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The following is a tutorial illustrating how you can use CATIA V5 MSC.Dynamic Designer from MSC.Software to understand how much motor torque is necessary to drive an assembly through its range of motion. Tools necessary to complete this exercise are CATIA V5 R8 GA or SP2 and MSC.Dynamic Designer for CATIA V5. If you do not have MSC.Dynamic Designer for CATIA V5, you can download a trial copy, along with the assembly for this tutorial, from the MSC.Dynamic Designer website at http://www.dynamicdesignermotion.com/CAT/
Step 1: Launching Dynamic Designer:
Starting from an open CATIA v5 Session you must first load the assembly, in this case a simple Crank-Slider mechanism called crankslider_exercise.CATProduct. Once the model is displayed on the screen, you need to start the Dynamic Designer application. This is done by going to your Start ->Digital Mockup->Dynamic Designer Motion pull down menu at the top of the screen. You will know that Dynamic Designer is loaded when you see the Motion pull down menu added to the menu set across the top of the screen and the Dynamic Designer Toolbar added to the right side of the screen.
Step 2: Creating the Motion Model:
A motion model is an assembly that contains all of the necessary information that is needed to perform a dynamic simulation. This means that the assembly is fully defined with respect to mass and inertial properties, external forces and moments and joints. Creating a motion model from a fully constrained CATIA V5 assembly is an extremely easy process. Once your fully constrained model is displayed on the screen, select the Motion ->New Mechanism Pull down and the New Mechanism dialog box titled will appear at the bottom of the screen. Click OK and your motion model, complete with mechanical joints is automatically created.
Step 3: Adding a spring to the assembly:
To add a spring force to the working assembly, go to the Motion-> Add Force -> Linear Spring Pull down. Next you must choose the appropriate Components and Points on your mechanism to determine the location and orientation of your spring. For the First Component choose the Collar. For the Second Component choose the shaft. For the point on the first component choose the right circular edge of the Collar. For the point on the second component, choose the right circular edge of the shaft. Next fill in the Dialog box with the appropriate spring stiffness and free length, in this case 25 Newton/mm and 100 mm respectively and press OK.
Step 4: Adding a Motion to the assembly:
The last step in defining our motion model is to apply a motion on the crank. For this we will add a constant velocity of 360 degrees per second. To do this you need to double click on the cylindrical joint located on the end of the crank. Fill in the dialog box and select OK. An arrow will appear over the cylindrical joint representing the motion that was just defined.
Step 5: Simulating the model and viewing the animation:
Now that the Motion model is complete, you need to run the simulation. To do this go to Motion -> Simulate pull down and the Simulate Dialog box will appear. The default settings are appropriate for this model, so click start to execute. The simulation process is very quick (approximately one second). Running the simulation produces two items on the Dynamic Designer Tree: 1. A result set (titled Results.1) containing all of the engineering data from the simulation and 2. A Replay set (titled DDM Results.1) containing the animation of the motion model. To view the animation, expand the Replay branch under the Dynamic Designer Tree. Double click DDM Results.1. This brings up the Replay Window. Press the play button to view the animation.
Step 6: Plotting Motor Torque Results:
To plot the motor torque necessary to drive the assembly, go to the Motion->Plot pull down. The Simulation Results dialog box appears asking for the desired results set to be reviewed. Expand the Results branch under the Dynamic Designer Tree located on the right side of the screen and select Results.1. Click OK on the Simulation Results dialog box. Another dialog box will appear asking for a name to assign to the results set. Give the file any name you choose and press save. A window indicating the post processor is loading will appear (this window may be on the screen for a few seconds). Once the post processor appears, you will be asked if you want to automatically generate plots. For the sake of this exercise we will select No because we are specifically interested in the motor torque necessary to drive our assembly. Selecting from right to left pick the appropriate items in each column and select Add Curves button. The resulting plot shows the maximum torque necessary to drive the assembly is approximately 50,000N-mm.
Step 7 (Optional): Making Changes:
At this point, you can go back to your model, make changes in the geometry or in the spring stiffness. Rerunning your simulation from this point and following the above steps will tell you how your assembly changes affect the motor torque necessary to drive the system.
Conclusion:
As you can see, Virtual Prototyping inside the CATIA V5 environment with the MSC.Dynamic Designer software is as easy to use as it is useful. By simulating reality with a Virtual Prototype, you can quickly determine important engineering data that can help you make decisions about your designs much faster and less expensive than making and testing a standard physical prototype. To view this article with illustrations go to: http://www.dynamicdesignermotion.com/cat/support/motor_torque_tutorial.htm
If you have any questions, please contact Michael Brewster, MSC.Software at Michael.Brewster@msc.software.com. | 
