Dan O.
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I'd wait for the Mark-II TT (see it in the background) that doesn't have a big hole in the middle. The ball or orange will be much more impressive then.
DDWFTTW - Tests.
- Thread starter ynot
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I'd wait for the Mark-II TT (see it in the background) that doesn't have a big hole in the middle. The ball or orange will be much more impressive then.
Dan O.
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The real wind profile is a little bit counter intuitive. If you think of the air as like layers of paper with very low friction between them, you would expect to see that uniform linear gradient between the non-moving air at the surface and the fast moving air at the top. But when the actual air gradient is measured, it fits closer to a power law with an exponent of 1/7th (linear would be an exponent of 1).
If anyone is interested here are a few basic specs and mug shot
The wheel is 8.5cm diameter
The circle travelled by the wheel is 120cm diameter
The prop is 12 x 6 slow air
Shafts run on roller bearings that have been washed of grease
Cable is from my son's BMX brake system
Hose clamps are optional
The wheel is 8.5cm diameter
The circle travelled by the wheel is 120cm diameter
The prop is 12 x 6 slow air
Shafts run on roller bearings that have been washed of grease
Cable is from my son's BMX brake system
Hose clamps are optional
D'OH! I tried to go back and fix it, but it's too late.
Whoops, I see. You probably just cut the wrong quote tags, spork. I'll boil you in oil another time!
Hey, at least I didn't put your name on a humber quote!
As far as boiling me in oil... get in line.
But there are MANY places where we force it to go slower. It then reaches and surpasses the wind speed on its own.
There's no need to take sides at all. The powered turntable tests are great. I personally think both the treadmill and turntable have their place. I'm quite certain there are sceptics that will have a problem with this thing going in a circle - just as there are sceptics that complain about gravity, inertial reference frames, or the color of the sky. But the turntable does have the very real advantage of letting the cart achieve steady-state speed. That's why Bauer used a turntable for his cart many years ago.
The reason JB and I are giving ynot a hard time is because of his earlier demands on us, his attacks, and his subsequent posts that have been less than forthcoming about the limitations of his experiments.
I find it somewhat ironic that in one of his recent videos he goes to some trouble to explain that this is NOT an experiment, and no conclusions should be drawn from it, but it IS the best evidence yet for DDWFTTW.
It appears to me that the cart in Ynot's experiment (!) is going 5.7 mph against a turntable speed of 13.5 mph in the opposite direction. That works out to .42 higher than windspeed (for those of us who can understand equivalence) on an advance ratio of .6, not bad!
So does that indicate an efficiency of 89% (1.42/1.6)? Ynot, what is the "balance speed" in turntable rpm of your cart? 17 rpm by some chance?
So does that indicate an efficiency of 89% (1.42/1.6)? Ynot, what is the "balance speed" in turntable rpm of your cart? 17 rpm by some chance?
Sorry but I’m just a “hack” so you’re going to have to work out the technical specs yourself. The best turntable to cart rotation achieved is around 2 turntable to 1 cart if that helps. If I get around to building the double cart I think it will do even better.
I have also tested it running for more than ten minutes without any noticeable loss of cart speed. When I quickly step in and slow the cart down it returns to it’s “cruise” speed quite quickly. My sceptic side is now happy to fully accept the effect is sustainable indefinitely.
Dan O.
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Well, your sceptic side has provided us with an excellent tool for investigating the cart's behavior when (all humbers should look away now) running the "equivalent" of DDWFTTW! As spork said, this proof is pretty solid! Nicely done!
17 rpm will be the same as having the turntable complete ten turns in 35 seconds. If you have an adjustable speed on your drill, I would really appreciate you checking this for me. The cart needs to stay more or less in one place while the tt is running. A slight tilt of the tt will likely show up as a low spot that the cart likes to stay close to on extended running. That's okay if it does that; might make it easier for now if it does that.
I don't think the double cart will do much different. The only external resistance is from the bearing on the shaft that holds the arm that holds the cart. I assume that amount of resistance is quite low; if so the double cart will be a very small amount faster than the single cart.
17 rpm will be the same as having the turntable complete ten turns in 35 seconds. If you have an adjustable speed on your drill, I would really appreciate you checking this for me. The cart needs to stay more or less in one place while the tt is running. A slight tilt of the tt will likely show up as a low spot that the cart likes to stay close to on extended running. That's okay if it does that; might make it easier for now if it does that.
I don't think the double cart will do much different. The only external resistance is from the bearing on the shaft that holds the arm that holds the cart. I assume that amount of resistance is quite low; if so the double cart will be a very small amount faster than the single cart.
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It was one of many spare cables he has, but he says brakes are for sissy’s anyway.I hope he doesn't discover it's missing at a critical time
I’m trying to think of experiments to do using a fan or fans to create the wind and having the turntable stationary. Something like a heap of fans around a stationary turntable all angled in the same direction to create a circular wind. Throw in a stream of bubbles and see if the cart beats them.
Ynot, I don't think you'll get much info from that but since it's your turntable and cart - ynot. Humber and that other guy would like it too since they wouldn't have to run around behind it (!) with a fan to see what is "happening"!
Any chance of doing the 17 rpm test?
Any chance of doing the 17 rpm test?
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Sure, I certainly didn’t mean to imply that two carts would give twice the speed or anything like it.
The drill only has two speeds and it is currently running on the slow speed. I could alter the size of the small driving wheel but don’t have much spare time right now. Wish I had the multi-speed motor you said you have.
Was actually thinking of a design where a fan chases the cart.
So you want me to tear my house apart now? Good idea though. Don’t think I have a spare dimmer but they might not be too expensive to buy. Come to think of it I think I do have a spare dimmer but don’t where it is. So I know what you want, is it to run the cart in a hover for some reason?
Yes; I want to see if the top speed of the vehicle when running in a decent wind is predictable based on the advance ratio and the "hover" speed.
The turntable speed that I'm after is one revolution every 3.5 seconds. If that can be maintained by hand, it might be easier than rewiring things. I know setting the drill would be more consistent.
Just had another thought: if you have another wheel like on the cart and a way of mounting that on your drill, you can vary the speed of the turntable by running the drill at a constant speed and moving the wheel in towards the centre or out towards the rim of the turntable to change the turntable speed. I don't know if that would get you in the right speed range though.
Unless you are already doing this of course!
The turntable speed that I'm after is one revolution every 3.5 seconds. If that can be maintained by hand, it might be easier than rewiring things. I know setting the drill would be more consistent.
Just had another thought: if you have another wheel like on the cart and a way of mounting that on your drill, you can vary the speed of the turntable by running the drill at a constant speed and moving the wheel in towards the centre or out towards the rim of the turntable to change the turntable speed. I don't know if that would get you in the right speed range though.
Unless you are already doing this of course!
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I may have thought of a a design that will test the principle without using a treadmill or turntable (or maybe it‘s just a stupid idea) . . .
Build a cart with an onboard motor powered prop at it’s rear end so it‘s driven forward by the thrust of the wind it creates (wind powered cart). At the front end put the DDWFTTW prop and drive wheel but don’t connect them together. Run the cart in calm conditions and measure it’s top speed. Then connect the DDWFTTW prop and drive wheel and repeat the test. The connected cart should run faster than the non-connected. A valid test?
Build a cart with an onboard motor powered prop at it’s rear end so it‘s driven forward by the thrust of the wind it creates (wind powered cart). At the front end put the DDWFTTW prop and drive wheel but don’t connect them together. Run the cart in calm conditions and measure it’s top speed. Then connect the DDWFTTW prop and drive wheel and repeat the test. The connected cart should run faster than the non-connected. A valid test?
John Freestone
Graduate Poster
That's interesting, Dan. Thanks. Nice decision on the other thread, BTW. I might be close behind.
Boiling in oil would be too quick.Hey, at least I didn't put your name on a humber quote!
Ynot - nice mugshot. While you've got that nice turntable, if you can see what speed is required to get different fruit and veg beating the wind, that would be a great boon to science. Well, you never know. I'm currently training cherries for an attempt on Everest.
John Freestone
Graduate Poster
Isn't the front prop in a headwind?
Sure but a “normal” cart travels in to a headwind after it reaches the speed of the wind as well (a lot less of headwind I know). The normal cart also progressively gets less power from the wind as it gathers speed but in the scenario I’m suggesting it always retains full power. I said it might be a silly idea but I think it’s worth thought and discussion.