I am an avid Gears of War fan, and one of my favorite weapons from that game is the torque bow. I've searched the Internet for such a creation made of Knex, and I did find one on this site. Even though it was a fine gun on it's own account, it was far from being and performing the way an actual torque bow does.
So I set off to make one myself. This is what I have so far: a near complete replica as close as I could make it to the actual weapon. The arms open and close, and lock in place in the open position, but not yet in the closed position. It uses a combination of string that runs through the arms and a rubber band to fire the arrow, and the act of placing the arrow into the firing chamber is what cocks the weapon. Unfortunately, I have not yet devised a method of holding back all of the potential energy of the arrow with a trigger system, although that is what I will be working on next.
I hope you enjoy this video of what I have been working on for quite a while now. Hopefully when I complete it, I will post instructions so that anyone with the right pieces can personally enjoy what I have created.