Using BBB for robotics

I plan to get a BBB for a robotic power shovel/dozer. I want to use the BBB to run OpenCV, but I am really hoping to communicate with an AVR chip to do all of the actual servo/motor controls. I’m worried about the USB ports though, I’m not sure one would be enough. I want to also have a camera mounted on the board for running OpenCV (which takes up the USB port). Basically the the beaglebone will just do all sensor operations and send instructions to the AVR chip to move the robot. Can I do this board to board communication through a USART, or is it usually done in USB (which is already taken by the camera)?