Arizona Science Olympiad
The Science Olympiad is an annual state and national competition for junior and high school students interested in STEM (Science, Technology, Engineering, and Math) fields. Several of my classmates and I agreed to be judges for the Wind Power Competition for the Arizona Science Olympiad in March 2016 to fulfill a project requirement for our university physics class. In this competition, students must build a set of windmill blades attached to a CD. The windmill blade set is then mounted on a stand containing a DC motor. An electric fan is placed in front of the windmill to simulate wind. The power that each windmill produces is determined with a voltmeter attached to the windmill stand.
For more information about the Science Olympiad, go to Science Olympiad National Website or to Arizona Science Olympiad.
As the judges for this contest, we were charged with building a stand for the windmill blades according to the specification laid out by the Science Olympiad. Some of the specifications were that the total resistance in the system needed to be between 5 to 7.5 Ohms and that motor/generator must be able to accommodate at standard CD. To accomplish the latter, I found an discarded CD player and removed the motor and related hardware that included a fitting for mounting a CD to it. That made the process of figuring out how to quickly mount each contestant's windmill blades easier. Unfortunately, the fitting had nothing on it to keep the blade assembly in place when the plane of rotation was vertical rather then horizontal. We experimented with different ideas on keeping the blade assembly in place and settled on a simple system of a CD with four binder clips that both effective at holding the blade assembly in place and made switching out different blade assemblies and quick and easy process.
To accomplish the former, we needed another resister mounted in parallel to the motor to bring the total resistance to between 5 to 7.5 Ohms. The motor's resistance was 11 Ohms. Using the formula for resisters in parallel (1/R1 + 1/R2 = 1/Rtotal), I calculated that adding a resistor of 22 Ohms would being the total resistance into spec with a combined resistance of 7.3 Ohms.
Electronics schematic of the windmill stand
The first completed windmill stand along with a test windmill blade assembly. The excellent woodwork was done by John Collins a member of the team. On the base of the stand are ports for the voltmeter probes to go into. That helped ensure a consistent connection to the generator circuit for more stable voltage readings. On the top of the stand is a flashing LED that John wanted on the stand for esthetic reasons. Its power is on a separate circuit from the motor/generator circuit and the power switch is next to the voltmeter probe ports.
Detail of the base of the windmill stand clearly showing the multi-meter probe ports with voltmeter plugged in and the LED on/off switch.
Underside of the windmill stand base showing the wiring for the generator and LED circuits. It's hard to tell, but the two are on separate circuits. The LED has two batteries in series because the 1.5 Volt AA battery we started with didn't have enough power to make the LED blink at a decent rate or very brightly. The way the LED circuit setup is sub-optimal, of course, and is the result of scrounging for available materials to boost the voltage. The soldering and applying shrink-wrap around the connections was done by Jerry Bray another member of the team.
Top of the windmill stand showing the blade assembly mounting bracket, test blade assembly, and red LED on the top
A closeup of our final design for securing the contestants' blade assemblies to the generator. Not much to look at, but it worked very well.
It turned out that we needed another windmill stand for the competition. Since John wasn't available to make another stand, Jerry and I put this one together using PVC pipe that included a piece that allowed adjustable height. Fortunately, I was able to find another CD drive motor to use and I had more 22 Ohm resisters. Another trip to Fry's Electronics got us another speaker wire jack that we used hold the voltmeter probes.