What is a Magnetic-Joint?

Add Magnetic-Joint pulls a circular Profile, that is in one Part, to be in continuous contact with an irregular Profile, that is in a different Part. One Profile is circular and the other Profile is irregular*.

Why use a Magnetic-Joint?

A frequent application of the Magnetic-Joint is to reverse-engineer a cam, and to find the motion of a Cam-Follower from the shape of an existing cam.

Add Magnetic Joint

Add Magnetic-Joint icon


[right of graphic-area] Machine Elements Toolbar : Add Ball-Joint icon


Add menu > Mechanism sub-menu > Add Magnetic-Joint

Ad Magnetic-Joint command to pull two Profiles that are in two different Parts, together so that they become in continuous contact.

One Profile is circular and the other Profile is irregular*.
Add Magnetic-Joint 'pulls' the circular Profile onto the irregular* Profile.
The Part with the irregular Profile rotates or slides.

* The shape of the 'irregular' Profile can be derived from a Point-Cloud or a sketch-loop.


Magnetic-Joint dialog-box



Two kinematically-defined chains,

At least one Part and one Profile in each kinematic-chain.

With reference to the image above:

KINEMATIC-CHAIN 1; PART 1: [see image to the left]

2s Has an irregular Profile , or a Curve derived from a Point-Cloud

1s-red A Motion-Dimension FB. It does not need a wire at its input-connector

The Part rotates in this model (it is a Rocker / Crank). It might also be a Slider.

Profile2s does not need to be a child to the Part that has its motion specified by the Motion-Dimension FB1s-red, it must only belong to Kinematic-Chain 1.

KINEMATIC-CHAIN; PART 2: [see image above]

3s A Motion-Dimension FB specifies the position of the Part before you apply the Magnetic-Joint. It is not necessary to connect a wire to its input-connector. If a wire is connected, then the motion-values are ignored.

4s Has a circular Profile as a child to the Part

This Part is pulled by the Magnetic-Joint so that the circular Profile4s becomes in continuous contact with the irregular Profile2s.

Profile4s does not need to be a child to the Part that has the Motion-Dimension FB3s, it must only belong to a Part in Kinematic-Chain 2.



1.Click Machine elements toolbar > Add Magnetic-Joint
2.Click the Profile [or Point-Cloud]2s that is the irregular shape
3.Click the Motion-Dimension FB3s to 'drive' by the new contact between the circular and irregular Profile.
4.Click the Profile4s with the circular shape.
5.Click OK-tiny-13-17 in the Command-Manager




The Magnetic-Joint 'pulls' the two Profiles2s4s together.
The Magnetic-Joint FB5s shows in the graphic-area
When you cycle the machine, the two Profiles stay in continuous contact.
The Motion-Dimension FB3s becomes 'driven' by the Magnetic-Joint.


1.Identify the Magnetic-Joint FB5s in the graphic-area
2.Double-click the Magnetic-Joint FB in the graphic-area

- or -

2.Click the Magnetic-Joint FB in the graphic-area so it shows in the Selection-Window
3.Right-click the Magnetic-Joint FB in the Selection-Window
4.Click 'Edit Element...' in the contextual-menu.

See: Magnetic-Joint dialog-box


Model: Unacceptable Irregular Profile.

The image shows a shape that is not acceptable.

The irregular Profile should:

NOT be to one side of the centre of rotation or its Origin
NOT form a 'horse-shoe' shape around the centre of rotation, or its Origin.
NOT have a radius-of-curvature that is less than the circular Profile.

If the irregular Profile is not acceptable, the circular Profile will jump to different contact solutions as you cycle the model.



How to...

Add Magnetic-Joint


The Magnetic-Joint does not use 'closed mathematical equations'. The motion of the Magnetic Driven Part is 'solved' using optimization techniques. Thus:

The modeling is slower.
A Magnetic-Joint may fail if the Profiles cannot stay in continuous contact for a complete Machine Cycle.

See Also: Magnetic-Joint dialog-box, Add Profile, Sketch-Loop, Add Motion-Dimension FB; YouTube Video : http://youtu.be/IME9Eb4mpQE

Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd