The Cog Shop
MIT Artificial Intelligence Laboratory
545 Technology Square, #920
Cambridge, MA 02139
Two fundamental goals guided the design of the body for Cog. First, the robot should be
anthropomorphic to encourage humans to interact with it in a natural way. The most
important human characteristics to emulate are size, speed, and range of motion. To
achieve natural human interactions, we felt it would be better to build a robot with
modest load-carrying capacity but human-like speed. Second, the robot's hardware should
use well-known technology and components to minimize design and construction time.
Cog's torso has six degrees of freedom: the waist bends side-to-side and
front-to-back, the "spine" can twist, and the neck tilts side-to-side,
front-to-back, and twists left-to-right. Mechanical stops on the body and neck give a
human-like range of motion, as shown below (Not shown are the neck twist (180 degrees) and
body twist (120 degrees)).
Cog resembles a human from the waist up. The robot is mounted on a
pedestal to simplify design, construction, and power-efficiency problems. By placing power
supplies and electronics in the base, it is easier to fit the robot in a human-sized torso
and provide ample power to the electronics and motors.
Table 1 (shown below) summarizes the actuator requirements for the six degrees of
freedom. The torque requirements were based on targets of a 5 lb head, 10 lb arms, and a
30 lb torso. The motors and mechanical components for the head weigh 3 lb, and for the
body weigh 24 lb. Electronics and wires consume the rest of the weight allowance. The
actuators in the robot are all DC gearmotors equipped with optical encoders for position
|Degree of Freedom
|Waist Roll (side to side)
|Waist Pitch (front to Back)
The robot has sensors on its body. Each degree of freedom has current sensing in the
motor controller to provide some force feedback. We avoided strain gages and other more
sophisticated force sensors because of the accelerated construction schedule. There is
also a temperature sensor on each motor and driver circuit. These sensors can warn the
robot when a motor is being overworked. In the future this may be used to implement a
"fatigue" sense. There are also currently plans to implement a "skin"
of touch sensors for Cog.