This work was conducted in an attempt to understand the mechanical stresses inside the beam of an existing trebuchet (the Renfrew trebuchet). After several years of usage this beam broke but the cause was initially not known.
As a first check on our calculations we used conservation of energy.
Secondly, by setting the mass of the projectile to near zero we are
able to simulate a classical double pendulum and successfully compared
our results to the results of the simulator available at
The input for the Standford simulator is somewhat restrictive but you can enter there
Θ1=90 ω1=0 mass1=20 length=25
Θ2=90 ω2=0 mass2=15 length=18
and click on to provide our program with the corresponding input.
at http://www.virtualtrebuchet.com/. You can enter there the input values of the Renfrew-trebuchet with
the following exceptions :
Projectile Diameter : 0.1 m
Pivot to Arm CG : +0.2 m
Inertia of Arm : 539.3 kg m^2 (they require central moment of intertia)
Release angle : 39.0 (what my program gets) for given sling finger angle
As a result you should get from them a flight time of 6.231 s, a distance of 132.591 m and a release velocity of 37.045 m/s.
My simulation produces a flight time of 6.26737 s, a distance of 136.2 m and a release velocity of 35.6 m/s. Note that my simulation does not include air resistance, but their's does.