A few more details of the design might be of interest.  The design is based around 2 micro-controllers; one that provides the user interface and acts as the master unit, and the other manages motor control and position tracking.  They communicate between each other using a proprietary command set over a 2 wire RS485 serial interface.  The baud rate is set at 19.2K and operates using a slow slew rate configuration to help keep communication noise minimized.

By using the 2 wire communications interface, we are able to keep the interconnecting cable at 4 conductors, 2 conductors for data and 2 conductors for power.  A design that required 2 bulky 7 – 8 conductor cable would defeat the purpose of a Portable system.

I also got a few comments regarding the serial interface as to making it wireless at Dayton last year.  We decided against it for a number of reasons, with cost being the biggest.  Adding Xbee or some other wireless interface will add to the unit cost and we are trying to keep the cost as low as possible.  Who knows, we might offer an add-on module someday, it would be easy to do.