Objective of this Step

To show how to delete a joint and to add a different type of joint.

To show how to use the Selection-Window, Assembly-Tree and the Kinematic-Tree to delete an element.

Summary of this Step

Delete a Pin-Joint with three different procedures
Add a Slide-Joint

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

tog_minusVideo of this Step

 

How to...

Delete a Pin-Joint, and Add a Slide-Joint


Delete the Pin-Joint

Here, we demonstrate how to delete the Pin-Joint with the:


It is also possible to delete Joints in the graphic-area with the 'Delete' key. You must hover above (only the joint must be red), then right-click the joint to show the 'Delete Element' icon.

You can use the Joint Filter in the Selection Filters Toolbar to help you select the Joint element.

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When you select one or more elements in the graphic-area, they show in the Selection-Window.

You can delete an element from the model if it shows in the Selection-Window.

Here, we delete the Pin-Joint in the Selection-Window.

STEP 1: Try to mouse select the Pin-Joint in the graphic-area.

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Look in the Selection-Window.

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


Here, there are six elements: the Pin-Joint and five other elements,

This is because the elements are near to the Pin-Joint in the graphic-area.

 

In the image to the left, we want to delete 'Pin-Joint6'.

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

The contextual menu shows.

STEP 3: Click 'Delete...'

You will delete the Pin-Joint.

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After you delete the Pin-Joint, the two Part-Outlines are Blue.

Blue Parts are not kinematically-defined.


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


 

First, we must replace the Pin-Joint. We can do this in two ways:

1.Add Pin-Joint

or

2.'CTRL+Z' to undo 'Delete Pin-Joint in Selection-Window' - see above.

Add Pin-Joint

When we use Add Pin-Joint, it is usually good practice to be able to see the two Points separately. However, the Points, immediately after 'Delete Pin-Joint' are above each other.

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

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


(Note: Occasionally, you can only hover to make a Part-Outline Red by hovering over the Part-Outline at the arcs, near the start and end Points,at each end of the Part].

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OR...

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

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.

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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-Joint6 - see Note 2 below.

Information

Note 1:

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

and

The element you click in the graphic-area shows 'selected' in the Assembly-Tree [a Red Square around its icon]

Information

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

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

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In the image to the left, we can see the Part-Outlines of the two Parts that belonged to the RRR Dyad (see Step 2.1) are now 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 and end-Point, at each end of the Part. This is more difficult to do. We will attempt to resolve this problem.

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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]

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

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

Information

Note 1: The more academic term for a Pin-Joint is a 'Revolute Joint'. Hence, 'R' in the 'RRR' Dyad.

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

Information

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

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The Pin-Joint is in the Selection-Window.

See above: 'Delete a Pin-Joint in the Selection-Window'

Information

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.

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Again, you will see, as in the image to the left, the Part-Outlines of the two Parts that belonged to the RRR Dyad (see Step 2.1) are now Blue.

This means they are now not kinematically-defined. You will find you can drag the Parts around.


Add a Slide-Joint.

The kinematic-chains we modelled in Tutorial 1, and Steps 2.1 and Step 2.2 of this Tutorial, used Pin-Joints.

A Pin-Joint is between 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).

A Slide-Joint

A Slide-Joint is a joint between 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).

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Add a 'Slide-Rail' to the Base-Part. A slider-rail is straight. We use a Line for a straight slide-rail.

STEP 1: Double-Click the Base-Part-Outline to Start the Part-Editor.
STEP 2: Add a Line.
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.

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

You can use a number of methods to close the Part-Editor. Here, we use the Edit Part icon EditPart-small. In the Part Local Toolbar.

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.

AddSlidingJoint

Add Slide-Joint

STEP 5: Click Add Slide-Joint in the Mechanism Local Toolbar.

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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.

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Step 6 is complete

The Lines are now co-linear. It is a Slide-Joint. The Slide-Joint has replaced the Pin-Joint.

 


DYAD CLOSURESWarning

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

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STEP 7: 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.

Slide-Joint2

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 actual model] gives 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'.

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