Saw this type of double pendulum on IMGUR or somewhere, recreated the idea here.

Giving the bar a spin or holding the bar to the side and giving the ring a spin seem to be the common ways to start.

Uses two 608 bearings but you can add four more to use a weights to change the action, other wise use the plugs printed somewhere hollow to solid, in whatever color is of interest.

(Had good luck finding old roler blades for cheap at the thrift store - each pair usually has sixteen 608 bearings in them)

Might not hurt to use free running bearings or use something to thin out the grease if they are stiffer. WD40, brake/throttle cleaner, or some other thinner or degreaser. Might not be required, but if it is not running well, that might be the reason.

Command strips, double sided tape, etc for the wall mount and probably some kinda clamp for the desk mount.

Used an infill modifier to make the bottom of the bar 100% infill for the weight

The idea for the center pin in the bearings if they are loose is to use a piece of raw filament, shaved into a bit of a wedge, held with pliers and stuck a few mm into the center then push the bearing on…or glue works too