I figure I can use a technic ball joint for the round parts, or a ski pole for the top part but I can't use them together as there's no open axle on top of the ball joint. Is there any kind of sphere that a bar can be put through?
There's downsides to this approach, though:
- The shape of the domes is not entirely round
- The 2x2 bottom dome in light grey colour is quite rare, and therefore relatively expensive in the aftermarket.
The 3x3 ball turret provides an axle on top - in order to provide a stud for supporting a minifig, you may modify a 6587 3L axle with stud, cutting it down to 1L so it fits flush within the top part of the ball turret. I know cutting down parts is frowned upon by purists; and fitting the axle flush may make it hard to get it out.