first post in Arduino,may well be teaching granny to suck eggs, been making a 2-wheel balancing robot for 12months now. earwig robot on youtube, The BMA180, arctan2, combined with the ADXR150 gyro(10-bit) gives a 1/16 of a degree resolution. Nice.complementary filter. After Hours spent tuning pid values the best solution I found was to have a timer giving a step change to the motor PID, the step level was interactive as were the pid values, this way you can see whare the Buzz and unstable parameters are. The balance equation,
vert_error+base_vel+body_vel+position_error.
if vert error is initially off, the robot drifts until the pos error cancels out and the bot oscillates around a + or -pos offset , this can be used to calibrate the true vertical.
trying to map now and getting lost.
i wouldn't be this far on without the help of others :o