Tiny robots test my mettle and patience.

I am puzzled that we (the scientific and technological 'we' that were supposed to deliver us flying cars and nuclear trifocals by the y2k) have not managed the feat of building a robot that intakes grass, water, and oxygen to produce milk, urine, feces, and CO2. How complex can a cow (or any other mammal) be? I have a puppy. And so far, all I can see is a little machine that breathes, drinks, shits, pees, and eats tasty Nutromax. Oh, digs. It digs as a side-effect. It especially likes to trench through ant hills; a most dangerous undertaking when spring returns. For this little machine I payed $50.