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.
Well done, YoungRichard- I'll have to pluck up the bandwidth to watch the video (dial-up) , but I had a similar moment of clarity after I diss-assembled an otherwise dead VCR.(That's Video Cassette Recorder,to the technically advanced). The mechanism which propelled the tape in and out of the machine has a nice little 12v motor and all the gearing to give a lovely gentle to-and fro motion to a dish or tank.
I think I will hook it out and see what happens..