I was preparing yeast for freezing the otherday and thinking how a centrifuge would be useful. Then I remembered one of my favorite toys as a kid...K-Nex
I calculated the rpm's to be around 350 to 400 with 2 arms, it can have up to 8 arms but the rpms would decrease. I just tape or rubberband the vials to the arms, haven't had any problems doing this. Just thought I'd share this.