Proof of concept.
I had an idea yesterday and just had to try it out
And, I made a youtube video.
Now, it's already been said that the action shown isn't enough to actually clean the brass. I know; I had it turned down just far enough to keep moving the brass around. As said, what's in the video is 5v p-p sine wave at 50hz; I can crank it up to around 11 or 12v p-p before I run out of power at the 12v supply (amp gets cranky, clip protection kicks in and it quits), and I've also got a working range from 0.1hz to somewhere around 2Mhz, though that's pointless :)
For best results, I run around 6-7 volts and manipulate the frequency till there's a resonance event... at that point I've got to watch for a bit to make sure the can doesn't get bounced off the speaker.
I titled this post proof of concept.. that's what it is. Speakers are fragile. As it's set up I could probably run for a few weeks before I burnt a cone out. What I *can* do though, is take the idea and custom make an oscillator and an amplifier that'll push a heavier coil with a steel "striker" bolted to the bottom of a plastic tub... essentially a linear motor. This will probably happen after I make a motor-driven tumbler though, 'cause I already know the issues involved with those.
Possibilities? Three coils per tub could allow me to phase the frequencies for a stirring action. That the action runs off an oscillator/amp set means that not only is it power adjustable, it's frequency adjustable... one could tune it to the resonance of the active mass for wahtever load you've got and use a lot less power for a lot more motion. And if you get really jiggy, run it empty as a big ole' tranducer and get some good bass for your Skynard :D
A fixed freq unit could even just be a coil plugged straight to the mains with a traic for power control... or maybe not even that much. That's be pretty powerful though, I'd hate to run it for a couple hours and find all my brass beaten flat...