Step 2.3: Delete Pin-Joint, reconfigure as Crank-Slider

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.

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.

A contextual-menu shows.

You will delete the Pin-Joint.

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

Blue Parts are not kinematically-defined.

This Why two Parts?

The two Parts belong to one Dyad.

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

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

or

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].

OR...

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.

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 and end-Point, at each end of the Part. This is more difficult to do. We will try to resolve this problem.

To replace the Pin-Joint

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

[You can also practice with Add Pin-Joint]

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

The Pin-Joint is in the Selection-Window.

You may also click the two Points that are at the centre of 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.

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

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

Introducing a Slide-Joint

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

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:

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

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 above the Geometry toolbar [left-side of Graphic-area].

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.

A Slide-Joint needs two Lines.

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.

DYAD CLOSURES

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:

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

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

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

In the image we can see:

A Wide rectangular box: It is along the Line of the moving* Part.

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.

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 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'.