Cambridge University Eco Racing













Cambridge University Eco Racing

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 fibre 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 six feet wide and almost 16 feet long. It is covered with 64.5 square feet (6 squre metres) of silicon solar cells that generate as much as 1.3 kilowatts, although one 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."

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 (220 kilos) without the driver, has a top speed of about 75 mph.

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.



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