Silicon Valley engineers peek at the Tesla

Mechanical engineers get a look at what makes Tesla Motors' electric sports car tick. Photos: Under the hood of the Tesla Roadster

Stefanie Olsen Staff writer, CNET News
Stefanie Olsen covers technology and science.
Stefanie Olsen
4 min read
MENLO PARK, Calif.--If you want to pack a room of mechanical engineers in Silicon Valley, just trot out its hottest new symbol of status and geekery, the Tesla Roadster.

Tesla Motors, maker of the electric-powered sports car formerly code-named DarkStar, showed off the Roadster's second engineering prototype here Thursday evening at a networking event of the American Society of Mechanical Engineers. Perhaps even more compelling for the engineers than to see the car was the chance to pick the brain of Doug Bourn, senior electrical engineer for Tesla, who tried to illuminate the inner workings of the Roadster to a sophisticated crowd.

Jean-Claude Roy, an engineer at Lockheed Martin, said: "Of course, this car is too expensive, but I wanted to understand it."

Tesla's first $92,000 two-seater sports car is expected to ship in November or December of this year, according to Bourn. Among the first 180 owners of the Tesla--125 of whom paid in full up front--will be Google co-founders Larry Page and Sergey Brin, who invested in the San Carlos, Calif., company.

Bourn touched on everything from the high-level thinking behind the car's development to the nuts and bolts of how it works, including describing the battery pack. He likely fielded some questions he didn't entirely know the answers to, given his curious audience of mechanical engineers who wanted to know some things that fell outside his field of expertise, electrical engineering. (Bourn worked primarily on the car's power module.)

The idea behind the Roadster, Bourn said, was to minimize resource consumption per mile, emit low carbon emissions and get away from America's destructive oil diet--all without sacrificing performance. And the company has done that: The car can accelerate from 0 to 60 mph in four seconds, topping out at about 130 mph. It runs completely on electricity and plugs into an electrical outlet in the wall, giving the car's battery a range of up to 250 miles, according to Bourn.

He offered efficiency comparisons of battery-powered cars versus other alternatively fueled cars. For example, his equation factoring how far a hydrogen-powered car could go on 1 megawatt hour of electricity showed that it would go about 1,800 miles, considering that efficiencies are lost in the conversion of producing hydrogen in a fuel cell. In contrast, the electric car can go 4,900 miles on 1 megawatt hour of electricity, according to Bourn's calculations.

Part of the car's secret sauce is in relying on lithium ion cells, commodity batteries that are commonly used in laptops. Using many small cells, Tesla has built its battery pack with 11 individual sheets of 621 cells. Each sheet has a semiconductor chip evaluating the cells for charge balancing and cooling, and the pack has built-in safety features so that if one cell were to spoil it would shut itself off so as not to degrade the rest of the car, according to Bourn.

Photos: Under the hood of the Tesla Roadster

The entire stack weighs about 950 pounds and packs higher energy density than previous electric cars like General Motors' EV1. The EV1 had an energy density of 300 kilowatts per hour, compared with the Roadster's 580. The company guarantees the life of the battery pack for 100,000 miles. Tesla hasn't established a cost for an extra battery pack yet.

Other details Bourn offered: The car weighs about 2,600 pounds. It has a carbon fiber body and a bonded aluminum chassis. It uses all LED lighting, with a 12-volt electronic system. It uses only rear-wheel drive and might not be ideal for a winter jaunt up to mountains given that chains wouldn't fit in its tire well.

Right now, the car's undergoing all of the standard tests of a regular vehicle: crash, cold weather, durability and road handling tests. It's been tested at length on European cobblestone streets that would make anyone's back hurt, and in snowy conditions in Sweden. Even in cold weather, the car's heating, ventilating and air conditioning system keeps a constant temperature inside the battery pack so it performs in inclement weather.

Still, engineers in the audience were concerned about how fast and far it could go at high speeds or while taking it up to Lake Tahoe (approximately 200 miles northeast of San Francisco), given that its battery range is between 200 to 250 miles and driving at a constant high speed can drain the battery length.

"It's designed as a sports car. Take it out, impress your friends and go out to dinner," Bourn said. Considering the crowd of lead foots, he added: "You guys aren't going to get 200 miles at all."

Tesla announced in recent months plans to open a factory in Albuquerque, N.M., to produce its next-generation car, a five-seat, electric-powered sedan code-named WhiteStar. That car will roll out in late 2009, according to a press representative from Tesla. It will start at $50,000 and sell for as much as $70,000 for the sport version.

The event was held here at TechShop, an open workshop that lets members, for $100 a month or $30 a day, have access to all manner of industrial tools like laser cutters, brake presses or a 3D printer. TechShop opened in October with little to no press and has so far attracted 120 members who have made things like robots, custom skateboards, espresso machines and car parts. The girl working the front desk etched her Mac laptop in flowers using one of the workshop's two laser printers.

"I've been a member since November, and it's fun," said one of the attendees.