JEC COMPOSITES MAGAZINE - Issue #87 - March 2014 Special JEC Europe - 83

Preparation for a day of racing

mize the performance of the composite
laminate, even when the laminate is very
thin.
During the early stages of development, DSM's Somos® stereo-lithography
materials were used for rapid prototyping. Later on, these same materials
found their way into several of Nuna7's
important lighting and power system
components.

The "winning factors"
Already early in the development process
of the Nuna7 vehicle, the team defined
the key factors that would determine
success in the World Solar Challenge. In
hindsight, these factors all turned out to
be instrumental in earning the number
one position during the race.
Rolling resistance and low weight
With the requirement to reduce energy
consumption, it was highly desired to
minimize the energy losses associated
with friction to road and air. Besides optimising the vehicle aerodynamics, this
meant the development of a low-friction
in-wheel motor, which could operate
reliably in the tough Australian environment. All components in the Nuna7
were designed with an integral approach
to reduce weight, as every gram of weight
savings would contribute to car performance. The use a composite material
based on styrene-free Daron® resin and
Textreme® carbon fibre proved to be key
in this respect.
Aerodynamics
The revolutionary asymmetric design of
the Nuna7 gave the best compromise in
aerodynamics and vehicle stability. In

this design, the driver's canopy has been
put in line with two of the wheels, counterbalanced by the weight of the batteries
and electronics. With the help of DSM
Somos® in rapid prototyping and the
evaluation of the prototypes in the wind
tunnel testing facility at the TU Delft,
the shape could be further optimised.
The versatility of the chosen composite
system allowed making this design at full
scale without problem.
Solar array and electronics
To achieve the maximum amount of
solar energy, the upper surface of Nuna7
was covered with 6 m2 of silicon (monocrystalline) solar cells with an antireflective coating. The electronic system
had to operate reliably in the extreme
race conditions and transfer the energy
from the cells to the motor with minimal losses. The robust electronic system
performed as anticipated during the race.
Energy not consumed by the motor was
used to charge the battery - a 5 kWh
package of 20 kg Li-ion cells. The Nuna7
also carried concentrated photovoltaic
(CPV) modules, made of lightweight
composites again based on styrene-free
Daron® resins. These special modules
were taken out of the car during control
stops. The modules consisted of very
small, high-efficiency solar cells within a
system of lenses, concentrating sunlight
and therefore capturing an additional
500 W of energy.
Handling and comfort
This year's race required a complete
redesign of the vehicle to ensure optimum driver safety. This meant that the
height of the driver's canopy had to be
increased, so that the driver could overlook the road and avoid any dangerous
situations. The high strength and stiffness
of the composite construction allowed
reducing vehicle vibrations, without any
compromise to safety. Special ventilation and heat insulation solutions were
required to help the driver cope with the
high temperatures. These were manufactured through stereo-lithography
from DSM Somos® materials. A modular

design allowed for easy disassembly during stops, and facilitated timely inspection and adjustment of critical vehicle
components.
Production quality and reliability
The application of a vacuum bagging process with only limited post-cure allowed
taking full advantage of the material
system versatility, leading to an excellent
through cure even in thin laminate sections. The Daron® resin proved to be very
easy to handle leading to a smooth and
robust manufacturing of the Nuna7.
Sponsoring
The financial and professional support of
the sponsors was the solid basis for the
Nuna7 project. The key sponsors Nuon,
DSM and TU Delft provided help at
every stage of the project.
Race strategy
Although it may not seem obvious, the
development of a proper race strategy
is very important in order to take full
advantage of changing weather and road
conditions. It may be required to sometimes reduce speed and save energy, in
order to be ready for taking steep hills or
"survive" bad weather. The last day of the
race had much rain and dark skies, making it important to save the energy for
the right moment. While the competitive
vehicle from Tokai University of Japan
came to a standstill, the Nuna7 proved
victorious and won the race 3.5 hours
ahead of the next contestant.
The perfect team
It was clear that without good teamwork
the whole project could not fly. Working

Set up of wind tunnel testing

No87 March 2014

/ jec composites magazine 83

JEC COMPOSITES MAGAZINE - Issue #87 - March 2014 Special JEC Europe

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