I've just finished building the prototype for the dual processor version of the HullPIxelBot. A single Arduino is a nice enough way to do simple robot control. But I want WiFi. And access points. And web servers. So I've coupled an ESP8266 device (in this case the Node MCU) up to an Arduino Pro-Mini. The Pro-Mini takes care of the low level motor control, producing the signals that will drive the steppers. The ESP8266 device doesn't really have enough pins for the motors, and it has better things to do than drive steppers, so I've linked the two with a serial connection.
Since the Pro-Mini costs around a pound and has a negligible effect on power consumption I reckon it is worth doing. At the moment we have a really simple one byte command protocol, but I can build that up a bit if I need to use the Pro-Mini to do some sensor integration.
Next step is to work up the web side so that I can make a wireless, web controlled robot. Then we add the coloured pixels to the bot and we are really in business.
I'll be releasing all the code and the circuit diagrams later. If you want to see the real thing, come along to C4DI tomorrow evening at 6:00 pm.