Physics Legs on Skeletal Mesh?

I have a character blueprint which flies around in-game, and I would like the legs be simulated so they just dangle around, but the rest of the character (root, arms, head) will be controlled by the blueprint. I know I need to use physics constraints, but I can’t seem to get it to work. I vaguely remember seeing a video tutorial on something like this a while back. Can anyone give me some tips? Thanks!