This apparatus is just a fire-proof turntable with a variable speed motor. The puck in the center is filled with an alcohol soaked wick and set alight. With the screen placed over it a small tornado of fire blazes away for a few minutes.
The old drive system had the pot controlling a 555 that generated the clock for a stepper. Over the years (>10) some part of this system seems to have lost its zip resulting in terrible acceleration and little torque once at speed. Rather than trouble shoot what I feel was the wrong solution in the first place I went with a DC helical gearmotor and feedback via optical tach.
Repairs are nearly done, the encoder assemble has to be mounted and the controller wired up. To the left is the old stepper and driver, the new driver and gearmotor, the underside of the turntable and some encoder wheels. The print pattern for those was generated with a postscript file made by NickAmes and can be found here: postscript encoder wheel generator