Morgan Quigley’s low-cost Robot possess 7 degree-of-freedom (7-DoF). It possess a series elastic actuator (SEA) arm that costs way under $5,000 The hand possess shape deposition manufacturing (SDM) that gives it reflexes to catch flying (tossed) balls.
Morgan calls it A Low-Cost Compliant 7-DOF Robotic Manipulator [PDF] that costs just $4135. The arm is made from lasercut plywood, and is powered by four stepper motors in the base and three small dynamixel servo motors in the lower arm. This is done via rubber tubes that get squished between two plates, as can be seen in the video. The arm is pretty light that makes it human-safe. The arm moves at 1.5m/s carrying a 2kg payload. The arm is used to demonstrate pancake cooking (pouring batter, flipping pancakes), using the intrinsic compliance of the arm to aid in interaction with objects.
The mechanism of catching the ball is based on inputs taken from multiple sensors. It uses accelerometers and magnetometers to detect the wearer’s pose. It then calculates the location of the thrower’s hand and inverse kinematics (tracking trajectory) are used to get the robot’s gripper to track that location. The robot is powered by the Robot Operating System (ROS).
Watch the Stanford’s creation in action:
Rollin Justin Robot, a much faster and mature version based on similar concept