kinematics and dynamics - lab4.pdf

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Kinematics and Dynamics of Mechanisms and Robot

Lab session 4 SolidWorks Motion Ball Throwing

2011

Tran Thi Luyen [email protected] Page 1

THE LABORATORY SESSION 4 FOR

DYNAMICS OF MECHANISMS AND

ROBOTS COURSE

I. Lab Objective

In this lesson, we will learn how to create a motion model to simulate the ball motion, run a

simulation, and calculate the position and velocity of the ball.

The physical model of the ball is very simple. The Ball is made of Cast Alloy Steel with the

radius of 10 inches. The gravitational acceleration is 386 in/sec2.

The ball and ground are assumed rigid. The ball will bounce back when it hits the ground.

A coefficient of restitution 0.75 is specified to determine the bounce velocity (therefore, the

force require for 3D contact constraint to act on the ball) when the impact occurs. CR = 0.75 =

Vf

/Vi

where Vi

and Vf

are the velocities of the ball before and after the impact. That is, thebounce velocity will be 75% of incoming velocity, and certainly, in the opposite direction

Figure 1- Ball throwing
mailto:[email protected]:[email protected]


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II. Lab Assessment

The scoring structure mentioned here is for this Lab only; final Lab score will be combined

from all individual Lab scores.

If in group, score will be same for all students in group.

In case a student is absent, he (she) will not get the Attendance score. However, he (she) still

can get other scores if he (she) submits (shows) the completion of assignments to the Lab

Instructor by the time students are working specified by the Lab Instructor. No group score

is applied for absent student.

Criteria Score (percent)

Attendance 20

Completion of Lab session 4 80

Total 100

III. Lab Setup

Convention: inches are used as units in this Lab session. Use the Solidworks 2009 software to

open the file Crank-Slider.sldasm in Lab 1. Choose from pull-downs menu: Tools

Add-insand click Solidworks Motion in both boxes then click OKto active this software.

IV. Using SolidWorks and SolidWorks Motion

Sketching the Ball and ground

You sketch the Ball with the radius 10 inches, and the Ground with the dimensions:

40x5000.04 in3, rectangular block.

Assembly Mates

The assembly consists of two parts: the ball and the ground. The ball is fully assembled with

the ground by three mates of three pairs od reference planes (Figure 3 Assembly mates).

The distance between the reference planes Top (ball) and Top (ground) is 100 inches. This

defines the initial position of the ball shown in as Figure 2


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Figure 2

Figure 3 Assembly mates

In this model, the ball will be the only movable body. Two assembly mates Distance1 and

Coincident3 will be suppressed to allow the ball to move on the X-Y plane. The ball will be

thrown with an initial velocity of V= 150 in/sec.

A gravitational acceleration - 386 in/sec2 is defined in the Y-direction of the globalcoordinate system. The ball will reveal a parabolic trajectory due to gravity. A 3D contact

will be added to characterize the impact between the ball and the ground. A coefficient of

restitution CR = 0.75 will be specified to determine the force that acts on the ball when the

impact occurs. No friction is assumed.


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Figure 4

Using SolidWorks Motion

Now you had the assembly file ballthrowing.SLDASM. From the Motion Manager , right click

on the ball choose initial velocity the box will appear:

Figure 5 setting the initial velocity for the ball

Clik checkmark to accept this define.

Defining Gravity

Click the Gravity buttion from theMotion toolbar to bring up the Gravity dialog box.

Choose Y and keep the value (386.09in/sec2) in the dialog box, as shown in Figure 6. In the

graphics area, an arrow appears at the right lower corner pointing downward indicating

the direction of the gravity.


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Click the checkmark on the top of the dialog box to accept the gravity.

Figure 6

Run Simulation

When you click the Calculate button, the ball will be drop from 100 in above the ground with

an initial horizontal velocity 150 in/sec. After few seconds, the ball starts moving. In this case

the ball falls through the ground and continues falling, as shown in fig. This is not realistic.

For the time being we will add a 3D Contact constraint between the ball and the ground in

order to make the ball bounce back when it hits the ground. This constraint will be only

activated if the ball comes into contact with the ground.

Figure 7


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Defining a 3D Contact

Click the Contact button from theMotion toolbar. The 3D Contact dialog box appears, pick

both ball and ground in the graphics area. Deselect Specify Materials and Friction, select

Restitution Coefficient for Elastic Prosperities, and enter 0.75 for coefficient. Click checkmark to

accept the contact.

Return Simulation

Click the Calculate button again to return the simulation. After a few seconds, the ball start

moving.

Figure 8

Save and Reviewing Result

We will create graphs for the model: Graph of Y- ball position, graph of X- velocity of the

ball, Y-velocity of the ball, and the trace path of the ball.


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Figure 9 Y- Ball Position


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Save your model.

This manual is referred toMotion Simulation and Mechanism Design with SolidWorks Motion

book.

kinematics and dynamics - lab4.pdf

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