Georgia Institute of Technology researchers have built a wearable robotic limb that allows drummers to play with three arms. The two-foot long “smart arm” can be attached to a musician’s shoulder. It responds to human gestures and the music it hears. When the drummer moves to play the high hat cymbal, for example, the robotic arm maneuvers to play the ride cymbal. When the drummer switches to the snare, the mechanical arm shifts to the tom. When the robot approaches an instrument, it uses built-in accelerometers to sense the distance and proximity. On-board motors make sure the stick is always parallel to the playing surface, allowing it to rise, lower or twist to ensure solid contact with the drum or cymbal. The next step is linking the arm’s movements to brain activity. The team is already experimenting with an electroencephalogram (EEG) headband that detects a drummer’s brain patterns. The researchers see doctors using a third arm to bring them tools, supplies, or even participate in surgeries.