pg_0182
5.
Process Improvement
5.4.
Analysis of DOE data
5.4.7.
Examples of DOE's
5.4.7.2.
Fractional factorial example
A "Catapult" Fractional Factorial Experiment
A step-by-step
analysis of a
fractional
factorial
"catapult"
experiment
This experiment was conducted by a team of students on a catapult C a table-top wooden device
used to teach design of experiments and statistical process control. The catapult has several
controllable factors and a response easily measured in a classroom setting. It has been used for
over 10 years in hundreds of classes. Below is a small picture of a catapult that can be opened to
view a larger version.
Catapult
Description of Experiment: Response and Factors
The experiment
has five factors
that might
affect the
distance the
golf ball
travels
Purpose: To determine the significant factors that affect the distance the ball is thrown by the
catapult, and to determine the settings required to reach 3 different distances (30, 60 and 90
inches).
Response Variable: The distance in inches from the front of the catapult to the spot where the ball
lands. The ball is a plastic golf ball.
Number of observations: 20 (a 2
5-1
resolution V design with 4 center points).
Variables:
Response Variable Y = distance
1.
Factor 1 = band height (height of the pivot point for the rubber bands C levels were 2.25
and 4.75 inches with a centerpoint level of 3.5)
2.
Factor 2 = start angle (location of the arm when the operator releasesC starts the forward
motion of the arm C levels were 0 and 20 degrees with a centerpoint level of 10 degrees)
3.
Factor 3 = rubber bands (number of rubber bands used on the catapultC levels were 1 and 2
bands)
4.
Factor 4 = arm length (distance the arm is extended C levels were 0 and 4 inches with a
centerpoint level of 2 inches)
5.
Factor 5 = stop angle (location of the arm where the forward motion of the arm is stopped
and the ball starts flying C levels were 45 and 80 degrees with a centerpoint level of 62
degrees)
6.
5.4.7.2. Fractional factorial example
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