In this project, I used ANSYS to design and analyze a lightweight motor controller mount. I learned how to use ANSYS Structural and greatly expanded my knowledge of finite element analysis. I also learned how to use the Creo sheet metal tool, and learned GD&T guidelines for sheet metal parts. The last major thing I learned was structural analysis of bolts, including bolt shear, shear tearout, bearing stress, and torque spec.
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Final design deflection under max loading
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The load case for the motor controller was its weight due to gravity and the acceleration of the car, a maximum of 2.8g forward, 2.5g sideways, and 2.5g vertically. I used a factor of safety of 1.25 because we have a fairly predictable and validated load case.
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Loading is applied to the center of mass of the motor controller over the area it covers on the mount
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Meshing the large plate was pretty difficult initially. I ended up using a hex dominant mesh on the main plate with spheres of influence near the bolts to refine the mesh in those areas.
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The entire assembly had 231,185 elements total
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I chose 5052 aluminum for the main plate because its ductility makes it much easier to bend without cracking. The disadvantage is it's weaker than other grades of aluminum, making it slightly heavier.
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Final result after several iterations of modeling and analyzing
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Modal analysis to make sure the car vibrations don't hit fundamental frequencies in the mounting
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I also learned how to do hand calculations for bolts and threads when working on this project. I did and calculations for bolt shear, plate shear tearout, bearing stress, and torque specs for all the bolts in the design.
As with other Formula SAE projects, I made an FMEA and full BOM for the competition. I also made a preliminary and critical design review which I presented to the team (available here).
I also made a few drawings for the manufactured parts:
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| Bending diagram for the main waterjet part |
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CNC blank for the mount to the chassis
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CNC Reference Drawing
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Update: the car is now put together and driving, here's a picture of the motor controller mount in action:
