|Table of Contents
Sources of Error
The objective of this experiment was to quantitatively measure how the
dependent variables, wind speed, mAmps, mVolts and revolutions per minute (RPM),
changed under varying experimental conditions. These changing conditions were
the independent variables as shown in the experimental design chart below.
Twelve rotor variations were tested with three sizes of DC motor at
medium and high fan speeds.
The resulting mAmps, mVolts, RPM and wind speed were measured ten
times per manipulation to ensure accuracy and reproducibility.
total, 720 measurements each of mAmps, mVolts, RPM and wind speed were planned.
In actual experimentation, some rotor variables failed to start and turn the
horizontal axis, making measurements of RPM and electrical output unavailable.
mAmps and mVolts were measured using a digital multimeter.
RPM were measured using a digital photo tachometer.
Wind speed was measured using a digital anemometer to ensure that it
was constant for each of the tests using a particular speed and calculate tip
4. Wind Speed
1. Fan speed
2. Number of rotors (1, 2 or 3)
3. Rotor spacing
4. Position of rotor on horizontal axis (i.e. rotor blades offset or in
5. Size of the DC motor (1.5-3V, 9-18V or 12V)
1. The same test station,
retort stand supporting the motor, and electric fan were used for all tests.
2. All of the testing was done in the same location at ambient temperature.
3. The equipment was positioned exactly the same for every test. The test
station and retort stand were clamped onto the workbench and the required fan
position was marked on the floor.
4. The rotor placement on the axis was checked with a T-square to ensure
that the rotors were perpendicular to the axis.
5. A ruler was used to mark the required distance between rotors.
6. The same measuring instruments were used for all tests.
7. The anemometer was held in approximately the same position for every
8. The tachometer was placed so that the beam was centered on the
reflective tape. 9. RPM and multimeter readings were not taken until the
rotors had reached maximum and stable rotational speed.
10. All testing was repeated a total of ten times to ensure accuracy and
Material & Equipment