Motion View tutorial: Four bar Mechanism

By Prakash Pagadala

In this tutorial we will model and analyse a four bar mechanism driven by a motion at one of the

joints. The aim of the tutorial is to output forces at on a specific body.

Note: Please refer to tutorial 1 for how to create entities, bodies, points, outputs, etc..

1. Start with creating points as below. Please refer to Motion View tutorial: Simple Pendulum in

the training center on how to create points.

2. Create bodies: Create three bodies with CM coordinates as points 3, 4 and 6 respectively.

Give a mass of 2 and Ixx, Iyy and Izz as 200 in properties while creating bodies.

3. Create Graphics: create three cylinders each with a radius of 0.1:

Cylinder 1

Cylinder 2

Cylinder 3

4. Create joints: create two revolute joints, one ball joint and a universal joint joints at points

5&7, 1, 2 respectively.

Joint 1: revolute joint for Body 1 and Ground body

Joint 2: revolute joint for Body 3 and ground body

The origin points are the points where the joint is placed and Alignment axis is the

orientation axis for the revolute joint. It could be either a vector or a point.

Joint 3: ball joint for body 2 and body 3

Joint 4: Universal joint for body 2 and body 1

5. Apply motion to a joint: create a motion (velocity) to joint 1

Switch to properties and specify 5 in the field. A rotational velocity of 5 units is specified to

the joint 1. In this case the units are rad/sec or sec-1. So a velocity of 5 Sec-1 is applied to joint

1.

To change units: Project browser>>Forms>>Units

Check the model: from top tools dropdown menu select check model. Switch to DoF section

and the total redundant DoFs. It should show zero. If the model is under constrained (not

constrained properly) or over constrained MotionView will show the number of redundancy

in the model.

6. Create an output for force: create an output with type force to output forces at joints

related to body 1

7. Enter run panel and run the analysis with a runtime of 5 seconds and print interval of 0.01. It

is a good practice to check the model before running for any errors and modelling issues.

8. Once the run is completed successfully animate the model.

9. Open Hypergraph and load the <model name>.abf file from the working directory.

10. Plot the graph for force Vs time for joints 1 and joint 4. Select the following:

X type Time

Y type Marker force

Y request Output request(s)

Y component FM (magnitude of force)

You can plot a similar graph using <file name>. plt

Model the with all joints as revolute and check the model. You will see that the model is over

constrained. Run the analysis and you should get the same result as above.

So, MotionSolve is smart enough to switch to the right constraint(s). But this need not happen

always. One should be careful while selecting the constraints for a kinematic analysis.