I've got an old electric can opener somewhere that I thought would make a good base for a tray rocker... it seemed to have a low enough RPM speed and I imagine, decent torque ( hey it opens steel cans) so should be able to lift the end of a tray up and down a bit. My thought was to have an elliptical roller under the tray to lift it up and down, but have never gotten around to trying to make it.