Aerial-Biped Is a Quadrotor With Legs That Can Fly-Walk

Walking around wouldn’t be nearly so hard if you could just shut gravity off for a bit

2 min read
Aerial Biped robot is a quadrotor with legs
Image: University of Tokyo

A couple years ago, we wrote about a robot called BALLU from Dennis Hong at UCLA—essentially a blimp with skinny little legs, BALLU made walking easier by taking gravity out of the equation. If your robot doesn’t weigh anything, you don’t have to worry about falling over, right? Inspired in part by BALLU, researchers from the University of Tokyo have developed a quadrotor with legs called Aerial-Biped. Designed primarily for entertainment, Aerial-Biped enables “a richer physical expression” by automatically generating walking gaits in sync with its quadrotor body.

Until someone invents a robot that can moonwalk, you can model a gait that appears normal by simply making sure that the velocity of a foot is zero as long as it’s in contact with the ground. The Aerial-Biped robot learns how to do this through reinforcement learning in a physics simulator, and the policy transfers to the robot well enough that the legs can appear to walk as the quadrotor moves.

Right now, getting this to work on the real robot involves using motion capture on the drone, so it’s not yet suitable for out-of-lab wandering. The researchers are working on adding more degrees of freedom to both the body and the legs, with the goal of being able to physically imitate the gaits of animated characters. 

For a bit more detail on this project, we spoke with lead author Azumi Maekawa from the University of Tokyo.

Where did you get the idea for this research?

We were inspired by bipedal robots that use invisible force to get stability, such as Magdan, created by Tomotaka Takahashi (an electromagnet on the bottom of its feet lets it walk on a metal plate), and BALLU (which uses buoyancy of a helium-filled balloon). The foot trajectory generation method is based on the assumption that one of the key features of walking (or at least the appearance of walking) is that the velocity of the foot in contact with the ground is zero.

What function do the legs serve on this robot? Or, what is the goal of adding legs to a quadrotor?

The goal is to develop a robot that has the ability to display the appearance of bipedal walking with dynamic mobility, and to provide a new visual experience. The robot enables walking motion with very slender legs like those of a flamingo without impairing dynamic mobility. This approach enables casual users to choreograph biped robot walking without expertise. In addition, it is much cheaper compared to a conventional bipedal walking robot.

Are there practical applications for a robot like this? What are you working on next?

Although it is at a prototype stage now, in the future, an entertainment application such as performance or animatronics can be considered. We aim to develop a biped robot that has the ability to display desired motions, including various dances, in addition to walking. I think this work has the potential to make virtual reality experiences possible in the physical world by enabling movements that have been impossible due to the constraints of the mechanisms and properties of real-world characters.

“Aerial-Biped: A New Physical Expression by the Biped Robot Using a Quadrotor,” by Azumi Maekawa, Ryuma Niiyama, and Shunji Yamanaka from the University of Tokyo, was presented at SIGGRAPH Emerging Technologies in Vancouver, Canada.

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Robot with threads near a fallen branch

RoMan, the Army Research Laboratory's robotic manipulator, considers the best way to grasp and move a tree branch at the Adelphi Laboratory Center, in Maryland.

Evan Ackerman
LightGreen

“I should probably not be standing this close," I think to myself, as the robot slowly approaches a large tree branch on the floor in front of me. It's not the size of the branch that makes me nervous—it's that the robot is operating autonomously, and that while I know what it's supposed to do, I'm not entirely sure what it will do. If everything works the way the roboticists at the U.S. Army Research Laboratory (ARL) in Adelphi, Md., expect, the robot will identify the branch, grasp it, and drag it out of the way. These folks know what they're doing, but I've spent enough time around robots that I take a small step backwards anyway.

This article is part of our special report on AI, “The Great AI Reckoning.”

The robot, named RoMan, for Robotic Manipulator, is about the size of a large lawn mower, with a tracked base that helps it handle most kinds of terrain. At the front, it has a squat torso equipped with cameras and depth sensors, as well as a pair of arms that were harvested from a prototype disaster-response robot originally developed at NASA's Jet Propulsion Laboratory for a DARPA robotics competition. RoMan's job today is roadway clearing, a multistep task that ARL wants the robot to complete as autonomously as possible. Instead of instructing the robot to grasp specific objects in specific ways and move them to specific places, the operators tell RoMan to "go clear a path." It's then up to the robot to make all the decisions necessary to achieve that objective.

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