Hello,
If I could get that Motor Bridge Cape to work, like other people who have tried and succeeded, you can make some items work. What kernel are you using, e.g. 4.9.x and what image?
Seth
P.S. In Stretch for our Debian Distro, you could use config-pin Px.xx uart to set up uart functionality. config-pin can be found around the realm of the BBB and variants. Oh and sir, try the bbb.io/latest-images for the current, most-rated images available for the BBB and variants (BBG and BBGW).