The 40 drives are powered by the Arduino mega. There are two channels. I know, I should have made 4 or more, but at this time I just implemented 2.
Pretty cool accomplishment. However I strongly suspect that the PC power supply is doing the powering of that project and the Arduino is just doing the controlling of the project? That may sound picky but a lot of people (especially beginners) have trouble separating those two functions and assume they can place a burden on the a Arduino board that it can never met.
Again cool project and sorry for one of my pet peeves.