UPDATE: The Automata / Automaton Blog is pleased to be the exclusive source for free plans for making your own ramp walking robot. Enjoy!
I've seen ramp walking toys of similar design before, but the robot figure created by Roberto LouMa seems particularly appropriate!
Here is a frightfully/delightfully technical look at the principles behind such toys: An Uncontrolled Walking Toy That Cannot Stand Still. Here is a more easily digestible summary of the ramp-walking tinker toy (a product of Cornell University).
Despite the academic research and how common such toys are, it is surprisingly hard to find plans that show how to make a ramp walker. I have heard that there are detailed plans for a lathe-turned penguin ramp walking toy in the book 52 Weekend Woodworking Projects by John A. Nelson. I don't have the book, though, so I am not certain of this. Does anyone out there know if there are plans for a ramp walker in this (or some other) book?