I finally gave it some decent feet. Any hardcore robotics enthusiast will instantly recognize one of these exotic hinged-ankle-mounted lightweight metal footpads as the same components regularly found on planetary surface landers to keep them from sinking into the Martian dust or Europan ice crystals. I just needed them to keep from sinking into the carpet. NASA wanted four thousand bucks apiece for 'em! Mine weren't even clean when they arrived; had something that looked like dried tomato sauce on them.
Alas, the incredibly expensive NASA feet had serious problems: The edges would occasionally hang up in thick carpet and the walker would get bogged down and eventually collapse in utter confusion. I had to come up with a better design for handling carpet.
What I needed was a smooth rounded base that pile carpet couldn't grab as well as a bottom that would rest flat on the floor and wouldn't slide on smooth surfaces like linoleum or hardwood. The bottom third of an Albertson's gourmet cat food can with some throw-rug anti-slip mat attached was the result. They appear to work pretty well - their edges don't grab the carpet.
The walker does have problems with carpet when using the same gaits that work on smooth hard surfaces, but this doesn't seem to be a problem with the feet. Rather, higher steps before moving a foot appear to be required because of the tendency for the two neighboring weight-bearing feet to sink into the carpet a little, causing some weight to remain on the moving foot for a slightly greater amount of time during a walking cycle. Exacerbating the problem, carpet also has a higher K value, or ability to brake or grab a foot when a foot is dragging. With the little 42 oz/in servos, I can get away with dragging the feet a little on linoleum, but not on carpet.
