Make the Leg Gantry
Cut out a T-shaped piece of cardboard like the one pictured.
Crease cardboard in two places so it can bend around cup.
Cut two slits down the side.
Fold into shape and use hot glue to attach a cardboard brace to hold in place.
Mount the DC Motor
Position DC motor inside cup and mark placement of holes with a marker.
Poke holes in cup using tweezers (or something else pointy).
Cut out a thin rectangle of cardboard and poke two holes, matching the spacing of the two holes in the cup.
Attach DC motor to inside and bar to outside of cup using two screws or a twist-tie.
Stick the eccentric hub on motor.
If the gantry feels sticky, now is the time to reposition the brace or widen the slits so that it can move up and down freely.
Cut the Cable Holes
Use a hobby knife to cut a hole in the top of the cup for the servo cable.
Add a cutout for the DC jack at the rim of the cup.
This cutout will allow you to easily plug/unplug your power cable.
Add a Face
Two jagged-cut pieces of cardstock glued to a popsicle stick make a scary looking face.
Use tape to affix servo motor arm to base of popsicle stick.
Hot glue or glue stick work well to attach googly eyes.
A short piece from a straw also works to attach eyes to the servo motor arm.