Engineers at the Robotics and AI Institute have built a two-armed robot that trades stiffness for speed, aiming to catch, throw and hand over objects in the way people do. The design is described in the journal Science Robotics.
Less inertia, more control
The robot, called AthenaZero, stands about 1.6 metres tall with a wingspan of roughly 1.8 metres. It has a single degree of freedom in its torso, two seven-joint arms and two underactuated hands with six joints each, driven by 22 actuators across 27 joints in total. The team used quasi-direct drive motors and moved the heavy transmission parts away from the joints. The result is an effective mass at the hand comparable to a human's, with reflected inertia about an order of magnitude lower than a conventional high-stiffness arm.
Why catching is hard
Most industrial arms are built to hold a position rigidly. That works for moving a tool along a known path, and badly when an object arrives with momentum. A stiff arm passes the shock of contact straight into the gearbox and the object, which is why robots struggle to catch a ball or hand something to a person without careful planning. A lighter arm gives up some trajectory tracking accuracy but gains the ability to accelerate quickly and absorb contact, so control comes from motion rather than force.
What it means for the wider field
AthenaZero still lifts more than 3 kg, enough for the small parts that move between workstations. The prototype matters because it carries a design lesson for anyone building machines that work near people: motors, gearboxes and bearings set how much mass the arm has to move, and every gram saved at the wrist is worth several at the shoulder. Dynamic manipulation — catching, throwing, sliding a part into place — is the next capability robotics researchers are chasing, and it needs hardware that can be pushed around by the world instead of fighting it.
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