After the failure of our arms in 2007, a new tactic was needed. Dave contacted his friends Karl Hamm and Kevin Cheney about designing and building a set of ballista arms out of aluminum. Aluminum was chosen for its strength and light weight.

Kevin Cheney's blueprints for the arms laid out on Karl's welding table in preparation for starting construction.

These arms were to have stays on the back of the arms to aid in deceleration, and hopefully prevent breakage.

The material started as a giant sheet of 3/8" thick aluminum plate. The next step was to cut it up into the different pieces that were to be used in welding the arms together.

Here are the main lengths (top and bottom) of the arms. The big round holes are the tips of the arms, and will hold aluminum pins to act as the bowstring connection points. The prominent shoulder seen near the butt of the arm will prevent the arms from sliding inward, through the bundle, when the bowstring goes taught at the end of a throw.

Here is an arm mostly assembled excluding the backside. Inside you can see a series of bulkheads which prevent the base of the arm from being crushed inside the rope and add overall strength. There is also a series of small holes through the bulkheads. These holes will later hold a steel cable that will run the entire length of the arm. The cable is our safety in case the arm fails catastrophically, and will prevent parts from flying off and hitting our neighbors.

Historically, the cable was made of leather, and was tied to the front of the arm, so this isn't a new idea.

Here are the stays before they are welded on. The stays will go on the back of the arm, and reduce forward deflection as the arms decelerate.

Karl just after grinding and sanding down the rough spots on the new arms. The back stays are now installed and the arms are ready to go.

And here are the two completed arms, ready to go for the 2008 Punkin Chunk.

Here they are about to throw a pumpkin a bit over 400 ft.

Unfortunately, the back stays failed, and the arm cracked near the shoulder.

2009 Upgrades

After breaking the arms in 2008, they needed to be repaired, and Karl Hamm and Kevin Cheney came through for us again.

The broken bit was cut apart, and welded back together. New plate was added to beef up that area on the arm, which can be seen here as a diamond shaped layer under Karl's feet. We opted to remove the stays and go with a different method of stopping the arms, such that the arms would not be stressed so much during deceleration.

Here is an aluminum post welded half way out. This post is to prevent the new arm stop rope from riding up the length of the arm allowing it to more effectively stop the arms before they bend around the outer stanchion.