Ballistics Device

The Catapult

As a freshman in high school, this was students’ first introduction to the PLTW design process. After sketching and brainstorming ideas, students split off into pairs and began to construct a solution of launching a ping pong ball into a designated area. The primary constraints required:

• A constant initial velocity throughout all tests

• A method in setting angles in increments of ten ranging from 10-80 degrees

• The device to fit in a 1’x1’x1’ box

• The device be assembled from common products or household items

• No high-pressure gas or combustible materials be involved in the propulsion of the projectile

The idea that won out in the end was initially a trebuchet that quickly morphed into a catapult design due to the lack of ideas in how to design a trebuchet’s sling. As a result, a common catapult placed on a ramp was created. Powered by a mousetrap and a large quantity of rubber bands, the ping pong ball was placed in the base of a reinforced plastic cup. The plane was held aloft by a dowel attached to the “wall” which had the eight different settings of the device drilled into it. A door hinge allowed for the rotational movement of the mousetrap’s plane.

As made obvious by the graph below, the device failed as firing angle increased. this is due to the rigid nature of the entire contraption. The mousetrap as a firing mechanism was primarily the issue as that was the cause for inflexibility of the launches. the only way to supply enough power for the firing arm was the copious amount of rubber bands to reach the desired ranges at small angle values. However, this additional power ruined the launches after 40 degrees as it continued to increase after 45 degrees.

In hindsight, it would have been a much more effective design had a trebuchet sling been employed as it would allow for the necessary pliability of the device.