﻿ MechDesigner Reference & User Interface > 2.2 Mechanism-Editor: > Kinematic Function-Blocks > Add Motion-Dimension FB

### A Motion-Dimension Function-Block

#### Terminology and Definitions

 Rocker : A Part whose Angle, relative to another Part, is specified by Motion-Dimension FB. Slider : A Part whose Distance, relative to another Part, is specified by Motion-Dimension FB. Motion-Dimension FB : A Motion-Dimension FB removes one degree-of-freedom from a Part so that it becomes a Motion-Part and a Part that is kinematically-defined. Motion-Part : The generic term for a Part whose position, relative to another Part, is specified by Motion-Dimension FB. A Motion-Part is a Rocker or a Slider.

#### Kinematic states of Parts

 Not kinematically-defined : The state of a Part when it has one or more degrees-of-freedom. kinematically-defined : The state of a Part when it has zero degrees-of-freedom. Its position, velocity, and acceleration are fully specified. All Parts in the model must be KINEMATICALLY-DEFINED before you should analyse any motion and force data.

### Motion-Dimension FB function

 A Motion-Dimension FB identifies a A Motion-Dimension FB can specify, relative to a different Part, the: •Angle of a Part - which we call a Rocker - or - •Distance to a Part - which we call a

### Motion-Dimension FB - Rocker

#### Preparation: Motion-Dimension - Rocker (typical)

 Preparation example: •Two(2) Parts. In this case the Base-Part and a rotating-Part •Lines in each Part •Pin-Joint joins the start-Point and/or end-Points of each Line •Part is kinematically-defined •Part is not kinematically-defined

STEP 1: Select the Add Motion-Dimension FB command

STEP 2: Select the three elements in the graphic-area (or Assembly-Tree)

 Element #1: PIN-JOINT 1.Click a Pin-Joint The Pin-Joint must be a joint between two(2) Parts, and: •One Part must be a kinematically-defined Part •The other Part must be a free Part. Elements #2 and Element #3: Lines Each Line must be a child to a Point and also a child to the Pin-Joint. (Element #1) 2.Click the Line in the kinematically-defined Part 3.Click the Line in the free Part

STEP 3: Complete the Command

 1.Click in the Command-Manager to complete Add Motion-Dimension FB (Rocker).

Result:

Part is now a Part that is kinematically-defined.

A Motion-Dimension and Motion-Dimension FB specifies the angle between the Lines

 The Motion-Dimension FB icon in the graphic-area for a Rocker.

Note: In the graphic-area:

To move the Motion-Dimension : CTRL+ Drag the FB icon

To move the Motion-Dimension FB : Drag the FB icon

To edit:

STEP 3: Open the dialog-box -

#### Kinematics Tree - Motion-Dimension (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: Part + Pin-Joint + Motion-Dimension = ROCKER

### Motion-Dimension FB and Slider

#### Preparation: Add Motion-Dimension - Slider (typical)

 Preparation example: 1.Two(2) Parts   One is a kinematically-defined Part ...the Base-Part The other is a free Part 2.The Parts are Joined... with a Slide-Joint 3.Start Point (or end-Point) of a Line in the kinematically-defined Part 4.start-Point (or end-Point) of a Line in the free Part The Lines are those that you select for the Slide-Joint.

STEP 1: Add the Motion-Dimension FB

STEP 2: Select three elements in the graphic-area (or Assembly-Tree)

 Element #1: PIN-JOINT 1.Click a Slide-Joint The Slide-Joint must be a joint between two(2) Parts, and: •One Part must be a kinematically-defined Part •The other Part must be a free Part Elements #2 and Element #3: POINTS Each Point must be a child to a Line that is also a child to the Slide-Joint. (Element #1) 2.Click the Point in the kinematically-defined Part 3.Click the Point in the free Part

STEP 3: Complete the Command

 1.Click in the Command-Manager to complete Add Motion-Dimension FB (Slider).

Result :

The free Part is now kinematically-defined.

A Motion-Dimension and Motion-Dimension FB specifies the angle between the Lines

 The Motion-Dimension FB icon in the graphic-area for a SLIDER.

Note: To drag in the graphic-area the:

Motion-Dimension : CTRL+ Drag the FB icon

Motion-Dimension FB : Drag the FB icon

STEP 4: Open the dialog-box -

#### Kinematics Tree - Motion-Dimension (Slider)

 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: •Part + •Slide-Joint + •Motion-Dimension = SLIDER

#### Add Motion-Dimension FB to a Pin-Joint

Video: Add Motion-Dimension FB - Rocker

#### Add Motion-Dimension FB to a Slide-Joint

Video: Add Motion-Dimension FB - Slider

Video: Add Motion-Dimension FB - Slider

### Special Methods

Frequently, in a machine, joints are coincident (co-axial).

For example, there are two or more rotating-Parts that rotate about one center, or two or more sliding-Parts that slide along one axis.

#### Special Method: Coincident Pin-Joints

If you want to specify the motion of each rotating-part with a different Motion-Dimension FB, you must carefully plan as to which Points you select when you add the Pin-Joints,

Then, when you add the Motion-Dimension FBs, the Motion-Dimensions can reference the correct Parts.

#### Special Method: Coincident Slide-Joints

If you want to specify the motion of each sliding-part with a different Motion-Dimension FB, you must carefully plan as to which Lines you select when you add the Slide-Joints,

Then, when you add the Motion-Dimension FBs, the Motion-Dimensions can reference the correct Parts.

The Lines you select when you add the Slide-Joint determine between which two Parts you can specify the Motion-Dimension FB.

### Special Method 1

The methods and principles described below apply to Rockers and Sliders. However, the descriptions below are given for Rockers only.

 Result of Special Method 1: The model shows •Two Motion-Dimension FBs •They reference the same Line in the Base-Part. You can see the dimension of the two Motion-Dimensions FBs start at the green horizontal Line.
 STEP 1: Add Pin-Joints two times
 STEP 2: Add Motion-Dimension FB two times

### Special Method 2:

 Result of Special Method 2 We want the two Motion-Dimensions FBs: •Motion-Dimension 1: From the Line in the Base-Part To a Line in 'Part 1' •Motion-Dimension 2: From the Line in 'Part 1' To the Line in 'Part 2'
 STEP 1: Add Pin-Joint two times
 STEP 2: Add Motion-Dimension FB two times

 Positive' Direction of Slide-Joints and Slider

The nursery rhyme : She swallowed a cat, that swallowed a mouse, that swallowed a spider, that swallowed a fly... will come to mind.