Six degrees of freedom

Six degrees of freedom (6DoF) refers to motion in three dimensional space, namely the ability to move forward/backward, up/down, left/right (translation in three perpendicular axes) combined with rotation about three perpendicular axes (yaw, pitch, roll). As the movement along each of the three axes is independent of each other and independent of the rotation about any of these axes, the motion indeed has six degrees of freedom.

Robot arms are often categorized by their degrees of freedom (typically achieving more than six degrees of freedom). This number typically refers to the number of single-axis rotational joints in the arm, where a higher number indicates an increased flexibility in positioning a tool. This is a practical metric, in contrast to the abstract definition of degrees of freedom which measures the aggregate positioning capability of a system. Dean Kamen, inventor of the Segway, recently unveiled a prototype robotic arm with 21 degrees of freedom for DARPA. Humanoid robots typically have 30 or more degrees of freedom, with six degrees of freedom per arm, five or six in each leg, and several more in torso and neck.

"Six degrees of freedom" is also a gameplay style wherein there is often no gravity, and players are free to move in any 3-dimensional direction. It is used in games such as "Descent" and its sequels, and to a lesser extent the "Homeworld" and "Zone Of The Enders" games.

First-person shooter (FPS) games generally provide four degrees of freedom (five counting jumping/crouching/swimming, or even six counting leaning.) The player can move in any direction along the ground and can alter pitch and yaw, but not roll.

The acronym 3DoF, meaning just movement in the three dimensions and not rotation, is sometimes encountered.

References

# Paul, Richard P., "Robot Manipulators: Mathematics, Programming, and Control", MIT Press, 1981.
# Craig, John J., "Introduction to Robotics: Mechanics and Control", Addison-Wesley, 1986.