### 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. IFTOMM Kinematic 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.

IMPORTANT: ...when we want to add a 'Rocker' Motion-Dimension FB and the Pin-Joint is to become the rotational axis joint, then the Pin-Joint MUST be between two Points that are at the ends of two Lines, which are in two different Parts.

Note:

Edit menu > Application-Settings > General tab > Theme Options > Active Theme: Charcoal Dark Slate,

Edit menu > Application-Settings > Graphics tab > Display Colours :  [Background : White] ;  [Part-Unsolved : Blue] ; [Part-Solved: Green] ;[ Joint-Solved : Green] ; [Joint-Unsolved : Blue]

#### Pin-Joint

Before you can do Kinematics-elements toolbar > add Pin-Joint, you need a minimum of one Point in two different Parts.  A minimum of one Part must be a Free-Part [Blue Part-Outline]

<<< A Line in the Base-Part, three Parts [with CAD-Lines], and a Point in two of the Parts.

 1 Point, , or are each a child to a Free-Part - with a Blue Part-Outline

and

 2 Point are each a child to:
 • a different Free-Part

- or -

 • a kinematically-defined Part.

The Base-Part is always a kinematically-defined Part. All sketch-elements you add to the Base-Part are also kinematically-defined.

- 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 the Pin-Joints , and Pin-Joint when you repeat the Add Pin-Joint.

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

 How to... Add a Pin-Joint - Simple-Case [R14]

#### Kinematics-Tree

 The Pin-Joints in the Kinematics-Tree may be a sub-element to different Machine-Elements: Motion-Parts Dyads [also termed Assur Groups] Gear-Rockers Belt and Pulley ...

#### SPECIAL CASE - two or more coincident Pin-Joints

Frequently, a design has two, or more, coincident[co-axial] Pin-Joints.

We always need to select two[2] Points [from different Parts] for a Pin-Joint.

However, we must be careful as to which two Points we select for Pin-Joint #2 when we want it to be co-axial with Pin-Joint #1,

From a total three Parts and Points, we must decide which two Points we want to select for each Pin-Joint.

Assuming that Pin-Joint#1 is between Points 1 & 2 [in Parts 1 & 2], then 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 & 1]

Option A and Option B becomes important when you need to add Motion-Dimension FBs to specify the motions of the two Parts

The image to the left shows:

 • A Line that is a child to a kinematically-defined Part – it is coloured Green. [e.g., a Line in the Base-Part]
 • A Free-Part joined with a Pin-Joint to a Point at one end of the Green Line.
 • A Completely Free Part – you can drag the Part-Outline freely.

We want to join the Completely Free-Part with a Pin-Joint that is co-axial with the existing Pin-Joint.

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

 STEP 2: Click the Point at the end of the 'Completely Free Part'

Top-Tip:

Select as the first element the Point in the Completely Free-Part

The first element you click become the TOP element in the Select-Elements dialog. This Point does not have any ambiguity. This becomes useful when the Select Elements dialog-box opens - see below.

 STEP 3: Click the Point at the centre of the Pin-Joint.

There is ambiguity at Point.

MechDesigner sees a total of three[3] Points:

 • one[1] Point in the Completely Free-Part, and

+

 • two[2] Points at the Pin-Joint

Select-Elements dialog-box

When there is ambiguity about which two Points you can select, the Select Elements dialog-box opens.

In this model, the three possible Points are:

 • Point11,
 • Point5 &
 • Point7

Notes: The Owner-Elements are three different Parts. Elements with the same element-name are appended with a number.

To select the Points:

 1 key-button down - do this before you click the Points in the box.
 2 Select all of the Points in the list to do the Add Pin-Joint command

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

 • Point11 and Point5

- or -

 • Point11 and Point7.

 • Point5 and Point7 are not possible.

Note: Red Circle at the bottom of the dialog - left.

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

 STEP 4: Select two Points.

Select the Point11 and Point5:

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

Note: The becomes colourized whee selections are compatible.

 STEP 5: Click  [top-right of Select-Elements dialog-box]

The Select-Elements dialog-box closes. The Points move together.

Now, there are two co-axial Pin-Joints.

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

 'Expand' then 'Play' How to... Add a Pin-Joint - Simple [R14]

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