for Y-down (from TD Matt):
COG: zxy
Hip: zxy
leg joints: yzx
shoulder/clav: yxz
upper arm: zyx (or yzx)
lower arm: zyx (or yzx)
wrist: yzx
spine base: zxy
mid spine: yzx
chest: zxy
neck: yxz
head: yxz
for X-down
COG: zxyHip: zxy
leg joints: xzy
shoulder/clav: xyz
upper arm: zxy
lower arm: zxy
wrist: xyz (or yzx?)
spine base: zxy
mid spine: xzy
chest: zxy
neck: yxz
head: yxz