Add Pin-Joint

See also: Edit-Pin-Joint ( Motor and Gearbox Sizing )

What is a Pin-Joint?

Typically, use a Pin-Joint to model a rotary bearing.

MechDesigner definition: a Pin-Joint makes a Point in a Part become co-axial (coincident) with a Point in a different Part. The two Parts can rotate relative to each other, on the Mechanism-Plane.

IFTOMM definition: a Pin-Joint makes an axis in one part become collinear with an axis in a different part, but allows the axes rotate relative to each other.



Kinematic Elements Toolbar : Add Pin-Joint icon

Menu :

Add menu > Mechanism sub-menu > Add Pin-Joint

Dialog-Box :

Kinetostatic Servomotor Sizing (motor and gearbox sizing)


Pin-Joints in the graphic-area

Red-14-1b PointSymbol the symbol of a Pin-Joint between an Added-Part and the Base-Part.

Red-14-2 PointandPinJoint-Symbol the outside circle is the symbol of a Pin-Joint between two Added-Parts

The 'inside circle'(o), which is 'inside' each Pin-Joint symbol, is the symbol for the two Points that have become coincident, and co-axial, when you add the Pin-Joint.

<<< Pin-JointRed-14-1b between a Part and the Base-Part

<<< Pin-JointRed-14-2  between two Added-Parts

See also:

Add Slide-Joint

Add Ball-Joint

Add Motion-Dimension FB

Add Pin-Joint


STEP 1: Add Pin-Joint


1.Add menu > Mechanism menu  > Add Pin-Joint

- or -

1.Kinematic-elements toolbar > Add Pin-Joint

STEP 2: Select two Points:

1.Click a Point in a free Part
2.Click a different Point in a different free Part

- or -

2.Click a Point in a kinematically-defined Part.

Note: If the Select-Elements dialog-box shows, see Pin-Joint Special Case

STEP 3: Complete the command:

If the Points do not snap together:

1.Click the graphic-area

The Points snap to become coincident to give Pin-JointRed-14-3 or Pin-JointRed-14-4




In this example, the kinematic-chains are not solved (kinematically-defined) and have Blue Parts.

Thus, the Kinematics-Tree shows only the simple elements in Unsolved Mechs

More typically, a Pin-Joint is an element in a complex machine element. For example:

Dyads (also termed Assur Groups)
Belt and Pulley

VIDEO : Add Pin-Joint - Simple-Case:


How to...

Add a Pin-Joint - Simple-Case



tog_minusSpecial-case - Add two coincident Pin-Joints

Frequently, a machine design has two (or more) Pin-Joints at the same position, that join three (or more) Parts.

When you add a each Pin-Joint, you must decide which two Points, and which two Parts, you want to join.


Join three(3) Parts at one position. We add two(2) Pin-Joints.

If, Pin-Joint#1 is between Points 1 & 2 (in Parts 1 & 2), there are two options for Pin-Joint#2:

Option A: Pin-Joint#2 between Points 3 & 1 (in Parts 3 & 1)

Option B: Pin-Joint#2 between Points 3 & 2 (in Parts 3 & 2)

When to do Option A or Option B becomes important when you need to also add Motion-Dimension FBs to specify the motions of the two Parts.


Preparation for this example

The image to the left shows:

A LineRed-14-1b in the Base-Part . It is a kinematically-defined Part – and it is coloured Green.
A completely-free PartRed-14-2 – you can drag the Part-Outline freely.
PartRed-14-3 is joined with a Pin-Joint to the start-Point at one end of the Green LineRed-14-1b.

We want to join the completely-free PartRed-14-2 with a Pin-Joint to become coincident with the existing Pin-Joint.


STEP 1: Click Kinematic-elements Toolbar > Add Pin-Joint



STEP 2: Click the PointRed-14-4 at the end of the Completely-Free Part



STEP 3: Click the PointRed-14-5 at the centre of the Pin-Joint.

There is ambiguity as to which Point you want to select at the Pin-JointRed-14-5.

MechDesigner sees a total of three(3) Points:

one(1) PointRed-14-4 in the Completely-Free Part


two(2) PointsRed-14-5 at the Pin-Joint


Select-Elements dialog-box

When there is ambiguity as to which two Points you want to select for a Pin-Joint, the Select Elements dialog-box opens.

In this model, the three possible Points are:


Notes: The Owner-Elements are also three different Parts.


To select the Points:

1.Ctrlb key down - do this before you click the Points in the box.
2.Select all of the Points in the list

There are three possible selections of two elements from three Points:

Select Point11 and Point5






- or -

Select Point11 and Point7.







You cannot select Point5 and Point7.

Why? Because Point5 and Point7 are joined with a Pin-Joint, already.

Note: Red Circle(O) in the image, at the bottom of the dialog - left.




STEP 4: Select two Points.

Select the Point11 and Point5:

Ctrlb key-button down
Click the two Points that you want to join with a Pin-Joint.

Note: The OK-tiny-11-15 becomes colourized when the selections are complete and compatible.

STEP 5: Click OK-tiny-11-15 (top-right of Select-Elements dialog-box)

The Select-Elements dialog-box closes. The Points move together to add the Pin-Joint.

Top-Tip: To add the Pin-Joint, click the Points in this order:

Click a Point in a Part that is completely-free before you click a Point that is more ambiguous.

If the Select-Elements dialog opens, the point that is completely-free is at the top of the list.

You know you must select the first Point in the list, plus one more Point from the list to add the Pin-Joint.

VIDEO - Add Pin-Joint - Special-Case:

'Expand' then 'Play'

How to...

Add a Pin-Joint - Simple


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