Solar racer

  • The University of Michigan"â„¢s solar car, Continuum, glides around Chrysler"â„¢s 7,5 km oval. Image credit: Zach Desart
  • Adviser Ignacio Garcia (third from left) with solar-car team members. Image credit: Zach Desart
  • Continuum"â„¢s rear aluminium wheels were custom-machined with integrated hubs to reduce weight. The front wheel houses the electric motor. California-based Viper Technologies donated two sets of wheels worth more than R425 000. Image credit: Zach Desart
  • Team members lower the top. The blue cloth in front of the driver is attached to the frame with velcro fasteners to keep road debris from entering the cockpit. It"â„¢s a cheap, light, effective reminder that the best solution is often the simplest. Image credit: Zach Desart
  • The solar array charges a R180 000, 6-kWh, 30 kg lithium-polymer battery pack. Image credit: Zach Desart
  • The team designed the vehicle"â„¢s wheels, brakes and hubs. The three-phase in-wheel electric motor kit is built by Australia"â„¢s national science agency. Image credit: Zach Desart
Date:30 April 2009 Tags:, ,

Looks like a UFO, starts like a tortoise, runs as long as the sun shines – driving the University of Michigan’s latest winner.

The car I’m sitting in is so futuristic and so technically advanced that it would cost nearly R10 million to duplicate. Yet this Jet Propulsion Lab on wheels lacks the basic features of even the humblest sedan: a radio, roll-down windows, a heater. I had to slither between the rails of a roll cage to access a cockpit so cramped that it feels as though I’m sitting upright in a Niagara Falls barrel.

The three-wheeled car, known as Continuum, isn’t built for comfort – and it’s not exactly built for speed. It’s built for distance. More precisely, it’s built to maximise the distance a featherlight electric car can travel in a given time powered solely by the amount of sunlight that falls on photovoltaic cells plastered all over its upper half.

Working under the supervision of two faculty advisers, more than 100 very bright and very motivated University of Michigan students took two years to build the vehicle, which is designed to compete in a pair of gruelling solar-car races. It’s the latest model in a programme that has racked up an impressive record since its 1990 inception: five wins in the college-only 3 860 km North American Solar Challenge and several top finishes running against Honda, GM and Ford in the 3 000 km Australia-based World Solar Challenge.

On this chilly and slightly overcast November morning, faculty adviser Ignacio Garcia, a retired engineering school machinist, and a dozen bleary-eyed team members trailered the car to Chrysler’s proving grounds in Chelsea, Michigan. Most team members have never driven Continuum; hence their nervous looks. I’m the first outsider ever to take a spin in a streamliner that cost them an awful lot of late nights and bloody knuckles.

“We have a saying,” says head strategist Alex Dowling, a 20-year-old from Saline, Michigan. “You can have a social life, get good grades or do solar car. Pick two.” A hardcore group of about 30 spends more than 30 hours a week on the project – designing, testing, fabricating and securing sponsorships for the R25 million two-year budget.

I’m about 1,8 m tall and weigh 81 kg, which is 76 mm and 9 kg too much for the cockpit. After an unsuccessful attempt with shoes on, I go socks-only and clear the small carbon-fibre steering wheel. My knees are practically kissing my chin. Luckily, the controls are on the steering wheel: a lever on the right works the “throttle” and one on the left activates the brakes.

The team designed a dash that displays speed, charge state and distance travelled. They also built a rearview video-camera system and a wireless network that links the car to chase vehicles, remotely monitoring Continuum with a Prius-like energy-flow graphic.

Once I’m buckled in, six students affix the upper part of the car’s body in a series of moves so effortlessly choreographed it would make a Sprint Cup team jealous. The top half carries the solar array; the bottom half is the carbon-fibre and Nomex-honeycomb main structure.

As I gingerly pull back on the accelerator, the car inches forward at a tortoise’s pace. It’s so leisurely that a few team members walk alongside as I get under way. Weighing a lithe 218 kg, Continuum gets all the propulsion it needs from an 11,9 kW electric motor that resides in the single front wheel. The trike design lowers the car’s surface area, which in turn reduces drag.

How slippery is it? “It’s a strategic advantage for other teams not to know,” a cagey Dowling says. He reveals that the team believes a Chevy Corvette has five times as much drag as Continuum. But as I am about to learn, when it comes to handling, this is no Corvette. With a single front wheel, I fear that any turn at speed will tip the car on to its outside edge, like a tricycle turned too hard by a reckless three-year-old. “We talked to a vehicle dynamics professor when we designed the car,” says John Federspiel, a 21-year-old junior.

“He had no idea about three-wheel dynamics. There’s not much on the subject, so we had to figure it out ourselves.” I creep up to about 50 km/h and gently turn. The car responds more predictably and confidently than I could have imagined. I progressively wind in more steering angle until I feel the front end safely wash out in classic understeer. It’s not fun, but it’s stable and there is little body roll – these kids have done their homework.

While crisscrossing a vast expanse of proving-ground asphalt known as Black Lake, I buzz by the students at 64 km/h. In 10 minutes, my hindquarters have gone numb, but I’m in the groove and ready to head over to Chrysler’s 7,5 km banked oval so that I can open this baby up. I pull on to a pockmarked two-lane road and brace for the first impact. There’s a loud thud, but the car isn’t bothered by bumps. It feels solid and well-built.

Because of the tight confines and lack of air, beads of sweat roll down my face despite the brisk weather. It’s windy too, and I’m a little nervous about how crosswinds might affect a car shaped like a huge Delta wing. So when I get to the oval, I stop and ask for a more experienced driver to try it first.

The team descends on the car. Jeff Rogers, a 22-year-old graduate student, shouts “Waist!”, and all six lift the top half about 30 cm. Someone unhooks two safety chains and disconnects the wires that connect the solar array to an electrical device called the maximum-power point-tracking system. The MPPT constantly changes the load on the solar array to extract maximum power. “Up!” barks Rogers. In another precisely timed manoeuvre, the team carries the top half away from the car and sets it down on trestles.

They’re careful with the array, since any scratch could reduce the efficiency of the 2 726 solar cells. (Racing rules limit the area of the array to 6 m.) Each R530 cell produces a maximum of 2,6 volts. In full sunlight, the array provides about 1,8 kW, which is roughly what it takes to hold the car at about 100 km/h on a flat road – less than an eighth of the power a normal car requires.

I wiggle out, and Federspiel takes the helm. He moves out with two chase cars in tow. Dowling sits in the lead chase vehicle, staring at a laptop screen. “We monitor everything,” he says. Obsessive Formula One engineers have nothing on these guys.

My legs are numb – again – so I prepare to stop. After I climb out, Dowling asks if other team members would like a turn. I can sense their excitement. I wander over to faculty adviser Ignacio Garcia. “So, these kids really built this thing?” I ask.

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