FXWars! Catapult! (Trebuchet) : Derby-Q Salano


Good idea… so far I did succesfull dynamics tests for both the arm and all the wire work between the arm and the frame… In the throw test I managed to throw a rock over 500 meters… all with realistic proportions and weights ofcourse. I put a brake on the arm ones it reaches a vertical position, to avoid problems with the upcoming wire work… Hope you like it…

Early Animation Test

Dynamics Test


did you key the release of the rock? or is there a hook of some sort?


I keyed it, I still feel it’s a challenge to create something using dynamics… Not to create something using nothing but dynamics… nobody will ever do that… the use of dynamics here is just a help here…


Here’s a dynamics test for the ropes. There’s going to be 8 animated ropes in the rig

[Rope Test](http://www.ronin3d.net/CGI_Files/Trebuchet/Trebuchet_Wire.avi)


that is nicely done. what prog is it, looks like maya.


Good guess. And thanks…


That is really nice. I think it would be worth having the wood in the frame flex. Even it you can’t simulate it, maybe just have a couple of bones driven by the arm. It would add a lot of realism. Good stuff.


Damn dude! I can’t believe you put all that together already. Looking great.


I think your ropes are moving like they’re underwater. Maybe increase the gravity? Have you taken into account that whole thing with Maya and gravity when it comes to centimeters? Gotta pump up that gravity to… 98 I think?, if you’re working in centimeters…

Other than that it looks great. You’re implementing dynamics more as one should in a production, ie. make it look good, not neccessarily deliver the most physically accurate launching. Nodoubt much more timeefficient than trying to do the whole thing dynamically :).

I’m toying with a trebuchet as well here, but I’m having a beast of a time getting the wires to do their thing. In your implementation, can you cock the weapon by pulling the arming-wire? Ie. can you arm it physically, or is it firing from the getgo?
I’m trying to do arm it “physically correct” (ie. pulling the arming-wire down and connecting it to the releasepin) but it’s not going too well.

On a possibly related note, how’d you attach the ball to the wire?

Anyway, what you’ve got looks promising. And the model itself looks intimidating already.


Good point, Novacaine. Although these are rigid bodies… so wont be able to do this dynamically, perhaps with bones yeah…

Gaggle, you’re right, the ropes are floating, but that’s caused by my high value in damping, not by the gravity, I need to fix that, but dynamic simulations can result in terrible noise in the motion, hence the high damping… Units in Maya are in meters according to me, do this: create an object, add gravity to it and playback exactly 1 second, your object will end up at y = -4.9 right? If you would put 1 second in the physical equation,

(y being distance, a acceleration and t time)

2 * y = a * t^2

You get 

2 * y = -9.81 * 1^2 s^2 m/s^2

y = -4.905 m

Common mistake though, besides if it was cm instead of m it would have been 981 cm/s^2 which is 9.81 m/s^2, not 98.

If you are not sure do a test like the one above...

On an other matter:

You can pull your arm down using a contraint for example a pin or spring, whatever you like, just animate the anchor point, I did that, but the ammo needs to be dragged in the slide though and that took a bit too much work.

The Ball is connected on the wire using a pin constraint, of which the on/off attribute is animated, so the constraint will brake after release…

Hope this is helpfull…

Thank you for the comments


Wow that looks great. Your almost done and I can’t even keep the pieces from going through each other… :banghead:

Luckily I have a month to figure it out.

Can’t wait to see the full thing.


lol, ya, after seeing that first maya test, i quit! :stuck_out_tongue:

but I was gonna ask, so can we also use expressions? is that fair?


I think the challenge is not about making a completely driven dynamics challenge…I think using an expression and a key for triggering a dynamic even is necessary, since a trebuchet is operated by humans in real life, there HAS to be human intervention in the animation, I only use a key to unlock the rock, and that’s about it I think, the pulley that’s rolling across the rope is also keyed, but the main things, the throwing of the rock, swinging of the arm, the weights, that’s all dynamic… I think I’m doing it by the rules :slight_smile:

Thanks for the comments.


hehe, i wasnt asking about you! :stuck_out_tongue:
I was just asking is it ok to mix expressions with Dynamics in LW?

your entry looks great! like I said, dont know if I even want to try this in LW!


i feel stupid asking this question, but the rope that is around your beams, how did u do it, I know its a nurbs curve and an extrude, but if i make the beam live the points are right etc, any clues.


What do you mean by beams? Most ropes are just cubes with pin constraints…, the ones to the pully are dynamic curves


sorry, i know how to make the rope dynamic, just not get it to wrap so neatly around the frame of the catapult. Like where it goes from the pegs to the frame and wraps around a few times.

If the frame is square it wraps nicely round it, making the surface live doesn’t work.


It’s modeled, not dynamic. That’s just detailing


yes i know, i want to know how u get it to wrap round the beam like that


Well… Quite some ways to easily do this. Model a loop either using smooth, a hp torus or an extrusion along a curve… take the torus: take a quartre of it, delete the other faces, fill hole on the remaining, extrude the new faces and duplicate the corner so you get a complete loop… Placing it shouldnt be hard, place the pivot point on an edge of the beam once the first loop is done, then duplicate and curve drag over that edge… I don’t know if you were looking for something like this… It’s pretty basic modeling though…