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A New Way for Robots to Balance on Two Feet

This robot keeps its feet firmly planted on the floor, even when kicked by a mean researcher or slammed with a heavy ball

2 min read
A New Way for Robots to Balance on Two Feet

It turns out that studying how to make robots grasp objects with their hands is helping researchers figure out how to make robots balance on their feet. 

Christian Ott and his team at the German Aerospace Center's Institute of Robotics and Mechatronics have discovered a way to keep bipedal robots from falling over by using principles from robot grasping.

As shown in this video released at the 2011 IEEE-RAS International Conference on Humanoid Robots in Bled, Slovenia, the new approach allows the DLR Biped, a legged robot based on KUKA's lightweight system, to keep its feet firmly planted on the floor, even when kicked by a mean researcher or slammed with a 5-kilogram medicine ball. You try to do that!

It may appear that the robot is not doing much. But in reality, upon getting hit or pushed, it is rapidly adjusting the torque of its joints to counteract the disturbance -- and avoid falling on its face (well, it has no face, but you get the idea).

Imagine you are standing and someone starts pushing on your back. You react by putting more pressure on your forefeet. This nonrigid way of reacting to external forces and perturbations is called compliance, and is highly sought-after in cutting edge robotics -- it's better to absorb an impact than break or fall over.

That's exactly what the DLR Biped is doing. It's using a balancing controller to adjust its center of mass in a compliant way.

DLR Biped

Today, most bipedal humanoid robots rely on a different balancing approach, known as Zero Moment Point (ZMP). It's been around since the mid-1980s and is used by many famous robots, such as ASIMO and WABIAN-2. With ZMP, robots rely on force sensors on their feet and a feedback control loop that constantly adjusts their position relative to this stable point (the ZMP) to keep balanced.

Ott's approach tackles the problem without needing the ZMP and foot sensors. Their technique "uses a formulation coming from the field of robot grasping, which considers at the same time a desired force and torque that allow the robot to recover the initial position and orientation [when disturbed]," the researchers write in "Posture and Balance Control for Biped Robots Based on Contact Force Optimization," which won the Best Paper award at the conference.

DLR Biped

Their grasping-inspired controller elegantly takes into account friction at the contact points with the ground. First, it uses an optimization algorithm that computes the forces needed at each point to neutralize the perturbation. Then it determines how to move the robot's torque-controlled joints to produce the desired forces. The result: equilibrium.

The next obvious step would be to keep the stability while walking. The challenge is that the method currently uses a finite set of predetermined contact points, but the researchers are confident that they can extend it to a more general model. And they say it could be applied to one-legged and multi-legged robots as well.

Some researchers remain skeptical that bipedal robots will ever work (especially with the slew of face-planting robot videos), but advances like this will allow them to better integrate into our environment -- even if people try to push them over.

Angelica Lim is a graduate student at the Okuno and Ogata Speech Media Processing Group at Kyoto University, Japan.

Images and video: DLR

UPDATED: 7:57 p.m.

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The Bionic-Hand Arms Race

The prosthetics industry is too focused on high-tech limbs that are complicated, costly, and often impractical

12 min read
A photograph of a young woman with brown eyes and neck length hair dyed rose gold sits at a white table. In one hand she holds a carbon fiber robotic arm and hand. Her other arm ends near her elbow. Her short sleeve shirt has a pattern on it of illustrated hands.

The author, Britt Young, holding her Ottobock bebionic bionic arm.

Gabriela Hasbun. Makeup: Maria Nguyen for MAC cosmetics; Hair: Joan Laqui for Living Proof

In Jules Verne’s 1865 novel From the Earth to the Moon, members of the fictitious Baltimore Gun Club, all disabled Civil War veterans, restlessly search for a new enemy to conquer. They had spent the war innovating new, deadlier weaponry. By the war’s end, with “not quite one arm between four persons, and exactly two legs between six,” these self-taught amputee-weaponsmiths decide to repurpose their skills toward a new projectile: a rocket ship.

The story of the Baltimore Gun Club propelling themselves to the moon is about the extraordinary masculine power of the veteran, who doesn’t simply “overcome” his disability; he derives power and ambition from it. Their “crutches, wooden legs, artificial arms, steel hooks, caoutchouc [rubber] jaws, silver craniums [and] platinum noses” don’t play leading roles in their personalities—they are merely tools on their bodies. These piecemeal men are unlikely crusaders of invention with an even more unlikely mission. And yet who better to design the next great leap in technology than men remade by technology themselves?

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