It's almost spooky what a robot will do with just a few simple rules, as with a PID controller. I use PID to keep this 6-foot tall Falling-Up Robot balanced using stepper motors. But I'm having trouble with Integral Windup. If I lift the robot, or if it gets stuck somewhere, it goes biserk. I'm researching the Back-Calculation method to help "unwind" the error. Look for a good book on this. Any recommendations on this? Thanks.