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There's just no decent mechanical equivalent of a switching regulator. All the variable-ratio transmissions seem to have power transmission limits and/or reliability problems.
If you map a synchronous buck switcher directly into mechanics, you get
input flywheel input cap
double clutch mosfets that switch from Vin to ground
spring inductor
output flywheel output cap
PWM controller PWM controller
Except that the mechanical version would shake/wear itself to death.
The non-synchronous version would use a single clutch (mosfet) and a ratchet (catch diode) and would have the same continuous/discontinuous behavior as a buck switcher.
John