I'm curious, would a indication of excellent control be the ability for the balancing robot to be able to 'balance' at any desired angle, rather then just at true vertical? Has anyone been able to do that or have witnessed that?
Lefty
I have seen an inverted pendulum which is capable of doing what you described (An inverted pendulum is similar to a balancing robot).
I think for the robot to move back to the balance angle from any initial angle, the controller must be a non-linear controller, i.e. Fuzzy Logic Controller or Adaptive Controller. A linear controller (like PID) will not do the job because with a broad range of angle's value, the robot can no longer be considered linear.