A couple of years ago I was planning on doing a theme based around robots. We only got as far as making a couple of drawing robots, which is basically a vibration robot. You offset a motor with something (we used a screw and a bit of gaffa tape). This makes the motor bounce around a bit. We then attached the motor to a paper cup and attached some textas to the cup. Below is a video of the testing out at home.
As part of the theme I also made up a set of robots as a play set. I bought some blank wooden dolls from Etsy. Then I collected up a few different metallic odds and ends, such as screws, hooks, wire, brooch findings etc. I painted the blank dolls with silver and gold paint. When it was dry I added the metallic odds and ends. A few bits needs some drilling and screwing in while others needed attaching with super glue. I also made some little robotic pets using a metallic polymer clay. Details were added with a black permanent marker and they were finished off with a coat of varnish.