[114Klutz]

We have a pic on a custom circuit board acting as a coprocessor. It communicates with the robot controller by way of the ttl serial port.

An RTOS isn't necessary, for one, it will have significant amounts of overhead and will require an auxiliary board to handle sensors, etc(Gumstix implementation). This further contributes to overhead. While any modern x86 style processor has the processing power to overcome such overhead - it still has significant amounts of I/O latency,

A microcontroller, such as the PIC, is likely a better solution, while far less powerful, it requires far less overhead, and because of this, can work with much lower latency.

We have a hardware counter chip to read in the quadrature encoders, this is probably not needed, but reduces overhead even more. A mentor designed and fabricated for us, and they have been incredibly useful so far.