As he pulls away from the headquarters of Tesla Motors in San Carlos, CA, JB Straubel apologizes for the condition of the car. The outside looks fine, a gleaming orange. But inside, instruments dangle from the dashboard. A message scrawled on blue masking tape warns that the passenger’s-side air bag is disabled. A bell chimes mysteriously. The car had been shipped to England and subjected to vibration tests designed to “shake it apart and kill it,” Straubel says. Now it’s an engineering car–one Straubel, the company’s chief technology officer, feels comfortable drilling holes in and bolting prototype hardware to. “It’s pretty much already written off,” he says. “But it’s also the fastest car in our fleet at the moment.”
He punctuates the sentence by hitting the accelerator. Straubel looks remarkably calm as the car surges forward, pressing him into the seat. From a dead stop at the on-ramp, it takes just a few seconds to overtake the vehicles on California’s Highway 101. In sports cars, this kind of acceleration is ordinarily accompanied by rapid-fire shifting, but Straubel never takes his hands off the steering wheel. Powered by batteries and an electric motor, the Tesla Roadster isn’t bound by the limits of old-fashioned gas-burning engines. At its top speed of over 120 miles per hour, it remains in its first and only gear.
Straubel doesn’t come close to 120 miles per hour today. Since the car can accelerate to 60 miles per hour from a stop in just under four seconds, “you get caught up to traffic pretty fast,” he says, easing off the accelerator. “It kind of spoils you.” It’s easy to see why this powerful alternative to gas-guzzling internal-combustion engines (see Hack, “Tesla Roadster”, September/October 2008) has generated such remarkable excitement.
Straubel, more than anyone else, is responsible for the car’s impressive acceleration. The Roadster is the first production model from Tesla, which was founded to mass-produce high-performance electric cars. The car’s carbon-fiber exterior and aluminum frame, which make it visually appealing but keep it light, are based on designs from British automaker Lotus. Straubel and his hand-picked team, however, engineered the car’s brains, muscles, and guts–the electronic controls, electric motor, and battery pack that enable the Roadster to beat many of even the quickest gas-powered cars off the starting line.
Electric cars are best known for their environmental benefits: they produce no harmful emissions, and they’re so efficient that they reduce total carbon emissions even if the electricity used to recharge them comes from power plants that burn fossil fuels. But Straubel’s achievements capitalize on another, less appreciated advantage. Gas engines deliver their peak torque–the key to acceleration–only within a limited range of engine speeds. Keeping the engine in its optimal range requires a convoluted system of gears and clutches, and acceleration is still compromised. Electric motors, however, deliver maximum torque from a standstill up through thousands of revolutions per minute. That makes it possible to use a transmission with just one or two speeds–and it makes electric cars more responsive than gas-powered ones. Yet most electric vehicles haven’t reaped the full benefit of their torque advantage, says Marc Tarpenning, one of Tesla’s founders. That’s because they have typically been underpowered, partly in an effort to make them as inexpensive as possible. Straubel set out to change that.
During his early days at Tesla, the company licensed a number of technologies from AC Propulsion, a small company that had pieced together a prototype electric car with acceleration similar to the Roadster’s. Tesla’s founders decided to use AC Propulsion’s parts to produce their own prototype. But those parts were “ruinously expensive,” Tarpenning says, “and no two were alike.” Straubel has since reëngineered almost every one of them.
It was soon clear that the extreme torque provided by electric motors can be a problem, especially in a high-powered car. Without a well-tuned motor controller, the torque can jerk the driver around, says Andrew Baglino, one of the engineers Straubel hired. What’s more, the complex interplay between the driver’s application of the accelerator, the conditions of the road, and the electronic characteristics of the battery and motor can have unexpected consequences. AC Propulsion’s controller was “a hokey analog system–messy circuitry that was 20 years old,” Straubel says. As he and his team worked to develop a production-ready car, they found that one controller would work well while another would inexplicably fail. “We’d debug it for weeks trying to figure out what the hell was different, and we never could,” Straubel says. The unreliable controllers would sometimes cause the motor to jitter. Worse, at times all power would cut out–once, as the car was hurtling down the highway.
Straubel reasoned that a digital control system would solve these problems. Switching to digital would require starting from scratch, but he was sure the new system would both improve performance and speed development. Yet the decision was made to stick with the analog system, in the hope that its kinks could be worked out.
Undeterred, Straubel put Baglino to work on what appeared to be a side project: designing test equipment that put the company’s motors and batteries through the paces of simulated driving cycles. This equipment was to have digital controls, which Straubel intended to translate into a digital controller for the car.
Meanwhile, the engineers continued to painstakingly debug the analog system. “It felt silly to be solving problems that we knew we were trying to make obsolete,” Straubel says.
After months of working on the digital test equipment, the engineers had learned enough to design a prototype digital controller. It worked, and soon the messy analog system was gone. The jittering and jerking gave way to a digitally controlled, reliably smooth ride–and a car that was, incidentally, far more responsive.
The Roadster’s exceptional motor, too, is a tribute to Straubel’s persistence. Tesla initially used a third-party transmission that included two gears–one to accelerate from a stop and the other to reach high speeds. The system gave the Roadster a top speed of more than 120 miles an hour. However, the shifting system routinely wore out after just a couple of thousand miles. So Straubel found a way to replace it with a single-speed gearbox. Early on, Straubel and his team had redesigned the patterned metal plates and wire coils at the heart of electric motors to improve both efficiency and torque. But the electronics feeding power from the battery to the motor still limited its output. To exploit the added torque, Straubel added higher-performance transistors and retooled the electrical connections between the motor and the gearbox. These changes increased the torque that the motor could deliver at low speeds and allowed the engineers to use a single-speed transmission without sacrificing either acceleration or maximum speed.
But Straubel’s most notable contribution may have been to keep the car from bursting into flames. Tesla’s founders decided from the start to power the car with lightweight lithium-ion batteries of the type used in laptops, and they knew they had their work cut out for them. If lithium-ion cells are pierced, crushed, overcharged, or overheated, they can combust. The challenge was even greater because the individual cells were small: it would take 6,831 of them to give the car a decent range. All those cells would have to be wired together into an ensemble that was durable but allowed the charging and temperature of each cell to be carefully controlled.
This was fine with Straubel, who had been building electric vehicles since before he was old enough to drive and had long wanted to make a laptop-battery-powered car. Under his direction, all those goals were reached. But along the way, the team discovered that in some (extremely rare) cases, manufacturing defects within a cell could cause it to heat up and catch fire without any outside cause. (This problem led to the recall of millions of laptop batteries in 2006.) Using computer models, Straubel found that if any one of the 6,831 cells caught fire, it could set off its neighbors, starting a chain reaction that could destroy the battery pack and turn the car into a smoldering wreck. Tarpenning asked at the time, “So, JB, what’s going to happen to our energy storage system?”
As it turned out, the solution was already at hand, largely because of an argument Straubel had won early in the development of the battery pack. The car’s initial design called for air cooling to control the temperature of the batteries and extend their lifetime. But Straubel quickly realized that that approach wouldn’t provide the necessary control.
“We had a lot of heated discussions about what direction we should go,” Straubel says. But his cool-headed logic, along with some hard figures, won the day. The resulting liquid cooling system–a network of tubes running past almost every cell in the pack–also offered a solution to the problem of the spontaneously combusting cell. With slight improvements, the system was able to evacuate the heat from a flaming cell so quickly that it couldn’t set off its neighbors. As with the digital controller, Straubel had been able to find a solution, even if it meant going against the grain.
Tesla began shipping Roadsters this year; the first four were delivered by June. Richard Chen, a former Google product manager who hopes to have his car by Christmas, mailed in a $100,000 check long before the production car existed, and before the company had even announced a price. His excitement is not unique: the car, which has a base price of $109,000, is back-ordered for at least a year.
Its success may have an impact well beyond Tesla’s bottom line. Bob Lutz, GM’s vice chairman, was quoted in Newsweek as saying that the Roadster was a deciding factor in GM’s decision to return to electric cars after abandoning them several years ago. If a Silicon Valley startup can do it, he reasoned, why can’t GM? What’s more, the Roadster may be changing the image of electric cars and increasing their chances for success. People such as Chen, who got to test-drive the car before finalizing his purchase, are buying it not to save the planet (though the green credentials are a nice side benefit, Chen says) but simply because it’s so much fun to drive.
These days, Straubel is focusing on improving the Roadster and engineering a sedan to open up a new, wider market for the company. And tentative plans are in the works for a small car, such as an electric version of Daimler’s tiny, inexpensive Smart car.
All that means long days for Straubel, and part of what keeps him going is the belief that he’s doing something important: finding a way to deal with the world’s energy woes. But he seems most driven by pure enjoyment. That’s clear enough when he’s behind the wheel of the latest version of the Roadster, whose new electronics can deliver far more power than the first version had. “It’s amazing what a few hundred more amps can do,” he says, laughing, after a burst of acceleration. “It’s fun, huh?” –Kevin Bullis