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Modeling a trebuchet


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I’m working on a code to model a floating-arm trebuchet. I’d planned to use the energy/momentum method. I’ve got the equations that relate the position of the arm and the location of the counterweight done correctly, as well as those for the moment of the arm. But I’ve gotten stuck on how to model the motion of the projectile and sling. I don’t see an easy way to solve for the momentum of the arm and the projectile simultaneously.

 

So I’m thinking of switching to the force/acceleration method. I can find the acceleration of the arm by treating the projectile mass as if it were located at the arm/sling joint, using the angle between the sling and the arm to divide that mass into its contribution to the linear and angular acceleration of the arm. Once I know the acceleration vector of the end of the arm I can apply it directly to the projectile.

 

Make sense?

 

Oh, yeah... I know about the shareware programs that are available, I have a couple of them. But I've got a unique design that won't work with the available programs, and I don't have background necessary to decompile them in an attempt to reverse-engineer.

 

Thx.

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I think you pretty much have to go for the latter approach. The arm is going to be accelerating due to gravity, and that will cause the spiral traced by the projectile on the sling to accelerate also.

 

Don't forget about the boundary value issue involved with the initial movement of the arm has to fight the initial friction of the projectile on the ground--if you've got a traditional trebuchet--and the fact that that initial dragging will affect the rate of change of the radius from the fulcrum of the arm to the projectile.

 

If they'll do neither, we will come to them, and make them skirr away, as swift as stones enforced from the old Assyrian slings, :rolleyes:

Buffy

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