Oh dear,
Here I was thinking I'd joined a group of skeptics and crtiical thinkers.
Hi Ross. You have, mostly. We're all a mixture, I think. The odd thing about this thread is it's quite unusual for JREF. A ridiculous-sounding claim that appears (on long consideration, for some) to be true. I dismissed it early on, and then realised that what I thought was my scepticism was in fact prejudice. I said I'd eat my hat if it turned out to be possible. I'm now working out amusing ways of getting out of actually choking myself. At least I'm able to learn. Some aren't.
Actually, I'm pretty sure I see a servo actuator about halfway on the chassis and I'd venture to guess that the other two little boxes are a battery and a radio control receiver. Not to mention that stalky bit that could quite conceivably be an antenna.
Yes. However, it has a brake, which might be RC, and it might even have RC steering. The first would make sense to put on it, instead of trying to grab a cart with a rotating prop or stick yer foot in front of it when it's going fast. The latter might answer some of the many people who have asked "So how does it stay in a straight line down the road". Any serious test like this would probably need those things. So an aerial and battery and servos are to be expected. Is the owner not on the forum to ask, or contactable? I haven't actually thought of that. Mr Goodman, isn't it?
C'mon, folks- IT'S BEING TOWED!!!!
See that's not scepticism.
Possible, but not necessary if you build the cart correctly.
Whereas that may be.
There seem to be only three possibilities: true, a genuine mistake, and cheating (whether for the hell of it or some other reason). The second seems extremely unlikely, since it is pretty difficult to try to get a treadmill sloping one way and accidentally slope it the other, and the result (cart moving faster than 'windspeed') is a simple observation; there are few other possibilities of how it could happen without happening really; it's not a phenomenon that is susceptible to confirmation bias! The explanations and general level of intelligence and seriousness of the protagonists persuade me that this is a real phenomenon, although it is reasonable scepticism to question and wonder whether there is some cheating going on. If there were, there are many opportunities, I imagine. If someone can do clever magic tricks that look real, I'm fairly sure they can fake some video. That is just an unfortunate reality of video evidence, perhaps even of seeing it in the flesh. So each of us must make of it what we will. The mechanical principles aren't too hard to get a grasp of, even without strictly following the maths and physics.
The absolutely key idea, I think, is that parts of a craft can keep moving backwards relative to the craft, and hence still harvest the wind energy (I know that may not be a strictly correct way of putting it, but it makes sense to bods like me) when the craft is moving at or above the speed of the wind pushing it. The simple wheel design with vanes below the centre is a good one to see that on.
I hope I am corrected if this is not quite right:
Points on the circumference of a rolling wheel accelerate to twice the speed of the centre (2v) at the apex, and slow again to come to rest as they touch the ground, moving in what are called cyclic paths. This in itself is a fact that most non-engineers probably don't know and would be amazed to hear, and consider woo on first hearing it. How else can it be though? If the ground's not going anywhere, the point of contact of the wheel can't be either, or the wheel would be skidding. In reality, of course, it is scrubbing slightly, since it's not a perfect wheel, and anyway, that point of contact is only motionless (in the perfect mathematical system) for an infintessimal time before accelerating again. If the point of contact is motionless, and the hub is moving at v, then this must mean that the top is going at 2v, since the wheel is pivoting at that moment about its point of contact, and the hub can only be going at v.
So, points at a smaller radius than the radius of the wheel edge must accelerate to something between v and 2v, and slow to something between 0 and v. Hence, if wind vanes can be made to open below the axel and close above it, those open vanes can be pushed by the wind when the wheel's centre is moving at or above v.
I even got this wrong, thinking that if you push below the axel, a wheel is tending to rotate backwards, but that's only because we tend to imagine a wheel held centrally and free to turn. A rolling wheel's axel is free to progress and its point of contact is held by the road, so wherever you push it above the ground, it rolls forward.
By some of the other analogous gear systems shown and described in the thread, it's not a long way from this principle to seeing that the prop is just doing the same thing, only it's geared from the wheel instead of fixed to it like the vanes, and rotating in a different plane. It's surfaces, however, given the right gear ratios, are moving significantly slower than the wind when the cart is moving at windspeed.
For some time something still niggled me about this. I kept looking for some principle that must oppose the above advantage and cancel it out. For all I know (because I'm not up to the maths of it yet) there might still turn out to be one, but that would mean that the treadmill and road test videos would have had to be faked, and that doesn't fit with my experience of the discussion as I've got to know the personalities involved more.
No, on this thread it's the woos who are the ones arriving and saying it's impossible, and sceptical investigation leads to belief.
