Re: ?Recommendations for HF 90cc Engine Kit
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.