Idea for a Quadraped Robot

While working on General Blackbeard I've started thinking about the design of my next robot. One idea I had was to create a quadraped robot, one that walks more like a cat or dog than like a turtle. Here is a sketch of a design I call AREQ (Autonomous Robot Equivalent of a Quadraped). Each leg would have a medium size sevo for  hip joint and a small servo for the knee and for the ankle for a total of 4 medium servos and 8 small servos for all four legs. I would use the pan and tilt mechanism from Mr. General, but would mount an ultransonic range finder on it. The top surface would be the mounting location for the circuitry. My scale is not accurate in the sketch. I would envision the this to be about 10" long, 6" wide and about 6-8" tall.  

I need advice on what the choice of servos to use ( good and cheap) and also what programming challenges anyone may think I'll have.  So far I'm thinking balance while walking could be  challenge. Are there any examples of similar robots on LMR? I couldn't find one.

 

AREQ_sketch.pdf|x

AREQ_sketch.pdf|x

I must admit that I have

I must admit that I have never built a walking robot. But with only 4 legs I think you need to shift the weight of the robot off the leg that you’re trying to move.
I might very well be wrong, but I can’t see this setup working.