Right now I am working on my BJD Arisu's hips. Since I have not drawn and posted a study on them on my blog yet, here it is.
You can see the numbers I put trying to figure out what level of flexibility I would like her to have. I am also trying to decide if I will add a rotation near the hip joint as well. The stops needed on the legs to keep it from doing unnatural motion seems straight forward. One unsightly thing is the slot you will likely see on the ball joint of the upper leg.
I try to label things correctly in my joint studies, but there is a good chance I will have labeled things incorrectly. So please forgive me if I have. I am an artist not a biologist, but I try to be as accurate as possible.
Range of Motion
Zen & The Art Of Articulating Dolls By Using Balljoints
Joint Range of Motion