Step 18: Firing and Fine Tuning
Hook one loop of the string on the basket to the loop in the copper wire in the swing arm. Loop the other end around the piece of copper loosely. Pull down on the projectile basket with a ball inside and pull through the center of the trebuchet (between the sides) as far as it can go. When ready to fire, let go of the projectile basket.
With the proper amount of weight in the basket, the trebuchet should throw the ball around 30ft. If the path of the ball falls too short, while standing behind the trebuchet (opposite side from where the ball flies), bend the copper wire back towards you if it's too late in releasing, and bend it forward away from you if its too early in releasing.
Also, the distance the ball goes largely depends on the amount of weight that is in the weight basket. More weight = further distance.