I'm planning on creating a simple robot like "Gwunderer" By. NilsB I have already created the mechanism. When you go in front of it, the servo goes to 180 (up) and when you move farther than 50cm it goes back to 90 (center). This uses an Arduino. I used an Arduino Mega 1280.
I uploaded a plan and photo of what it looks like.
It seems as though I cannot find my camera...
BUT here is the plan: