
Joints 
A joint is an object that has at least one intrinsic Degree of Freedom (DoF). Joints are used to build mechanisms and to move objects as can be seen in following figures:

[Robotic manipulator (left) and visible joints/motor (right)]
Joints are added to the scene with [menu bar --> Add --> Joint]. When positioning joints in the scene, use the coordinate and transformation dialog if you know the exact desired position and orientation. In other situations, when for instance you imported meshes without knowing the exact position/orientation of associated joints, follow following steps:
Identify the shape that is directly linked to the joint.
Isolate the shape into a different scene (copy the shape from the current scene, create a new scene and paste the shape).
Enter the triangle edit mode or vertex edit mode and simplify the shape until you are left with a tube (or similar). Leave the edit mode.
Now the remaining of the original shape should have the same position and orientation as the joint you wish to add.
Add a joint.
Select the joint then the shape, and in the coordinate and transformation dialog, click apply to selection for the orientation and position part of the coordinates section. The joint should now be correctly positioned.
The joint orientation might have to be adjusted by a 90 degrees rotation about its x or y-axis. This can be done in the transformations part of the same dialog (make sure own frame is selected).
The joint now has the correct position and orientation, and can be copied/pasted into the original scene.
Following figures illustrate above procedure:

[Positioning and orienting a joint appropriately]
Some joint data can be recorded by graph objects. Refer to graphs and graph data streams for more information about how to record joint data.
Recommended topics
Joint types and operation
Joint dialog
Coordinate and transformation dialog
Shape edit modes
Graphs
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