It is made of plywood, a few 2 x 6's, and a lot of plumbing parts. The folding design is great for storage, and in my case, the catapult actually went up on the roof of a church for the main launching event. It fit up a ladder through a roof hatch with no trouble. (Well, other than the fact that it is bulky and heavy).
The counterweight is two 60 pound bags of concrete, which gave about a 100:1 ratio for the pie pumpkins and basketballs. After the pictures were taken I also added several bungee cords (2 x 18" and 2 x 24") to assist with pulling the weight down, and it added another 20 feet or so to overall distance.
Just something fun about catapults!
Step 1: Building the Platform
When you cut the plywood sections to size there are three pieces of wood per section. The platform piece itself, and then two narrow reinforcing pieces that go along the edges.
Cut the plywood and 2 x 6s to size, and glue and screw together.
Step 2: Assembling the Folding Base
Step 3: Attaching the Uprights to the Base
Also in this step, attach 1" flanges to the uprights, which will hold the throwing arm assembly.
Two screw eyes go in the top of each upright, and then matching screw eyes go on the base platform, in line with the uprights. This is where the wire will attach to hold things in place.
Step 4: Wire Rigging for Uprights
Step 5: The Counterpoise - Concrete Holder
Step 6: Assembling the Throwing Arm
Drill a hole through the cross to insert a long eye bolt. Two other eye bolts are also inserted into the throwing arm, one at the end, and one at midpoint.
A cap is attached at the end of the throwing arm, with a hole drilled through to allow insertion of a bolt. This will be what the free end of the sling attaches to.
The counterpoise assembly connects to the opposite end of the cross fitting, and two 8" nipples are attached to the sides of the cross fitting.
The arm assembly is attached to the uprights with close nipples and 1" pipe unions. Thread the close nipples into the flanges on the uprights, and then thread the non-removable side of the union onto the close nipple.
Step 7: Attach Throwing Arm to Uprights.
Step 8: Quick Release Mechanism
In order to be able to remotely trigger the panic snap, I lashed some cord around the body, and liberally soaked with thin CA glue. The cord then goes through an eye attached to the deck of the catapult.
Step 9: Sling and Final Assembly
I wrapped some duct tape around the bolt to allow the ring to slide off more easily.
Step 10: Final Notes
Also during testing, the sling would drag slightly on the plywood platform, so I added a piece of horse butt leather for testing. This was later replaced by a piece of slick MDO plywood.
Basketballs were launching from 60 - 80 feet, and footballs about the same. It actually throws a football in a spiral, which is cool to see. The furthest pie pumpkin (1 - 1.5 pounds) went over 100 feet.