All the information I can find on the internet about IK involves a single chain which starts at a root and ends at the end effector. However, I’m trying to figure out how to solve for when theres multiple roots that join into an end effector.
An example of this would be the R6 character. Imagine 3 of its 4 limbs attached to anchored parts with Motor6Ds. These are the three roots which join together on the Torso. I then want to solve for the angles of the Motor6D for the 4th (free) limb to reach a point.
I cannot find any information on this online and I really don’t know what I would search either.
Example diagram:
(Yellow blocks are anchored, red circles are the joints, green circle is the end tip of the end of the chain)
(Any information would help, I pretty much looked through the first few pages on google and the only thing I could find was information about a single chain)
(I suspect what im calling this is very innacurate but tbh I genuinely dont even know what its supposed to be called)
You can actually get FABRIK to solve this, using a similar method to how multiple end effectors are handled in the original paper. Your case is different, in that you don’t have a single root with multiple end-effectors competing for influence over “sub bases”, but you can employ a similar methodology of solving the chains from each root to the end effector separately, and then resolving all of the constraints, and iterating until it converges.
What you have with the R6 so constrained is effectively a 3-leg parallel, closed-loop system with one additional free link; kind of like a delta platform plus an extra link from the platform to the end effector. Closed loop systems of this nature are normally solved differently from open chains, but iterative systems like FABRIK can usually handle provided that you don’t let them get into cycles where solving leg A unsolves leg B, etc… which is generally avoidable by taking small steps and enforcing all of the constraints on each step.
FWIW, the physics solver could also solve this, simply by ragdolling the avatar and pulling the free hand towards the target with a spring. XD
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