‘Astrum’ solar car shoots for the stars by pushing energy efficiency
With a name inspired by the Latin phrase “ad astra,” which means “to the stars,” the University of Michigan Solar Car Team unveiled its first three-wheeled, bullet-style vehicle today at the Michigan Theater.
“Astrum,” is scheduled to race in this year’s Bridgestone World Solar Challenge, a biannual, 1,800-mile race from Darwin on Australia’s northern coast to Adelaide on the country’s southern coast. The race begins Oct. 22.
“The car’s name represents the team’s ‘dream shot’ aspiration to win this year’s race, the first since the COVID-19 pandemic paused the international contest,” said Will Jones, a rising senior in mechanical engineering and the team’s race manager.
“We are thrilled to be back at the Bridgestone World Solar Challenge. For many of us, this competition is what we live for, and it is super exciting to have the opportunity to race against the best teams in the world and represent the University of Michigan and the United States. Our team has had a hard reset with the four-year break in competition, and we are eager to show the world what the University of Michigan is capable of.”
If the team meets their ambitious goal, they would ascend the podium from their 3rd place position achieved in 2019.
To make their dream a reality, the team optimized Astrum’s energy efficiency by meticulously refining systems across the car. That improved efficiency will allow Astrum to drive faster and with fewer stops to recharge the battery.
“Fundamentally, there was a shift in ethos and the team went from trying to have these grand-slam innovations to looking closely at every single thing we have and trying to perfect it,” said Leo Intelisano, a sophomore majoring in computer engineering and one of the team’s microsystems engineers.
The team strove to perfect nearly every nut and bolt on the vehicle. For starters, Astrum’s battery has 25% higher capacity than Aevum, their previous car, said Ian Bakker, an electrical engineering sophomore and the team’s high-voltage engineer. To go along with the new battery, the team built their own battery management system, the platform that keeps the battery operating safely and measures and communicates its charge level. To do that, they had to characterize the properties of their battery cells, such as precisely measuring how their efficiency changes with temperature. Because the team knows their battery inside and out, they believe they can better plan and tune their racing strategy to varying weather conditions.
Further improvements to Astrum’s efficiency came from other parts of its design. Some team members worked long and hard to ensure the car’s carbon fiber body is as light, smooth and streamlined as possible. Taking advantage of the race’s new regulations allowing three-wheeled cars provided even more benefits. Ditching a wheel reduced the car’s size and weight, the friction of the tires on the road, and the drag around the wheels, said Nate Gustafson, a mechanical engineering senior and the team’s crew chief and manufacturing director.
But while three-wheeled cars are typically more energy efficient than their four-wheeled counterparts, they can also be less stable. That trade-off became a design challenge for the team, which needed to ensure that the car not only reaches Adelaide quickly, but also safely.
“The dynamics in how a three-wheeled car handles are pretty complicated, and we put a lot of effort into ensuring the car is stable,” Gustafson said.
A stable car has its center of gravity at its widest point, which for Astrum is directly at the two front wheels. That means the team had to position the heaviest part of the car—the driver—as close to the front wheels as possible. Past solar cars typically placed the driver around two feet behind the front wheels, the sweet spot where the steering apparatus’s position can simply and optimally translate the driver’s input to the vehicle’s wheels. Shifting the driver forward created challenges in designing Astrum’s steering, suspension and braking systems.
“If the driver’s hands are parallel with the center of the wheel, you need to have quite a strange shape of steering system to steer the car efficiently and design that nicely. It’s a headache for the entire front-end mechanical system. It required a lot of very, very tight clearances between parts and a lot of brainstorming,” Gustafson said.
To better suit the driver’s new position relative to the wheels, the team designed their own extensions to the steering system, which in turn allowed them to move a key joint to its optimal location.
The team is the only U.S. university competing in the challenger class this year, along with entrants from Australia, Canada, East Asia, Europe, the Middle East and South America.
Astrum is the 17th car made by the Michigan Solar Car Team since its founding in 1989. The team has won the American Solar Challenge nine times, had podium finishes in the Bridgestone World Solar Challenge seven times, and won its first international championship in 2015 at the Abu Dhabi Solar Challenge. With more than 90 students from schools and colleges across the university, it’s one of the largest student organizations on campus. For those students, the Bridgestone World Solar Challenge presents an exciting opportunity to develop their skills by pitting them against some of the world’s best solar car design teams.
“The race is a fantastic opportunity for students to get excited about advancing sustainable technology,” said Jones, the team’s race manager. “It’s one thing to learn in a class about clean energy solutions, but the genius of the Bridgestone World Solar Challenge is that it combines learning with an incredible adventure. In striving to design and build the most competitive solar car, students from all around the world are able to come together with the single goal of making the world a better place.”