IMPORTANT: Background to this Step.

You will see that the Part in the model, after STEP 1.4, 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 the Part has Blue Part-Outline [Blue is the default colour], we say it is:

A 'Free-Part'
An unsolved Part
A Part that is NOT kinematically-defined

However, in the end, we want the Part to be:

A solved Part
A kinematically-defined Part

In this state, the Part has a Green Part-Outline. This is the indication to you that the model is kinematically correct. It is important that every Part in your model has a Green Part-Outline.

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 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



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 -
Use Add menu > Add Motion-Dimension FB


The Command-Manager opens starts a  dialog. You need to select three elements from the graphic-area.

Add Motion-Dimension FB: Click in turn: a Slide or Pin-Joint, a Green-Line or Point, a Blue Line or Point.

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 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.

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

Its icon, which is 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