Beginning in May 2009, the ASME Idaho Section, BYU-Idaho (BYU-I) Mechanical Engineering students, and Diversified Metal Products, Inc. (DMP) began designing and planning a trebuchet for this year’s competition in Salmon, Idaho. Design meetings were held every two weeks and the BYU-Idaho engineers used advanced 3D modeling to engineer the trebuchet. The design was based on the floating-arm trebuchet design by trebuchet designer Ron Toms. The goal was to design and fabricate a trebuchet capable of throwing a 3lb projectile over 600 ft, a significant improvement from previous years. The only design constraint was that they could use a maximum of 250 lbs of counterweight. They also decided that we should make the machine as safe as possible for obvious reasons. Once the design was finalized, Diversified Metal Products donated time and material to fabricate and paint the trebuchet. The final trebuchet stands over 11 feet tall and weighs in at over 1500 lbs.

Once the fabrication was finished in August, they immediately began test firing the machine. The goal was to be able to dial-in the distance that the trebuchet fired by adjusting several parameters. It was quickly discovered that behavior of the projectile was extremely sensitive to the 4 independent parameters. Great effort was made to reduce the number of variables in order to have an easily adjustable system. Very consistent performance was achieved in early September. The only uncontrollable variable was the ballistic flight characteristics of the medicine balls that were being used as a projectile. The force of the launch caused most of the medicine balls to fly like discs through the air. This caused their path to be very unpredictable. By modifying the medicine balls to be more firm, the trebuchet became much more predictable. The trebuchet was now able to hit a target with distance accuracy of +/- 2 yards at over 100 yards. Right to left accuracy remained +/- 5 yards.

On September 23rd the Team competed at the River of No Return Catapult Challenge in Salmon, Idaho. The whole event was to benefit rural central Idaho high school students. High school students designed and built trebuchets to compete for a $5000 award to be applied to a science, engineering, or industrial arts program at their school. This year, Salmon High School won the $5000 prize by launching a water balloon nearly 100 yards with their floating arm trebuchet. Premier Technologies competed against the ASME/BYU-I/DMP team in the unlimited class for distance and accuracy. This warm competition was intended to get high school students excited about careers in science and engineering. The ASME trebuchet launched a 3lb medicine ball 202 yards in the distance competition while Premier Technologies threw for over 380 yards with their 30 foot tall machine. However, the ASME trebuchet showed its strength in the accuracy competition. A target was placed at 110 yards, and they were able to land a medicine ball at 111 yards out and less than 8 yards to the left. This easily beat the much larger Premier Technologies trebuchet which overshot the target by over 100 yards.

This project served as a great learning experience for the BYU-Idaho engineers and was a great opportunity to experience the engineering and testing process. The trebuchet was also a great way to get the high school students excited about science, engineering, and mathematics.