Ball

A ball joint (also known as a spherical joint; socket joint) is a three degree-of-freedom kinematic pair used in mechanisms. Ball joints provide three-axis rotation function used in many places, such as steering racks to knuckles via tie-rods and knuckle-to-control arm joints.

1. If the Joints panel is not currently displayed, select the desired joint by clicking on it in the Project Browser or in the modeling window.
   The Joints panel is automatically displayed.
2. From the Connectivity tab, click Body 1 and pick a body from the modeling window, or double-click Body 1 to open the Model Tree (from which the desired body can be selected).
   Note: If the selected joint is a pair entity, first distinguish between the Left and Right tabs in the panel, and then edit the properties. When defining a pair joint, use pair entities for Body, Origin, etc.
3. Similarly, click Body 2 and select the desired body from the modeling window (or use the Model Tree).
4. Click the Point collector (under Origin) and select a point from the modeling window, or double click the Point collector to open the Model Tree (from which the desired point can be selected).
5. Specify the frictional properties for the joint.
   1. Activate the Use Friction check box from the Friction Properties tab.
      The Friction Properties tab displays.
   2. Specify the friction coefficients, effect options, and geometrical parameters.
      • The Stiction Transition Velocity determines the velocity at which the friction regime transitions from stiction to dynamic friction.
      • Torque Preload: Specify the preload torque in the joint (*if a preload effect is activated).
      • Ball Radius: Specify the radius of the ball joint.
   3. Click the LuGre Parameters tab and input desired values.
      MotionSolve uses the LuGre (Lundt-Grenoble) model for friction. Refer to the MotionSolve Force_JointFriction modeling statement for additional details.

      • Bristle stiffness: Specify the bristle stiffness in the LuGre model. This models the stiffness resisting micro-deformation in the friction element.
      • Damping Coefficient: Specify the damping coefficient for the pre-displacement (or stiction) regime. This damps out bristle vibrations in the pre-displacement regime.
      • Viscous Coefficient: Specify the coefficient for the viscous damping force that occurs when relative sliding actually begins. This is responsible for the increase in friction force with the increase in the slip velocity.