With the development of armor and the emergence of fortifications, Dongfang has developed a composite bow made of animal horns, tendons, horns, hardwood, silk and other materials. This is a leaf spring structure that combines the advantages of multiple biological materials. Makes the composite bow very powerful. Foreign experiments show that the energy of a composite bow with a pull ten times less than that of a steel crossbow with a pull of 740 pounds is more than twice that of a steel crossbow (this is because the energy storage rate of steel is very poor. Up to one-tenth of the material of the ribs and corners, the steel bow itself is very heavy, and a lot of energy is consumed in the bow instead of being transferred to the arrow).
The ballista designed by the Greeks has a sturdy bracket. The main beam is placed on the bracket. Two torsion spring groups are installed on both sides of the front end. Each spring group drives a crossbow arm. The end of the crossbow arm is connected to the bowstring, and the bowstring is in the middle. It is a woven mesh bag that holds the projectile.