Development of Cog started in 1993. The robot's first incarnation was as a 14-DOF upper torso with one arm and a rudimentary visual system. The robot was later upgraded to include two arms, a head, and more sensors. Many graduate students worked on the robot, including Brian Scassellati (now a Yale professor), Aaron Edsinger (founder of Meka Robotics), and Cynthia Breazeal (now an MIT professor). There were no blueprints or schematics. "The robot is just hack on a kludge to a 'temporary solution,' held together with Velcro, 24AWG wire, and solder," the researchers wrote on their website, only half jokingly. Cog was one of the first humanoid robots to use series elastic actuators: The motors on the arms were connected to the joints in series with a torsional spring, which protected the gearbox and provided compliance and more safety for people interacting with the arms.