The Formula SAE Michigan competition, held at the Michigan International Speedway in May, consists of events to test the design, acceleration, skid-pad performance, autocross, and endurance of the student-designed cars. The racecars go through an acceleration event where they travel 75 meters as fast as possible. Most will take less than 5 seconds and reach over 60 mph. Then, their cornering ability is tested in a constant radius turn as drivers make continuous figure eights with 25 foot radius circles. The autocross event tests the racecar’s braking and maneuverability around cones. Finally, endurance and fuel economy are tested over a 13.66 mile heat.

The most recent Formula SAE competition brought together 107 teams from the USA, Canada, Mexico, Poland, Germany, Austria, Venezuela, Brazil, Singapore, and South Korea.  Only half of the teams finished the final Endurance event, including Purdue (for the second year in a row).  Overall, Purdue's Formula team finished 33rd out of the 107 schools.

History of Speed

The Purdue University FSAE team has been a fixture at the school for 27 years. The team, which has between 30 and 40 active members, has students from all of the university’s engineering schools and all year classes. Former FSAE team member and Purdue alum Todd Nelson is the team’s advisor. “It was what I learned at FSAE that I took with me and used pretty much every day in the workforce. And so coming back to be with these guys is really about trying to get them to have the best learning experience possible,” said Nelson.

Purdue owns a Grand Prix track just off campus, which students can reserve for FSAE preparation when there are no other major Purdue events. In addition, the School of Mechanical Engineering provides the team access to its Student Machine Shop which has six manual mills, four manual lathes, two CNC mills, and one CNC lathe among a variety of other metal and wood working machines.  Nelson explained, “The ME Student Machine Shop has 2 full-time professional machinists that help students learn how to use the equipment and work along-side the students to use the CNC machines.

The students perform all the design and fabrication for the vehicle which requires a lot of hands-on application of their engineering curriculum. “We’ll basically make the entire car,” said sophomore Adam Dewey, Drivetrain Team Leader, “There are a few things that we don’t make, like the engine, the shocks, and the tires. Other than that we essentially make everything in-house.” The club is divided into subteams like Suspension, Chassis, Powertrain, and Aerodynamics, each with its own student leader.

Design Challenges

This year’s car boasts an 85 horsepower engine that allows a 0 to 60 acceleration in 3.5 seconds and a maximum speed of over 90 mph. While all the body work and aero components are carbon fiber, most of the racecar is made from 4130 steel and 6061/7055 aluminum. Almost every mold and CNC-machined component is made in-house with Mastercam® CAD/CAM software (CNC Software, Inc., Tolland, CT).

“I think the feature we find most beneficial is the simulation,” said Dewey, “We can model the toolpaths to see if there’s going to be any unexpected failures due to the tool maybe not being long enough or running into the tool holder. It also helps us estimate time and figure out what would be the best way to simplify the tool path and maybe save some time on the machining.” The Simulator feature within Mastercam includes Verify and Backplot options to anticipate and correct any machining problems before they occur. Verify is especially useful in customizing parts with specific tolerances, modeling the finished part, and comparing the preview with an external STL model.

This simulation is invaluable when the crew works on difficult parts. The drivetrain and suspension components, such as the suspension uprights, have been a source of strain for the Purdue team. “This was a tricky piece of geometry. The uprights connect a lot of different points of the suspension together, and they have to be perfect so we can fasten as much of the other components on the race car as possible. We make it in two halves and then we’ll flip it over so we can get the other half of the part,” explained senior Alex Roberts, Suspension Team Leader. To machine a billet of 7055 aluminum into the uprights, the team relies on the software’s Contour toolpaths and pocketing solutions. Contour toolpaths use high speed strategies to remove material along walls, supporting multiple passes and even allowing finishing passes.

The differential supports are made in a similar fashion. “We machine the uprights in two set-ups,” continued Dewey, “We bore out a pocket for the bearing and we leave about 30/thousandths (0.0030”) off of it so we can bore the upright out for a pressed fit on a manual mill. We try to get that within 1/thousandth (0.001”), ideally. We use 3/8” end mills for many of the pockets as well as ¾” end mills for the larger bearing pocket. And then in terms of fixturing, we’re using a sacrificial aluminum block that we’ve modeled in CAD, and we’ll bolt our uprights to that. When we’re machining the outer geometry of the upright, we can bolt the upright to the sac-block so that part doesn’t come flying out at us.” The result is a part that is just as functional as it is safe.

Roberts explained that, while speed and maneuverability are paramount to a good competition racecar, the Purdue team places most importance on strength and safety. Chief Engineer and senior Adam Christopherson clarified: “Aside from safety, strength in the sense that something does not fail during our entire season is our next biggest priority, because as soon as something fails that means we lose our testing time. Obviously we try to reduce weight as much as possible but we don’t want to reduce weight to the point where we’re sacrificing our chances of being able to run the car.”

During the 4 days of competition, the student engineers not only have to drive their racecar in multiple events to test every facet of their design, they also are expected to deliver presentations to the judges. During the Design Event, judges with decades of experience in the racing and auto industries ask the students to explain their all their design choices for the vehicle, including detailed design on individual components.   This explanation must include a detailed overview of the manufacturing process, the design parameters, and the empirical reasons behind these design and manufacturing choices.

The team are also expected to have a cost report and a sales presentation prepared. The goal of assigning these projects is to mimic how a real racecar designing firm might pitch its prototype to a manufacturing company. The car with the lowest retail cost automatically wins 30 points. The students are not only responsible for tracking expenses and weighing financial decisions, they are also in charge of securing much of the project’s funding. Every year, the team raises $35,000-$40,000 through fundraising and establishing sponsorships. “This is a team that does a lot of outreach, and the responsibility is distributed across the whole team to do their best to get the resources, get good people, and see what additional options we could have in the design and competition,” said Roberts.

Even though this year's competition is over, the Purdue team is wasting no time. Next year’s design starts immediately for those returning to the university, regardless of summer break. The students who are graduating are equally as busy preparing for their new careers. “This experience gives students exceptional opportunities to develop their skillset. By the end, they’re fully prepared engineers entering the workforce,” shared Nelson, “They not only get jobs because of it, they excel in their jobs because of this experience. We’re focusing on our team members by making sure that we’re trying to design winning race cars, but we’re also trying to prepare our students to be great employees that make an incredible impact on our world.”

Christopherson will be pursuing a PhD in Aerospace Engineering Sciences at the University of Colorado Boulder next school year. Roberts will soon be taking his automotive knowledge to Honda R&D Americas and working with chassis and suspension design. Both thank the FSAE program for equipping them with invaluable skills.

“I still would maintain that FSAE is the best program because of the experience that you get working with other students. The leadership that goes into it, the cooperation; there’s definitely a lot of non-technical things that are really crucial for success in any path that you want to take in the future. It teaches you how to go beyond the standard stuff in the classroom,” said Christopherson.

Writer: Mary Ellen Klukow, mastercam.com

Source: Todd Nelson, tnelson1@purdue.edu