﻿ Kinematics: Motion Driven Parts

# Motion-Parts and Motion-Points

### Motion-Parts and Motion-Points

Comparisons between the Motion-Part and Motion-Point

Motion-Parts are:

 • Parts that have their motion specified by a Motion-Dimension FB
 • A Joint constraint the Part to either Rotate or Slide

Motion-Points are:

 • Points that have their motion specified by a Motion-Path FB
 • A sketch-element constraints the Point to slide along its length

Motion-Point <

> Motion-Part

Constrained by a Sketch-Element <

> Constrained by a Joint

Motion-Path FB <

> Motion-Dimension FB

### Motion Dimension FB

A Motion Dimension FB:

 • identifies a Part - that becomes a Motion-Part - we want to move with a specified motion
 • specifies the position of the Part relative to a different Part • Rocker

A Rocker is a Part joined to a kinematically-defined Part with a Pin-Joint that uses a Motion Dimension Function-Block to define its directional angle between Lines in the two Parts that radiate from the Pin-Joint. • Slider

A Slider is a Part joined to a kinematically-defined Part with a Slide-Joint, that uses a Motion Dimension Function-Block to define the directional distance between Points at the end of the Lines used to define the Slide-Joint.

### Motion-Path FB

A Motion-Path FB is similar to a Motion-Dimension.

A Motion-Path FB

 • adds a Motion-Point to a sketch-element and identifies it as the Point we want to move with a specified motion
 • specifies the position of the Motion-Point along the sketch-element or sketch-loop

There are many application that can use a Motion-Path FB.  However, there are two useful 'Motion-Dyads'.

See Tutorial 16. • Ram-R

The Ram-R is a similar to an RRR Dyad, but one of the Parts extends.

The Ram-R makes use of the Motion-Path FB. The Motion-Path FB adds a Motion-Point to a sketch-element (CAD-Line) in one Part.

The other Part is joined to the Motion-Point with a Pin-Joint.

motion-values are given to the Motion-Path FB by Motion FB.

The Red Arrow in the image shows the Motion-Path of the Motion-Point along the CAD-Line of one of the Parts. • Ram-P

The Ram-P is a similar to an RRP Dyad, but one of the Parts extends.

The Ram-P makes use of the Motion-Path FB. The Motion-Path FB adds a Motion-Point to a sketch-element (CAD-Line) in one Part.

The other Part is joined to the Motion-Point with a Pin-Joint.

motion-values are given to the Motion-Path FB by Motion FB.

The Red Arrow in the image shows the Motion-Path of a Point along the CAD-Line of one of the Parts.

#### Degrees-of-Freedom & Mobility of Motion-Parts

 Gruebler Equation: F = 3*(N-1) – 2*L- H F = 3 * (2-1) – 2*1 –0 F = 3 – 2 F= 1 Degrees-of-Freedom = 1 Parts N = 2. There are two parts: the Part we wish to specify with a Motion Dimension FB and the kinematically-defined Part to which it is joined Lower Pairs (Joints) L = 1 There is one joint. Higher Pairs (Cams or Gears) H = 0 There are no Cams or Gear-Pairs The Mobility - or Kutzbach Criterion - shows that a Motion Part has a Mobility of Zero. Mobility = Degrees-of-Freedom – Motion Dimensions Mobility = 1 – 1 = 0 Each Motion-Part has one Motion-Dimension that defines its Position.

#### Rocker 1 Add a Part The Part is a 'Free' Part.

The Part has three Degrees-of-Freedom 2 Add a Pin-Joint between two Points The Pin-Joint removes two Degrees-of-Freedom.

The Part now has one Degree-of-Freedom 3 Add a Motion-Dimension FB  This is the FB icon in the graphic-area for the Motion-Dimension FB when you add it to a Pin-Joint.

The Part has Zero (0) Mobility. Notice the Part-Outline and Pin-Joint are green See Video to the Left.

#### Kinematics-Tree The elements that define a Rocker are: • Pin-Joint • Part • Mot-Dim Rocker

#### Slider 1 Add a Part The Part is a 'Free' Part.

It has a blue Part-Outline

A 'Free' has three Degrees-of-Freedom 2 Add a Slide-Joint between two Lines The Slide-Joint removes two Degrees-of-Freedom.

The Part has one Degree-of-Freedom

Notice the Arrowhead at the 'Origin' of the Line in the kinematically-defined Part . It points in the Positive direction of the dimension. Add Motion-Dimension FB is available in the Kinematic-FB toolbar. This is the FB icon in the graphic-area of the Motion-Dimension FB when you add it to a Slide-Joint.

The Part has Zero Mobility. Notice the Part-Outline and the Slide-Joint are green See Video to the Left.

#### Kinematics-Tree The elements that define a Slider are: • Slide-Joint • Part • Mot-Dim Slider

#### Ram-R 1 Add a Part The Part is a Free Part.

The Part has three Degrees-of-Freedom 2 Add a Pin-Joint between two Points

The Pin-Joint removes two Degrees-of-Freedom.

The Part now has one Degree-of-Freedom The Motion-Path FB adds a Motion-Point at the start of the sketch-element to which you add the Motion-Path FB. The Motion-Point is coincident with the Origin at the start of the CAD-Line.

The Part is a still a Free-Part 4 Edit the Motion-Path FB

The Ram-P does not usually work when the Motion-Point is at the Origin of the CAD-Line.

Note: If the Motion-Point is at the Origin of the CAD-Line in the first Part, then the second Part would need to have a length exactly the same as the distance between the two Pin-Joints in the Base-Part. This is kinematically impossible. 5 Add a Part and Pin-Joint

This Part is a Free-Part 6 Add a Pin-Joint between the new Part and the Motion-Point The kinematic-chain is now kinematically-defined chain.

It is a Ram-R

#### Ram-P 1 Add a Part The Part is a 'Free' Part.

It has a blue Part-Outline

A 'Free' has three Degrees-of-Freedom 2 Add a Pin-Joint between two Points

The Pin-Joint removes two Degrees-of-Freedom.

The Part now has one Degree-of-Freedom The Motion-Path FB adds a Motion-Point at the start of the sketch-element to which you add the Motion-Path FB. The Motion-Point is coincident with the Origin at the start of the CAD-Line.

The Part is a still a Free-Part 4 Edit the Motion-Path FB

The Ram-P does not usually work when the Motion-Point is at the Origin of the CAD-Line.

Why? It becomes clear later. 5 Add a Part and Slide-Joint
 6 Add a short Line to the Sliding-Part 7 Add a Pin-Joint between the short-line in new Part and the Motion-Point The kinematic-chain is now kinematically-defined chain.

It is a Ram-R

Note: If the Motion-Point is at the Origin of the CAD-Line in the first Part, then the second Part would need to have a length that is exactly the same as the distance between the two Pin-Joints in the Base-Part. This is kinematically impossible.

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