In 1995, Bob Pease wrote a great article about a ball-on-beam balancer (BOBB) he designed. Making a servo system that can keep a ball balanced on a beam is an interesting control challenge, similar to the inverted pendulum. Pease was inspired to create one because he was exasperated with Fuzzy Logic (Parts I, II, III, IV, V, VI). Now Pease was a famous analog engineer, but he wasn’t bothered by the fact that Fuzzy Logic was digital. Indeed, in Part I, he said, “...a well-designed digital controller can obviously operate as smoothly as you would like.” He also readily admitted that a Fuzzy Logic controller might be simpler and better suited to some nonlinear problems.
What bothered Pease were all of the wild claims that Fuzzy Logic was superior, combined with the assertion that you don’t even have to understand how the controller works. It was some kind of new-age fuzzy magic. Like digital power a decade later, a bunch of exaggerated claims were made by well-meaning software engineers who never had a control theory course in college. Pease wrote an article about the PID (proportional, integral, derivative) controller to help expose the engineering community to the beauties of modern linear control theory. There are videos of PID controllers running on an Arduino that make a serviceable BOBB.
Pease had become incensed at a paper from Texas Tech that showed a Fuzzy Logic BOBB, and even presented a prototype. So he set out to design a controller with pure analog. The one he came up with used six op amps. I am not sure what happened to it; it may be in an archive at Texas Instruments.
You can imagine my delight when Reginald Neale contacted me and said he had a video Pease sent him of the BOBB working at the Wescon show in San Francisco circa 1995.