Add Pin-Joint

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Add Pin-Joint

Add Pin-Joint

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

Pin-Joints in MechDesigner

Pin-Joints in MechDesigner




MechDesigner equivalent : Pin-Joint :

A Pin-Joint forces a Point in a Part to be coincident with a Point in a different Part.

A Pin-Joint removes two degrees-of-freedom from the model.

A Pin-Joint allows only rotary motion between two Parts.

Technical Definition: Revolute Joint :

A Pin-Joint is identical to a Revolute-Joint


* Point, start-Point, end-Point, or center-Point.

Pin-Joints in the Graphic-Area


There are two symbols for a Pin-Joint:

Red-14-1b MD-Dowel-Symbol  - symbol for a Pin-Joint that is fixed to the Base-Part.

Red-14-2 MD-PointandPinJoint-Symbol  - the outer circle is the symbol for a Pin-Joint that moves relative to the Base-Part

The inner circle is the symbol for the Points that become coincident when you do Add Pin-Joint.

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

<<< Pin-JointRed-14-2  between two(2) added Parts.

Simple Case - Add Pin-Joint


STEP 1: Start the Add Pin-Joint command


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


Mechanism-Editor: Kinematic-elements toolbar > Add Pin-Joint

STEP 2: Select two(2) Points:

At least one of the Point you select must be in a free Part.

1.Mechanism-Editor: Click a PointRed-14-1 in a Part

2.Mechanism-Editor: Click a different PointRed-14-2 in a Part

The two(2) Points become coincident at the Pin-Joint.

If the Select-Elements dialog opens, see Special-Case.


See also:

Add Slide-Joint

Add Ball-Joint

Add Motion-Dimension FB

VIDEO : Add Pin-Joint - Simple-Case


Video: Add Pin-Joint (Simple Case)


Special-Case - Add Coincident Pin-Joints

Frequently, a design has more than one Pin-Joint at the same position, which join together more than two Parts.

The rules to add coincident Pin-Joints, explained below, become important when you need to also add Motion-Dimension FBs to specify the motions of one or two(2) of the Parts at the Pin-Joint.


We want to join Points(1,2,3) that are in Parts(1,2,3) with Pin-Joints(1,2) at one position.

Pin-Joint#1 is between Points 1 & 2 (in Parts 1 & 2)

Then, Pin-Joint#2 has two(2) options:

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

- or -

Option B: Pin-Joint#2 is 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(2) Parts.


Preparation example:

Red-14-1b Line in the Base-Part

Red-14-2 Completely-free Part

Red-14-3 free Part

Pin-JointRed-14-4 that joins the start-Point of LineRed-14-1b, to the start-Point of PartRed-14-3

We want to join the completely-free PartRed-14-2 with a Pin-Joint to become coincident with the existing Pin-JointRed-14-4.


STEP 1:Add Pin-Joint #2


1.Click Kinematic-elements toolbar > Add Pin-Joint

1.Click PointRed-14-5 at the end of the Completely-Free PartRed-14-2

2.Click Point at the Pin-JointRed-14-6

We have clicked a total of three(3) Points.

One Point at Red-14-5

Two Points at Red-14-6

However, the Pin-Joint is between two(2) Points.

Therefore, there is ambiguity as to which two(2) Points you want for the Pin-Joint.

Ambiguity: when MechDesigner is not sure which element to select.


Select-Elements dialog-box

When there is ambiguity as to which elements you want to select to add a new element, the Select Elements dialog-box opens.

In this model, there are three possible Points:

Point11 (the start-Point of the Completely-Free Part)



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


STEP 2:Select the Points in the Select-Elements dialog-box:

1.MD-Ctrlb key down - do this before you click the Points in the box.

2.Click the two Points you want to use for the Pin-Joint


Which two Points do we select from the three Points?

There are three ways to select two(2) elements from three elements

You can select Point11 and Point5


- or -

You can select Point11 and Point7.


However, you cannot select Point5 and Point7.

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

Note: the word 'not' the image to the left, at the bottom of the dialog


STEP 2:To confirm again, select the Points:

1.MD-Ctrlb key down - do this before you click the Points in the box.

2.Click the two Points you want to use for the Pin-Joint

The MD-OK-tiny-11-15 colorizes only when you select the elements that can do the command.

3.Click MD-OK-tiny-11-15

The Select-Elements dialog-box closes.

The Points move together to add the Pin-Joint.


When you know there is ambiguity - and the Select-Elements dialog will open - then click (in the Select-Elements dialog-box) click an element that does not have ambiguity before you click elements where there is ambiguity.

If the Select-Elements dialog opens, the element you click first is at the top of the list.

It is useful to know you must select the element at the top of the list, plus one more element.

VIDEO - Add Pin-Joint - Special-Case:


Add Pin-Joint - Special Case