I did just recently come across someone that has been driving Dynamixel directly from a PyBoard.
He did write his driver some time ago when the bioloid was the current system before Engineering kit came out with the new servos. This was also before Robotis released their python SDK so his driver has both the low level fuctions for sending packets via half duplex but also his own SDK.
At some stage I would like take just his low level fuctions to operate the half duplex UART then add the official Robotis python SDK that way code will portable between PyBoard, PC and RPi.
see his driver here bioloid3/stm_uart_port.py at master · dhylands/bioloid3 · GitHub