the 1/r2 nature of light. When the
racers doubled their distance from
the light source, the light’s intensity
on their solar array dropped off by a
factor of four. A second factor that
appeared to be an issue was the light
racer’s inability to rotate their solar
cell. Therefore, as they drove down
the track, the orientation between
their solar array and the light beam
became less perpendicular. The
combination of reduced light
intensity and less than optimal orientation resulted in lower power being
generated for the racer’s drive motor.
Even with these problems, there
was a winner this year. The families
of the Kansas City Space Pirates
spent about an hour building their
racer (since it was cloudy, they
couldn’t run their climber) and for
their entry fee and hour of work, they
won $2,500. Figures 1-7 show my
scrapbook of the 2007 light racers.
■ FIGURE 1. A four-sided array of Power
Film ( www.powerfilmsolar.com) sits on
top of this racer. There’s no pointing
problem here, but unfortunately, this
array is only on the order of 9% efficient.
■ FIGURE 2. This array rotated to face
the light beam as the racer drove down
the track. A set of photocells were the
array’s light orientation sensors.
■ FIGURE 3. This racer was radio
controlled. If I remember correctly,
the R/C kept the array pointed at the
best angle as the racer drove down
IDEAS FOR MY 2008
LIGHT RACER ENTRY
While I don’t know which motor
or solar cells I’ll use (yet), I do have
an idea for my light racer’s chassis.
I often make booms for my near
spacecraft out of Styrofoam sheet
laminated in thin plywood. And in my
experience, the resulting booms are
very stiff, strong, and lightweight.
Therefore, I plan to make my light
racer’s chassis from 1/2-inch thick
Styrofoam cut to the proper shape
and then epoxy 1/32-inch plywood
over it. It’s easy to attach a solar
array and motors to the chassis using
epoxy and basswood blocks. By the
way, I’ll use Cell Foam 88 for the
chassis — a new Styrofoam sheet
material available at most hobby stores.
I’d like to use plastic peanut
butter jar lids for the wheels and I’ll
drill large holes into them (especially
near the rims) to reduce their angular
momentum. With holes, the wheels
will spin up to speed faster. Then I’ll
add traction to the wheels by
wrapping their rims with rubber
bands. Because the lids are made of
thin plastic, it will be easy to add
something like a servo horn to them
■ FIGURE 4. I don’t remember
how the race went for this entry.
■ FIGURE 5. This is another racer that
I don’t recall how the drive went.
■ FIGURE 6. This year’s winner by
the Kansas City Space Pirates.
■ FIGURE 7. The children of
the Kansas City Space Pirates
and their winning entry.
May 2008 85