Degrees of Freedom

• In rigid body kinematic and dynamic modeling, each body has only 6 allowed degrees of freedom (DOF), translation in Global X, Y and Z and rotation about Global X, Y and Z.

 

• Kinematic constraints remove DOF from bodies. For example, a revolute joint allows one rotational DOF. In other words, you can say it removes 5 DOF.

• Which of the six DOF are removed from a body depends on the type of constraints and the number of constraints used on that body.

Example:
A pendulum is connected to a fixed block using a revolute joint. The revolute constraint removes 5 DOF from the pendulum and leaves 1 rotational DOF.

If a motor was used in place of the revolute constraint, the motor is also considered a constraint and removes the same DOF as a Revolute but it also removes a DOF for the main rotational axis. In this case, the system would have 0 DOF. Even though it would still rotate about the Z axis, this rotation is fully controlled (or defined).