You can see that this project uses the make controller as well as an erector set. I used a HiTec 645MG servo for the agitation.
I didn't have anything to etch at the moment, so the video shows the tub with Mountain Dew in it instead. Maybe that would be good for etching designs in teeth...
As you can see, the servo oscillates above and below the horizontal. This ensures that the acid flows both ways.
I made a circuit board for a device we're calling FreePoint. This is the prototype design that's made to plug in as an arduino shield. The final version will be standalone.