FXWars! Catapult! (Trebuchet) : Westiemad


Looks good! The wooden boards are awesome.


i’m still endevouring to make it as dynamic as possible, it now rolls and moves like a real one (sort of :wink: ) and I playing with the release mechanism, so its dynamic also, going for the sack on a piece of rope, i fear I might have bitten off more than I can chew, although I am like every other typical male, who likes cars, and blowing stuff up.


That’s a nice model man! I love the wooden planks and the projectile just looks great! How about throwing a cage with a man inside? Aparently that was a popular thing to do… :slight_smile:


Thanks echo and flipped :slight_smile: .

At the moment I’m having problems getting the cloth looking sack to work, its very twitchy, and the normals are either one way or the other so it won’t collide, or it won’t grab the ball. Any clues would be handy.

Here is a shot of it wheeling.



Looks pretty good, but the wheels don’t rotate quite right. The front left one slides backwards at the start, for instance. And looking around the forum, it seems that getting the rolling to work is problematic for more than just you.


yeah i think it might tilt the frame slightly, i’ll have to have a look, i tried a few values.


Could you post a shot of the rig? Maybe just the constraints visible, or explain how it’s set up or whatever you want. What kind of constraints are holding the whole thing together and such.

Not just to satisfy my curiosity :), I was thinking someone here could maybe come up with a solution for those wheels once the details are known.



The Rig:
The major parts are all grouped together, so u have each wheel, the frame and the arm all in seperate groups. These are then all made in active rigid bodies. Hinge constaints are then made between the arm and the frame, then each wheel and the frame. The hinges can then be moved into position (of where u want it to pivot). I had a problem with whated out hinge constraints, so i created pins, then moved them into position, changed them to directionalhinge, and rotated them, and then changed those to hinge. You can just create hinge tho. All parts have gravity. I have changed the collision layers for the objects. Basically, if you have a number of objects and they are all on different collision layers, they will never hit each other. This makes it easier on the solver to deal with everything. The frame is on layer 0, arm is on layer 1, and the wheels on layer 2. I have used stand ins for the wheels. A stand in is exactly that, it stands in to the object, but is perfect in tesselation, so the wheels are spheres. To make the arm swing I have used a spring constraint. One end is on the arm, (which has its centre of mass out towards the weights), and the other end is parented to the frame (not constrained to it, eg i didn’t select the arm and the frame and make a hinge, as this causes the 2 to jump together). Its parented to the frame so that as the catapult moves, the arm can still return to the centre of the swing, and not try and go back to its original position somewhere in the distance.

Things to check> normals, bit me again today, mass, things act very differently on the mass attribute, collision layers.

I’m having probs with the sack, still its all good fun, i don’t think this is gonna be as impressive as Derbys tho (by a long way).


i made my catapult completely dynamic, it releases the stone exactly like one would in the real world, and it plated back in the viewport. The downside was that after much tweaking, I couldn’t get the stone to fly more than 50ft. So I have taken that completely dynamic idea away, and have stuck to a rope and a large fireball. Not as complete as Derby’s, but hey ho.


mental note large fluid containers take far to long to render, although the effects look nice. 191 640*480 frames took a night to render, way to slow for me. must finish destory and cache all.


I’m not dead. Or have i finished, I have to finish writing a script and then rendering it out (after baking it), here is a render of the catapult, not in its final surroundings mind, but i hope its dynamic enough for u, no keyframes at all.

To do:
Landscape - model the ground, and maybe a tree (only 1 tho, jk)
Rigid body expression - clever bit to make it play in the viewport
Bake simulations - make everything predictable
Render - yes you will have to perfom a crappy lighting job on it all, and not make everyone sick with your camera cuts.


www.members.lycos.co.uk/westiemad/catapult.avi (1.36mb)


yay the coding is complete, after spending the morning trying debug something. Hopefully u guys will give me some feedback on the animation on the above post, that fireball will smash into the tower on the first or second page. Can get on with that bit now.


Hey Westie atlast we got to see your fireball it looks really good. The particles may be to big and to few, when its sitting still its buring the frame to much (maybe lowering the wind) and it looks too systematic. Ofcourse i can understand that adding more particles could make the rendering time unbearable.

Have fun


many thanks squire, I shall make the changes, I’m sure if i ramp the rate up a few times it won’t make too much difference.

Thanks for the feedback.


Good job so far! Could you please explain how you did the ropes?


Looks awesome :slight_smile: although, maybe after it rolls forward,and goes back, make the front ropes go taught and have a slight bit of roll the other direction agtain, just to show this is an incredible force.



Make a cylinder and scale it out.

Increase the number of divisions along its length (i think mine are 10)

Select all the points at each division and make a cluster (you’ll end up with 10 clusters i think)

next create a poly cube (i scaled my cubes to 0.5 in all axis)

point snap the cube to a cluster, then duplicate the cube and point snap it to the next one and so on, until you have a cube at the position of each cluster.

freeze transform all the cube values

select the cubes and make them active rigid bodies

with the still selected add them to gravity

press play to check that the all fall, then rewind

create a pin constraint between all the cubes, first and second, second and thrid, thrid and fourth etc.

press play and they will all fall to earth connected

you can then pin or spring constrain one of the end cubes to a passive rigid body so it doesn’t fall forever.

Thanks for the feedback guys, I will try and get it all sorted. Much appriciated


damn i forgot to mention. once the cubes all fall how you want, point constain the coresponding cluster to its cube this way it will move the cylinder, don’t orient constrain it tho as the cubes will spin.


hey Westie

tx for the info on the ropes…
im begining to work my dynamics, and was craking my head on that :slight_smile:
cool work M8


glad i could help you out m8, any questions just post them.