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View Full Version : Metal chains breaking effect - advice welcome



markjores
04-13-2005, 09:04 AM
Hi there

I have a visual shot to work on that involves metal chains that bind a humanoid that are being pulled taught - with some shaking with the effort, the main link bending and separating before the chain links snap and break in at least one location (in slow motion) and then whats left of the chain parts fly apart & away from the figure. Has to be a very Matrix / superman type thing here, though I can probably use 2 shots (link bending and chain snapping) to get the scene across

I'm not familiar enough with dynamics so I was thinking of creating a 2 chains of metal links that are driven by bones and an Ik chain with master nulls at the ends and then a separate metal "master link" that I position between them that can morph into the bent shape. I would hand animate the nulls at the ends of the other two chains so that it looks like they are all joined together & pulling apart.

For the second shot where the chain actually breaks I was thinking of rigging sections of IK chain into the right shapes with polygon chain links between them that use the C4 detonate plugin to shatter them - seems to produce a nice broken effect from the demo.

I would then use a master null for each segment of chain so I could key frame the whipping away motion as they are released and then jiggle the end nulls so that the remaining sections "whip around " as they fly.

Well that's my plan.

Anyone got a better idea of how to do it?

I'm still working with lw 7.5d but I've got an upgrade to 8 sitting in its box next to my desk if that will help?

markjores
01-15-2006, 08:30 AM
Well the response has been underwhelming, but now I have to look at this again

I need to look at getting closeup shots of the chains breaking which will mean making sure the cloth of the figures suit doesn't intersect with the chain link objects.

I guess that I'll have to set up portions of the characters suit with cloth dynamics that deform with the ik chain objects? The chains wont be dynamically driven - I was intending to keyframe their motions.

Does this sound like a real heavy undertaking here ? - I havent used the dynamics much before. I'll post some tests as I work through it.

Wonderpup
01-16-2006, 02:52 PM
Hi markjores,

It might be worth looking at the linking options in dynamics that allow you to apply the dynamics to two point polychains that are hard linked to drive the higher res objects.

Like you I have almost no experience with dynamics but I did see a lightwave 8 demo where Proton set up a hardlink in about a minute- so it may not be that painfull and could give you better results quicker than keyframing.

Especialy if you can split the 'breaking' shot out from the 'flying away' shot, and only use dynamics for the the flyaway bits.

byte_fx
01-17-2006, 04:01 AM
Don't know if it'll work but for the closeup you could try using morpmixer to animate the link snapping and opening up.

If dynamics reads the morph then that should keep the cloth from intersecting with the chain link as it opens.

Haven't tried it but I think the dynamics will calculate based on the morph - not the original.

byte_fx

markjores
03-01-2006, 03:33 PM
Well thanks for the suggestions but I've still managed to come unstuck.

I opted to avoid the collision detection method because I wanted to control the chains whipping towards you as the figure breaks free but also avoid them obviously penetrating the figure. So I've gone down the IK & goal route.

I've tried to keep it simple and created chains controlled with two bone setups and two goal nulls, with the middle nulll being the goal of the first chain and the base of the second. (see Pic). Each chain also has a master null with all the other nulls as children to help with easy placing without distorting.

This seemed to be the best way of placing them without having to pose every single bone (about 30 per 2 lengths of chain)

I've got the man squirming and snapping his arms free realisticaly & I thought I could parent the chains to his root and make minor amends to the nulls to prevent the chains going through the body.

Unfortunately the ik makes the chains writhe rather oddly. I've tried to kill off all the extra correction keyframes for the nulls & then go back to the first posed frame and parent the master nulls to one of the spine bones but the chains just start to fly around after the 1st posed frame. I have no idea why they are doing this since I got rid of all their keyframes after frame 1.

Anyone got any suggestions how I can salvage this. I need to pull this off somehow. I was even thinking if I can get the chains to stay on the body and not writhe then I could render them out separately from the man and then comp it back on top in After effects - no need to worry about chains slipping under the surface then.

This is a real short shot (2- 3 secs) & I cant afford to spend much more time on it. That said its a critical shot & people are breathing down my neck.

Any suggestions gratefully received