Objective of this Step

To use different method of the user-interface to delete an element. In this case we will delete a Pin-Joint using the Selection-Window, Assembly-Tree and the Kinematic-Tree.

Introduce, the RRR Dyad

To replace a Pin-Joint with a Slide-Joint.

Summary of this Step

Delete a Pin-Joint using different procedures
Add a Slide-Joint

After this step, in the Kinematics-Tree, the RRR Dyad becomes an RRP Dyad.

Video 1: Delete Pin-Joint with different Procedures


Tutorial 2: STEP 2.3

Different ways to Delete a Pin-Joint


Video 2: Add Slide-Joint


Tutorial 2: STEP 2.3

To add a Slide-Joint

Delete the Pin-Joint

This part of the tutorials shows you how to delete an element from different areas of the interface.

In this case we delete a Pin-Joint, using contextual-menus, form the:


Note: It is also possible to delete joints in the graphic-area if you click it and the press with the 'delete' key on your keyboard.

Delete a Pin-Joint with the Selection Window

When you click one or more elements in the graphic-area, Assembly-Tree or Kinematics-Tree, they show in the Selection-Window.

You can delete the element using the Selection-Window.

Here, the element we will delete is a Pin-Joint.


STEP 1: Try to mouse-over and click the Pin-Joint in the graphic-area.


After you click the Pin-Joint, look in the Selection-Window.

It is possible, and even likely, that you will select more than one element.

In this case, we have clicked the Pin-Joint and a CAD-Line.

STEP 2: Right-click the Pin-Joint in the Selection-Window.

A contextual-menu shows.

STEP 3: Click 'Delete...'

You will delete the Pin-Joint.


After you delete the Pin-Joint, you will see that the Part-Outlines of the two Parts become Blue.

Blue Parts are not kinematically-defined.



Note: MechDesigner removes the RRR Dyad from the Kinematics-Tree.


Delete a Pin-Joint from the Assembly-Tree

First, we will replace the Pin-Joint that we deleted above. We can do this in two ways:

Before we do Add Pin-Joint the Points are above each other, as before we deleted the Pin-Joint above.

To see the two Points again, we must drag the Part-Outline of a Part.

To drag a Part-Outline:  hover above one Part-Outlines to make it RED, then 'drag'. It is sometimes difficult to drag. Experiment!

Note: Occasionally, you can only make a Part-Outline Red if you hover above the arc near the start-Point of the Part.


STEP 1: Use Edit menu > Undo, or the Edit Toolbar > Undo icon
- or - use the Ctrl + Z key combination.
- or - do Kinematic elements toolbar > Add Pin-Joint again

In the graphic-area, you can see the Pin-Joint is in the model again.

The two Parts are Green again.

Parts with Green Part-Outlines are Kinematically Defined Parts, again.


STEP 2: Click the Assembly tab in the Element Explorer to show the Mechanism Assembly-Tree.
STEP 3: 'Explore' the Assembly-Tree to find the Pin-Joint that you want to delete - here Pin-Joint7 - see Note 2 below.



Note 1:

The element you click in the Assembly-Tree becomes red in the graphic-area.


The element you click in the graphic-area is 'selected' in the Assembly-Tree [an Orange Square around its icon]

Note 2:

A Pin-Joint has two different symbols:

DowelSymbol The symbol for a Pin-Joint that uses the Base-Part, is similar to a dowel symbol in a technical drawing.

Pin-Joint The symbol for a Pin-Joint that does not use the Base-Part

STEP 4: Right-click the Pin-Joint in the Assembly-Tree -DowelSymbol
STEP 5: Select 'Delete' in the contextual-menu.



In the image to the left, we can see the Part-Outlines of the two Parts that were in the RRR Dyad (see Step 2.1) have become Blue.

This means the Parts are now not kinematically-defined. You can drag the Blue Parts if you drag their Part-Outlines.

[To Drag: hover above the Part-Outline to make it Red, then Drag.

Note: Occasionally, you can only hover to make a Part-Outline Red by hovering over the Part-Outline at the arcs, near to the start-Point, at each end of the Part. This is more difficult to do. We will try to resolve this problem.

Delete a Pin-Joint from the Kinematic Tree


To replace the Pin-Joint

STEP 1: Use Edit menu > Undo, or the Edit Toolbar > Undo icon
- or -
Use the Ctrl + Z key combination.

The two Parts-Outlines are now green, again, as they are now kinematically-defined.

[You can also practice with Add Pin-Joint]


STEP 2: Click on the Kinematics tab in the Project-Explorer to open the Kinematics-Tree.
STEP 3: 'Expand' the R-R-R dyad.

You can see the list of three Pin-Joints and two Parts.

Note 1: The more academic term for a Pin-Joint is a Revolute Joint.

Hence, 'R' in the 'R-R-R' Dyad.

STEP 4: Click the Pin-Joint that has the 'Grounded Pin-Joint Symbol'

Note 2: Each time you select an element, Dyad, or kinematic-chain in the Kinematics-Tree, it becomes red in the graphic-area.


The Pin-Joint is in the Selection-Window.

Note 3: When you select the Pin-Joint in the Kinematics-Tree, you also see in the Selection-Window the Points that we use for the Pin-Joint.


Again, you will see, as in the image to the left, the Part-Outlines of the two Parts (see Step 2.1) have become Blue.

This means they are now not kinematically-defined. You can drag the Part-Outline.

Add a Slide-Joint.

The kinematic-chains we have modelled has Pin-Joint, only.

A Pin-Joint is between two Points
Each Point must be a child to a different Part

Imagine one Point is the 'Bearing Shaft' (on Part 1), the other Point is the 'Bearing Housing' (on Part 2).

Introducing a Slide-Joint

A Slide-Joint is a joint between two Lines
Each Line must be a child to a different Part

Imagine one Line is a 'Slide-Rail' (on Part 1), the other Line is a 'Slide-Block' (on Part 2)

Add a Line to the BasePart for the Slide-Joint

To add a Slide-Joint, we need a Line in two different Parts. We are going to add a Slide-Joint between an Added-Part and the Base-Part.

For the Slide-Joint, we will use the:

CAD-Line along the centre of the Part, although we can use any Line we add to an Added-Part.
A new Line in the Base-Part, although we can use any Line in the Base-Part.


Add a 'Slide-Rail' to the Base-Part. We need a Line in the Base-Part. We will edit the Base-Part to add a new Line

STEP 1: Double-Click the rectangular Part-Outline to edit the Base-Part with the Part-Editor.
STEP 2: Add a Line: Drag from left to right and slightly upwards - the direction becomes important later.
STEP 3: Add Dimensions to specify the position of the Line and the Line becomes Black

The Line is the Slide-Rail for the Slide-Joint in the Crank-Slider.

It is important to understand that you can add this Line anywhere in the Base-Part.


After you add the Line you will close the Part-Editor.

To close the Part-Editor, we can use the Edit Part icon Icon-EditPart above the Geometry toolbar [left of Graphic-area].

STEP 4: Click the Edit Part icon to cancel it.

The Line is Green in the graphic-area of the Mechanism-Editor.

The Line is green in the Mechanism-Editor because it is a child to a kinematically-defined Part – the Base-Part

The Base-Part is ALWAYS a kinematically-defined Part.

Add the Slide-Joint


STEP 5: Click Kinematic-elements toolbar >Add Slide-Joint


A Slide-Joint needs two Lines.

STEP 6: Click the Line in the Base-Part
STEP 7: Click the CAD-Line along the centre of the Part

See the pointer in the image to the left.


Step 6 is complete

The Lines are now co-linear. It is a Slide-Joint.

The Slide-Joint has replaced the Pin-Joint.



If the Parts jump to a different position: See Dyad Closures

If, when you use Run menu [or toolbar] > Cycle, the Parts in the Dyad do not move, and the joints brake : See Dyad Closures


STEP 6: Expand the Kinematics-Tree

The Parts that were in the RRR Dyad [see above : Delete a Pin-Joint in the Kinematics-Tree], are now in an RRP Dyad.

The three Joints in the RRP Dyad are:

Two Revolute-Joints, (R-R-P],
One Prismatic-Joint (R-R-P).

A Revolute-Joint is the same as a Pin-Joint.

A Prismatic-Joint is the same as a Slide-Joint.

The Slide-Joint in the graphic area


There are a three symbols to represent a Slide-Joint.

In the image we can see:

1s-red A Wide rectangular box: It is along the Line of the moving* Part.

2s A Narrow rectangular box: It is along the Line of the fixed* Part.

* Remember, the two Parts might move. Thus, this it is not a fixed rule.

3s A small arrowhead at the start-Point of one of the Lines that you select for the Slide-Joint shows the 'Positive Direction' of the Slide-Joint.

The 4s Red arrow in the image [not visible in the graphic-area. Here, we use it to show the positive direction of the Slide-Joint.

The positive direction is important, for example, if you use add a Motion-Dimension FB and select the Slide-Joint as the 'Joint'.

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