Hi, I'm struggling to get my head around how to use rbdhingeconstraint in a dopnet

I have an animated object and I'd like to attach another object to that so that it sways about dynamically.
I can't seem to attach the rbdhingeconstraint goals to any animated geo. They stay fixed a world space location, even if I set a goal object?

What am I missing?

The hinge (animated moves off but the goal position remains at 0,0,0 (world space)

Thanks