The configuration space of a robotic arm in a tunnel
  We study the motion of a robotic arm inside a rectangular tunnel. We prove that the configuration space of all possible positions of the robot is a CAT(0) cubical complex. This allows us to use techniques from geometric group theory to find the optimal way of moving the arm from one position to another. We also compute the diameter of the configuration space, that is, the longest distance between two positions of the robot. 
Federico Ardila, Hanner Bastidas, Cesar Ceballos, John Guo
math.CO math.MG