Gimbal controller BGC 3.1 with atmega328, gimbal motor EMAX 2806100KV, magnetic encoder AS5048A connected over SPI.
RC servos SG90 for driving and turn. One servo redesigned to rotate continuously.

This project is open source https://github.com/remrc/ReactionWhe...
STL files https://www.thingiverse.com/remrc

One more bike:
   • DIY 3D printed self balancing bike  
   • DIY reaction wheel bike  what inside