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A profile of the University's solar car team
by Alyson-Kathleen Riley
I'm sitting in a dark and dusty classroom on the third floor of the Mechanical Engineering (ME) building, my notebook in front of me on one of several long wooden tables that look like they've been here since the founding of the University. The lights are low, there are slides up on a projection screen, and the other students around me are intently scribbling down notes on the "calculation of roll-over conditions using distributed inertial loads." These students, under the guidance of Dr. Pat Starr, meet twice a week to discuss electric vehicles, solar power, composites, aerodynamics, chassis and suspension design, and telemetry. I'm an obvious outsider here, and I know it. I'm getting paid by Technolog to learn and write about this stuff, but these people are here during their free time, dedicated to continuing a University tradition started several years ago.
The University of Minnesota's Solar Vehicle Project teams have achieved unprecedented success. But how does one make the leap from slides and sketches in a dimly lit classroom on a sub-zero Monday afternoon to a second place victory in North America's largest solar vehicle race? For Alex Detrick, the Electrical Team leader for Aurora-II, the University's second solar car, the thrill of jumping from the engineering classroom into real-world competition was the experience of a lifetime. "Now that I've gone through this whole thing, I look back, and it's fulfilling. I went though all this and it's unbelievable." Aurora-II was the product of history and the hard work of a dedicated team of students and faculty, where the catalyst for success was a mix of hard science, creativity, and ambition.
The development and success of the Aurora-II project in Sunrayce '95 can be traced to early competitions and the involvement of the University of Minnesota in previous Sunrayces.
Sunrayce 1993: Two years after the first Sunrayce, GM and the U.S. Department of Energy (DOE) sponsored Sunrayce '93, where the University of Minnesota solar vehicle team made its debut in solar car racing. Aurora-I competed with 34 other cars in a collegiate race that extended from Arlington, Texas, to the Minnesota Zoo. Once again, the University of Michigan captured top honors, followed by California Polytechnic Institute at Pomona and California State University at Los Angeles. Aurora-I finished in 21st place and was later displayed by the Minnesota High Technology Council at the Minnesota State Fair.
Sunrayce '95 saw 38 university teams compete over nine days in a staged, cross-country race that covered a 1,000-mile course from Indianapolis to Golden, Colorado. To make the most of daylight hours, the race began at 10:00 a.m. and ended at 7:10 p.m. each day. Aurora-II broke the Sunrayce record for average daily speed, setting a new standard of 50.4 mph. In addition, the U team won the Electronic Data Systems (EDS) award for "Best Use of Aerodynamics in Design." The University of Minnesota finished in second place.
The 1995 World Solar Car Rally: Just three weeks after Sunrayce '95, the U team flew to Akita, Japan to compete with top international teams in the 1995 World Solar Car Rally. In this race, laps were completed on a closed track of 19.3 miles without public road intersections. The competition, which included 24 hours of racing, tested the cars' endurance.
On the first day, Aurora-II's fastest lap was 32 mph and its position just three laps down from Honda's Dream, the overall and Free class leader. Aurora-II took second place in the Junior class and ninth overall at the 1995 World Solar Rally.
The Rayce Itself: During Sunrayce '95, the University of Minnesota's Solar Vehicle Project achieved its highest level of success to date. Aurora-II entered the competition in January of 1994, when the U of M team answered an invitation to submit a proposal detailing its solar car project. Every college in North America was invited, and 65 schools, including all Big 10 universities, responded. A team of experts from the list of Sunrayce sponsors evaluated the proposals, choosing the best thirty and ranking them as seeded teams. Each seeded team received $2,000 from the DOE in addition to $1,000 from the Environmental Protection Agency (EPA).
On June 14 and 15, all solar vehicle entries raced in a qualifying event that reduced the number of teams from 65 to 38. After undergoing a rigorous inspection process called "scrutineering," teams were required to drive a minimum of 50 miles within two hours around a closed course in order to qualify. Seeded teams automatically qualified by meeting this standard, but unseeded teams competed for the remaining ten places in the race.
Aurora-II and the University of Minnesota Team: The University of Minnesota Solar Vehicle Project team entered Aurora-II in Sunrayce '95 after many hours of marketing, design, and fabrication. The Aurora-II project, whose teams included both engineering and liberal arts undergraduates, consisted of co-project managers Jessica Gallagher (Business) and Paul Kelsey (Technical) and the following people: the Aero/Shell Team, led by Lance Molby (one of the drivers); the Solar Array Team, led by Steve White; the Electrical Team, led by Alex Detrick; the Mechanical Team, led by Dan Evanson (one of the drivers); the Logistics Team, led by Charles Habermann; the fundraising and marketing team; the Executive Advisory Board of eleven mentors; the graduate advisor, Scott Grabow; and the faculty advisors, Dr. Pat Starr and Dr. Virgil Marple.
The Mechanical Team, led by Dan Evanson, designed and built the car chassis, suspension, steering and braking systems, and the frame. Initially, team members considered using an aluminum frame but, given the project's limited time span, opted to simplify construction by using fiberglass composite panels. Very stiff and light, composites solved another problem--the "jolt" factor. The electrically conductive carbon frame of Aurora-I had occasionally shocked team members.
To estimate the construction time for the real Aurora-II, the Mechanical Team built a full-scale model from plywood in just two days. They used the model as a guide when cutting the final chassis, a composite monocoque much like an Indy racing car. The final design included the three-wheel concept adopted in 1994, A-arm suspension, and a hydraulic disc braking system. The rear wheel, mountain bike style brakes, and the motor were held in a four-bar swing arm located directly behind the driver. In anticipation of possible flat tires during the race, wheels were designed to be changed quickly. The team shaved every available ounce from the chassis, which eventually weighed in at only 105 pounds.
The Electrical Team's duties included choosing batteries, developing a data acquisition (telemetry) system, and determining motor type and specifications. Aurora-II used a battery pack to store energy collected from the sun during non-driving parts of the day, a crucial component of its success. Energy stored in the batteries was used during cloudy weather or in hilly areas, serving to supplement the solar array. According to Sunrayce rules, teams could only use 309 pounds of commercially available lead-acid batteries. Aurora-II used seven Delco Remy batteries.
To determine the amount of available energy from the batteries, the team needed to create a powerful and accurate telemetry system. The Electrical Team looked at data acquisition systems that monitored the amount of battery power used by the motor, sending that information real-time via a wireless system to a computer located in the support vehicle. The system would be equally effective in monitoring the solar array and track speed, distance, acceleration and g-force. In choosing the best-suited motor and controller system, the team tested Aurora-I's to answer questions about the car's energy consumption, the size of the motor needed to propel the car, and what type of forces were acting upon the car while it was moving. By meticulously testing Aurora-I's motor, the Electrical Team reviewed the repeatable data to determine which motor and telemetry system would best fit their application. In the end, the team adopted a Fluke Hydra Datalogger telemetry system to test electrical and array components for performance.
Since it was a difficult task to find a charger capable of charging 7 batteries with a constant voltage and current profile, the Electrical Team also decided to build its own battery chargers. The charger created by the team was composed of two ferro-resonant transformers and materials obtained from the Electrical Engineering department.
The Solar Array Team: The responsibilities of the Array Team included determining solar array size, selecting the kind of solar cells to use, and then laying those cells out on the array itself. After considering several major U.S. manufacturers of solar cells, the team decided to use cells from Photon Technologies that were cheaper and 1% more efficient than the next-best brand (Siemens Solar Industries). These cells were also available presorted, which eliminated the need to presort over 1,500 cells. Once the cell manufacturer was known, the team could make the final decisions about the design and layout of the cells on the array. The trick was to find the maximum number of cells to fit into the allowable array area.
Once the design was completed, the team could focus on the actual solar cells. According to Steve White, the Array Team leader, "a solar panel is only as good as its worst cell." With this in mind, the team decided to gather like cells into panels to prevent the bad cells from limiting the output of good cells, and to increase the overall solar array power. The team connected string of cells (or modules) together by using a flat copper ribbon and special solder paste compatible with silver pickup traces on the cell. The students then grouped three strings together into larger, stronger modules which were then mounted to a thin Tedlar film. The modules had to be placed one by one on the shell, with holes drilled into the shell at each end of the string to create interconnections between the strings of solar cells. The modules were then fastened to the shell with 3M Very High Bond joining tape.
Once the modules were connected to the shell, they were encapsulated to keep them clean and insulated from the environment and the internal vibrations of the vehicle. With materials donated by 3M, DuPont, and E. Jordan Brookes, the team vacuum-wrapped the car using a large sheet of clear, lightweight optical plastic whose light properties would not interfere with solar transmissions and the efficiency of the cells. The film was glued to the surface of the vehicle with a silicone-based, two-part adhesive mixture that White characterized as having "the consistency of Karo syrup."
The Aero Team was responsible for designing, manufacturing, and testing the outer shell of the solar car, including the car's shape and the canopy. The team decided to use a modular chassis and shell layout, both of which were independently designed and could be constructed simultaneously. If changes needed to be made to one component, the other would remain unaffected, and the shell design could change without greatly affecting the rest of the vehicle.
This year, the biggest factor to be considered was the direction of the race. In the Sunrayces of the past, the direction of the race was north to south, but in Sunrayce '95, the route was east to west, and the shell design made allowances for this environmental condition. The final shape decision was based on a light weight requirement (790 pounds total in the end), small size, and aerodynamic efficiency given the particulars of the race.
To manufacture the final product, the team used a large gantry robot donated by PaR Systems to mill the molds for Aurora-II, thus reducing the mold-making time by about two months. These molds greatly increased the accuracy and surface quality, reducing the time necessary to make shell pieces. Once completed, the two shell halves were permanently glued together into a final product strong enough to withstand the driving environment of the race, yet light enough for several people to lift without difficulty.
The University of Minnesota solar vehicle was without doubt a high-tech project. In April 1994, the first Computer-Aided Design (CAD) of the car was created, and the model was simulated in a wind tunnel using Computational Fluid Dynamics. The CAD model was also used for chassis development, solar cell layout, and additional shape changes to improve performance. From these CAD drawings, the team was able to create two different solid models using Stereo Lithography (SLA). This process uses lasers to harden resins into the shape of the car. Stereo Lithography was a key element used when the team incorporated safety features into the design of the vehicle and the final nose shape , resulting in improved aerodynamics.
Aurora-II was the result of the combined efforts of many talented individuals. The way in which the various teams worked together to create their technical masterpiece could only have been accomplished with a great deal of personal motivation, commitment, and creativity.
As may be expected, there were many issues both personal and professional facing the team members. "As a team," Detrick observed, "most of [our problems] were scheduling conflicts, classes, keeping our grades up, and trying to work as a community. It's always kind of hard for college students to do that. Eventually, you're just with each other long enough and you become good as working as a team." Paul Kelsey, Technical Manager, agreed. "[Aurora-II] was built between 6 p.m. and 6 a.m., and often in 24-hour shifts with very little sleep. There was a drive to push each other, to get the job done. And someone was always there to pick things up when you fell down in a corner from lack of sleep." Kelsey also found this teamwork to be an important component of his education. "In any classroom the normal academic environment pits you against the rest of the worldÐtests are curved and all that nonsense. [Working with the Solar Vehicle Project] takes you out of that environment and puts you in contact with a good group of people and a good team. A place where my part affected your part affected their part. I hadn't had that in the normal classroom environment. Any engineer needs exposure to that, because that's what they will encounter in the real world: team-based productivity."
Both men agreed that working with the Solar Vehicle Project was worth the long hours of hard work and continues to be beneficial. "While I was job-hunting," Detrick commented, "people were looking to see the qualities I had gained from my experience with the project. What's the point of going to college? Getting a job. The Solar Vehicle Project made it a piece of cake. Granted I had to work really hard ... but it paid off in the end." Once again, Kelsey agreed. "The project positioned us well when we hit the industry. " The real-world experience added a dimension to these students' educations that could never be simulated in a classroom. "In engineering, you have magic equations and calculators and computers, but it isn't necessarily the real world. There's always an answer in the back of the book when you're doing homework problems. We knew if we had the wrong answer if a part fell off the car when we were going down the road at 65 or 70 miles an hour," Kelsey commented.
The most obvious characteristic of the team members past and present seems to be the level of loyalty, energy and excitement they hold for the project. "You almost live on the adrenaline," Kelsey laughed. Laurie Miller, an Electrical Engineering junior and novice team member, is just getting started with the project, but spoke with the enthusiasm of a veteran. "Part of what's so exciting about this," she notes, "is that we are talking about dealing with cutting-edge technology." She goes on to explain that the reason she's "willing to commit so strongly to this project, allotting time in [her] schedule for the next year and a half, is that she's going to the U to get the best engineering education [she] can, and this is an excellent opportunity to round out that education." Miller is already thinking about new Sunrayce speed limits and new technology. "It keeps it exciting," she comments. "There's no prize for taking your car home in a bucket."
Back to the classroom and the sketches. In this dark old room in the ME building, a new team of students is ready to commit to the project and the creation of the next solar vehicle. Rules for Sunrayce '97 are different than those for previous races, and it's time for a new car. As of Monday, Jan. 29, 29 students had turned in Solar Vehicle Project interest sheets to Professor Starr. Miller noted that they are "expecting a slow trickle of new people all the way through," and that there will always be places for "self-motivated and hard-working" students to become involved in the project and assume leadership roles. The next race is not far off, and the team's excitement is contagious. When they talk to me about their plans, it is impossible not the feel the effects of their adrenaline.
But before the next win comes the months of hard work. "Stick with it," Detrick advises. "It's all an experience and if you go through with [it] it will pay off in the end. You just have to be patient."
