Automotive

Under the hood of University of Michigan's challenge-winning solar car

Under the hood of University o...
Aurum has an asymmetrical catamaran body that is designed for aerodynamic efficiency
Aurum has an asymmetrical catamaran body that is designed for aerodynamic efficiency
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Aurum has an asymmetrical catamaran body that is designed for aerodynamic efficiency
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Aurum has an asymmetrical catamaran body that is designed for aerodynamic efficiency
The car is powered by a 6-sq m (65-sq ft) solar array
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The car is powered by a 6-sq m (65-sq ft) solar array
Energy harvested is stored in a lithium ion battery pack with a capacity of about 5 kWh
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Energy harvested is stored in a lithium ion battery pack with a capacity of about 5 kWh
The motors used to propel are Aurum said to be built more for efficiency than power and to run at around 98 percent efficiency
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The motors used to propel are Aurum said to be built more for efficiency than power and to run at around 98 percent efficiency
The top of the car can be tiled up towards the sun for more efficient charging while at a standstill
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The top of the car can be tiled up towards the sun for more efficient charging while at a standstill
Keeping Aurum's solar panels clean helps to improve its charging performance
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Keeping Aurum's solar panels clean helps to improve its charging performance
An overcast final three days meant that Aurum was the only vehicle to complete the American Solar Challenge entirely on solar power
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An overcast final three days meant that Aurum was the only vehicle to complete the American Solar Challenge entirely on solar power
Aurum finished 11 hours, 3 minutes and 36 seconds ahead of its closest competitor
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Aurum finished 11 hours, 3 minutes and 36 seconds ahead of its closest competitor
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Earlier this month, the University of Michigan (UM) won the American Solar Challenge, a biennial competition to design, build and drive solar-powered cars across the US. Its car, Aurum, finished a remarkable 11 hours ahead of the second placed car, so we took a look at what makes it tick.

UM has dominated the American Solar Challenge in recent years, winning every event since 2005. Aurum, though, was actually built for last year's World Solar Challenge, another biennial race in which competitors traverse 3,000 km (1,864 mi) from Darwin to Adelaide in Australia. In that, UM finished fourth out of 29 teams in its class, with a time of 34 hours, 15 minutes, 25 seconds.

Having been designed specifically for the World Solar Challenge, though, the car didn't meet the required specifications for this year's American Solar Challenge and some changes had to be made in order for it to comply with the rules.

The motors used to propel are Aurum said to be built more for efficiency than power and to run at around 98 percent efficiency
The motors used to propel are Aurum said to be built more for efficiency than power and to run at around 98 percent efficiency

Most significantly, the team had to increase the protective foam-filled bulge on the right-hand side of the car to provide more protection for the driver. Naturally, this would affect the car's aerodynamics, but also resulted in it being slightly larger, resulting in a seven-minute daily penalty that added 48 minutes on to the team's final time. Elsewhere, more signal lights were added, the horn was made louder and a rear strobe light that flashes when the battery hits performance limits was installed.

The car is powered by a 6-sq m (65-sq ft) solar array. Electricity produced is stored in a lithium-ion battery pack with a capacity of about 5 kWh that was designed and built by the team itself. The printed circuit boards used to control the battery, the solar array and the car's electronics were also designed and assembled by the team.

Two custom Marand hub motors propel Aurum via its rear wheels and run at around 98 percent efficiency. Indeed, the motors are built specifically for efficiency rather than power, with only a small gap between their magnets and coils to minimize power loss. Though actual power figures are not known, the UM says that the power produced is ample and that, critically, it is used sparingly.

Keeping Aurum's solar panels clean helps to improve its charging performance
Keeping Aurum's solar panels clean helps to improve its charging performance

The car has been tested up to speeds of 80 mph (129 km/h), to which the tires are rated, but was limited to 65 mph (105 km/h) for the American Solar Challenge. It weighs 600 lb (272 kg) when fully loaded with battery and driver and measures 4.5-m (14.8-ft) long and 1.8-m (5.9-ft) wide.

To keep weight to a minimum, but to provide the required levels of strength, the rest of the car is made almost entirely from carbon fiber. This, coupled with an aerodynamic design is what the UM team tells New Atlas is key to the car's performance. Indeed, Aurum's asymmetrical catamaran body is said to be more aerodynamic than any vehicle UM has ever produced.

The steering wheel is custom-designed and built, with a display and controls for the driver. It is configured to have a tight steering setup, much like a race car, so that a small rotation of the results in a relatively large response by the wheels of the car.

Custom-designed and -machined aluminum wheels are employed, with Bridgestone tires made especially for solar car racing. The tires are designed to have very low rolling resistance, allowing the car to maintain speed while minimizing energy loss.

The modified car was tested at Michigan's lower peninsula, and also along the full 3,178 km (1,975 mi) of the actual race route. The team was able to test it at Ford's Jacobs Wind Tunnel, too, by way of the carmaker's sponsorship. There, a laser scanner was used to calculate the frontal area of the Aurum and three aerodynamic tests carried out. This allowed the team to calculate the aerodynamic forces that would act on the car, and to test its own aerodynamic instruments.

Aurum finished 11 hours, 3 minutes and 36 seconds ahead of its closest competitor
Aurum finished 11 hours, 3 minutes and 36 seconds ahead of its closest competitor

The eight-day race began on July 30 at Cuyahoga Valley National Park in Ohio and finished at Wind Cave National Park in North Dakota on August 6. Aurum completed the route in a total time of 48 hours, 26 minutes and 46 seconds, ahead of its closest competitor by 11 hours, 3 minutes and 36 seconds, even with its penalties included. It was the only vehicle to complete the entire race route on entirely solar power, due to an overcast final three days.

Sources: University of Michigan, University of Michigan Solar Car Team

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4 comments
Howell Haus
Schweet... now, let's work to transfer that technology and those achievements to a real-world human-assisted vehicle that people can use to commute and commune with...
My question might be, 'Great, but how does this apply to making a better world, and... why not integrate pedaling and human effort into the mix' ?
Paul Anthony
What Howell Haus said! I was wondering the exact same thing. Can there be a consumer version of this?
Don Duncan
My first two questions for any EV: 1. Weight. 2. Drag. These tell me the two fundamental aspects of the platform. Stu left out the drag coefficient. Additionally, what were those 3 aerodynamic tests? Why no detailed pictures of aerodynamics? Is it all passive, no active parts? The aerodynamics is just as important as light weighting. So what are the details of this unique design that give it the least drag?
Island Architect
Go Blue! AndBravo!
Bill Allison would love this! He too was a Michigan Engine grad back when Kelly Johnson was in school as well.
Bill spent a lifetime in Suspension Design and designed the suspensions for Hudson that were referenced in the movie "Cars" and he invented the Torsion Ride Suspension for Packard and finished his Career at Ford, designing the Wind Star suspension.
I talked with Sir Clive Moulton about Bill and he commented that when he was a young buck that a neighbor bought the Packard Torsion Ride and he and his friends would climb in and out of the car and enjoyed the self leveling feature.
Bill influenced Clive tremendously and you are aware of his design for the Mini Cooper so I exchanged greetings between them.
In his retirement Bill Perfected two things. He perfected the wind engine by hitting the Betz limit with his beautiful fans. And he laughed like Mr. Peepers at the ignominious lemming instinct 3 bladed fans that never get much beyond 20% efficiency. I assume that you know what the Betz limit is.
He also commented that it was a shame that he perfected the automotive suspension by achieving very low rolling resistances in his retirement. His method of testing them was with a 1" x 8" inclined. Always the best design won out by scooting across the floor as much a 6 or more times farther.
There is an engineering myth that 4 wheels provides the least rolling resistance. This is entirely and completely false. Bill built essentially the same model with 4, 6, and 8 wheels. The 8 always won out. The Elica in Japan illustrates this.
Now one of the reasons that this has worked so well is that there are only two fairings, one on each side. With Multiple fairings you are picking up far more wind resistance. Maybe as much as 2X or more.
Now the next move is to install 8 wheels and bogie them in pairs, the same way that rail cars are configured. There is a reason for the bogied pairs... less energy lost in heat. So that is exactly why all rail cars around the world operate with 4 bogied pairs, one in each corner.
The single fairing on a side can accommodate them.
So once again, Go Blue! Michigan has produced some wonderful engineers and some idiots too. Don't forget the P-38 Lightning, the U2, the SR-71, the PT Boat, were designed by grads, and the bulbous prows were tested there as well.
I happened to work on the wind tunnel so that is a surprise and a pleasure to hear.
bill