For a 1-turn pot, I always use a
Bourns 6639 Series Potentiometer.
They're pretty cheap, and they're continuous so you won't destroy them if you drive them past their extents.
I will never use a fixed 1-turn pot ever again.
We've had success with
LV-MaxSonar-EZ Ultrasonic Rangefinders as well. They're easy to work with, and give reliable reads in the right conditions with a simple median filter.
When it comes to optical sensors,
Banner's WorldBeam QS18 Series have never let me down. We like to use a visible light one, so we know whether the sensor is working, and what it's pointing at. They've held up in high-speed applications too, as we used one of these to measure our shooter speed by colouring parts of it black and white.
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