PIDDYBOT is an Open Source Balancing Robot with the aim of teaching PID control.
Check out the Video:
Do not populate F1 or D6
I somehow lost the original EagleCAD files for the PIDDYBOT. I still have the .BRD file, but no schem. I have plans to update the design with the SAMD21 instead of the Atmel, and it will be done in KiCad not Eagle. Stay Tuned
There is an instructables on building the PIDDYBOT which contains the parts needed: https://www.instructables.com/id/PIDDYBOT-DIY-Arduino-Balancing-Robot/