Arm RatioThe general working principle of a trebuchet isnt too complicated where gravity is the source of energy for this. In order to construct a trebuchet, the ratio of theshortarmto the projectile arm must be considered at the first place. The greater the speed of projectile arm will reach when the longer the arm ratio with more force is required to move it quickly. According to Donald B. Siano (2001), in his analysis of trebuchet mechanics, based on his definition of "range efficiency", the optimal release position and design are:- The initial release position is such that the beam on the counterweight side makes an angle of 45 with the vertical. The length of the long arm of the beam (on the payload side) is 3.75 times the length of the short arm of the beam (on the counterweight side). The length of the sling is equal to the length of the long arm of the beam (on the payload side).In order to decide the arm ratio of a trebuchet, the distance between the fulcrum (pivot) and counterweight must be calculate precisely as this will significantly affect the performance of a trebuchet.

Figure (): The "see-saw' trebuchet.Figure () show a basic concept of a "see-saw' trebuchet. In order to know how the performance of a trebuchet is or how far a trebuchet can throw a mass, the range of travel distance of projectile mass will be calculated.When a trebuchet operated, the torque will be created by the motion of the arm and is given by

Since torque is also given by

Where, Therefore angular acceleration will be given by

The angular velocity of the projectile mass can be calculated from

Where, 2 = the final angular velocity 1 = the initial angular velocity The angular acceleration = Angular displacementThen the velocity of the projectile mass can be calculated by

Where, r = Projectile Fulcrum distanceFinally, the range of travel distance of projectile mass is given by:

Where, h = Vertical height of trebuchet arm above groundBased on the theory and equations above, if the distance between the fulcrum (pivot) and counterweight is too big, this will cause each end of the arm would turn almost at the same distance at the same time, thus causing the torque of the projectile arm would be reduced. As the torque decrease, angular acceleration will also decrease and the travel distance of the projectile mass will be short. On the other hands, the distance between the fulcrum (pivot) and counterweight should not be too small also. If the distance is small, the projectile arm will be long, even the torque will increase but this will also significantly slow down the motion of projectile arm.