Well I finally got back to this… I tore apart Tobs’ Foot rigging tutorial. It is the worst kind! Low volume, soft voice, an accent, and really great information that makes you listen over and over to get the gold nuggets. I downloaded all ten parts and played it locally probably about 50 times. I’d play with bones a bit, watch again, then play some more.
Finally, I loaded my model and top down rebuilt the rig, without the video. I think I nailed it. I do need to build a few more, and I’m sure I will, but I’ve got the basics down I think. I didn’t add the roll controllers he does in the last vids. The main foot target gives decent twist and roll control plus at this point in my career it’s expected that my feet should poke through the floor every now and then.
Here’s the .blend file if anyone cares to critique it. Now I’ve just got to get back to modeling(and rigging) the upper body, then we can blow her up, or set her on fire, or something.
EDIT: I forgot to ask. The hydraulic cylinders at the knee are about as simple as you can get. The top and bottom portions just “track to” each other. But they do weird things. They rotate on axis’ they shouldn’t and when I clear transforms to reset the pose I need to do it twice or the cylinders don’t line up. Any Ideas?
EDIT AGAIN: I did get the answer to my original question. As Norvman said, the joint was done with three bones each aligned with, and constrained to an odd angle. The the main foot bone was constrained to no rotation and the IK percolates up through the three ankle bones which each of the pieces are parented to. While the model does have problems with self intersection, the ankle remains pretty faithful to the angles it was built to bend at.