Kinematics | Add Motion-Dimension FB

Menu :

Add menu > Add Motion-Dimension FB

How to Add :

The elements you select to add a Rocker are different to those you select to add a Slider.

Dialog box:

Motion-Dimension FB dialog-box

Notes:

After you add the Motion-Dimension FB, and you want to move the:

See also:

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

Selection Filters

Connecting FBs

Prepare the model so that these elements have these properties.

Preparation example:

•

Pin-Joint

•	The Points at Pin-Joint are at the ends of Lines.

•	Lines in two different Parts that radiate from two Points

•	Part is a kinematically-defined Part (Green Part-Outline).

•	Part is a free Part (Blue Part-Outline)

Kinematic FB toolbar > Motion-Dimension FB [right of Graphic-Area >>]

Element #1: PIN-JOINT

The Pin-Joint is a joint between two Parts, and:

Elements #2 and #3: LINES

Each Line must be a child to a Point that is also a child to the Pin-Joint. [Element #1]

Click in the Command-Manager

Result: a Rocker

A Motion-Dimension FB to specify the angle between Lines, Elements #2 and #3

The dimension is an Orange 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 are:

Prepare the model so that these elements have these properties.

Preparation example:

1.

Two Parts

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

The other is a free Part (Blue Part-Outline)

2.	The Parts are Joined... with a Slide-Joint

Note the Points are the start-Points and end-Points of the Lines that are selected for the Slide-Joint

Kinematic FB toolbar > Motion-Dimension FB [right of Graphic-Area >>]

Element #1: SLIDE-JOINT

The Slide-Joint is a joint between two Parts, and:

Elements #2 and #3: POINTS

Each Point must be a child to a Line that is also a child to the Slide-Joint. [Element #1]

Click in the Command-Manager

Result: a Slider

The Motion-Dimension FB to specify the linear distance between Points, Elements #2 and #3

All Parts are now kinematically-defined Parts

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 kinematic elements are:

Result of Special Procedure 1:

The model shows

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

There are two Parts and a Line in 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 Point7 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

2.

Click

The two Parts are now joined with a Pin-Joint to the Point at the left end of the Line in the Base-Part.

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

Now, use the Motion-Dimension FB two times

The Command-Manager show that we must select three elements , and .

The first-element must be a Pin-Joint or Slide-Joint.

We have two Pin-Joints!

When we click the Pin-Joints in the graphic-area the Select-Elements dialog-box opens as there are two Pin-Joints.

In the Select-Elements dialog box:

Click the Pin-Joint5 - the one with the lower Element-Number if the names are different to those in the image.

Now we must select two Lines.

Click the horizontal Line as the second element

Click the CAD-Line along one the Parts with which the Pin-Joint is made.

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 Function-Block Toolbar > Motion-Dimension FB in the  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 in 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.

Result of Special Procedure 2

We want the two Motion-Dimensions FB:

From the Line in the Base-Part

To a Line in 'Part 1'

From the Line in 'Part 1'

To the Line in 'Part 2'

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 Point11 and Point7.

The two Parts become joined with a Pin-Joint.

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

A Slider:

When you add the Motion-Dimension FB, to add a Slider, you must select a Slide-Joint, as the first element, then two Points.

You might be surprised by how many elements properties we need to consider to understand and plan the Positive-Direction of the Motion-Dimension FB for a Slider:

Thus, the behaviour of the Motion-Dimension FB is a function of the order of the Points for each of the two Lines

Thus if the Motion-Dimension does not work in the way you want, you may need to add the Slide-Joint, and even the Lines again.

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

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

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