Russell,

Use of a pot in this case would have been MY first choice, too. And I have available to me a fair quantity of resources from which to purchase new pots (without worn spots which cause noise on position indication and greatly amplified noise on derived angular speed - whether derived via analog or digital). (As a student in the early 1970's, I had a tough time finding $8.95 to purchase an Intersil ICL8038 so I could build my first function generator.)

I suspect the reason Bartosz' instructor nixed use of a pot, which (almost) required use of an encoder was to expose Bartosz and other students to the inherent perverseness associated with some of devices we use to achieve functional and robust designs.

Cheers,

Bruce