The Trabuco (often referred to as a balancing Trabuco), can trace its roots back to ancient China in 400BC, and was used by the Mongols. It was later brought to Europe around 600BC, and the European armies of the Middle Ages used this weapon during the Crusades to battle the Muslims. Arab merchants would also use this weapon against their Egyptian opponents. It was similar to the standard catapult but was easier to maintain and produce.
This siege weapon was able to hurl different projectile materials such as heavy stones, fireballs, and even animals a great distance in order to demolish the walls of an enemy fortress, and to also hurl those projectiles over the wall. This weapon was also known as a balancing Trabuco, and usually required as many as 45 men to operate. The men would work in pairs pulling ropes in order to provide traction. It was often very difficult to get the men to pull the ropes at the same comparable speed each time it was used. The speed of the projectiles was determined by the size of the machine. The Trabuco employed the same principle as a sling in that gravitational potential energy is converted into kinetic energy, which provides the power necessary to hurl whatever projectiles are being used. Some energy would be lost because of friction and would dissipate. The size of the ammo used had to be carefully calculated before firing, due to the kinetic energy that was expended according to priberam.pt.
The Trabuco came in two types, the hybrid and the tensile. The hybrid was capable of throwing projectiles that weighed 400 pounds, whereas the tensile could only throw material that weighed 140 pounds. The Trabuco was a very effective weapon against targets that were up to 80 meters away. With the development of gunpowder, the Trabuco was abandoned around the 11th century.
Search more about Trabuco: http://www.wordreference.com/pten/trabuco