(Solved) How do you calculate torque on a trebuchet lever arm?

The site http://ronleigh.com/ivytech/_ref-trebuchet-range.htm says that to calculate torque on the counterweight arm of a trebuchet, the formula is as following:

Torque on counterweight arm = Length of counterweight arm ? ((counterweight mass x 9.8 N/kg) + ½ weight of counterweight arm)

I had thought that the formula for torque was torque=Frsinx, with F being the force acting on the lever arm, r being the length of the lever arm, and x being the angle at which the force acts (often, as is the case here, x is assumed to be 90 degrees, making sin x = 1, so it can be disregarded in the equation).

The equation provided by the website is in accordance with torque=Frsinx, excepting the fact that the quantity of force (½ weight of counterweight arm) is added to the force provided by the counterweight itself. I am wondering as to why this is; if anyone could explain specifically why half the weight of the counterweight arm (i.e., .5 x mass of counterweight arm x (9.8 N/kg)) is added to the total force acting on the counterweight arm to calculate the torque, this would be a great help.

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How do you calculate torque on a trebuchet lever arm?

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