﻿ MechDesigner Reference & User Interface > 2.2 Mechanism-Editor: > Kinematic elements > Add Pin-Joint

 Pin-Joints in MechDesigner Pin-Jointsin SOLIDWORKS

#### Terminology

 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:

 - symbol for a Pin-Joint that is fixed to the Base-Part.  - 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-Joint between a Part and the Base-Part.

<<< Pin-Joint  between two(2) added Parts.

### Simple Case - Add Pin-Joint

STEP 1: Start the Add Pin-Joint command

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 Point in a Part 2.Mechanism-Editor: Click a different Point in a Part

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

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

### VIDEO : Add Pin-Joint - Simple-Case

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.

Example:

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:

 Line in the Base-Part Pin-Joint that joins the start-Point of Line, to the start-Point of Part We want to join the completely-free Part with a Pin-Joint to become coincident with the existing Pin-Joint.

 1.Click Kinematic-elements toolbar > Add Pin-Joint 1.Click Point at the end of the Completely-Free Part 2.Click Point at the Pin-Joint

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

One Point at

Two Points at

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) •Point5 •Point7 Note: The Owner-Elements are also three different Parts.

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

 1. 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. 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 colorizes only when you select the elements that can do the command. 3.Click

The Select-Elements dialog-box closes.

The Points move together to add the Pin-Joint.

Top-Tip:

 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.