You'll need the following parts:
1) 2 3mm diameter, 1mm thick neodymium magnets.
2) 1 "6VDC 45 RPM Pinky Finger Sized Gear Motor 1" Long x 15/32" x 3/8"" from either amazon.com or directly from http://sciplus.com/p/MICROMOTOR_47952. There are other sources but I've not tried them.
3) Small rubber band. I used one that came of a bunch of green onions found at the local market.
4) 6 VDC power supply.
Study "Assembly.skp" for the assembly.
Press one of the magnets on the bottom side of "Duck 3D.stl". Cyanoacrylate can be used to hold it in place. I printed "Duck 3D.stl" in white, then used permanent ink markers to color the beak and eyes.
Place the other magnet in the container on "Plunger.stl", and seal with a small wad of painters tape, masking tape, etc. The magnet should move freely in the container so that it will self orient when it comes close to the magnet on the bottom of "Duck 3D.stl".
After "Plunger.stl" is inserted into "Gear Main.stl", place the rubber band through the hole in "Plunger.stl", then through and around the two remaining towers on "Gear Main.stl". Once completed, "Plunger.stl" should slide smoothly. If not, remove it, sand it, and repeat until smooth.