Step 1: Parts
K'nex (can be substituted with any other structure-building thing)
Wire (Hookup, and stranded wire)
Cardboard, Plastic, or similar
Aluminum Foil (Conductive ink of some kind is a preferable substitute. I didn't have any.)
Wood or something to form a base
Step 2: Foil
If you are using conductive ink, skip this step.
First, trace a circle in the foil.
Next, cut it out (carefully as foil has a tendency to tear).
You will need to cut two out.
Then, cut out a hole in the center of each circle.
Cut out two smaller ones to fit inside the larger ring (leave some room between the smaller one and the ring).
Step 3: Disc 1
Cut out a circular piece of cardboard (or plastic, or whatever you have).
Aluminum Foil-Mount the foil to the disc by poking wire through each side and twisting it to secure the foil.
Conductive Ink-If you are using conductive ink, just make a thick ring around the edge of each side, maybe a centimeter thick depending on the size of your disc. Make a thick circle in the center as well. Then put a piece of wire through one side and out the other. Secure it there to make the ring on each side one conductor.