I was in a discussion the other day about the advantages and disadvantages of mechanical systems like the Reeves drive vs. electronic controllers.
For those unfamiliar with one, a Reeves drive is a speed control system that uses variable diameter pulleys to vary the speed of a machine. These were common until they were superseded by electronic controllers.
Electronic speed control has been integrated into not only large machinery but also smaller hand-held tools like routers in which the integration of a Reeves drive would not be possible. Chalk up one for the electronic controller. And a Reeves drive does not provide for reversing direction. Another point for the electronics.
On the side of the "old school" is the fact that the Reeves drive varies the spindle speed by altering the pulley ratios, not by actually slowing down or speeding up the motor. Therefore, the motor is always running at full rpm so there is no decrease in torque at slow speeds.
But the biggie comes when you need to fix the thing. The electronic device is, more likely than not, going to require replacement. Once you let the smoke out, these things are simply not fixable. The Reeves drive, on the other hand, can be dismantled, repaired and reassembled by anyone with a modicum of mechanical ability. Such is the nature of progress.