Four Bar Velocity

7/29/2019 Four Bar Velocity

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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 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 Problem

In the four-bar linkage shown, control linkOA has a counterclockwise angular velocity omega= 10 rad/s

during a short interval of motion. When the linkCB 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 ofAB and

BC.

This problem asks for the rotational velocity of segment BCwhen 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 conditionsand 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 Accomplish


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Creating 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 Marker

b

c


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

b. Make revolute joints between two links at pointsAand B, and between link and ground at Oand C.

Create Links and Joints


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Add 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 when

your model is complete

Model


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a. Create a CM position measure for linkOA in X component

b. Create a CM angular velocity measure for linkAB 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 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

Results

Textbook solution:

Angular velocity ofAB = 2.5 rad/s

Angular velocity ofBC= 5.83 rad/s

Angular velocity ofAB

Angular velocity ofBC


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In this tutorial you learned how to:

Topics 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 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 ofAB andBCat

the correct time.

Documents

Four Bar Velocity