Interesting! Well 2cm for the potentiometer diameter is fine as long as it turns easily. Its purpose is to sense wind direction, and I'll be attaching it to a wind vane.
Originally I was thinking of using two potentiometers actually, one for the horizontal plane and another for a vertical angle (pan and tilt angles so to speak). However the vertical angle would only work if the potentiometer was almost frictionless, due to gravity, and I doubt I'd be able to find that, so I'm thinking of using a bank of tilt sensors instead. Not sure how well that would work but I'll give it a try.
So ball-bearing (or servo mounted?) potentiometers don't have so much friction... great I'll try one for the yaw angle. Thanks.
Regarding the 360 rotating servo, yeah I've pretty much given up on finding one of those. I think I'm going to use a 2:1 teeth ratio gearing system and build a standard servo into a housing for that.