download and install this library https://github.com/jrowberg/i2cdevlib
demonstration here https://youtu.be/gLAljH-oAIQ
All instructions here https://www.instructables.com/id/Self-Balancing-Robot-With-ESP8266-WiFi-PID-Tuning-/
To do
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update webpage, add a text field to show pid configured data, remove JS alert.
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robot sometimes goes out of control, need fix
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utilize ESP EEPROM to store configured PID parameters,