[mman1506]

The problem with the beaglebone is it does not have a Real time operating system. This means that there is a delay when inputting data and things don't always work in real time. This becomes an issue for safety as proccesing can become delayed as you can not expect it to processe an input in a certain time frame.
If you're looking for a cheap and simple set-up I would try the robot open http://www.team221.com/robotopen/