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Dynamic IK advice please.

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I've made a simple joint chain with an IK tag that I want to be able to control at either end with control nulls. 

It works fine, until I make the IK tag dynamic, then the end joint falls away from it's Joint Goal, even though I have enabled "Keep Goal" and "Contstrain Goal".


I'm trying to copy the same functionality you get with spline dynamics, where a spline can attached to an object at either end, and as you move the each controller the spline with dynamics moves accordingly, but the ends vertices stay attached to the controllers.


Is the problem a priority order issue? Or is the joint IK just not meant to work in this fashion?


The scene file is attached. Try enabling/disabling the Dynamics box and you see the end joint slip away from the Goal Null.

Dynamic Joint Chain.c4d

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  • @digivisions, 

    Thanks for the reply. I was beginning to suspect this. Tried a few workarounds like adding a 2nd goal, and extra PSR constraints, but nothing has worked so far. 


    Thanks again.

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  • For anyone who is interested, I've attached a scene file that seems to fix the problem I had with the joint goal slipping away from from the control null, and the problem of how to control a  joint chain from either end using Joints and a Spline IK tag.


    Selecting the Spline IK tag, then in the Attributes Manager,  setting Type to "Equal" rather than "Fit" seems to keep the final joint in the chain attached to it's target.

    I used Clamp constraints to prevent the control nulls from travelling past a given distance for one another, to avoid the stretching you get with dynamic spines.


    Hit play on the timeline, then move the control nulls around to see the effect. 


    Hope this helps someone with a similar problem in the future.

    Spine IK.zip

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