E. Rex Is a 3-Wheeled Electric Hooligan
By Chuck Squatriglia April 22, 2010
The E. Rex is the three-wheeled, electric equivalent of … well, we’re not quite sure. Something absurdly fast, ridiculously fun and more than a little impractical. But then that describes just about any vehicle capable of zero to 60 in less than 5 seconds.
Silicon Valley startup OptaMotive is building the E. Rex for the Progressive Automotive X Prize. It is essentially an electrified Campagna Motors T-Rex, which is itself a 144-mph exercise in vehicular overkill. OptaMotive says the E. Rex is three times more efficient than a Toyota Prius, delivers a range of 100 miles and has a top speed well into three digits.
Why build something so extreme?
“We wanted to focus on the driving experience,” OptaMotive founder Micheal Worry says. “We wanted a car that is exciting and fun to drive.”
Tiny, isn't it?
Worry and the rest of the crew got the idea for the car about a year ago and spent two months planning the build. They decided early on to start with a T-Rex — a three-wheeled two-seater powered by a motorcycle engine — because it provided a ready-made chassis with good brakes and suspension components.
“We didn’t want to reinvent the wheel,” says computer engineer Murat Ozkan.
Campagna gave the team a deal on a T-Rex sans engine, and OptaMotive set to work in a garage in a suburban neighborhood in Campbell, California. Tinkering around with electronics and batteries is nothing new for the team. It has won the RoboGames four times with Ziggy, a robot capable of, among other things, making field goals from the 40-yard line.
“We view this as basically a big robot,” Ozkan says.
E. Rex sports a water-cooled permanent-magnet DC brushless motor made by UQM. It produces 45 kilowatts (60 horsepower) continuous and 125 kilowatts (167 horsepower) peak. That might not sound like much, but the E. Rex produces 220 pound feet of torque and will weigh less than 2,000 pounds when done.
The team built the battery pack using 96 lithium–iron phosphate cells from Thunder Sky Battery. The 13.6–kilowatt-hour pack has a claimed range of 100 miles and a claimed recharge time of 2.5 hours at 220 volts and 20 amps.
The air-cooled battery pack weighs 400 pounds and cost about $10,000. OptaMotive also built the battery-management system, which monitors each cell’s temperature and voltage while ensuring even charging of cells.
Of course the E. Rex has regenerative braking to return energy to the battery, and Mazat says the regen system has 80 percent efficiency. He is confident the drivetrain should be about 90 percent efficient.
Most of the rest of the E. Rex is just as it was when it left Campagna. The chassis features triangulated side walls, a reinforced roll cage and three-point safety belts. The team is working on an enclosed body with proper doors and a windshield.
“It will be a combination of eye-catching and streamlined,” says engineer Eliot Barker.
Just how streamlined remains to be seen because the team isn’t shooting for a particular drag coefficient. They want to make sure it’s as aerodynamic as possible while still looking normal. Well, as normal as a three-wheeled car can look, anyway. The T-Rex has small frontal area and a teardrop shape, Ozkan says, so aerodynamic efficiency shouldn’t be a problem.
So what’s it like on the road?
Worry wouldn’t let us drive it — something about insurance, liability and it being the only one — so we had to ride shotgun. The first thing you notice about the E. Rex is it’s tiny. At just 138 inches long and 42 inches tall, it’s smaller than a first-generation Honda CR-X. Getting in is a challenge, as you snake through the roll cage. Once inside things are very tight. The E. Rex makes the Tesla Roadster feel roomy.
Comfort aside, the E. Rex is impressively quick. Stomp on it, and it will push you, quite hard, back in your seat. The fact there’s no windshield and you’re sitting just inches off the ground makes it feel faster still. OptaMotive is shooting for a zero-to-60 time of less than five seconds, which would make it about a second slower than the T-Rex and Tesla Roadster. The E. Rex, like the T-Rex, uses a chain — a very noisy one — to drive the 10.5-inch wide rear wheel. With the current gearing, the team says E. Rex should be capable of 160 mph.
“We haven’t actually tested that,” Mazat said.
The ride is firm but not harsh, and Worry says the E. Rex handles like it’s on rails. We’ll have to take his word for it because Worry couldn’t properly wring the car out on city streets. But the T-Rex is capable of 1.3-g lateral acceleration — in other words, it sticks to the road like gum on a taxicab floor — so it’s a safe bet the E. Rex would be fun on a winding road.
“It’s like an open-wheel race car, but it handles like a normal car,” he says.
It won’t be priced like one, if it ever sees production. The T-Rex starts at $51,999, and “we think the electric would command a premium initially,” Worry says. That would come down over time, he said, but how quickly remains to be seen. But Worry says Campagna is ready to work with Optamotive should the company decide to build the E. Rex.