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

Pin-Joint

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

Pin-Joints in MechDesigner

Pin Joint: Connecting-Rod and Piston

Pin-Joint in CAD model.

Terminology

Pin-Joint :	A Pin-Joint makes a Point* in a Part to be coincident with a Point* in a different Part. A Pin-Joint allows only rotary motion between two Parts. A Pin-Joint removes two degrees-of-freedom from the model.
rotating-Part :	A Part that that can rotate relative to a different Part.
Revolute-Joint :	The kinematic and equivalent term of a Pin-Joint.
Kinematics-Tree :	In Dyads, Pin-Joints are represented by the letter R, which is from the kinematic term: Revolute-Joint.
* Point, start-Point, end-Point, or center-Point.

Pin-Joints in the Graphic-Area

There are two symbols for a Pin-Joint:

<<< Pin-Joint between a Part and the Base-Part.

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

- the symbol for a Pin-Joint that cannot move relative to the Base-Part.

- the outer circle is the symbol for a Pin-Joint that can move relative to the Base-Part.

Simple Case - Add Pin-Joint

STEP 1: Start the Add Pin-Joint command

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

Kinematic elements toolbar > Add Pin-Joint

STEP 2: Select two(2) Points:

At least one Point must be in a free Part.

1.Click a Point in a free Part

2.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.

Two Pin-Joints

VIDEO : Add Pin-Joint - Simple-Case

Special-Case - Add two or more coincident Pin-Joints

Frequently, a design has Pin-Joints that are coincident, to join more than two Parts.

Example:

You want to join Points(#1,#2,#3), in Parts(#1,#2,#3). with Pin-Joints(#1,#2).

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

When you add Pin-Joint#2, you have two(2) options:

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

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

To select Option A or Option B is important if you also select the Pin-Joints to add Motion-Dimension FBs.

Preparation example:

Line in the Base-Part (any Part that is kinematically-defined )

Part that is completely-free

Part that is free

Pin-Joint Red-14-4 joins the start-Point of Line to the start-Point of Part

You want to join Part that is completely-free with a Pin-Joint that is coincident with Pin-Joint Red-14-4 .

STEP 1:Add Pin-Joint #2

1.Click Kinematic elements toolbar > Add Pin-Joint

1.Click Point at the end of the Completely-Free-Part

2.Click the Pin-Joint to select a Point - see below

You have actually 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 ...

... Which two(2) Points, of the three(3) Points, do you want the Pin-Joint to select?

Definition:

Ambiguity: it is not clear which element(s) to select.

Select-Elements dialog

When there is ambiguity as to which elements you want to select, the Select Elements dialog opens.

In this model, there are three(3) possible Points from which you want to select two(2) Points.

•Point11 (the start-Point of the Part that is completely-free)

•Point5 (the Point at the left of the Line in the Base-Part)

•Point7 (the start-Point of the Part that is free)

TOP-TIP: The element at the top of the list is the first element you click. Therefore, click the element you know you need before you click the other elements. Then, you know you need to select the top element.

OPTION A

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

1. key down

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

3. key up

The colorizes only when you select the elements that are compatible .

4.Click at the top, right of the dialog

Which two Points do you select from the three Points?

There are three options to select two(2) elements from three(3) elements.

•Option A: Two elements are compatible or NOT compatible.

•Yes, you can select Point11 and Point5

OPTION B

•Option B: Yes, you can select Point11 and Point7.

OPTION C

Option C: No, you cannot select Point5 and Point7.

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

Note: In the image to the left, see the word 'not' in the message that is below the element-box

'Two selected elements are not compatible'

Option A

STEP 2:To confirm again, select the TWO Points:

1. key down

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

3. key up

The colorizes only when you select the elements that are compatible .

4.Click at the top right of the dialog

The Select-Elements dialog closes.

The Points (and completely free-Part) are coincident, at the new Pin-Joint.

Top-Tip:

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

Therefore, if I know there will be ambiguity, I click the element that I know I need to select before the elements that cause the ambiguity. Then, when the Select-Elements dialog open, the element I click first will at the top of the list.