Mr S Vijay, MTech student (2002-04), along with the catapult, designed and fabricated by him. Click on the image to see an enlarged view of the catapult.
A device, viz. a catapult, has been fabricated to demonstrate Design of Experiments in a class room environment. The catapult is a simple mechanism which can throw a ball to a distance. We can set the catapult start angle, end angle, clamp height, spring hook position and arm length at various levels. How do we set the levels to maximise the throw distance? Or, how can we set the levels so that the ball hits a target kept at a certain distance? One can attempt a theoretical analysis to solve these problems, but much simpler is to carry out a properly designed experiment to develop a mathematical model which can be used to predict the throw distance in terms of the other factors.
Mr S Vijay, MTech student (2002-04), along with the catapult, designed and fabricated by him. Click on the image to see an enlarged view of the catapult.
The catapult can also be used to demonstrate Statistical Process Control, by repeated firing in a single position, without changing the settings. It is even possible to demonstrate the effect of overadjustment, similar to Deming's funnel experiment, by adjusting the settings between firings suitably.
Those who wish to buy a catapult may please contact
Link to another version of the catapult (from Engineering Statistics Handbook) and analysis of an experiment on it.
Link to procedure and forms on how to conduct the catapult experiment (Brigham Young University).
Link to David Stienstra's tutorial on DoE and analysis of a catapult experiment.
Link to a commercial manufacturer of catapult.
Acknowledgement: The cost of development of the catapult was met out of a project "Development of Centre for Quality Engineering" sponsored by the Ministry of Human Resources Development, Government of India.