MANAGING CAD/CAM/CAE


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User Story

Principia : AMD

A big engineering project is underway at small, liberal arts-based Principia College located outside St. Louis, MO. The fact that there is no engineering department at Principia makes this project unique. Jonathan Hess, a Principia sophomore, began designing and building a solar automobile as a 1998 physics project. Today, using donated materials such as Mechanical Desktop software from Autodesk, Hess has nearly completed the vehicle's very innovative design.

For Hess, getting started using Mechanical Desktop was easy. Admittedly, Hess says, "I had a small advantage because I worked as an intern at Autodesk for two summers during high school. While there, I learned to use AutoCAD. Once we implemented Mechanical Desktop at Principia, I spent two or three days intensely using the software. Within two weeks, I felt very confident. I especially appreciate its solid and mechanical modeling capabilities, as well as the ability to transfer 3D models to 2D drawings so they can be sent to fabricators."

The last Principia car that was built for the solar car race, held in June 1997, was designed from napkin sketches. Hess adds, "The car was put together like a backyard project. However, using professional CAD software has enabled us to treat this work as it should be a true engineering project. We have been able to design parts in solids as well as review designs before anything on the car is actually built. Mechanical Desktop takes us ways beyond the last team's engineering environment."

Design complexity
Hess notes that this year's vehicle is as complex mechanically as a standard automobile. "The front and rear suspension systems each comprise 50-60 parts. With geometry as complex as today's design, modeling it in 3D is the only way to go. We've been able to design the whole care using Mechanical Desktop. That has been a real advantage. I may be a college student, however, this is as tough and real a project as any engineer has to deal with," says Hess. "We visualize the assemblies to make sure all the parts fit together properly. For example, when we were trying to determine how to mount the shock absorbers on the front suspension, we weren't sure how large to make the A-arms. (Double A-arm suspensions are similar to real racecar suspension systems.) However, thanks to Mechanical Desktop's solid modeling capabilities and our knowledge of the size of the shock absorber, we designed the A-arms around the shock absorber and mounted it without interfering with any other parts. Because we could test it on-screen, we already knew that when we built it, all the parts would fit together perfectly."

The car's chassis was built in North Carolina between September and December of 1998. During that time, Hess and his team started building the mold for the body. He says, "We were able to do both tasks concurrently because we could generate drawings of the chassis and the body, fit them together in Mechanical Desktop, and send the drawings to fabricators.

"Without Mechanical Desktop, many situations could have caused major headaches. However, using its parametric dimensioning, we could change one dimension, and the whole drawing would be updated--chassis, body, or suspension. This feature saved us hours and hours of redrawing work."

In the course of designing the body, decisions needed to be made regarding where to locate solar cells on the vehicle's roof. Because solar cells vary in size, each design layout was different depending on the cells used. "When we finally made a decision," notes Hess, "the updated geometry provided us with a final drawing without having to entirely redraw the body. Parametric dimensioning is a very key tool."

Today, Hess and his team are in the construction phase and finalizing the design for the car. Small issues such as seat and headlight placements have yet to be finalized for the one-person vehicle. The chassis is built and the body is molded and being built. Driver Hess will participate in the 1,300-mile Sun Rayce event sponsored by EDS and General Motors beginning on June 20, 1999 in Washington D.C. and ending June 29, 1999 at DisneyWorld in Orlando, FL. Most of the race takes place on back roads. He concludes, "The prize for this academic adventure is notoriety and pride in knowing that we built the whole car ourselves." For more information about Sun Rayce visit http://ns3.vsat.net/sunrayce/sunrayce/index.html.

Author: Laura Carrabine





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