Getting Started Tutorials - MechDesigner > Tutorial 2A: Four-bar Kinematic-Chains

Build a 'Crank-Rocker' Kinematic-Chain

A Crank-Rocker is the term for a mechanism. Its input rotates (the Crank) and its output oscillates (the Rocker).

Reminder:

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

The color of the Part-Outline of a Part that is kinematically-defined (usually a type of Green) is different to the colour a Part that is NOT kinematically-defined (usually a type of Blue).

Summary of this Step

1.Add two(2) more Parts and three(3) more Joints to the model

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

3.Use the Change Dyad Closure tool

4.Review the Kinematics-Tree

New Terminology

Rocker :	The name in the Kinematics-Tree for a Motion-Part that rotates, and usually oscillates back-and-forth. We use the derived name: Crank If the Rocker rotates continuously.
Motion-Part :	A Part that is directly driven by motion-values at the input to 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 five(5) possible Dyads that we can construct on a Plane.
Dyad Closure :	Different ways to assembly (construct) the same Dyad with Parts of the same Length.
Four-bar :	A kinematic-chain with one Motion-Part and one Dyad - most typically an R-R-R dyad.

Video of Tutorial 2A: STEP 2.1

Add the Parts and Pin-Joints

GA-AddRRR-Part1

STEP 1: Do Step 1.2: Add a Part

To add a Part:

1.Mechanism-Editor: Click Kinematic-elements toolbar > Add Part, or click the INSERT key on your keyboard.

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

The Part has a derived-name completely-free Part. Its Part-Outline is a Blue (or type of blue).

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

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 of the free-Part

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

The Part has a derived-name free Part.

<<< The image shows the click at the end-Point of the Rocker. Then, the Pin-Joint is in the model.

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

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

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

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 - see STEP 1

3.Mechanism-Editor: Click the end-Point of the Part - see STEP 3

The two Parts are kinematically-defined Parts. Their Part-Outlines are Green (or type of green).

The Parts may not be in the same configuration as the Parts in the image to the left!

See Step 2.1A to reconfigure the Closure.