Shade Tree Kings: Project Report
The project team intended to create a windmill that can successfully harness the wind provided
by one box fan and produce electricity. This windmill was designed and built by the project team, using
inexpensive readily available materials. This windmill needed to produce 1.4 volts of electricity to light
a Light Emitting Diode, which it did.
The design process began with Bernoulli's principle. The original design intended to use the
continuity equation to produce a high velocity stream of air which would then rotate a small turbine at
high speed. The turbine output shaft would be connected to the generator. It would then rotate two
disks with magnets attached around a fixed wire coil. The wire coil was initially wound perpendicular
to the disks. This worked in initial trials but in full scale up tests was proven inadequate. The generator
design then moved to a rotating magnetic armature inside a magnetic coil. That was t he final design
form that was used.
The duct that was used, ultimately proved to be a failure. The duct was constructed from a non-
rigid material. Due to the non-rigid material, it caused turbulence that slowed the air down. This failed
to spin the turbine fast enough to create enough electricity. Thus, the duct design was shelved.
The second design was the use two wheels that would harness the air without the use of a duct.
This design caught air fairly well, but yet again did not spin the generator fast enough. Without the
generator spinning fast enough, the electricity generated was not enough. The two wheels also placed a
large amount of parasitic forces on the system. This was due to the wheels being unbalanced and also
the negative torque on the shaft due to the paddles encountering wind in the opposite direction. These
disadvantages caused the wheel design to be shelved.
The final design was a large bladed turbine to catch the air. This design generated much larger
amounts of torque upon the central shaft due to the radius of the blades. This allowed the shaft to spin
at higher revolutions per second and generate more electricity. The initial shaft design had problems
with attaching the blades to the hub. The second hub design used dowels and zip ties to attach the
blades to the hub. That design worked and kept the blades locked into position. Through testing, it was
determined that 15 degrees was the optimal angle for the blades. This was the final design as used.
The fan hub was not perfectly balanced and produced a large amount of circular oscillation.
This required it to be held by hand for initial testing. That would not do for the final test. To combat the
oscillation the vertical supporting shaft was glued into the wooden base. Two wooden support beams
were glued to each other and the PVC shaft. They were also locked into place using duct tape. In
addition to support, the duct tape also improved the aesthetics.
One last item had to be overcome in order to generate enough electricity. The generator using
the magnets we had only produced 1.2 Volts. Using rare earth magnets, the generator was able to
produce 1.36 Volts. The only thing left to do was to increase the number of wire coils. Attaching these
additional coils to the exit wires allowed the generator to produce 1.5 Volts. Although it was peaking at
1.5 Volts, it was desired for more power. Thus one more coil was added to the generator. This final
generator design allowed the generator to produce a peak of 2.16 Volts on the monitored run. Thus the
design was a success, it lit the light emitting diode and also produced excess power.
The windmill final design is fairly simple. It incorporates a large fan made of wooden blades
that harnesses the air to rotate a wooden shaft. The PVC hub connects the fan blades to the shaft via a
circular bearing. The fan blades are attached to the hub using 4 dowels, each dowel is zip tied to the
blades and superglued to the hub. The shaft is approximately 12 inches long and is a direct drive to our
magnetic armature. This rotates inside a wire coil producing the electricity. The shaft is housed inside a
PVC pipe and rotates on two skateboard bearings. The PVC pipe is glued into the base and duct taped
and glued to two wooden support beams.
Using the equations given it was estimated using:
Power = ½ * Rho(air) * Area * V^3
that the device would produce .55 Watts. During testing it was determined that 1.7 Volts were created at
a current of 0.1 Amps (those numbers were obtained during Sunday evening testing). Thus using:
Power = Voltage * Amperes
that the device actually produced .17 Watts. Thus the efficiency was calculated to be 31%.
The bill of materials included the following:
PVC Pipe: $2
Zip ties: $2
Total cost: $35
In conclusion the project was successful as it accomplished the objectives set out. It lit the 1.4
Volt Light Emitting Diode and produced even more power than that. It also was accomplished within
the $40 cost limit. It also required teamwork to overcome the trials and tribulations that occurred
during the design, construction, and testing.
Wind Energy FAQ. American Wind Energy Association http://www.awea.org/faq/windpower.html.