You add motion drivers to define the movement of a joint or part over time. The motion is defined on the Motion tab in the Joint or Part Motion dialog box.
The only difference in motions on joints compared to parts is that the joint already defined the available directions that motions can be applied in whereas for a part motion, the user must define the direction by geometry selection. See Defining Motion on Parts.
A motion dictates the displacement, velocity, or acceleration of as a function of time. For example, the following expression function defines a constant velocity motion driver that can be used to rotate the first rigid body one complete revolution (360 degrees) per unit time with respect to the second rigid body:
360d * TIME
Learn more about motion expression functions.
The motion driver supplies the force required satisfy the defined motion. This force is available as an output at each motion driver in COSMOSMotion. This output can be used to properly size a motor or actuator.
Because motions are enforced constraints,
they will apply as much force as is needed to achieve the requested movement.
This may cause a simulation to fail if it reaches a locked-up condition
or excessively high force values for models with 3D contact or joint limits.
Think of motions as having infinite power.
In the DOF text box on the Motion panel, you can select the degree of freedom to which the motion is applied. The degrees of freedom can be either rotational or translational. For example, revolute joints have one rotational degree of freedom. You may apply only one rotational motion to a revolute joint. Planar joints have two translational and one rotational degree of freedom. Therefore, you can apply two translational motions and one rotational motion to a planar joint. You can apply a motion to any degree of freedom on a joint. Part motion always lists 6 degrees of freedom.
A motion driver can define the joint displacement, velocity, or acceleration. By default, the motion driver type is set to Free, meaning that the joint is free to move as driven by the rest of the mechanism. You can set the motion type in the Insert Joint dialog box on the Motion panel. The simplest motions to define are the constant displacement, constant velocity, or constant acceleration motions.
Constant Displacement - Specify a constant value in the Motion Expression text box when the motion type is set to Displacement. A constant displacement motion holds the joint in a fixed position. The rigid bodies that the joint connects do not move relative to each other during simulation. The effect is like using a fixed joint to constrain the two rigid bodies. The advantage of constraining two parts with a constant displacement motion is that the motion can be adjusted to different positions. Constraining two rigid bodies with a fixed joint, however, is computationally more efficient.
Constant Velocity - Specify a constant value in the Motion Expression text box when the motion type is set to Velocity. This moves the joint with the required force to produce a constant velocity.
Constant Acceleration - Specify a constant value in the Motion Expression text box when the motion type is set to Acceleration. This motion moves the joint with the required force to produce a constant acceleration.