IMPORTANT: Background to this Step.

Part's have two states

Unsolved, also called Free-Parts, an not kinematically-defined.
Solved, also called kinematically-defined Parts.

The state of the Part after STEP 1.4 is unsolved. With a little skill, you can drag the Part-Outline about the Pin-Joint. It has one degree-of-freedom. When the Part is unsolved, we do not know where to find the Part.

Objective of this Step

To change the state of the Part to solved, so that it becomes a kinematically-defined Part.

We introduce the Motion-Dimension and its Motion-Dimension Function-Block [FB].

The Part-Outline will change from a Blue to Green [as default colours to indicate its state.

Summary of this Step

Add a Motion-Dimension FB to a Part joined with a Pin-Joint.

Edit the Part's start position.

Note: we can also add a Motion-Dimension FB to a Slide-Joint - See Tutorial Step 2.5



Tutorial 1: Step 1.5

Add a Motion-Dimension FB
Edit a Motion-Dimension FB


A: Add a Motion-Dimension FB to a Part


STEP 1: Click Kinematic-FB toolbar > Motion-Dimension FB [right of graphic-area]
- or -
Add menu > Add Motion-Dimension FB


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:

1s-red Pin-Joint

2s Solved-Line

3s 'Free' Line

Command Manager ready for selections

Command Manager ready for selections

Commandd Manager with selections

Commandd Manager with selections

Click, in order, refer to elements 1s-red 2s 3s in the image above.

a.Pin-Joint1s-red  - see Step 1.4
b.Line2s in the Base-Part - see Step 1.3.

Line2s in the Base-Part is a solved-line because the Base-Part is a kinematically-defined Part.

Line2s radiates (is a 'ray') from the Pin-Joint1s-red.

c.CAD-Line3s along the centre of the Added-Part. See Step 1.2

Added-Part is a Free Part . The CAD-Line along its centre is a child to the Added-Part.

Line3s also radiates (is a 'ray') from the Pin-Joint1s-red.

The order you click the elements is important: 1s-red then 2s then 3s

STEP 2: Click OK

Note: The numbers that append [at the end of] the Element-name.

The numbers become greater as you add more elements with the same name.


The Motion-Dimension FB has two features in the graphic-area:

Its motion-value, dimension line, and arrowhead to indicates its positive [increasing] direction.

CTRL+Drag to move the motion-value in the graphic-area.

The FB.

You can drag the icon.


The colour of the Part-Outline3s is Green. Parts with Green Part-Outlines are kinematically-defined Part.
The design of the icon in the graphic-area is different to the icon in the Kinematic-FB toolbar.
Its design is similar to a Pin-Joint, which is to help you see that that Motion-Dimension FB specifies the angle of a Part.

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.

Motion-Dimension FB dialog-box

Motion-Dimension FB dialog-box

1.There are many ways to open dialog-boxes.

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:

2.Edit the:

- or -

oBase-Value1s-red + Motion Value2s = 'current positional value' of the Motion-Part3s

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.


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:

Icon: Drag the Function-Block
Dimension: CTRL+Hover+Drag the dimension arrowhead.

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.

If you explore the Kinematics-Tree, you can see the three elements for the Rocker:

Kinematic-Tree with Elements for a Rocker

Kinematic-Tree with Elements for a Rocker






Mot-Dim Rocker

Important Kinematic Terms

Some terminology: See also Basic Kinematics for more information.

Degrees-of-Freedom (DOF) The number of coordinates that you need to specify the position and orientation of a Part.
oMobility = Degrees-of-Freedom – Number of Motion-Dimensions
oRocker: a Part joined with a Pin-Joint to a kinematically-defined Part. The angle of the Rocker is given by a Motion-Dimension FB.
oSlider: a Part joined with a Slide-Joint to a kinematically-defined Part. The position of the Slider is given by a Motion-Dimension FB.
Kinematically-Defined Part: a Part that is a child to a kinematically-defined chain
Kinematically-Defined Chain: a kinematic-chain that has Mobility equal to Zero.

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.

Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd