Kinematics | Add Motion-Dimension FB

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Add menu > Add Motion-Dimension FB

In the graphic-area: Motion-Dimension FB  if a parameter is an element-row in a Design-Set.

How to Add:

The Motion-Dimension FB is the most complex FB to add to the model. However, it is easy when you can identify the three elements you must select.

See also Videos

Add Motion-Dimension FB to become a Rocker: [see more details here]

Add Motion-Dimension FB to become a Slider: [see more details here]

Note 1: When Element #1 is a Pin-Joint ...

Thus, the two Lines radiate from the Pin-Joint.

Elements #2 & #3 must be:

Note 2: When Element #1 is a Slide-Joint ...

There is a Point at the end of each Lines 1 & 2.

Elements #2 & #3 must be:

Special Procedures

When there are two or more joints that coincident to each other, you must specify which joint to apply the Motion-Dimension FB.

Coincident Pin-Joints

When there are two or more coincident Pin-Joints, and three or more Lines radiate from the same location, you must take care when you select the Pin-Joint as the first element.

The second and third elements you select can only be Lines that are parents to Points and the Pin-Joint you select as the first element.

Coincident Slide-Joints

When there are two or more coincident Slide-Joints, and three or more Lines are along the same 'ray', you must take care when you select the Slide-Joint as the first element.

The second and third elements you select can only be the Points that are children to the Lines to the Slide-Joint you select as the first element.

See Special Condition below.

See Add Pin-Joint - Special Condition and Add Slide-Joint - Special Condition

Note: In the graphic-area:

Possible Messages:

If there is more than one Joint at the Pin-Joint you select as the 'first' element in the command manager, (a different Pin-Joint or a different Slide-Joint), and that Joint joins two kinematically-defined Parts, then you will get the message:

Joints: - Joint: X-Joint, it is not possible to add a Motion-Dimension FB to Green Parts.

If the Line you select as 'second' element is superimposed above a different Line that does not radiate from the Joint, then you will get the message:

Line is not a child to the same Part as the Joint.

See Also:

Connecting FBs

       Videos: Add Motion Dimension FB to a Pin-Joint and Slide-Joint: General Procedure

Add a Motion-Dimension FB to a Pin-Joint – General Procedure	Add a Motion-Dimension FB to a Slide-Joint – General Procedure

[Right-side of Graphic-Area]: Kinematic FB toolbar > Motion-Dimension FB

When you start Add Motion-Dimension FB, the Command-Manager needs you to select three elements to complete the command.

The selection-box hints are:

Elements 2 and 3 are in two different Parts.

The two sketch-elements must also construct the Joint

*'Solved' is kinematically-defined, 'Unsolved' is not kinematically-defined.

Preparation:

1.

Two Parts

o	One Part is a kinematically-defined Part (Green Part-Outline)...the Base-Part

o	The other Part is a Free Part (Blue Part-Outline)

2.	The two Parts are Joined together with a Pin-Joint

3.	Lines radiate from the Pin-Joint

It is also important that the Points that were selected to assemble the Pin-Joint are at the ends of Lines.

Select the First Element: PIN-JOINT

When you select a Pin-Joint, the second and third elements are Lines.

This means the Pin-Joint must join a Free Part to a kinematically-defined Part.

Select the Second and Third Elements: LINES

The Lines that you select for the second and third elements are 'parents' to the Points that specify the Pin-Joint.

Result: The Motion-Dimension FB is added to define the rotation angle of a Rocker.

You can see the dimension is a Green colour in the graphic-area.

Kinematics-Tree for a Rocker

When we add a Motion-Dimension FB to a Pin-Joint, we identify it as a Rocker in the Kinematics-Tree.

The kinematic elements that construct the Rocker are:

At the end of Special Procedure 1:

Two Motion-Dimension FBs to reference the same Line in the Base-Part.

You can see the angle dimension of the two Motion-Dimensions FBs start at the horizontal Line.

There are two Parts and a Line to the Base-Part - three Parts in total.

The Points at the ends of the lines are 5, 7 and 11.

In the image to the left, we have joined Point7 to Point5 with the first Pin-Joint.

Now we must add a second Pin-Joint.

PROCEDURE 1

We will add the second Pin-Joint between Point11 and Point5.

Q: Why Point5 and not Point7?

A:  Point5 is a child to the horizontal Line .
We want two Motion-Dimensions to reference the same horizontal Line .

To add the Pin-Joint: select Point11 and then try to select Point5.

Because Point5 and Point 7 are at the same position, MechDesigner does not know which Point you want to select.

There is ambiguity between Point5 and Point7. Hence, the Select Elements dialog-box opens.

The Select Elements dialog-box:

CTRL +Click ALL of the elements you need to complete the command.

Here, we have selected Point 11 and Point5

The two Parts are now joined to the Base-Part with two Pin-Joints

Now, use the Motion-Dimension FB two times

We must click the three elements: , and .

Elements 1:

There are two Pin-Joints that are at the same position.

Hence, MechDesigner opens the 'Select Elements' dialog-box.

Select the first Pin-Joint , at the top of the list.

Elements 2 & 3: Two Lines – a 'Solved Line' then a 'Free Line'

3.	Click the horizontal Line

4.	Click the CAD-Line along one of the Parts

This image shows the three elements in the Command-Manager boxes.

The first Rocker Motion-Dimension FB.

Now, add the second Motion-Dimension FB

We must now select another three elements,

Select Add Motion-Dimension FB in the Function-Block Toolbar again.

These are the elements.

1.	Joint: Pin-Joint2.

Now, there is not ambiguity. There is only one Pin-Joint available.

2.	Line – Solved: select the horizontal Line.

3.	Line – Free: select the CAD-Line along the center of the Blue Part.

Here, you can see the result.

Both Motion-Dimensions FBs use the Horizontal Line that is a child to the Base-Part as a reference for the motion-dimension.

Note: When you add two Motion-Dimensions, the FBs may be on top of each other.

Drag each FB so you can see them.

At the end of Special Procedure 2

We want the two Motion-Dimensions FB as:

Again, there are two Parts and a Line in the Base-Part.

The Points at the ends of the lines are 5, 7 and 11.

We want to:

In the image to the left, Point7 is joined to Point5

CONDITION 2

Add the second Pin-Joint between Point11 to Point7.

•	A:  Because Point7 is a child to CAD-Line and we want this Motion-Dimension to reference CAD-Line.

Select Point11.

Then try to select Point7

There is ambiguity between Point5 and Point7. Hence, the Select Elements dialog-box opens.

In the image to the left, we have selected Point 11 and Point7.

The two Parts become joined with a Pin-Joint.

To add two Motion-Dimension FBs, use Add Motion-Dimension FB tow times.

The Add Motion-Dimension FB requires three elements.

Element 1: A Joint.

There is ambiguity when we select the Pin-Joint, hence the Select Elements dialog-box opens.

Here, I have selected the first Pin-Joint at the top of the list.

Then, Click 'OK'.

Elements 2 & 3: Two Lines – a Solved Line then a Free Line

There are three Lines to select from.

Select the Horizontal Line and the CAD-Line along one of the Parts

The three elements in the Command-Manager

Click OK in the Command-Manager

You can see the First Motion-Dimension FB.

Add the second Motion-Dimension.

We must now select another three elements,

These are the elements:

You must select this line because the Pin-Joint4 uses Point7 on this Line.

This image shows the end result.

First Motion-Dimensions FB: uses the Horizontal Line that is a child to the Base-Part as a reference Line.

Second Motion-Dimension FB: uses the CAD-Line along the center of the Added-Part that is kinematically-defined by virtue of the First Motion-Dimension FB - see Procedure 1

Note: When you add two Motion-Dimensions, the FBs may be on top of each other.

DRAG each FB so you can see them.

Preparation: Motion-Dimension to be added to a Slide-Joint

1.

Two Parts

2.	One is a kinematically-defined Part (Green Part-Outline)...the Base-Part

3.	The other is a Free Part (Blue Part-Outline)

4.	The Two Parts are Joined... with a Slide-Joint

Note the Points that  the Lines selected for the Slide-Joint

Select the First Element: SLIDE-JOINT

When you select a Slide-Joint, the second and third elements are Points.

Each Point must be a child to the Lines that were used for the Slide-Joint.

Hence, the Slide-Joint should join a kinematically-defined Part and a Free Part.

Select the Second and Third Elements: POINTS

The second and third elements are children to the Points to the the Lines used for the Slide-Joint.

Result: The Motion-Dimension FB is added to define the linear distance of a Slider

You can see the dimension is a Gold colour.

Kinematics-Tree

When we add a Motion-Dimension FB to a Slide-Joint, we identify it as a Slider in the Kinematics-Tree.

The Positive-Direction of a Motion-Dimension for a Slider is logical, but needs some thought.

Always, the positive-direction of a Slider Motion-Dimension is:

'...the positive direction of the Line, or CAD-Line, that is kinematically-defined before you add the Motion-Dimension to the Slide Joint'.

What is the Positive-Direction of a Line or CAD-Line?

The direction with which you drag - from its start-Point to its end-Point - when you add a new Line or new CAD-Line, and a new Part (its CAD-Line).

Example Sliders. Here, there are four.

Note:

I have used the red arrow-heads to show the direction in which I 'dragged' to add the Lines and Parts

The Motion-Dimension is '12.0000'.

Increasing the value, say to 16, will move the Motion-Part(Slider) to the right.

The small green arrowhead at the start-Point of Line 1 shows the positive direction of the Line and the Slider.

The Motion-Dimension is '11'.

Increasing the value, say to 16, will move the Motion-Part(Slider) to the right.

The small arrowhead shows the positive direction

The Motion-Dimension is -10'.

Increasing the value, say to -6, will move the Motion-Part(Slider) to the left.

The small arrowhead shows the positive direction

The Motion-Dimension is -10'.

Increasing the value, say to -6, will move the Motion-Part(Slider) to the left.

The small arrowhead shows the positive direction