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Four Bar Velocity

Estimated time required: 15 min

GUI familiarity level required: Higher

MSC.ADAMS 2005 r2

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Topics CoveredTopics Covered

If you have any difficulties, import the “Four_Bar_Acceleration_complete.cmd” from pg 10

In this tutorial, you will learn how to:

1. Create a marker

2. Change angle units

3. Add motion

4. Create center of mass angular velocity measurements

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Four Bar Velocity ProblemFour Bar Velocity Problem

In the four-bar linkage shown, control link OA has a counterclockwise angular velocity omega = 10 rad/s during a short interval of motion. When the link CB passes the vertical position shown, point A has

coordinates x = -60 mm and y = 80 mm. By means of vector algebra, determine the angular velocity of AB and BC.

This problem asks for the rotational velocity of segment BC when it is in the pictured position given a constant and known rotational velocity for segment OA. We will use ADAMS to create a model with the given conditions

and collect the data needed.

Problem 5/84 from J. L. Meriam and L. G. Kraige, Engineering Mechanics: Volume 2, Dynamics 3rd edition. John Wiley & Sons, Inc.

Copyright © 1992, by John Wiley & Sons, Inc. This material is used by permission of John Wiley & Sons, Inc.

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If you are successful, you should end up with a ADAMS model that illustrates angular velocity of the links in a

four bar mechanism.

What You Should AccomplishWhat You Should Accomplish

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Creating the ModelCreating the Model

a. Start ADAMS.

b. Create a new model. (Model Name = fourbar, Units = mmks, Gravity = none)

c. Modify the spacing of the Working Grid (X = 10mm, Y= 10mm)

d. Click Units from Settings menu

e. Select Radian from Angle pull down menu

f. Click OK

d

e

f

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a. Open Coordinate Window

b. Select Marker tool from Rigid Body tool stack

c. Create a marker at each of the following coordinates: O (0, 0, 0); A (-60, 80, 0); B (180, 180, 0); C (180, 0, 0)

Create a MarkerCreate a Marker

bc

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a. Create links OA, AB, and BC, using the markers as end points.

b. Make revolute joints between two links at points A and B, and between link and ground at O and C.

Create Links and JointsCreate Links and Joints

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Add MotionAdd Motion

a. Select Rotational Motion from motion tool stack

b. Enter (10rad) in Speed text field

c. Select joint at point O

b

a

c

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This is what your screen should look like whenyour model is complete

ModelModel

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a. Create a CM position measure for link OA in X component

b. Create a CM angular velocity measure for link AB and BC in mag component

c. Run a simulation with Duration = 1.25, Step Size = 0.01

d. Transfer to Full Plot

e. Use the Display Plot Statistics tool to follow the plot curve. Find the angular velocity at X = 0.0

Testing the ModelTesting the Model

Notice when the four bar returns to the original position you will have the same answers

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Theoretical Solution ADAMS solution

ResultsResults

Textbook solution:Angular velocity of AB = 2.5 rad/sAngular velocity of BC = 5.83 rad/s                                                                            

Angular velocity of AB

Angular velocity of BC

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In this tutorial you learned how to:

Topics CoveredTopics Covered

1. Create a marker

2. Change angle units

3. Add motion

4. Create center of mass angular velocity measurements

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Best PracticesBest Practices

• Make sure correct units are set to mmks and the viewing area is zoomed in or out enough to see the model. It may be helpful to set the working grid to 10mm spacing and change the icon size to 10mm under the Settings menu.

• Make sure gravity is turned off.

• Make sure the revolute joints are in the z direction.

• Check dimensions of the part to make sure they are correct.

• Make sure the measures are set correctly.

• Make sure the plot is displaying the correct set of results.

• Make sure there are enough output steps to observe the angular velocity of AB and BC at the correct time.