There are quite a few fan ducts on thingiverse, but I didn't find any for a Gen7/Sanguinololu style row of pololu drivers. So here's mine. It is sized for a 60mm fan. I'm working on an 80 mm version in case I need more oomph. (I naively bought 2A steppers before realizing that the pololu's won't do anywhere near that without serious cooling.)The aerodynamics of this duct are very poor. I'll try a more curvy version when I get around to it. I just clamped a piece of scrap threaded rod to the top of the frame with a Prusa rod clamp to serve as my mount, and then screwed a strip of sheet aluminum to the fan duct and bolted it to the rod. This way it swings up and out of the way when you need to work on stuff, and you can bend the sheet metal to get any angle you want.