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My controls lab in college (University of Washington, Aeronautics & Astronautics) had an inverted pendulum. I designed a controller to balance it and maintain position along the track for a controls class. We took a picture of Gumby standing on top of it for our report. It used rotary optical encoders to measure the angle, and a motor driven belt to move the base along the track. Somebody in our department developed a controller to flip the inverted pendulum up and balance it. Another stabilized a jointed pendulum in various configurations (both arms up, one up & one down, one down & one up). All are non-trivial problems. Combining them is commendable.