Bipedal Robot Uses Jet-Powered Feet to Step Over Large Gaps

Ducted fans in its toes help this robot to balance while taking giant steps

As you may have noticed, bipedal robots have a tendency to fall over. This often happens when the robots are trying to take a step, because stepping involves balancing on one foot while moving. All steps aren’t equal, of course—you’ve got easy steps, when you’re walking slowly across a flat surface, and you’ve got hard steps, when you’re trying to avoid an obstacle by stepping over it or across it. Both robots and humans are constrained in the kinds of steps we’re able to take by (among other things) how far we can stick a leg out without falling over. Humans mitigate this to some extent by dynamic walking, also known as constantly falling forward, but for less dynamic (quasi-static) robots, step length puts a significant limitation on the kinds of obstacles they can deal with.

The fundamental problem here is that the longer the step you want to take, the more your center of gravity moves out toward the leg you’re taking the step with. Try to take too big of a step, and you’ll fall forwards while extending your leg. Go on, try it!*

Solving this for a quasi-static robot (or human) can be done by changing the center of gravity somehow, either by reducing the weight of the leg you’re sticking out, or increasing the weight of all of the rest of you. At Guangdong University of Technology’s School of Automation in China roboticists are experimenting with using small ducted fans embedded in the feet of a bipedal robot. The idea is to change the robot’s center of gravity to help it balance as it takes giant steps over a wide gap that it normally wouldn’t be able to cross.

The robot, called Jet-HR1, weighs 6.5 kilograms and has a height of 65 centimeters. On the end of each foot is a ducted fan jet engine, which weighs just 232 grams but can output up to 2 kg of thrust, nearly a third of the weight of the entire robot.

In one experiment, Jet-HR1 was tasked with stepping over a gaping chasm 37 cm wide, which required a step length of 80 percent of its leg. To make this work, the robot spooled up the ducted fan as it stuck its leg out, essentially holding the leg up and preventing the robot from tipping forwards. Once the robot has its jet foot planted on the far side of the gap, it repeats the procedure with its back leg to complete the crossing. The entire maneuver can be completed in well under a minute, which is pretty quick, as is appropriate for a robot with two jet engines on it.

The researchers suggest that this general technique could be adapted to many more challenging situations, by helping robots control their balance when facing large obstacles that they need to step over, or even just keeping them from falling over when managing rough terrain in general. Since the jet engines allow the robot to dynamically adjust its center of mass without the need for specific ground contacts, you can imagine all kinds of crazy things, like robots that tilt themselves sideways or even do the limbo to navigate complex environments.

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