ME 240 Fall 1998

Problem Statement: In this assignment, we use Working Model to illustrate the kinematics of a three-bar linkage system. The general motion of these linkages is somewhat complex, as will be seen. However, the relative motion of the bodies, as seen from the rotating coordinate frames, can be surprisingly simple. It is the objective of this exercise to study velocities points on rigid bodies and the relative velocities of these points as seen from different frames of reference. Also we are interested in the relative motion of different points of the linkages as we choose different reference frames (in this Working Model program, we can choose from 4 different reference frames, "ground" , "bar AB", "bar DE" and "point C" where "point C" really means the frame of "bar BD" to observe the motion).

The Working Model file for this assignment is called "linkage2". For instructions on downloading the file and running Working Model, click here.

Below is a screen shot of the Working Model program for the three-bar linkage system.

Reference on the Ground

1. Set the angular velocity of the bar AB as 200 rad/sec. by moving the slider or input a number in the box.
2. Select a reference frame on the ground by clicking "ground" button. If the system is out of the window, use the scroll bars on the side and bottom of the window to move it back.
Let the program Run for a while then stop it.
3. What is the trajectory of point B? (Describe each trajectory by its shape, e.g., "circle", "arc", etc.) What is the trajectory of point D? And what is the trajectory of point C -- is it simple?

1. Hit Reset. Select a reference frame on the bar AB by clicking "AB" button. Now we are seeing the motion of the other bars relative to the rotating frame attached to bar "AB" (i.e., we are looking at the relative velocity of point "C" or "D", for instance). Let the program Run for a while then stop it.
2. What is the trajectory of point C measured in this frame? And what is the trajectory of point E measured in this frame?

1. Hit Reset. Select a reference frame on the bar DE by clicking "DE" button. Now we are looking at the world from reference frame attached to "DE". Let the program Run for a while then stop it.
2. What is the trajectory of point C measured in this frame? And what is the trajectory of point A measured in this frame?

1. Hit Reset. Select a reference frame at point C by clicking "C" button. Let the program Run for a while then stop it.
2. What is the trajectory of point A measured in this frame? And what is the trajectory of point E measured in this frame?