Hall effect sensors output a voltage that varies in proportion to the presence of a magnetic field, which is typically provided by a nearby magnet.

Linear Hall-Effect Sensor According to the datasheet, SS49E is a linear hall-effect sensor that is operated by the magnetic field from a permanent magnet or an electromagnet. The linear sourcing ...

Even with Hall Effect sensors, I found that sometimes small movements would not be picked up by the controller —sometimes to catastrophic in-game results.

The solution is to add hall effect sensors to the motor. [Robert] did all that, tested all the 36 combinations of hall effect and coil wiring, and it STILL didn’t work.