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Pit stops in this section:
Frequently Asked Questions
Specifications
Behind The Wheel
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How fast does it go?
UNSW Sunswift II has been driven at up to 140km/h, however
it could probably go faster than this. As the speed increases
the power required increases roughly with the cube of the speed,
so at higher speeds the power usage increases dramatically. In
NSW we have to stick to the speed limit which is 110km/h. On the
run from Canberra to Sydney during AGO SunRace 2002 the car
averaged over 100 km/h, easily keeping up with the other freeway
traffic. The cruising speed for a race such as the World Solar
Challenge (WSC) is about 70-90km/h.
Does it get hot in there?
Yes. The temperature in the car is usually about 10°C above ambient
temperature when the car is running. On a sunny day, if the
outside air temperature is 35°C, then it will be 45°C inside
UNSW Sunswift II. However, when the car is stopped by the
side of the road, it can get even hotter as there is no movement
of air inside the car.
Does it have air conditioning?
No. Well, not really... The air flowing over the outside of the car
helps to cool it down. Fresh air also enters the car through a
NACA duct inlet on the bottom shell. This is enough to keep the
driver reasonably comfortable when the car is moving.
Does it have a driver?
Yes, but there's only room for one person in there.
How does the driver fit in there?
The entire top shell lifts off and the driver climbs in. They lie
down in a seat similar to a deckchair. Anyone less than 6ft tall
can fit it, however it might not be that comfortable for them...
The driver's head sticks up inside the bubble and their toes
come down almost to the front of the car. It is fairly cosy, but
there is enough room to be comfortable. The driver's head
touches the inside of the bubble, the visor sweeps down close to
their face, and their toes can touch the underside of the array.
Can the driver see out?
Yes the driver has about 200° of vision. Because the visor is so
close to the driver's head the view is pretty good, and it
allows driver can see the road ahead. The low driver eye height
can sometimes make it difficult to see what is around, but there
is always a support car in front and behind the solar car to
look out for hazards.
What are those things covering the top of the
car?
They are the solar cells. There are two different types of solar
cells on UNSW Sunswift II. The dark blue cells are PERL cells
which were developed and are made at UNSW. This type of cell
holds the world record for efficiency in a silicon solar cell.
PERL stands for Passivated Emitter Rear Locally diffused. The
grey ones are Buried Contact (BC) cells and were made by
students of the team over the summer of 2000-01 in the Topcell
project. These cells are also made out of silicon but have an
efficiency of 2-3% less than the PERL cells. This type of cell
was also developed at UNSW, and is made under licence by BP
Solar. Students spent 10,000 hours manufacturing and testing the
BC cells, and then another 5,000 hours assembling them into
solar panels. The PERL and BC cells are encapsulated inside a
sandwich of polycarbonate and EVA plastics which protects them
from damage.
So how many solar cells are there all up?
There are about 1500 PERL and 2000 BC cells. Each one of the small
rectangles is an individual solar cell.
Why are the solar cells arranged in a
'L-shaped' pattern?
When the route for the WSC was analysed, it was found the sun spent
more time on the left hand side of the car. Since they are of a
higher efficiency, it was decided to place the better cells,
generally PERL cells, where they would capture the most sunlight
during the day. This is also why the PERL cells tend to be on
the flatter areas of the car.
What sort of motor do you use?
We use a motor built by the team and developed by the CSIRO. This
is a 3 phase, 40 pole DC brushless motor. It has a wound stator
which does not move at the centre, and two rings of magnets
which rotate with the wheel. It has an efficiency of about 98%.
The motor is built into the rear wheel of the car, eliminating
any losses from having chains, etc. to drive the rear wheel. We
use a motor controller to switch the phases and control the
motor's speed. The motor is also capable of regenerative
braking, so the energy used to slow down is converted into
electrical energy to charge the batteries.
Why do you have batteries?
We have a relatively small battery pack to store energy for when
higher current is required by the motor. This is needed when it
is cloudy or when the car is going uphill, and it is also used
to even out the speed during the day. It is made up of about
36kg of SAFT Lithium-Ion cells. They are very similar to the
batteries you would find in camcorders and laptop computers.
They are very energy dense so they are relatively light for the
amount of energy you can store. They can store enough energy to
allow us to travel about 500km at 80kmh or 300km at 100kmh. The
range depends on the speed of the car and the terrain.
What is the fin at the top for?
The regulations for the World Solar Challenge and other races
dictate that the car be at least 1m high. UNSW Sunswift II,
like many others, was built lower than this at 900mm high, and
so we needed to add the surfboard fin to make up the height.
Does the car have to be registered?
Yes, the car is conditionally registered which allows it to drive
on public roads so long as it is surrounded by a trailing and
leading vehicle, does not drive at night, and the police in the
area are notified. It even has its own number plate.
How does it operate?
The solar cells which cover most of the top surface of the car
convert energy from sunlight into electricity. The cells are
connected into strings of about 120 cells, and then these
strings are connected into devices called Maximum Power Point
Trackers (MPPTs). The MPPTs regulate the voltage across the
cells so that they produce the maximum possible amount of power
from the available sun. The output from the trackers is then
floated across the battery packs. The car can be run on a
combination of battery and array power, from battery power only
or from array power only. Excess array power can also be used to
charge the batteries.
The energy from the battery packs and array is then used to
drive the electric motor which is inside the rear wheel. A motor
controller switches the current to the motor to control its
speed depending on the throttle position set by the driver. The
car has regenerative braking, which means that the motor can
also become a generator, producing energy which is used to
charge the batteries while slowing the car down.
What events has the car been in?
The team began racing in 1996, buying the Aurora Q1 from the Aurora
Vehicles Association, and renaming it Sunswift. That year it
finished 9th in the WSC. Following that race design work began
on a new car, Sunswift II.
In early 1999 the team attempted to break the Perth-Sydney
record with NRMA Sunswift II, but was thwarted by poor weather.
The team then went on to race in the Citipower SunRace a few
days after returning to Sydney. Later that year it raced in the
World Solar Challenge, finishing 18th.
In 2000 the team raced in Whirlpool SunRace 2000, but was forced
to withdraw when running second due to a motor accident.
Following this race the car was rebuilt, with many of the solar
cells required being manufactured by the team, for the 2001
World Solar Challenge. UNSW Sunswift II finished 11th in
this race. Then in early 2002 the team raced in AGO SunRace
2002, placing 2nd. UNSW Solar Racing Team was awarded the
inaugural SunRace Enterprise Award for innovation for our
project to manufacture solar cells and develop our method for
encapsulating curved panels. The team again raced over the same route in SunRace 2003,
finishing as the second placed solar car.
What events are coming up?
In October 2003 the team will race in the World Solar Challenge. This
race runs 3000km from Darwin to Adelaide, and is the most significant race
for solar cars in the world. Cars from around the world, particularly Japan
and North America, travel to Australia to compete in this highly
prestigious event. The team is focusing its efforts on preparing UNSW
Sunswift II for this race.
Back to top
UNSW Sunswift II is a three-wheeled solar-electric vehicle
that has been designed to make the most efficient use of every
watt of energy its solar panel can collect. This means
minimising aerodynamic drag, rolling resistance and other
mechanical and electrical losses, and maximising the efficiency
of the motor, batteries and solar array. The end result is that
the vehicle will travel at 120km/hr using the same power as a
hair drier, a fraction of a normal car's power needs.
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Length
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4.5m
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Width
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2m
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Height
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1m
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Weight
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200kg
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Max Speed
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140km/h
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Cruising Speed
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70-90km/h
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CdA
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0.10
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Occupants
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One
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Chassis/seat
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Chromoly space frame with structural carbon fibre seat
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Suspension
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Twin aluminium double wishbone front
Double trailing arm rear
Ohlins motorcycle shock absorbers
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Steering
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Linear track rod connecting front wheels actuated by handlebar
push-pull linkage.
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Wheels
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UNSW SRT custom carbon fibre disc front
CSIRO/UNSW SRT wheel motor rear
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Brakes
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Hydraulic disc brakes front
Regenerative braking rear
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Tyres
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Michelin solar radials, ultra low rolling resistance
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Body Shell
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Carbon fibre/Nomex honeycomb sandwich (bottom)
Carbon fibre skeleton supporting solar panels (top)
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Solar Array
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Approximately 4,000 PERL and Buried Contact cells manufactured
by the UNSW SRT
(Cells are laminated in polycarbonate & EVA)
Power output approximately 1400W
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Array Electronics
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Biel MPPTs, UNSW SRT-developed tracking software
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Batteries
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240 Worley Lithium-Ion cells
Weight 35kg
Nominal voltage 148V
Capacity 5kWh
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Motor
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UNSW SRT/CSIRO-developed brushless DC electric wheel motor
Maximum power 3kW
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Telemetry
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Custom CAN control and data acquisition system
Wireless Ethernet network
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Back to top
Taking my seat in UNSW Sunswift II I always feel a little
nervous, the butterflies in my stomach working overtime. You
step into the seat, then wriggle your way under the handlebars,
lying back as though sitting in a deck chair. Then you strap
yourself into the 5-point racing harness, put the radio headset
on and make sure you can reach the tube which lets you drink
water while you drive. After a quick check to see that the motor
and radio works, the top of the car's shell is lowered on top of
you. You wriggle down further to make sure the canopy doesn't
hit your head on the way down.
The car's shell envelopes you, and your head sticks up in a
small bubble. The top of your head rests against the inside of
the canopy, and your toes can touch the underside of the array.
There's just enough room to fit the driver in with little to
spare. These cars are built for speed, not comfort. The visor
sweeps down just inches from your face. Through this tiny window
you get a pretty good view of the world around you to the front
and to the side. A small video camera in the shell and a screen
inside the car gives a view of what's behind you.
If it's a hot day, sweat immediately starts to form, and before
long it starts running down your forehead, especially if you
have to sit still for a long time. Even as the shell comes down
you can feel the heat radiating off the underside of the array.
While the car is moving there is enough fresh air coming in to
keep you comfortable, but when still the air in the cockpit is
stagnant.
When it's time to move off the lead car will pull out, then you
follow. You turn the throttle dial a little and the car slowly
begins to move. You settle in for a driving stint which may be
as long as 6 hours or as short as 40 minutes, depending on the
race. As you get up to speed the road noise in the cockpit
increases, and you are greeted by the familiar bumps, squeaks
and shaking noises that the car makes. If the road's rough the
noise can get so loud that you can barely hear the radio, and
your ears ring when you step out at the end of your driving
stint.
Because you're so low to the ground, with your bum barely a foot
from the road, everything feels like it's going by very fast.
But soon enough you get used to this, and like the noise you can
block it out. On a race like SunRace, which has short stages
each day, you would often maintain the speed limit of 110km/h
for long periods along country highways. The speed and frequent
corners are enough to keep your attention firmly focused on
driving, and this type of driving is particularly exciting.
Rough roads which can throw the light solar car around like a
toy add to the excitement.
On a race like the World Solar Challenge the speeds are generally far more
sedate, and the roads long and straight. When you're cruising at
70-80 km/h along a dead straight road for hours on end boredom
can become an issue. There’s only so long that you can entertain
yourself watching the readout on the driver's display. There's
usually little you can do about this but sing, singing whatever
tune happens to be in your head at the time. A voice from the
control car will keep you in touch with the outside world, every
now and then making comments, instructions, or giving warnings
of the road conditions.
Occasionally the monotony will be broken by passing traffic,
like the huge road trains which thunder up and down the Stuart
Highway. As imposing as these monsters are, the solar car is not
disturbed very much and continues on its straight path. If
you’re lucky, you'll get to overtake other traffic, or even
other solar cars. This manoeuvre involves carefully leapfrogging
the slower traffic - first the scout, then lead car, solar car,
control car then other support cars.
Probably the best aspect of driving the car is the amount of
attention you get when you're out on the road. Driving along
highways and freeways people in passing cars will honk their
horns, wave and shout at you from windows and take photos.
Whenever you pass through a town, people stand dead in their
tracks and stare as your space age machine glides quietly past.
When you stop, people flock around the car asking questions,
bright-eyed and amazed at seeing a solar car in the flesh, and
commenting that they'd only seen these cars on TV.
The driver may have the most glamorous position on a race team,
but in reality their job is just to sit in the car and do what
they're told. It is the strategists sitting in the car behind,
and everyone on your team who has made a contribution to
designing and building the car itself, who deserve the credit
for how well your race goes.
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