I already spoke to some teams on the German Open about this. After having big problems with the walking on the artificial grass, I searched for a solution how we can manage it to get our Darwins to walk in China. Our idea was to use force sensors and a different bottom side for the feet. Fortunatly, I discovered a master thesis, in which exactly such a foot was developed.
You can find it here: http://iris.lib.neu.edu/elec_comp_theses/135/
I established contact to the author and he send me the files for the parts. We then redesigned the board to make it easier to produce and to use TTL or RS-485 (half and full duplex).
I just asked the author if it is ok to upload the files (exspecially his CAD files) to github. I have no response yet, but I'm quiet positive, that he will allow it.
I will provide the link to the files here, as soon they are availible.