Twister 1
Windmill Energy
Lab B2
Project Report
John Smolko
Michael Warden
Anthony Hathaway
Tim Pobst
Twister
We were given the task of designing and building a windmill that will generate
electricity. We decided on an upright windmill design similar to the type you can see in
Holland or a pinwheel that you blow on. We used a home built electric generator made
from magnets spinning inside copper wire coils. The fan is attached to the generator
using Lego parts including gears. We were required to keep the windmill small enough
to fit in 0.5m x 0.5m x 0.8m box and the windmill had to run without our help. The
materials used needed to be readily available and total cost had to be less than $40
dollars, which we easily achieved. We showed that our windmill could generate
electricity by attaching the leads to a small LED light, which did light up and we
measured the voltage at 3 volts with the amperes at 5E-4. This device is not very
efficient power wise but it was very cheap and easy to build and it worked brilliantly.
We had a couple of ideas at the beginning, mostly just dealing with the
placement of parts. The overall design was a simple fan attached to a simple generator
and to do this as simply as possible. The main goal in building a fan to spin a generator
is to get the magnets to spin as fast as possible. Keeping our restraints in mind of cost,
materials and using a house fan we decided on keeping the parts light. Lighter parts
Twister 2
were generally cheaper and they could be easily moved by a house fan. The base and
the stem that hold our fan is made from scrap wood we found in Estabrook 13. The fan
consists of Styrofoam also from Estabrook 13 and blades made from a priority mail
cardboard box. Originally we were going to make the blades from wood but they were
going to be too heavy and hard to deal with, so we decided against it. There is an axel
rod going through the middle of the fan and then through a hole near the top of the stem
wood. This axel is a Lego piece and connects to some Lego gears with a ratio of 1:3.
These gears have another Lego rod attached going out the other side. This rod goes
though a kind of Lego wall that is used for support, then straight into the generator.
Inside the cardboard generator are a couple of neodymium magnets that are attached
to the rod using cheaper refrigerator magnets. Wrapped around the outside of the
cardboard housing is copper magnet wire with the two ends coming out so we could
attach a LED light to it, which just hangs down off of the generator.
Along with the goal to make the materials light we had a budget of $40. Some of
the materials we used from Estabrook 13 and Michael was pretty much in charge of any
materials we had to buy. Michael’s daughter is doing a very similar science fair project,
and so he had to get the materials anyway. He bought the bulb for $1.70, the wire for
$1.75 and the magnets for $6.00. The wood was scrap wood, the Styrofoam and the
cardboard were free materials. The Lego pieces were on loan to us from Michael. So
the total he spent on materials was $9.45 all of which he would use again for his
daughter’s project. I would assume that cost wise, our project is the most cost efficient
in the class, everything will be recycled. The cost efficiency of our project is
1-($spent/$allowed)*100,
Twister 3
which is 1-(9.45/40)*100 and that equals 76%.
Power efficiency is another story. Power efficiency is measured with
(Power out/Power in)*100.
We measured the power out as
watts=volts*amps.
This came out to be 3 volts * 5E-4 amps which equals .0015 watts. The power in
equation is
P(watts)=0.5*rho*A*Cp*V^3*Ng*Nb
Rho is air density and I used average air density of 1.225 Kg/m^3. A is the area of our
fan, the fan radius was .1778m so the area was .099m. Cp is coefficient of
performance, and we made an educated guess that Cp=.35. V is wind speed which
was given to us at 1.7m/s. Ng is generator efficiency, we assumed the generator itself
is pretty efficient because of its simplicity so we said Ng= .80. Nb is the
gearbox/bearings efficiency, our gears have a 1/3 ratio so Nb=.33. This equation gave
us .028 watts in. Then plugging in our numbers for Power out and in into the efficiency
equation we got 5.36%, which is horrible. However, seeing as our goal was to
illuminate the light; we did that and this windmill could continue to power the light.
In class we tested our windmill and it worked. We lit up our light plus the class
light and we got a measurement of 3 volts, which was third in the class. We learned
Twister 4
enough about electricity to make our generator and we learned that sometimes simple
can get the job done. From looks alone we had the second worst appearance, which
correlates to time spent on project. Our simple design didn’t take much time to build but
it was the cheapest out of the class and got third in power out. It costs $3.15 per watt to
run our windmill, which is better than the majority of groups, many of which spent the
allotted $40 dollars and had less power output. We didn’t have any major problems
while building it. We did have to choose cardboard blades instead of wooden ones out
of convenience and we had a problem with keeping the magnets on the axel rod. We
solved this by putting lesser refrigerator magnets in between the neodymium magnets
to keep them in place. We had little problems of fan blades hitting the stem and too
much friction between the fan and the generator, but these problems were solved with
different placements and Legos. If we had to get a higher power efficiency we would
have to cut down on the friction in the middle. The design was light and unbalanced
and if it was allowed to run for awhile it would probably wobble itself out of existence.
This could be fixed with sturdier connections around the gears, because that is the
weakest point. And of course ball bearings could be used in many places along with
better gearing, tighter and more coils and better connections to the light can improve
our power efficiency. All in all we feel we were very successful in fulfilling the
requirements of the project, all while keeping way under budget.