I've made a decision based upon disassembling and evaluating the clutch that was on my machine.
The existing clutch is a single friction disk, two pressure plate spring- loaded clutch that releases from stiction at about 21 ft-lbs, and maintains about 11 ft-lbs in slip. Lousy hysteresis.
I have evaluated hysteresis clutches, magnetic particle clutches, and multi-plate friction varieties. The hysteresis types don't reach the desired torque, the mag-particle clutches in the 20 ft-lb maximum I need are thousands of dollars each, and the mechanical ones have too much hysteresis, even in multi-plate, wet versions.
So... A small (1/6 hp) split-phase gear motor running at 67rpm with
55in-lb torque will be pulley'd down 4:1, giving roughly 220in-lb torque (around 20 ft-lb max) -- about the max the original clutch would deliver.
That will spool up the roving via a dancer arm sprung with a LONG, strong spring that will vary only about 4% in tension over the throw I need. That dancer arm will have two limit switches. One to turn the motor on or off as the arm moves through the acceptable tension range, and another to turn the whole machine off if too low a tension is detected. A momentary "override" switch will allow me to run up the tension when first spooling the roving.
I think this electro-mechanical "bang-bang" servo will work as well as a higher-tech solution.
LLoyd