Cambridge Engineers Endeavour to Win Aussie Solar Race
- By Chuck Squatriglia
- June 7, 2011 |
- 7:00 am |
- Categories: Cool Cars, EVs and Hybrids
Of all the challenges that come with racing across Australia in a solar car, Alisdair McClymont is most worried about bugs. Not the kind you find in software. The kind you find on the ground.
Australia is full of them, often big and occasionally poisonous. This is not something to be taken lightly if you’re a stranger to the outback, as McClymont and his mates on the Cambridge University Eco Racing team are, so you can see why it might be a concern.
“Being from the U.K., we’re not used to bugs and spiders. Or all the heat,” he says. “The environment is not something we’re used to.”
If watching out for spiders is the worst of the things they’ll face competing in the World Solar Challenge in October, they’ll be fine. The biennial 1,800-mile sprint through the outback is the oldest and most prestigious race of its kind, a test of engineering and endurance that draws dozens of teams from around the world. The Cambridge crew is wrapping up work on Endeavour, version 2.0 of the car that placed 14th in 2009 after being sidelined by a bad battery.
“We had quite a good car, but it wasn’t reliable enough,” McClymont says. “We’ve made a lot of modifications to ensure it is reliable. Our goal is to finish as highly as possible.”
Endeavour in the outback during the 2009 World Solar Challenge.
The team will face intense competition, and the race long been dominated by the defending champions from Tokai University in Japan and the Nuon Solar Team of Delft University, the Dutch team that won the four previous races. The University of Michigan is another powerhouse, having spent more than $1 million on its latest car in a bid to bring the United States its first world title since 1987.
Cambridge University Eco Racing was founded in 2007 by veterans of MIT’s solar-racing team. Its first car, Infinity, drove the length of Britain in a goodwill tour to raise awareness of the esoteric sport of solar racing. That was fun and all, but the goal from the start was to compete in the World Solar Challenge.
To that end, the team set to work on Endeavour, a carbon-fiber sliver of a car with an aluminum frame, lithium-polymer battery and state-of-the-art motor. It was impressive, especially for a first attempt, and McClymont believes it would have done better than 14th if the battery hadn’t started blowing cells.
Rather than start from scratch for this year’s race, the team opted to improve Endeavour. It started by replacing the 5-kilowatt-hour lithium-polymer battery pack with a 4-kilowatt-hour lithium–iron phospate unit. It’s heavier, but cheaper and more robust.
“The battery won’t be a problem this year,” McClymont says.
Using the same car means the team can’t change the layout of the wheels, which are something of an anomaly. Almost everyone runs three wheels because they offer less rolling resistance than four. But most cars have two at the front and one at the rear. The Cambridge team built its car the other way around.
“We thought we could make it more aerodynamically efficient having one wheel at the front,” McClymont says. “We’re not convinced that was the right decision to make. But we don’t think it will make that big a difference.”
The team designed the body using computational fluid dynamics to make the car as slick as possible. The car has a drag coefficient of 0.17, which makes it more aerodynamic than any production car but not quite as slippery as the competition. Top-tier solar racers are in the hyperefficient 0.07-to-0.1 range. Endeavour’s problem isn’t the shape, it’s the surface. The team did all the work by hand, so it’s a bit rough.
“The surface isn’t as smooth as we’d like it,” McClymont says. “Carbon fiber is tricky to work with.”
Still, the team is confident it can improve the drag coefficient by refining the wheel fairings and modifying the canopy.
The car is not quite 6 feet wide and almost 16 feet long. It is covered with 64.5 square feet of silicon solar cells that generate as much as 1.3 kilowatts, although 1 kilowatt is more typical. That’s enough to keep the car cruising at 43 mph all day long. The battery is there to provide extra oomph as needed.
“The amount of power you get from the sun changes quite dramatically throughout the day,” McClymont says. “You’re getting much less power at the beginning of the day and the end of the day, so you need a buffer. That buffer is the battery.”
Endeavour, on the road Down Under in 2009. The team is running essentially the same car in this year's race but has changed the battery and made small modifications to the bodywork.
Typically, teams will start the day with a fully charged battery and end with a depleted one.
“The ideal strategy is to drive all day at constant speed and end up with no battery left,” McClymont says.
The cells and pack send power to a CSIRO hub motor that drives the front wheel. The motor is 98 percent efficient and generates 1.8 kilowatts, or 2.4 horsepower. McClymont says the car, which weighs 485 pounds without the driver, has a top speed of about 75 mph.
Many people roll their eyes at solar-car racing, but the admittedly arcane endeavor has real-world applications. Solar cars are nothing more than highly efficient electric vehicles. The technology involved, from the batteries to the motors to the electronics controlling it all, has direct applications in the automotive sector. That’s why everyone from Ford Motor Co. to Intel works closely with the teams.
“All of these technologies inform the development of electric vehicles and contribute to a more sustainable future,” says Mark Green, technical marketing engineer at Intel, which sponsors the Cambridge University Eco Racing team. Intel provided the computing power needed to run the computational fluid dynamics and other simulations to design the car, and there are Intel Atom processors in the car’s on-board electronics. The interior of a solar car can reach 130 degrees or more, and the cars vibrate like mad because they’ve got minimal suspension, so solar racing is a good test of Intel’s technology, Green says.
Doing well in a solar race demands more than getting in and mashing the accelerator. It’s a marathon, not a sprint, and the defending champs finished the 2009 race in 29 hours, 49 minutes at an average speed of 63 mph. There is a tremendous amount of strategy involved, as teams manage their energy and keep an eye on the weather.
It’s also a grueling test of the endurance of the drivers. Each team has at least two drivers who pull four-hour stints. Although vents provide a modicum of cooling air through the vehicle and everyone carries plenty of water, it’s still a tough job.
“You know you’re going to be knackered by the end of the day, but that’s just the price you pay,” McClymont says.
Photos: Cambridge University Eco Racing
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