Before the Trabuco was a type of gun revolver, it was a large metal device that looked similar to the symbol of the Libra astrological sign except that one side had the weight on the end of rod used to fling rocks over the wall of the enemy.
According to pt.bab.la, the Trabuco was created by the Chinese around the year of 400 BC. The ancient weapon was brought to Europe by the Chinese in 600 AD and used to fight the Crusades. The weapon was abandoned after the invention of gunpowder in the 10th century. The Trabuco structure was based on the original sling shot depicted in the bible, only much larger. and made of metal. The Chinese added a traction bolt the large, metal structure version of the sling shot.
There is an online site according to dicio.com.br that gives step by step instructions on how to create a wooden, small scale model Trabuco. The main parts of the Trabuco are the A-shaped stand, the swing arm, and fulcrum axel. The fulcrum pivots on the stand. It has a counterweight on one end and a sling at the other. The stand is made with two A-line wooden structures and a base at the bottom to keep the stand from falling over. Unlike the Libras scale, the Trabuco sides are not equal. The swing arm is one 1 centimeter where the counterweight is, and the swing arm beyond the stand is 3.75 centimeters. The Trabuco is the most dangerous and throws rocks farther than any medieval weapon that ever was. The weight is the what really makes the weapon powerful; the counterweight weighs about 750 lbs. There is string attached that is the sling part and should be the same length as the entire swing arm in order to work properly. The rock at the other end needs to be attached to a cup that will sling it forward by the force of the counterweight. Although it is not used as a weapon today based on banco.bradesco, they are being made as science projects in middle schools across the country.
Learn more about Trabuco: http://help.madmoo.com/pt_BR/khanwars-new-1792-1896.html