I thought I would try to document a little bit of the build for the Angry Birds build that I did for my son's birthday.The pigs are simple milk cartons that we spray painted green (florescent because the cartons were white), then we hot glued the googly eyes on and drew nostrils with a sharpie on the lids.
The Giant Sling Shot was a design that I came up with just from wood that I had around. I wanted something that wouldn't bend, warp, or flex when it was pulled on. I knew it had to be mounted so I figured I would just dig a hole and plant it.
The wood is the pre-treated 4x4 posts from the big box stores then cut into three pieces. The main post is cut at two 45 degree angles that come to a point in the middle at the top. Then the two Y arms are each cut straight then mitered where they meet in the middle above the point of the main post. This is so that they will always be in contact with each other at every point of intersection.
I then used two 90 degree L brackets on the outside where all three pieces meet. I then used another 90 degree face bracket in between the Y to support the two Y arms. I then put two 45 degree brackets where the main post meets each of the Y arms on the outside edges.
The sling was built from two bungee cords that had to be easy enough for the kids to pull. I didn't want to permanently attach them to the Y arms so I just notched the Y arms with a groove on each corner of the posts to provide a track for the bungee cords. I then wrapped the bungee around itself and zip tied it as a preventative measure in case it got pulled too strongly.
The other end of the bungees are then looped through and zip tied to the 4 tarp clips which are then attached to the shop towel.
Everything came from the big box store
4x4 posts - 14.75
90 degree L plates - $4.20 x 2