Reverse foot flippage (SC/RP issue)

#1

Hi,

I’ve got a standard IK chain setup for a leg with an RP IK for the main thigh-knee then two single SC IK chains for the ankle and toe. This is connected to a reverse foot setup in a reasonably standard way (parent the effectors to the RV joints etc).

For some reason when I set this up sometimes the RP and SC chains start flipping but the problem is intermittent. I can usually fix it just by rebuilding the offending IK chain but this can be a real pain when I start automating the rigging process because I don’t really know why it’s happening so I don’t know how to begin making a check for it, or just avoiding it.

Has anyone else had this problem and could shed some light on why it’s happening and what I can do to avoid it?

I’m not sure if it’s relevent but this is in a quadrapeds feet, so the foot is sort of long and vertical (walking on its toes) rather than the usual more horizontal setup.

#2

Difficult to say without seeing the file but at a guess I’d say you need to tweak the position of the pole vector for the IK chain. If it’s very close to where the joints bend and the leg is pretty straight then flipping can easily happen as the IK handle crosses over the rotation plane.

Cheers,
Brian

#3

Sorry if I made myself unclear, the problem isn’t with the RP IK chain flipping, it’s with the SC IK chains. For example sometimes I’ll slide the foot control forward and the ankle joint will spin 180 degrees.

The wierd bit is that if I recreate the SC chain and re-parent everything the problem is often solved.

It kinda feels like its the order of the parent constraints or something that causes the problem :frowning:

#4

The best thing right now for you to do to get a reasonable answer, would probably be either post the scene, or if you can’t, put together a proxy one, so that we can see your foot setup and comment on actual things. it might be an error in your hierarchical setup or such.

#5

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