Step 1.5: Add and Edit a Motion-Dimension FB
Contents
IMPORTANT: Background to this Step.
You will see that the Part in the model has a Blue Part-Outline. With a little skill, you can drag the Part-Outline so that it rotates freely about the Pin-Joint. It has one degree-of-freedom. When a Part is in this state we call it:
| • | A 'Free-Part' |
| • | An 'unsolved Part' |
| • | A Part that is 'NOT kinematically-defined'. |
This is NOT the state we want for the Part. We want the Part to be:
| • | A 'solved Part' |
| • | A 'kinematically-defined Part'. |
When the Part is in this state, it will have a Green Part-Outline. This is our indication to you that the model is kinematically correct. This is important.
Objective of this Step
Introduce the Motion-Dimension Function-Block (FB).
To move a Part with a specified motion, we must:
| • | Add a Motion-Dimension FB to a Part. |
| • | Connect wires to the input-connector of the Motion-Dimension FB from other FBs. See Step 1.6 |
A Motion-Dimension FB identifies a Part we want to move with a specified motion...and...it specifies the Part's starting position.
When we add a Motion-Dimension FB, the Part-Outline will change from a Blue Part-Outline to a Green Part-Outline.
It will become a 'kinematically-defined Part', and a 'solved Part'.
Summary of this Step
Add a Motion-Dimension FB to a Part.
Edit the Part's initial position.
Note: we can also add a Motion-Dimension FB to a Slide-Joint - See Tutorial Step 2.5
Video of this Step
 How to...Add a Motion-Dimension FB to 'Kinematically-Define the Part' |
A: Add a Motion-Dimension FB to a Part
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The Command-Manager opens starts a dialog. You need to select three elements from the graphic-area.
We must a select three elements in the correct order:
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 Command Manager ready for selections  Commandd Manager with selections |
Click, in order, refer to elements
Line Line
Added-Part is a Free Part. The CAD-Line along its centre is a child to the Added-Part. Line The order you click the elements is important:
Note: The numbers that append [at the end of] the Element-name. The numbers become greater as you add elements with the same name. |
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The Motion-Dimension FB has two features in the graphic-area:
You must CTRL+Drag to move the motion-value in the graphic-area.
You can drag the icon. |
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Notes:
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Edit the Part's initial position.
To edit the Part's initial position, we must edit its Base-Value parameter in the Motion-Dimension FB dialog-box. |
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 Motion-Dimension FB dialog-box |
For example: Double-click the Motion-Dimension FB in the graphic-area [See How to open a dialog-box]. See also: How to open a dialog-box. Use Motion-Dimension FB dialog-box to:
- or -
It is sometimes useful to edit its current positional value rather than its Base-Value. The Base-Value... ... is the angle of the Joint when there is not a wire at the input-connector of the Motion-Dimension FB. ... is the 'offset' of to the Line in the Motion-Parts from the Line in the 'solved' Part. Directions It is possible to 'negate' the sense of the 'Base-Value' and the 'Motion-Values'. [I rarely use these options, I use a Gearing FB]. Notes: There are two Parts to the Motion-Dimension FB in the graphic-area: Icon and the Dimension. To move the:
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The Kinematics Tree
The Part, Pin-Joint and Motion-Dimension are the elements that make a Rocker. A Rocker is one of the two Motion-Parts. |
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If you explore the Kinematics-Tree, you can see the three elements for the Rocker: |
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 Kinematic-Tree with Elements for a Rocker |
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Part |
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Pin-Joint |
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Mot-Dim Rocker |
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Important Kinematic Terms
Some terminology: See also Basic Kinematics for more information.
A Completely Free-Part has three degrees-of-freedom (on a Plane) A Pin-Joint removes two degrees-of-freedom. A Motion-Dimension removes one degree-of-freedom. |