Catapult

This is a simple catapult we created in an engineering physics course as a junior in high school.  The project was to build a marble launcher which could be no larger than 1.5 feet by 1 foot by 1 foot..  Our design is simple and powerful.  We used 15 celery rubber bands as the driving force behind the catapult.  This created approximately 450 pounds of tension, when fully extended.  Below is a picture of the catapult in "relaxed" mode.

We used pine to build the thing, which we found was almost inadequate.  The tension of the device was almost pulling itself apart when it was entirely built.  As seen above, steel reinforcements were placed on the throwing arm to prevent the arm from going too far, were the cabling to snap (which it did in test runs).

Here you seethe catapult with a single rubber band pulling the throwing arm.  550 lb test cable was used to hold the arm back and create release points.  A plumb bob was used to mark release angles.  For furthest distance, 45 degrees was used.  When it was tested, it launched a marble over 40 meters.