Six degrees of freedom

"Six axis" redirects here. For the Playstation 3 video game console controller, see Sixaxis.

The six degrees of freedom: forward/back, up/down, left/right, pitch, yaw, roll

Six degrees of freedom (6DoF) refers to the freedom of movement of a rigid body in three-dimensional space. Specifically, the body is free to move forward/backward, up/down, left/right (translation in three perpendicular axes) combined with rotation about three perpendicular axes, often termed pitch, yaw, and roll.

Robotics

Serial and parallel manipulator systems are generally designed to position an end-effector with six degrees of freedom, consisting of three in translation and three in orientation. This provides a direct relationship between actuator positions and the configuration of the manipulator defined by its forward and inverse kinematics.

Robot arms are described by their 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.

In 2007, Dean Kamen, inventor of the Segway, unveiled a prototype robotic arm with 14 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.

Engineering

The term is important in mechanical systems, especially biomechanical systems for analyzing and measuring properties of these types of systems that need to account for all six degrees of freedom. Measurement of the six degrees of freedom is accomplished today through both AC and DC magnetic or electromagnetic fields in sensors that transmit positional and angular data to a processing unit. The data are made relevant through software that integrate the data based on the needs and programming of the users.

Ascension Technology Corporation has recently created a 6DoF device small enough to fit in a biopsy needle, allowing physicians to better research at minute levels. The new sensor passively senses pulsed DC magnetic fields generated by either a cubic transmitter or a flat transmitter and is available for integration and manufacturability by medical OEMs.

An example of six degree of freedom movement is the motion of a ship at sea. It is described as:

Translation:

1. Moving up and down (heaving);
2. Moving left and right (swaying);
3. Moving forward and backward (surging);

Rotation

1. Tilting forward and backward (pitching);
2. Turning left and right (yawing);
3. Tilting side to side (rolling).

See also: Euler angles

Game controllers

Six degrees of freedom also refers to movement in video game-play.

First-person shooter (FPS) games generally provide five degrees of freedom: forwards/backwards, slide left/right, up/down (crouch/lie), yaw (turn left/right), and pitch (look up/down). If the game allows leaning control, then some consider it a sixth DoF; however, this may not be completely accurate, as a lean is a limited partial rotation.

The term 6DoF has sometimes been used to describe games which allow freedom of movement, but do not necessarily meet the full 6DoF criteria. For example, 6DoF has been used to describe some space combat games like Namco's Star Luster, Bandai's Kidou Senshi Z-Gundam: Hot Scramble, and Arysis Software's Star Cruiser, where players or vehicles are free to move in any 3-dimensional direction, but may not have all three rotational axes. Dead Space 2, and to a lesser extent, Homeworld and Zone Of The Enders similarly allow freedom of movement.

Some examples of true 6DoF games, which allow independent control of all three movement axes and all three rotational axes, include Futuremark Games Studio's Shattered Horizon, Descent and its sequels, Miner Wars and Forsaken.

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

The game controller of the PlayStation 3 contains a "Sixaxis" feature, which makes use of the six degrees of freedom. The Sixense TrueMotion is similar but for the PC.

See also

• Degrees of freedom (mechanics)
• Ship motions, an example in a vehicle.