Six degrees of freedom (6DOF), or sometimessix degrees of movement, refers to the sixmechanical degrees of freedom of movement of arigid body inthree-dimensional space. Specifically, the body is free to changeposition as forward/backward (surge), up/down (heave), left/right (sway)translation in threeperpendicularaxes, combined with changes inorientation throughrotation about three perpendicular axes, often termed yaw (normal axis), pitch (transverse axis), and roll (longitudinal axis).
Three degrees of freedom (3DOF), a term often used in the context ofvirtual reality, typically refers to tracking of rotational motion only: pitch, yaw, and roll.[1][2]
Serial andparallel manipulator systems are generally designed to position anend-effector with sixdegrees 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 itsforward andinverse kinematics.
Robot arms are described by theirdegrees of freedom. This is a practical metric, in contrast to the abstract definition of degrees of freedom which measures the aggregate positioning capability of a system.[3]
In 2007,Dean Kamen, inventor of theSegway, unveiled a prototype robotic arm[4] with 14 degrees of freedom forDARPA.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 intorso andneck.[5]
The term is important inmechanical systems, especiallybiomechanical 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 is made relevant through software that integrates the data based on the needs and programming of the users.
The six degrees of freedom of a mobile unit are divided in two motional classes as described below.
Translational envelopes:
Rotational envelopes:
In terms of aheadset, such as the kind used forvirtual reality, rotational envelopes can also be thought of in the following terms:
There are three types of operational envelope in the Six degrees of freedom. These types areDirect,Semi-direct (conditional) andNon-direct, all regardless of the time remaining for the execution of the maneuver, the energy remaining to execute the maneuver and finally, if the motion is commanded via a biological entity (e.g. human), a robotical entity (e.g. computer) or both.
Transitional type also exists in some vehicles. For example, when theSpace Shuttle operated inlow Earth orbit, the craft was described as fully-direct-six because in the vacuum of space, its six degrees could be commanded viareaction wheels andRCS thrusters. However, when the Space Shuttle was descending through the Earth's atmosphere for its return, the fully-direct-six degrees were no longer applicable as it wasgliding through the air using its wings and control surfaces.
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 (jump/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. Earlier first-person games such asWolfenstein 3D andDoom also lacked pitch rotation, and were only able to offer four degrees of freedom.
The term6DOF has sometimes been used to describe games which allow freedom of movement, but do not necessarily meet the full 6DOF criteria. For example,Dead Space 2, and to a lesser extent,Homeworld andZone Of The Enders allow freedom of movement.
Some examples of true 6DOF games, which allow independent control of all three movement axes and all three rotational axes, includeElite Dangerous,Shattered Horizon, theDescent franchise, theEverspace franchise,Retrovirus,Miner Wars,Space Engineers,Forsaken andOverload (from the same creators ofDescent). The space MMOVendetta Online also features 6 degrees of freedom.
Motion tracking hardware devices such asTrackIR and software-based apps likeEyeware Beam are used for 6DOF head tracking. This device often finds its places inflight simulators and other vehicle simulators that require looking around the cockpit to locate enemies or simply avoiding accidents in-game.
The acronym3DOF, meaning movement in the three dimensions but not rotation, is sometimes encountered.
TheRazer Hydra, a motion controller for PC, tracks position and rotation of two wirednunchucks, providing six degrees of freedom on each hand.
TheSpaceOrb 360 is a 6DOF computer input device released in 1996 originally manufactured and sold by the SpaceTec IMC company (first bought byLabtec, which itself was later bought byLogitech). They now offer the3Dconnexion range of 6DOF controllers, primarily targeting the professionalCAD industry.
The controllers sold with HTC VIVE provide 6DOF information by the lighthouse, which adopts Time of Flight (TOF) technology to determine the position of controllers.
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