... with the right materials (elasticity/stiffness/friction/wear/surface) for the flexspline and the teeth a harmonic drive can perform myriads of turns!
I've assembled some really small (0.7mm diameter for the planetary gears, 1.9mm diameter for the gear-box) 3-staged HD's made of plastic for Faulhaber, where the micro-motor has more than 100k rpms, that were continuous running for some weeks without remarkable wear.
Have another micro-HD with flexspline, where all parts are LIGA.fabricated from Ni, that has similar lifetime-expectations.
So a lifetime-test could be a really long-lasting job ;)
I've assembled some really small (0.7mm diameter for the planetary gears, 1.9mm diameter for the gear-box) 3-staged HD's made of plastic for Faulhaber, where the micro-motor has more than 100k rpms, that were continuous running for some weeks without remarkable wear.
Have another micro-HD with flexspline, where all parts are LIGA.fabricated from Ni, that has similar lifetime-expectations.
So a lifetime-test could be a really long-lasting job ;)