Universal

A universal joint is a two degree-of-freedom kinematic pair used in mechanisms. It is functionally identical to, and also referred to as a Hooke joint. The only difference between these two joints is the way that the joint is defined. Universal joints provide two rotational functions in applications such as propeller shafts, drive shafts, and steering columns.

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. Define the orientation of the shafts of the joint by selecting Shaft or Crosspin (or a combination of both) from the Orient using drop-down menus.
6. Use the corresponding drop-down menus and collectors to specify the Shaft or Crosspin orientations.
   • Point - Select a point that lies on the desired alignment axis for shafts/bodies connected by the joint.
   • Vector - Global axes can be used for vectors by clicking on the desired axis (x, y, or z) in the modeling window or by browsing through the Model Tree.
7. 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).
      • Friction Arm: Specify the effective radius at which the axial force acts on a revolute or universal joint.
      • Pin Radius: Specify the pin radius for a revolute, cylindrical, or universal joint.
      • Bending Arm: Specify the effective length of a joint to calculate the reaction bending moment on the joint.
      • Rot. Constraint: Specify the rotational constraint on which the joint friction acts.
   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.