Hi,
Not an expert myself, but interested in how you might make a slip ring.
In attempts at making wind turbines, I have used capsule slip rings which you can buy reasonably cheap from Ebay, (UK or China).
3 circuit/wires which you can configure for 3 phase AC or DC generators giving you 30A max throughput.
Position these towards the top of the generator mount running down the middle of the shaft/tower.
Samples below of pic and link to a Youtube vid might give you ideas.
https://www.youtube.com/watch?v=N5jC_sIFRWc