NXTSegway Revision 0.4 Final: New Design (Again) and PID Controller!

This is the fourth public release of my NXTSegway, and I am quite pleased with the results. I re-re-designed the robot: Dean Hystad informed me on the NXTStep forums of the benefit that a higher center of gravity can give to a balancing robot like NXTSegway. He gave an excellent example: it is much easier to balance a golf club on your finger than a pen. Along with the bigger wheels, as the title says, I also implemented a PID motion control system that solved all my balance problems. The program uses three error components (kp, kd, and ki), multiplies them by three constants, adds them together to form the PID value, scales the PID value to fit in the motors' power range (-100 to 100), and sets the motor power equal to the scaled PID value. The three error components work like this: kp (proportional) changes proportionally to the error, kd (differential) changes proportionally to the rate of change of error, and ki (integral) changes proportionally to the sum of all previous error values; the constant multipliers weight these components based on need. For a complete, technical PID tutorial, check out this site. As you can see from the video below, this controller is highly effective in creating a stable inverted pendulum. Note: if you want to use my source code and have a working robot, you must use a very similar design and adjust the kp, kd, ki, adj, and scale values to fit your robot and its environment. My values (especially the kp value) are extremely high due to the fact that the batteries were low...once I replaced the batteries, there was WAY too much overshoot.

Annotated source code can be found here (4KB)