What is a Ball-Joint?

A Ball-Joint makes a Point in one Part coincide with a Point in a different Part. The Parts can be in two different Mechanisms.

You must do Add Ball-Joint two times, with a Ball-Joint at each end of one Part.


Connecting Part : a Part that has a Ball-Joint at each end.

Completely-Free Part : a Part with 3 degrees-of-freedom and needs at least two joints.

Free Part : a Part with 1 degrees-of-freedom

See: Ball-Joint dialog-box, Ball-Joint configurations, How to Edit a Connecting Part,

Add Ball-Joint

Add Ball-Joint icon

Kinematic Elements Toolbar : Add Ball-Joint icon

Menu :

Add menu > Mechanism sub-menu > Add Ball-Joint

Dialog-Box :

Ball-Joint dialog-Box

You must know :

How to add Mechanism-Editors to different Planes.

The difference between a Free-Part and a Completely Free Part.


Add two Mechanism-Editors and the kinematic elements before you add the Ball-Joints.

The Mechanism-Editors cannot be parallel to each other. They are typically perpendicular() to each other.

Below: an example preparation


Mechanism-Editor A

Mechanism-Editor B - the active Mechanism-Editor

A kinematic-chain that is not kinematically-definedRed-14-4.

A typical arrangement has:

A Free-PartRed-14-4 (with a Pin-Joint or a Slide-Joint).

Do Add Ball-Joint TWO TIMES.

Do Add Ball-Joint to the two ends of the Completely Free Part.


Add Ball-Joint #1

1.Make Mechanism-Editor B active.
2.Click PointRed-14-1b in the Completely-Free Part
3.Click PointRed-14-2 in the Free Part

Note: if you cannot select the two Points to add a Ball-Joint:

Toggle-Off the Auto-Update tool.


When you add Ball-Joint #1 you can see the Ball-Joint symbol.

However, the PointsRed-14-1bRed-14-2 do not snap together.

They will snap together when you add Ball-Joint #2



Add Ball-Joint #2

4.Click PointRed-14-3 at the other end of the Completely-Free Part
5.Click PointRed-14-4 - the Grey Point - in the kinematically-defined Part that is in Mechanism-Editor(A)



The Ball-JointsRed-14-6Red-14-7 snap to the Points in Mechanism(A) and (B).

The Completely-Free Part and the Free Part are kinematically-definedRed-14-8



1.Edit the Connecting-Part to edit its length and to diameter of the shaft-symbol.
2.Edit the Ball-Joint to edit the diameter of the ball-symbol.

In the Kinematics-Tree, each Ball-Joint is represented by the letter S, which is for Spherical-Joint.

The Ball-JointsRed-14-6Red-14-7 are the S Joints in the S-S-R and the S-S-P Dyad.

A Connecting PartRed-14-5 is a Part with two Ball-Joints.

tog_minusEdit the Connecting-Part: Length and Shaft Diameter and Ball-Diameter

You cannot add Solids to Connecting-Parts.

However, it is possible to add and edit the shaft-diameter of the rod between the Ball-Joints.

To edit the Ball-Diameter of the Ball-Joints - see Ball-Joint dialog-box


Edit the Connecting-Part

MechDesigner uses the first dimension you add to the Part in the Part-Editor as the symbolic radius for the Connecting-Part.

To add and edit the Dimension, you must edit the Connecting-Part

1.Double-click the symbol for the Connecting-Part

MechDesigner opens the Connecting-Part in the Part-Editor.


2.Add a Line or Circle to the Part
3.Add a dimension to the Line or Circle


When you edit dimensions in a Part and the view is not the Front View, the CAD-Line, Axes, sketch-elements and dimensions may show in unusual places!

If you cannot add or edit a dimension, then click View | Front Plane.

4.Edit the Dimension to 7mm, with the dimension tool
5.Edit the Length of the Connecting-Part to 100mm, in the usual way.


6.Close the Part-Editor

Use Visibility toolbar > Show Model in Mechanism

It still is not very attractive!

Tutorials and Reference Help Files for MechDesigner and MotionDesigner 14.2 + © Machine, Cam, Mechanism, and Motion Design Software by PSMotion Ltd