Add Magnetic-Joint

See also : Magnetic-Joint dialog

What is a Magnetic-Joint?

A Magnetic-Joint pulls a circular Profile, that is in one Part, to become in continuous contact with an 'irregular' Profile, that is in a different Part.

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

Why use a Magnetic-Joint?

A frequent application of the Magnetic-Joint is to reverse-engineer a cam. And then to find the motion of a Cam-Follower from the shape of the cam.

Prepare Magnetic-Joint


Two kinematically-defined chains,  There must be a Profile in each kinematic-chain.



An irregular Profile2s as a child to a Part1s-red.
This might be a Curve derived from a Point-Cloud or a Profile from a sketch-loop.
Profile2s does not need to be a child to Part1s-red, it must only be a child to Kinematic-Chain 1.

In this model, a Part continually rotates in this model (it is a Crank). It might also be a Slider.


Motion-Dimension FB3s specifies the position of a Part5s
Motion-values at the input to Motion-Dimension FB are ignored after Magnetic-Joint is applied.
A circular Profile4s is a child to the Part5s
Part5s 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 Part5s whose position is defined by Motion-Dimension FB3s, it must only belong to a Part in Kinematic-Chain 2.

Add Magnetic-Joint

Add Magnetic-Joint icon

Machine Elements Toolbar : Add Magnetic-Joint icon


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

Dialog :

Magnetic-Joint dialog-box



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 magnetic-joint 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.



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.


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 :



How to...

Add Magnetic-Joint

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