# Perpendicular Axes

A perpendicular axes joint is a five degree-of-freedom primitive constraint. The constraint is imposed such that the Z axis of a reference marker on one body (Body 2) remains perpendicular to the Z axis of a reference marker on the other body (Body 1) connected by the joint. All three translations are free along with two rotations about the Z axis of markers on both of the bodies defining the joint orientation. Joint primitives like perpendicular axes joints may not have a physical existence. These types of joints can be used to impose unique constraints where using a regular joint would not be possible.

The perpendicular axes joint needs two axes (Axis 1 and Axis 2) that are mutually perpendicular and each belonging to Body 1 and Body 2 respectively.
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 Axis 1.
• Point - Select a point that lies on the desired alignment axis for 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.
6. Define Axis 2 using the same steps.
If editing a compliant joint, see Edit Compliant Joints or Bushings. To edit user-defined properties, see Edit User-Defined Joints.