wipe the tendrils of drool off your chin, and then find your way back up here for an explanation.

Without making this accomplishment any less awesome, these robot legs — called BlueBiped, and made by researchers at the Nagoya Institute of Technology in Japan — are basically just an imitation of human physiology. There are thighs and lower legs made out of aluminium that are the same length as their human counterparts, and ankles and knee joints for articulation, but… that’s it. No sensors, no computers, no “musculature” — the legs are completely passive, you just give them a push… and they carry on walking. As long as there’s a slight downwards slope, anyway — there has to be some source of energy, after all, and in this case it’s gravity.

BlueBiped uses the “principle of falling,” much in the same way that humans walk by falling forward. As long as the robot’s weight is pitched slightly forward, the momentum of each step is enough to throw it into another step, and so on. Presumably, with the addition of motors, BlueBiped could also walk horizontally and up hill, but then you’re into MABEL or AlphaDog territory — and that doesn’t seem to be the purpose of this project.

Last year, BlueBiped successfully walked for 13 hours continuously — 100,000 consecutive steps, 9 miles (15km) — without human intervention. Now the researchers seem to be thinking of actual, commercial applications for BlueBiped. They have tested a modified version that can be worn like an exoskeleton, which apparently can help people walk. In the video, “sports equipment” is also mentioned, though we’re not sure what that means — robot tennis instructors, perhaps?

Read (a little bit) more at Sano Lab, Nagoya Institute of Technology [translated], or watch the videos below.