Rapid Prototyping System Helps Students Create A Formula Car

The Thayer School of Engineering at Dartmouth College was established in 1867, making it the oldest American professional school of engineering. Graduates of Thayer School's engineering programs are sought after by such manufacturers as Chrysler, Ford and General Motors. Located in Hanover, New Hampshire, the school stresses practical, hands-on projects for their Bachelor of Engineering program. So, when engineering student Jeff Buck decided he wanted to build a Formula-type race car for the 1996 Formula SAE competition, his advisors agreed the project was a perfect fit for the the school's engineering program.

The Formula SAE competition has been held every year since 1981. Over 120 schools have sent teams to the competition over the years. The student teams have 12 to 18 months to conceive, design and fabricate a Formula-type race car. The competition not only requires engineering knowledge, but also creativity. Race administrators set power restrictions and frame guidelines for the entries. Judges evaluate the cars for engineering design, performance and endurance.

In the past, Thayer School students have built a variety of cars including solar-powered vehicles, but never a high performance race car. For the SAE competition, the students are asked to design scaled-down versions of the Formula One cars driven by professional racers.

The Dartmouth students were the first to admit they had very little knowledge of automotive engineering at the time they took on the Formula car project. Most had never been to a race or seen a race car up close. "To an engineer, a car is a pretty amazing thing. You have electronics, mechanical devices, fluid flow, thermodynamics, materials science—every aspect of engineering comes together in this one object. Every piece of it has to work together. This is something a lot of students don't get to experience in their classes," says Mr. Buck. The opportunity to learn about so many practical engineering applications, combined with the excitement about being involved in such a high-profile project was said to be exhilarating for the students. According to Alison Japikse, a graduate student in fluid mechanics, the Formula-car project was a great lesson in collaboration as well. "We had to rely on each other a lot," she indicates.

A 30-student team known as the "Dartmouth Formula Racing Team," led by co-captains Jeff Buck and Jeff Gilberstein, and a 12-member student SAE chapter, started work on the large project. First, the students knew they would need a relatively large budget to accomplish their goals. Because they needed between $20,000 and $25,000 to build the car and enter the race, they became as accomplished fund raisers as well. Mr. Buck approached nearly 100 companies for funding and several months went by before he got his first major funding commitment—Ford Motor Company had agreed to donate $5,000 to the team. With a large portion of the funds they needed in place, the team was well on its way down the road to the competition. In total, they raised $22,000 to cover manufacturing expenses.

One of the many tasks the students faced while designing their car was meeting SAE standards. The annual Formula SAE competition has strict guidelines each race car must meet. Among the requirements: a four-stroke, internal combustion engine; a 20-mm diameter restrictor to limit air intake, thus limiting power; high performance acceleration, braking and handling; easy-to-maintain and economical design (designed for amateur racers); and estimated manufacturing costs must be documented and must stay within an $8500 budget, based on a 1,000-car production run.

To tackle the project, the team split into smaller design groups, each focused on a particular component of the car. Many teams entering the competition incorporate parts of existing commercial engines into their cars. The Dartmouth team, however, wanted a bigger challenge. To increase efficiency and horsepower, one design group focused on the fuel injection system. They started by adapting a motorcycle engine, but soon decided to develop their own electronic system instead. During the summer of 1995, the fuel-injection system component team spent 12 hours a day, seven days a week, working on their design in the sub-basement of the school.

The students' fuel injection system included a special air-intake manifold design to force air into the engine at high speeds. The higher the velocity of air passing through the engine, the more power the air can generate. Ms. Japikse, responsible for the manifold, created a complex yet efficient design using a leading solid modeling software package. The manifold has a four-two-one configuration—the only one of its kind in the `96 competition. "Most manifolds are static boxes full of dead air. Our four-two-one design maintains air velocity all the way through, from air intake to engine, for better throttle response and more power," says Jeff Gilberstein. When the component design teams were finished with their initial designs, they regrouped to see how the individual systems would work together.

Although each of the component systems was well designed, the students soon discovered the parts didn't work together. "Our first design iterations were clearly not compatible," admits Ms. Japikse. "At that point, we realized we needed to build functional prototypes, so we turned to the school's machine shop technician for advice."

Brian Locke, manufacturing technician, has several years of experience working in a machine shop. Thayer School's machine shop is equipped with a full range of CNC equipment and a Stratasys Fused Deposition Modeling (FDM) (Stratasys, Eden Prairie, Minnesota) rapid prototyping system for student use. "When the students approached me for prototyping advice, I recommended FDM," says Mr. Locke. "They needed the ability to build a prototype, conduct functional testing, revise the design and build another prototype in short order. The speed of the system and its ability to generate prototypes in ABS made FDM the only option available to achieve their goals."

The team cut their prototyping time about 85 percent by using the FDM. Design revisions and prototyping took just two weeks with the FDM, whereas previous methods would have taken at least 14 weeks, forcing the team to abandon its special intake design. After analyzing their initial designs, the students redesigned the manifold, drive train and suspension. Under Mr. Locke's supervision, they built the parts in ABS on the FDM system. Then they installed the ABS parts on the car for testing.

With the ABS manifold installed, the students took the car out to the parking lot for a spin. "We conducted extensive functional testing on the ABS parts. We actually test drove the car with the the FDM parts in it. That allowed us to analyze the suspension and drive train performance," Ms. Japikse remarks. The first test drive went even better than the students expected.

Once the manifold design was finalized, Ms. Japikse built another iteration on the FDM system—this time in investment casting wax. The manifold was cast in 6061 aluminum, using traditional casting methods. The moldmaker simply coated the wax FDM prototype in ceramic, let it set, melted out the wax and pour in the metal. "Given time and budget constraints, the students couldn't have achieved this...efficient manifold design without FDM rapid prototyping," maintains Mr. Locke.

The Dartmouth team did extremely well for a rookie entry. Their car was one of only 36 cars to complete all four days of competition without a breakdown. Of the 15 teams that had never competed before, Dartmouth took second place. They placed 39th overall out of 85 teams. The Dartmouth manifold and fuel-injection system captured the attention of the Formula SAE judges and several of the sponsors at the competition. Currently, the `96 Dartmouth Formula car is on display at Thayer School of Engineering. MMS