Although this robot is still under development, it is able to stand on it’s own. The maker has posted several videos and the source code so you can get started on making your own.
The system features a kalman filter to acquire data from the IMU and a PID controller to control the motors. The robot is actually able to stand by itself indefinitely, but it’s not completely stable, either because of my software or because of the motors that have a little “loosiness” (a couple of degrees of “free” rotation). I’m still working on it
More about making a Self-balancing robot powered by an Arduino
In the Maker Shed: Make: Arduino