I once considered using a Hall effect sensor for determining wheel position, but as I saw it, you'd only get one revolution accuracy.
Recently I saw the angular magnetic sensors - with fractional degree accuracy, but they seemed kind of pricey.
Now I find that NXP has KMZ60 http://www.nxp.com/documents/dat... available from DigiKey for under $3 ($1.14 ea/1000) and this is getting close to inexpensive enough.
I'm not finding much on applications like robot wheel position so I'm wondering if anyone here has any experience with these things? Like maybe this is too good to be true (0.1 degree accruacy!) - so what are the gotchas?