Andres de Mingo, author of this realistic shot, kindly explains us how he did the dynamics effects using nCloth combined with Pulldownit plugin inside Maya.
This time I proposed myself to reproduce a believable crane accident all inside Maya, the final shot involves 3 different effects, simulating the crane cable in motion, the tearing of the ropes attaching the pipes and the final falling and breaking of the pallet , all along with sound efects to increase realism.
Animating the Crane Cable
The motion of the crane cable is very simple, but I wanted the cable to show some tension and curvature when moving because of this I decided to use nCloth for animating it. In addition the hook has to follow the motion of the cable but with its own independent swinging so I created a nCloth shape for it as well, however the hook model was a little complex, including a support with nuts and bolts, so I made a more simple shape to use it in simulation. Finally, the pallet and pipes has to follow also the animation of the cable and hook but again with its own relative motion, I included them in nCloth as a single simple shape wrapping the original objects.
In order to link the different parts together I created several Point to Surface nConstraints attaching the end vertexes of each object to the previous object in the chain. When computing, the crane transferred its motion to the nCloth cable and so on because of the links between them.
Tearing the Pallet Ropes
For tearing the ropes I made a simple trick, I removed some small polys of the original ropes model in the areas where I wanted them to tear and move away, then I made each separated part an independent node in Maya and create nCloth shapes for them. Finally I assigned nConstraints joining the ends of each piece of rope to make them moving together, this time I used Component to Component constraints to select carefully the attaching vertexes. I also set the pallet proxy object and the containers nearby as passive colliders in Nucleus so they can collide with the falling ropes. At this point I had only to make the constraints attaching the ropes to disable at the frame I wanted, I got it just by animating this parameter of the nCloth shapes. Everything worked nicely except the ropes were trembling too much when around the pallet, I increased its rigidity to remove the problem but this caused the ropes not bending after tearing and colliding with other objects so I had to animate also rigidity to reduce it a lot after separating the ropes in dynamics.
Simulating the Pipes
For simulating the pipes falling I used Pulldownit, contrary to nCloth this Maya plugin acquires automatically the velocity from animated objects without the need of any additional setup, besides the pallet breaks when colliding so PDI was perfect for the task.
At this point I had cached all nCloth simulations with Alembic, my original idea was to make the pipes child’s of the Alembic cable so they will acquire its velocity before falling, sadly it didn’t work; the reason seems to be PDI only acquire velocity from keyframed objects but Alembic nodes are made of vertexes animated. I solved the issue by creating a duplicated version of the pipes and making they follow the cable motion using a wrap deform in Maya, then I had to keyframe the original pipes group to match the motion of the wrapped version, I had to do this only for the last swing of the cable so it wasn’t difficult. Afterwards setting all pipes as PDI rigid bodies and making them activate at frame did the work.
I did the same trick for the pallet but this time creating a PDI fracture body and setting it to activate at the desired frame. Finally animating visibility for each version of the pallet, the wrapped and the simulated one, I got the complete smooth effect.
Render and sound effects
For rendering the scene I used Arnold in Maya with just an Skydome light, as being an outdoor scene Arnold was pretty fast and the render looks very realistic, I composed the final shot in Davinci Resolve and adding sound effects there, I must say doing it was fun and easy, Davinci is a great software specially its latest version.
It has been an interesting experience working in this project, specially I learned how to combine different solvers , nCloth and PDI, nCloth worked well, and the fact you can animate its parameters to get different cloth behaviour at different moments of the simulation helps a lot. PDI was easy to use and you can get different outcomes by tweaking parameters almost instantly. It would be great a more direct connection between both solvers to need less steps when combining them in the same effect.