Building a Ballista...

It has been decided between myself and some friends of mine that we are going to build a ballista. It will live in my friend's garage next to their already-popular-at-family-gatherings trebuchet, which has a throwing arm that's approximately 8' long (perfect for hurling small melons or giant wads of duct tape
)
Anyway, I will be using this thread to document our progress and also I wanted to reach out to our very knowledgable community for ideas, tips and possible resources.
The main site that I'm using for reference is http://www.siege-engine.com
it's a very informative and interesting site. I recommend you give it a quick perusal.
I guess I'll start the journey by telling you that we spent a few hours hunkered over our smart phones brainstorming at a recent gathering. They initially came to me to get an "engineer's opinion" of their idea, which was to build basically a large crossbow. After googling "build your own ballista" I found that a more accurate version would use twisted rope to propel the projectile, and I think we've decided to go that route. Here is our inspirational picture, though we will probably aim to build one about 1/2 to 1/3 the size of the one in the image below:


Anyway, I will be using this thread to document our progress and also I wanted to reach out to our very knowledgable community for ideas, tips and possible resources.
The main site that I'm using for reference is http://www.siege-engine.com
it's a very informative and interesting site. I recommend you give it a quick perusal.
I guess I'll start the journey by telling you that we spent a few hours hunkered over our smart phones brainstorming at a recent gathering. They initially came to me to get an "engineer's opinion" of their idea, which was to build basically a large crossbow. After googling "build your own ballista" I found that a more accurate version would use twisted rope to propel the projectile, and I think we've decided to go that route. Here is our inspirational picture, though we will probably aim to build one about 1/2 to 1/3 the size of the one in the image below:
