Adrian and Matt over at RepRap decided to give themselves a sixth sense. They rapidly prototyped a solution that provides a way to feel their surroundings. They were inspired by the FeelSpace Project which is a belt that gently vibrates in front, back or to the sides based on a smartphone navigational app.
The RepRap folks took a slightly different approach and attached ultrasonic rangefinders and cellular phone vibrators to their arms. They 3D printed cases for the distance sensors and vibrators directly on fabric to be attached to each arm. An Arduino was used to constantly scan in data from the distance sensors and directly drive the motors.