Here is Frank's windrower. It's a very cool model.
http://www.rctruckandconstruction.co...ead.php?t=2435
Basically anything can cut grass, if it is swung hard enough. Have you ever goofed around as a kid, swinging a stick in tall grass? If you swing it hard enough, it will cut grass too, and it doesn't even have to be sharp. But the biggest thing to remember is to design a deck that gets the clippings out, as soon as they are cut. A design that keeps recirculating the clippings through the blades take a lot of power. Simple decks that throw the grass out right away stay cleaner, and use less power. This is why mulching decks don't work well in tall grass.