create joints and move to the position like the below picture then do the smooth skin
use expression to adjust the joints and control locator
a. CnLocator translateX, L and R joint Up and Dn rotate outward, the bottom joint also move up
b. CnLocator translateX, Mid joint Up and Dn translate into center
Step 02:use component editor to change the vertex weight in the bottom to 1
Step 03:use component editor to change the vertex weight on the side
from top column to the bottom column
Mid_jointDn Bottom_joint
1 0
0.7 0.3
0.6 0.4
0.5 0.5
0.4 0.6
0.25 0.75
0.1 0.9
Do the adjustments depend on the demand
Step 04:Do the same thing on the vertex on the other side again
Sample:
