3dsmax Spline IK issues

StJoris

Hi all,

I'm trying to animate a cable chain using Spline IK but running into some issues.



as you can tell from the picture, it's slipping/popping past the control spline



I have it set up so that it links rigidly to a bone chain, pretty straightforward.



The problems become less if it's closer to the end, which leads me to believe the Spline IK makes it a little bit springy instead of rigid. I've searched all the options in hierarchy IK and motion, for all the parts but found no way to control the springiness or otherwise influence this behaviour.




Which leads to some ugly stuff happening too when animating

Any idea how to mitigate this effect? My guess is that's just a edge-case that Spline IK can't handle. So if you have pointers for alternatives, maybe constraining all the bones themselves to a path (tried that, all the bones just end up in the same spot), yeah any pointers are welcome.

monster

I can't repro this problem, but Spline IK almost always starts flipping on me so I tend to avoid it.

Your problem (when bones don't travel on the spline) usually stem from needing to reset xforms on the spline.

StJoris

thanks monster, should have thought about that one, usually when something is inexplicably strange in 3dsmax it's xforms.

I did have transforms on the spline and reset it and redid the IK, but no change really. Also tried a new spline, without transforms.




as you can see, it does follow ok, except for when there are lot of bones on either side of the bend. I also tried resizing the whole scene, maybe anything is linked to the size. it does have ALOT of bones, maybe that throws issues.

Sounds like I better manually recreate the intended spline IK behaviour with wiring and constraining.

StJoris

I'm truly at a loss here, that manual recreation of the behaviour is harder than I thought. I tried the path constraint route, where you have each element at an offset percentage along path, but even with constant velocity ticked, it starts to deviate quite fast. It needs two constraints, stay on the path, and stay a fixed distance away from the next link. A position constraint added to it, doesn't really work out, since it will only weigh the two not combine.

An expression or scripted position controller maybe could do the trick, but no good clue where to start.

I'm fairly proficient in grasshopper, a visual programming environment for rhino3d, maybe I'll animate it there and try somehow to export that back to 3dsmax, not really elegant, should not be this hard..

StJoris

For reference, I found a workaround and the probable cause. When looking at the target of the IK, you can see it targets not the parent bone, which is what it says it does, but some amount of bones back up the chain. Found out this limit goes to 30 bones. Workaround consists of just chaining a whole bunch of IK's together.