On Sat, Nov 6, 2010 at 4:53 PM, YES NOPE9 wrote: > After watching this video .... > http://www.youtube.com/watch?v=3Dk-trDF8Yldc&NR=3D1 > I feel my grip on reality is more tenuous than before > ( especially during the latter parts of the video ) > gus in Denver Try http://www.youtube.com/watch?v=3DE7vcQcIaWSQ&feature=3Drelated instead - exactly the same principle, but with less moving parts it's somewhat easier to understand. Fundamentally what's happening here is that when the cotton reel rolls to the right, the bottom of the inner part also moves to the right, but slower than the reel does.- not hard to analyse that as it's basic gears, with the very top of the outside of the reel moving fastest to the right and the bottom where it's touching the ground stationary, with a linear continuity between. Therefore when there's a force to the right on the bottom of the inner part, that moves to the right, with the reel itself moving to the right at a faster rate. Now I wonder what would happen if you could make paddles attached to the underneath of the inner part of the reel which would completely stop the wind, and then direct a jet of air onto them... The truck in the video you linked works in _exactly_ the same way - the only difference is that they're using the big wheel to move the point of application of force from underneath the centre of the reels to on top. The top of the big wheel moves to the right at exactly the same speed as the bottom of the inner part of the reel. The only difference being that it seems a lot more complicated, but if you can understand the example with a single reel you're most of the way there. To come back to the original ddwfttw machine, the principle this starts from is that a sailing yacht can travel to a point directly downwind of where it starts faster than the a balloon floating in the wind. It does this not by going straight, but by travelling on broad reaches and using the "gearing" power of the wind on the sail, to drive it downwind faster than the wind - you just need to gybe at some point to go directly downwind. All you need to do to go directly downwind is continuously gybe! The ddwfttw machine kind of combines these principles. The propellor is effectively acting like a sail on a boat on a broad reach - extracting energy from the wind despite moving downwind faster than the wind. The cotton reel examples above also illustrate the principle, that when the vehicle attached to the prop moves downwind, the prop itself also moves downwind, but the surfaces of the prop effectively move downwind slower than the vehicle because the prop is spinning. http://www.youtube.com/watch?v=3D7xL8gRJ5F6k&feature=3Drelated shows the principle at work quite neatly - I wonder how hard it is to make one (goes to check out instructables). Chris --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .