Originally Posted by The_Aleman
There are several different ways to attach sprocket to rear wheel.
1 - the (in)famous ragjoint. 2 pieces of rubber and some curved plates that attach the sprocket to your wheel. It works when done right and it's cheap.
2nd, you can use a hub adapter. The adapter clamps to the bicycle hub and 3 bolts attach a sprocket to it. It's a step up from a ragjoint, but costs a lot more.
3rd, you have the method you mention, sprocket bolted to disc rotor holes. it's probably the most reliable method and easiest to set up. Also not cheap, perhaps.
Lace a moped rear hub into your bicycle rim. Not necessarily cheap, and definitely not easy, but should be bomb-proof unless you are running a lot of HP