Mechanism Design and Mechanism Dynamics > Mechanism Dynamics > Bushing Loads > About Bushing Loads
About Bushing Loads
You can create a Bushing Load feature to simulate movement between two bodies. Although a bushing load is ignored in kinematic studies (including kinematic drag), it is a factor in dynamic studies (dynamic, static and force balance analyses). If you use a weld connection for the bushing load, you can lock a motion axis and apply spring stiffness and damping force or torque to each of the six degrees of freedom. This is equivalent to applying an infinite spring stiffness to the axis, effectively removing the corresponding degree of freedom.
It is often assumed that a bushing between two bodies transfers movement directly. However, when studying dynamic model behavior, best practice is to assume that two bodies with a bushing between them move separately. The Bushing Load feature simulates the movement between the bodies. When you use a bushing load in a dynamic analysis, you apply springs and dampers to each axis of the referenced connection and adjust the spring stiffness and damper coefficients as required.
You can check this behavior when modeling. Create a bushing load on a Weld or a 6DOF connection, and then set the spring stiffness and the damping coefficient for each motion axis (the value of the unstretched length of each spring is zero).
If you create a bushing load on a weld connection, you can lock any motion axis (degree of freedom) by setting an infinite value for the spring stiffness and typing “Locked” in the definition dialog box. When you lock a motion axis, you are ensuring direct transmission of movement. The coefficient values are stored in the feature definition as valid parameters, and are named as follows:
<AXIS_NAME>_STIFFNESS or <AXIS_NAME>_DAMPING_COEFFICIENT where AXIS_NAME is one of the TR1, TR2, TR3, ROT1, ROT2, and ROT3 strings (translational axes 1, 2, 3 and rotational axes 1, 2, 3).