Step 2.1: Build a 4-bar Crank-Rocker

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Step 2.1: Build a 4-bar Crank-Rocker

Build a 'Crank-Rocker' Kinematic-Chain

A Crank-Rocker is a convenient name we give to a mechanism that has an input that rotates continuously (the Crank), and an output that oscillates (the Rocker).


Reminder:

Kinematically-Defined Parts have Green Part-Outlines. We know the position, velocity, and acceleration of all Points in a Part that is kinematically-defined.

Parts that are NOT kinematically-defined have Blue Part-Outlines.

To model a machine correctly, we MUST make sure all of the Parts in the model are kinematically-defined Parts.

At the end of all Tutorials, the Parts should have Green Part-Outlines.


Summary of this Step

1.Add two more Parts and three more Joints to the model.

2.Explain the concept of the R-R-R Dyad.

3.Use Change Dyad Closure

4.We review the Kinematics-Tree

New Terminology

Rocker :

The name in the Kinematics-Tree for a Motion-Part that rotates - it may index progressively, rotate continuously, or oscillate back-and-forth.

Motion-Part :

A Part that is directly driven by a Motion-Dimension FB.

Dyad :

An assembly of two Parts and three Joints

R-R-R Dyad :

A Dyad with 3 Pin-Joints - this is one Dyad of 5 possible Dyads that we can construct on a Plane.

Dyad Closure :

Different ways to assembly the same Dyad

Four-bar :

A kinematic-chain with one Motion-Part and one Dyad - most typically an R-R-R dyad.

Video of this Step

 

Tutorial 2: STEP 2.1

Add

2 Parts and

3 Pin-Joints (R-R-R Dyad)

Change Dyad Closure

 

Add the Parts and Pin-Joints

GA-AddRRR-Part1

STEP 1: Do Step 1.2: Add a Part

As you drag in the graphic-area to add the Part, try to make its length approximately 1.5× longer than the length of the Rocker.


To add a Part:

1.Mechanism-Editor: Click Kinematic-elements toolbar > Add Part

2.Mechanism-Editor: Drag to add the Part (Left-mouse-button-down, Move your mouse, Left-mouse-button-up)

The Part has a derived name of free-Part. - it  has a Blue Part-Outline

GA-AddRRR-Pin1

STEP 2: Do Step 1.4: Add a Pin-Joint

To add a Pin-Joint:

1.Mechanism-Editor: Click Kinematic-elements toolbar > Add Pin-Joint

2.Mechanism-Editor: Click the start-Point at the origin of the free-Part

3.Mechanism-Editor: Click the end-Point at the end of the Rocker

GA-AddRRR-2Parts-2Pin

STEP 3: Do STEP 1 and STEP 2 again

1.Mechanism-Editor: Click Kinematic-elements toolbar > Add Part

2.Mechanism-Editor: Click Kinematic-elements toolbar > Add Pin-Joint

See image to the Left. There is a Pin-Joint at the other of the Line in the Base-Part ( see Tutorial1, Step 3).

The two Parts are free Parts and have Blue Part-Outlines.

GA-AddRRR-DyadComplete

STEP 4: Add a Pin-Joint

1.Mechanism-Editor: Click Kinematic-elements toolbar > Add Pin-Joint

2.Mechanism-Editor: Click the end-Point of the Part we added in STEP 1

3.Mechanism-Editor: Click the end-Point of the Part we added in STEP 3

The two Parts are kinematically-defined Parts and have Green Part-Outlines.


The Parts may not be in the configuration as shown to the left.

See Step 2.1A to reconfigure the Closure.