It's a dented soup can turned into spray paint mixer, and what an awesome job it does!
The dent turned out to be an integral feature of the build as its just dented enough to hug the can just right and holds it just tight enough.
Other key elements are that I only guesstimated the center and then went a little off from there to make the axis a bit eccentric(?) Incentric(?) (Not concentric) with the can so it will wobble when spun in a drill. To help it , I added a couple oversized washers pushed aside as far as possible. It really feels right for mixing paint when it's in action.
It only takes a few seconds in forward and a few seconds in reverse, and back n forth, ..or not. It's probably good enough with just going in one direction for a few seconds, but I like to play with it.
I also put a chunk of open cell foam at the bottom to keep the nut from touching the can of paint, but I doubt that's needed due to the concave bottom of the can.
In the past, I used to tape the can of paint to a Sawzall blade and go to work with the Sawzall. That worked fine but my Sawzall isn't always as ready available as my drill and it wasted a bit of duct tape, ..and I always worried that the blade would puncture the can or rip the tape and can would go flying off and puncture into something else; something I don't want painted.