Trebuchet

Centuries before the development of cannons, trebuchetwas a common siege engine to destroy the fortified walls of a fortress from safety distance. In the medieval period, engineers have been modifying the trebuchet in order to improve the power and accuracy of the trebuchet. Until today, trebuchets were built to find out the how does the dimensions of each part in trebuchet could affect its functionality.

In design project two for MMAE 232, a trebuchet was built to launch a water-filled ping pong ball for 12 meters. A 2kg wooden box was used as a counterweight in this project. 10 pieces of 24”x18”x1/4” MDF, 10 pieces of 24”x18”x1/8” MDF and a 1/4” acrylic rod was given to build the trebuchet. Acrylic rod was used as pivotal in the trebuchet and it is a brittle material thus reaction force acting on the pivot had to be taken into consideration. Matlab was used in this project to estimate the distance travelled of ping pong ball, reaction force on the pivot, and the time frame of launching the ping pong ball while reaching the estimated distance travelled.

Design Process

In this project a trebuchet transformed the potential energy from counterweight into the kinetic energy water filled ping pong ball. The ping pong ball travelled in a projectile motion and the equations below shows the relationship between the distance travelled and the energy transformation.

As a conclusion, height of the trebuchet is proportional to the distance travelled by ping pong ball. Thus height of the trebuchet had been increased from the original design by adding some legs. A hinged counterweight design had been decided as the hinge significantly increased the amount of energy that can be used for projectile. This design slightly increased the distance travelled of the counterweight throughout the firing process and hence increase the energy transformed. Furthermore, ductility of acrylic rod had to be taken into consideration as the reaction force reacted on the pivot might cause the acrylic rod to be broken. Therefore, a hollow base had been made to allow the counterweight to pass through.

Result

The shooting range of trebuchet was unstable. A maximum of 10 meters shooting distance and an average 9 meters shooting distance were obtained during the tuning process. However, a maximum of 5 meters shooting distance was obtained out of 5 trials during trebuchet launching session.

To see thie project in more detailed project form and calculations for this projects,

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