Sunswift team enters World Solar Challenge 2013

The University of New South Wales’s Sunswift team has pulled the wraps off its competitor vehicle for this year’s World Solar Challenge. 

Dubbed eVe, the vehicle represents a quantum leap over predecessor IVy, run by the team in 2011 event. In that car, the team took out the Transcontinental Land Speed Record for a solar vehicle, along with the Guinness World Record for the world’s fastest solar-powered vehicle. Reduced to just 140kg by the removal of its battery pack, IVy made 88.5km/h on pure solar power.

In the course of the WSC, running 3000km down the centre of Australia from Darwin-to-Adelaide, the team expects the new car to hit speeds of 110km/h, albeit under battery power. It’s capable of up to 140km/h. The car will be running at steady cruising speeds of 100 to 110km/h between Tennant Creek and Alice Springs.

eVe is an altogether different design from its predecessor. For a start, it has four wheels rather than three and two seats rather than one – prerequisites for running in the Cruiser class in this year’s Challenge. 

Power comes from a combination of a 16kWh battery pack made up of Panasonic-sourced lithium-ion laptop cells, arranged in combination of series and parallel for a total output of 140V.

It and the four photovoltaic cells taking up most of the car’s upward exterior surface feed a pair of 10kW hub motors on the rear wheels. Combined, they’re good for around 200Nm of torque, powering a super-lightweight total package weighing in at about 300kg.

Braking is both mechanical – discs up front because the rules require it – and regenerative. Battery charge comes care of continuous top-up from the PV cells, with opportunities for major fills from the grid at points in Tennant Creek, Alice and Coober Pedy. 

Grid charging is kept to as little as possible, however, Sunswift project manager Sam Paterson told motoring.com.au at the reveal event. 

“They score you on the energy you use as well as on your race time. Elapsed time is the most important thing – that’s the main reason we’re going with a single driver, even though the car has room for two and they also score you partly on the number of person-kilometres your vehicle puts in.”

Although the new car has twice the frontal area of its blade-like predecessor, Sunswift has achieved a similar drag coefficient. It’s managed this partly by the use of a smaller PV cell area, and partly through a unique high-set “tunnel” underside design, giving the car the look of a catamaran.

“That means it’s not pushing as much air away around it and creating that natural diffuser effect underneath, which sucks conventional cars downwards, increasing resistance and consuming energy,” said Mr Paterson.

The WSC being as strategy-driven as it is, they’re not disclosing Cd figures. “But by what we understand, our competitors’ drag numbers are about 30 per cent higher than this car’s,” Mr Paterson added.

Aerodynamics get further help from fairings enclosing the front wheels. Partly by virtue of the car’s slim 95mm wheels, shod in specialist Michelin Solar Radial rubber, there’s enough leeway inside the fairings for all the turning circle the car needs.

To allow rear-end aerodynamic tapering, the team came up with a swing-arm design for each rear wheel, hinged at the bulkhead forming the rear of the cabin. With the battery pack mounted up front, eVe’s designers have managed a 60:40 front-rear weight distribution.

“It was simply the cheapest way to get it done,” Mr Paterson said. Cost-effective it may have been, but getting it done took members of the team a fortnight’s worth of 14 to 16 hour days at Core Builders’ plant near the NZ town of Warkworth.

The result is a structure of immense strength, with the only metal component a steel roll bar, there for compliance with FIA motorsport standards. 

The carbon fibre derives its unusual checkerboard finish from its state-of-the-art thick weave, using fibres that are flat rather than round. Able to be processed thinner than its conventional counterpart, the result is a stronger, lighter material – this car’s entire monocoque weighs in at around 80kg. It derives most of its strength from its internal walls. 

The formula also turns out a smoother finish, Mr Paterson said. “What you see here’s essentially straight out of the mould with a light sand and a clear coat on top. It saves a fair amount of weight on paint and filler.”

The interior remains a mystery. It sits empty while the team waits for the seats to arrive from the UK. What is evident is that despite the cab-forward appearance, the driver will sit a fair way back in the car, with feet adjacent to the dash rather than up against a firewall well under it.

Instrumentation will be kept to the bare minimum, Sam Paterson said. “That means GPS and monitoring for nodes around the car: solar array power, battery power, motor power, temperatures of various components. For reliability’s sake, simplicity is king in an event like the WSC.”

Ms Hutchinson told motoring.com.au the ride will be decidedly on the sporting side. “We’ve calibrated it for a 2.1 motion ratio, which approximates a hard track car, so it’s going to be a little stiff, a little bumpy at times, even without the weight of a conventional car over it.”

This, she said, is why the team is putting its drivers through intensive training. “Partly because it’s a fair bit lighter than conventional cars. Despite its rigidity, that makes it more susceptible to rough stuff. More so because it’s hand built by students.”

Both Mr Paterson and Ms Hutchinson concur that the total cost of the project is hard to gauge but would run into the millions. The team ran a successful five-week, $20K fundraising campaign via crowdfunding platform Pozible, but this forms a tiny the total value.  Input from concept through modelling, execution and associated activities such as marketing, publicity, in-kind sponsorship – materials, facilities and hours of raw human labour – would amount to several million dollars. In commercial terms, the bodywork alone is worth hundreds of thousands.

Mr Paterson said the team is looking towards a hi-po version of the car using motors on all four wheels. “We’d have to soup up the battery, though, so it’s a fair way away yet.”

Starting in Darwin, the WSC bisects the country via 3000km of highway taking in Katherine, Tennant Creek and Alice Springs before crossing the SA border and heading down through Coober Pedy and Port Augusta on its way to the finish line in Adelaide.

The 2013 event takes in three classes: Challenger (four wheels, single seat; 28 entrants including the University of Western Sydney’s vehicle “Solace”); Cruiser (four wheels, two seats; eight entrants including Sunswift with eVe) and Adventure (three wheels, one driver; seven entrants).

The WSC is the world’s premier solar vehicle race. Sunswift is up against competitor teams from the US, Japan, the UK and the Netherlands, a number with the backing of big auto brands and universities of the calibre of Stanford and Cambridge.

Although speed comes into it, the race is heavily skewed towards energy efficiency strategy. Sunswift’s Sam Paterson explained it to the reveal audience in the simplest possible terms: “You have a fixed amount of power to work with, with a small amount of variance care of the solar cells. 

“You know your course profile, you know your electrical losses and your mechanical limitations via rolling and aero resistance. You chuck it all into a computer and it spits out a number which basically amounts to how fast you should be going. That’s the race – if you try simply to race another team [head to head], you run out of battery, then you have to push your car up the hills.”

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