Field rotation is exactly that, it's like walking in a circle around your EP the view seems to rotate around. Not noticable much due east and west, terrible at zenith. It's okay if you do really short exposures of the planets but not good at all for DSO. I tried bartelising my dob but I really had no idea what I was doing with the mechanics so gave it away, might take it up again one day. I tried making my own worm gear using Selleys Kneadit and a threaded rod, work to a degree, but I think I rushed it a bit. I think I will try friction drive next time.
I remember when the scope did move on it's own a great feeling of satisfaction came over me, until it stopped and stripped the gears.
Good luck with it anyway.
mel's website -
http://www.bbastrodesigns.com