If you find my design interesting, you could make a small donation:
http://paypal.me/RegisHsu

Instruction guide:
Thanks for JJRobots sharing this such great project.
I am using ESP8266 as the host CPU and I port the code from Arduino Uno to ESP8266.
it works pretty great!
my project configuration is:
ESP-12F(ESP8266 module) x 1
MPU6050 x 1
A4988 x 2
NEMA39 stepper x 2
SG90 servo x 1
12v Lipro battery x 1
DIY the motor board.
here is my blog for you reference. http://regishsu.blogspot.tw/search/label/1.Balance%20car%E8%87%AA%E5%B9%B3%E8%A1%A1%E8%BB%8A