Venturi

Venturi

Venturi

Venturi

Jonathan Gitlin

Jonathan Gitlin

Jonathan Gitlin

Jonathan Gitlin

Jonathan Gitlin

Jonathan Gitlin

Jonathan Gitlin

The Venturi Buckeye Bullet-3 combines two things we love here at Ars Technica: land speed records and electric vehicles. It's a collaboration between Venturi—a Monegasque electric car company—and the Ohio State University that aims to break 400mph (644km/h) on the Bonneville salt flats while simultaneously acting as a testbed for future electric vehicles and the young engineers who work on it. Fortunately Columbus, Ohio, is less than a day's drive from Washington, DC, so I took advantage and paid the land speed car a visit.

VBB-3—its nickname—is the third land speed car to come from the Center for Automotive Research (CAR) in Columbus. Its long, thin shape has been dictated by aerodynamics, unencumbered by the draggy intakes required to feed air-breathing engines. It has a pair of electric motors, each good for 1,500 horsepower (1,119kW) and powered by eight large lithium-ion battery packs. Earlier VBBs set records in 2009 and 2010, but last summer terrible salt conditions prevented VBB-3 from running a proper test program to 400mph and beyond.

Each axle is powered by its own electric motor. The starting point is the same EV motor Venturi builds for its sports cars, running here at a much higher voltage. In fact, there are actually two EV motors in each unit. "It's two motors sharing a cooling system and a common shaft," team leader (and former graduate student) David Cooke told us. "It makes more manufacturing sense to build smaller motors and couple them together than trying to build one big motor. Today that motor is putting out about 1,000 horsepower in the dyno, but it's capable of 1,500." The team is continuing to develop the powertrain—particularly the inverter control—to give VBB-3 the 3,000hp it needs.

"Motor technology is already there," Cooke said. "The real limit is where you get the energy from." For VBB-3, that means lithium-ion battery packs from A123 (VBB-2 used hydrogen fuel cells). The team—engineering students at OSU, remember—did the rest, integrating them in the powertrain, cooling them, and so on. There's a total of eight battery packs on the car, four on either side of the carbon fiber cockpit tub (enjoying a new life after retiring from its previous career as a Dallara IR03 IndyCar).

Two battery packs are bussed together and fed into each inverter, the hardware for which is supplied by American Traction Systems. The inverters just look like large metal boxes ahead or behind the wheels, but they convert DC from the batteries into the AC needed by the motors.

Keeping the motors cool enough during the car's minute-long runs is crucial. "The real limit to how hard you can push the motors is ensuring you don't exceed the temperature limits of the magnets and electrical windings and insulation," Cooke said. "These motors have oil cooling jackets over the stator, and we also pump oil over the magnets for the best possible cooling."

Radiators would mean vents or intakes, which would in turn mean drag. Therefore VBB-3 has closed-loop cooling systems instead. "We have a water tank we pack full of ice and prechill as much as humanly possible before the race," Cooke explained. (That's all in one big aluminum housing up front.) "This year we also developed an off-board cooling loop for the motors so we have an ATF [automatic transmission fluid] oil chilling circuit that circulates around the motors. We get the motors and inverters down to about 0 degrees Celsius before the start of a run, and they're at operating temperature in around 60 seconds."

The gearbox—a two-speed—is custom made by Hewland in the UK. "The amount of torque the motors put out—and how quickly they can do it—requires some special things from the transmission. By that point, with a really custom solution we were able to do all the other things we wanted," Cooke said. One of those was hanging the suspensions from the gearbox casing, something you usually see on prototype or open-wheel race cars. "Another neat system we've developed is a full brake. We're the only land speed car with a friction brake that will work at over 300mph."

At the back of each gearbox is an auxiliary shaft connected to the brakes. "At Bonneville, if you do have an incident, it's almost always linked to tires or parachutes, so we tried to look for all the measures we could take in both those directions," Cooke told Ars. The carbon-carbon brake discs come from an Embraer 145—it turns out that the brakes needed to stop a regional jet on a rejected take off are just about exactly what's needed to slow VBB-3 from 400mph in two miles.

Goodrich donated the discs after the team presented them with a well-engineered system. Cook said Goodrich was excited to be involved in this kind of industry partnership, supplying the parts and letting experimenters do interesting work. Having functional brakes has also been a boon for lower-speed testing, we're told.

Given the link between power, weight, and top speed, we were a little surprised to see so much steel rather than composites or more exotic alloys. But while Cook admitted it's not always practical to not use steel, "it's still one of the strongest alloys we have." Even so, the initial design for VBB-3 was going to feature a carbon fiber monocoque. The car was to be designed around a fast-change battery system where a forklift could change the cells within two minutes. (Both the US and international land speed record rules require two runs to be completed within an hour of each other.)

But using carbon fiber instead of steel had a few challenges. "The modeling methods to understand beam strength of a 40-foot structure are a lot more proven for steel tube frames than they are composites. That's not to say you couldn't do it—we have the software, we got the results, but we'd have added a much bigger factor of safety [than with steel]," Cook said. "It's difficult to gauge at this scale of program, with this number of students working on it—this isn't Boeing designing plane wings. So what we ended up with was a really robust structure that's extremely stiff, but equally heavy, between 30lbs lighter and 300lbs heavier than the steel tube frame before you can have confidence in it."

Taking on this type of engineering is no, ahem, small feat. Manufacturing 40-foot-long pieces of structural carbon means even bigger equipment, adding between $500,000 and $1 million to the budget. And then there's the problem of modifications.

"This is a very, very prototype vehicle," Cooke admits. "A Great example from this year is the gearbox—we really needed to be able to slow down the motors faster to reduce the speed to implement the shift." Decreasing the shift speed down to half a second means adding three components to the car. Pointing at a part of the suspension frame, Cooke explained that "we're even looking at slicing this tube or modifying this part of the chassis. With carbon you'd now have this beautiful million dollar monocoque that's useless because there's no way to modify it."

The tolerances required by the suspension and powertrain were also proving to be tricky. "Very few outfits in the US were willing to even consider manufacturing for us, so that got us away from wanting to build it out of composites," he said. Ultimately the team put "about 18 months" into it and worked through three different models.

Listing image by Venturi