It's an issue when you've built something from many props with many constraints and the only way to show it functionally held together is to lengthen the speed of the clip to give it more time to calculate but then you'd have to shrink it back to the original size later.

I've also found that Render Resolutions directly correspond to physics calculations. 4k output prevented my chain links from holding together but the iPhone Portrait resolution allowed the chains to remain intact. 

***Update: I was able to get close to 30 FPS when not using screen video capture*** 


I've posted this on the feedback tracker https://www.reallusion.com/FeedBackTracker/Issue/Adjustable-Physics-Calculation-Time-for-Sophisticated-Scenes

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That's kind of strange. I mean different outcome with different resolution. I have a similar chain with 20 links and it does render fine in 4K.
Try running a pass in ByFrame mode in view-port and then disable rigid body in Project settings before rendering (rigid animations are getting baked on the fly).
And while there try playing with World Scale.

The longer the chain, and the smaller the chain, the smaller the world scale should be. Average chains seem fine at 5 (default), but longer and smaller chains work a lot better at 2 or 3. My system cannot really handle 1 very well.

Using world scale down to 1 does help and I have been using frame by frame. I've noticed more stability using chain Mass and Dampening and have yet to apply new parameters. Changing viewport to a low resolution resolution does help and it's interesting that when rendering, the by frame calc it does is better than by frame in the viewport.

The thing is, I'm also using soft cloth and that is likely slowing it down as well. Rampa had suggested a good alternative which was to lower the speed of the clip, bake then shrink it back to normal size.

Just for comparison, would you mind sharing your chain physics settings?  currently I have Mass and Dampening both set to 100, in the past I had both of these in the thousands, I might have to go between this. Thanks for your feedback.

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The thing is, I'm also using soft cloth and that is likely slowing it down as well

You may try to bake them separately in 2 passes. Like disable 1 and bake the other and vice versa. Or bake soft cloth and have rigid render live to *save* on performance.
I have posted this project couple of month back: https://forum.reallusion.com/FindPost479774.aspx That chain is large though.

This is exactly why I think Reallusion should add a deeper physics calculator.. who wants to go through tons of files, settings perhaps missing some before export? with deadlines, limited personal time etc it's a bit of night mare for very sophisticated scenes. 

I hope they either add a strict calculator or are upgrading colliders with faster screen space particle colliders. 

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I do not think they can do much tweaking/optimizing performance of an existed engine, as there is a 3-rd party dependency - NVIDIA Physix SDK.
Maybe to roll to a latest versions 4 or 5 with GPU support in addition to CPU.
Not sure if they would go for that in iClone 8, but would have been great for sure.

I think they can by having a script to change screen resolution, maybe ideal world & gravity settings if there is such a thing based on items and settings currently in the scene and or temporarily time stretch out all the clips that have physics and revert back to the original but with the new keyframes. Stretching out the clips and temp screen resolution adjustment just to get a better bake maybe the easiest solution if Reallusion doesn't have any plans to change their physics engine. 

I had a request on the feedback tracker about having support for Vulkan for multi GPU + CPU core, card and shared Vram support between cards since it has a history of being more stable/functional in comparison to DX12. 

Reallusion might be able to tap into PopcornFX's screen based particle colliders or write their own for iClone 8.   I've used Particle colliders in Unity, they are far easier to manage than what we have now and are not as heavy on resources. 

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