Originally Posted by
wphamilton
It was "phase shift" that threw me off - to me that means wave mechanics.
That's what I outlined in the first post, utilizing timing to measure the translation. But if your beam and detector are both rotating (originating at the hub and reflecting back to a detector on the hub) that isn't available. Specifically what arrangement are you proposing? How would you get the potentially continuous sampling?
He is proposing to measure the signal from the rim at the hub or vice-versa. The rim and hub are at fixed relationship to each other except for the windup. What is needed is a light detector that can capture a signal that will vary in position. To know how long the detector has to be, you would have to first specify how great a power range you want to measure and know the hub windup at that power. Assume zeo power = zero windup. A digital photo sensor 1 mm long would probably do the trick. Just a guess. You would need some pretty good resolution though.