Offsets

I've been having an interesting thing happen on about 25% of the rigs I've been working on, on the right arm only. I have since figured it out, but I was wondering if anyone had any feedback on this.

I would set up the triple arm in either one of two ways - either using a blendColors node to average the rotations between IK and FK, or just orient constraining each and using set driven keys. The setup itself didn't matter. Upon getting all of the controls for the arm set, I would go to test out the blend. On the right arm, if the wrist wasn't rotated in either FK or IK, it would blend fine. However, if any rotation was there at all, it would flip halfway through the blend.

First, I thought I had messed up somewhere, but then this was happening on more than one rig, and I couldn't figure out why. Everything was frozen, everything was zeroed, all history had been deleted before applying controllers (and after building them). Interesting. I also noticed that even just translating the IK wrist would cause the wrist to go to -357ish, which made no sense to me either.

Then I saw the offset of the orient constraints were at either 180 or -180, most often on the Z or X axis. Odd - the there was nothing unusual about the trash groups or the controls themselves. So I undid the constraint, then added a -180 rotation to the trash group, and re constrained it. Bingo, no flip, no crazy IK wrist rotations. Then I tried adding the rotation (for both IK and FK wrist controllers), and re-freezing transformations. No flip.

The fact that the rotations are on the trash group means this doesn't affect the actual controller at all, but what I'm wondering is why Maya behaves this way - all the controllers were zeroed, frozen, and had all history deleted. All of the skeletons had correct joint orientations, and this only happened a few times, on various (most bipedal) rigs.

Then I thought maybe it was something in the way my joints were oriented. So redid the rig a few times with a few different joint orientations, and the same thing happened. Hmmm.

Does Maya have something to do with this? Is there something somewhere that affects things that are rigged in the 2nd and 3rd quadrant? It's not some huge deal that slows things down, but why should I have to rotate my trash groups 180 degrees and then freeze transforms to get rotations to blend? I notice sometimes I get interesting offsets on the right foot as well, but never to the point where it has caused the rig to flip.

Just something interesting I've come across. Rotations are quite complex, this I know, (entanglement theory - gahhh) but this just seems odd to me.