The location of the pivots is not critical. The closer to the base, the more counterweight mass is required and the heavier the entire sculpture becomes. Upper part is balanced first. Balancing the middle part includes incorporating the weight of the upper part (rotation of upper part is irrelevant for balancing). Balancing the lower part is done last and includes incorporating the weight of both middle and upper part. Counterweight mass is slighty oversized so sculpture has a tendency to be upright most of the time. Box sections are hollow. Titanium was used to reduce weight. Too much counterweight mass would stop the sculpture swaying in the breeze.
There are a number of considerations to take into account:
A thrust bearing is a type of axial bearing and consists of an upper and lower race, with a cage sandwiched in between, containing small needle or ball bearings. The needle bearings are oriented ‘axially’, like spokes in a bicycle wheel.
Drop a thrust bearing into a one-side hollow pipe. Find a rod that fits inside the thrust bearing. Weld a round washer a few mm from the base of the rod. Insert the rod and washer into the hollow pipe. The round washer will butt up against the thrust washer. The rod will spin very easily.
Place a plain ball bearing at the top in between the rod and pipe to take the slop / sway out by ensuring there is no gap.
Or even better, use a linear bearing at the top:
Or even better, flip the whole thing upside down and have the outer rod spin and the inner rod stationary (to stop rainwater ingress).
This is similar to the previous scenario, except that it is not held in place using gravity. This design makes me think of a garden gate hinge. This setup remains intact when held upside down. Click image to enlarge.
This setup uses an adjustable linear bearing (= has a lengthwise cut) around a metal shaft. This allows it to be compressed into the hole it sits in. Upon closer inspection, it is likely two adjustable linear bearings are used in series. An Allen Key set screw sits in between the two adjustable linear bearings. The tip of the Allen Key set screw most likely sits in a groove of the metal shaft. This will allow the metal shaft to rotate but prevents it from sliding off the linear bearings. The Allen Key requires Locktite to secure it in place.
The metal shaft is likely a threaded rod with one half smoothed in a lathe. The threaded half of the rod screws into a (slightly larger but shorter) threaded cylinder with a hex nut to lock the threads. The hex nut also acts as spacer.
It is a bit confusing as the Allen Key set screw seems to sit on opposite halves in the two pictures. I guess by welding a washer onto one end up the metal rod it also prevents it from sliding off the linear bearing, thus eliminating the need for an Allen Key set screw. If the threaded part of the rod is not threaded at all, we can use an Allen Key set screw to secure it instead. This also allows us to slide on the linear bearing as one of the last steps. It appears there are a number of variations to implement this setup.
Even though linear bearings are intended to move in a linear direction, it appears they can sustain rotational movement as well.