A proof of concept: ESP8266 alone is more than enough to run steppers, servos and PWMs. There is no need for an auxiliary, slow, ATMEGA.
Youtube video of it in action. RepRap Forum discussion.
- You will need a linux machine.
- Clone this repository, then create an empty bin directory.
- Follow the remaining instructions here.
- A breakout for ESP8266 that includes I2S pins. I used NodeMCU, ESP12 would do, ESP01 would not.
- 32-bit buffered output shift register: Shift-out-32-HC595.
- A4988 or DRV8833 stepper drivers.