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DDWFTTW - Tests.

And then I couldn’t resist going to the next step and test if the cart would develop enough speed to travel against the turntable when it wasn’t forced to do so. Very crude equipment and testing method but look at the result and draw your own conclusions . . .

http://www.youtube.com/watch?v=9zw2FJfBte8
 
That's an interesting design. It looks like you've got a cable or something from the axle straight to the prop shaft, bending 90 degrees, is that right? Nifty idea, if it's efficient enough.

I wonder what effect there is on the DDW physics of putting your prop at a greater radius than the wheel, as it seems to be. I'm trying to work out if it provides some unique advantage. I think the prop is travelling 2pi(Rprop-Rwheel) further than the wheel per revolution of the turntable, which means it's in a faster wind. I hope it's not setting you up for some criticism from nay-sayers, if you care about that.

Maybe it just acts similarly to a change in gear ratio. Or maybe it is equivalent to a cart with a prop high up, in a faster stream of wind than there is nearer ground level. I'm not clear on those points in my own head, what the difference is in practical terms, but the former would seem perfectly innocent, whereas the latter would seem potentially a cheat.
 
The prop radius to wheel radius just changes the gearing. But that flex cable from the wheel to the prop... that's going to store a lot of energy like a spring. :)
 
ynot said:
And then I couldn’t resist going to the next step and test if the cart would develop enough speed to travel against the turntable when it wasn’t forced to do so. Very crude equipment and testing method but look at the result and draw your own conclusions . . .

http://www.youtube.com/watch?v=9zw2FJfBte8
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Well, based on your wording either I don't understand this test, or I don't understand the last test. What is the difference between the two?

What do you mean by "wasn't forced to do so"? and conversely, then in the other test, how was it "forced to do so"?

JB
 
ThinAirDesigns said:
Well, based on your wording either I don't understand this test, or I don't understand the last test. What is the difference between the two?

What do you mean by "wasn't forced to do so"? and conversely, then in the other test, how was it "forced to do so"?

JB
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In the previous video (and all other videos I've seen) the cart was held against the moving surface until it reached the speed of the surface. In other words it was forced to do so. Holding the cart against the moving surface until it gains speed is essentially the same as forcing a cart up to the speed of the wind in an outside test by pushing it. In the last video however the cart wasn’t held against the turntable at all and it reached (and exceeded) the speed of the turntable/wind without being forced to do so. In other words it did it only using the speed of the wind. There is a small amount of “holding” due to inertia but I think this is so slight it doesn’t need to be considered.

The most “telling” part of the video for me is from around 18 to 24 seconds in. The turntable isn’t being sped up (in fact it’s slightly slowing) and yet the cart goes from travelling with the turntable to moving against it. It takes the cart a bit of time to “settle” to it’s speed.

I don’t see how the turntable's poor condition would have helped the cart’s performance, in fact it should have hindered it. I think this is the best proof provided so far in support of the DDWFTTW claim. In fact I’m not sure I need to continue testing but will wait to see what objections if any arise to explain how it wasn’t the wind alone that gave the cart it’s speed.

ETA - The latest video is the same as putting a cart on a very long stationary treadmill and then starting it up and not restricting the movement of the cart. Initially the cart will travel backwards with the moving tread. As the wind created by the cart moving through still air increases the prop will develop enough thrust to travel forward back up and against the motion of the tread (also against a headwind).
 
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Dan O. said:
The prop radius to wheel radius just changes the gearing. But that flex cable from the wheel to the prop... that's going to store a lot of energy like a spring. :)
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Sorry but the secret is actually in the vice grips - They have been sprinkled with fairy dust ;)

ETA - Hope people appreciate the danger involved with this test. I could have had my guts ripped open with the prop or my fingers torn off with the spokes. :eye-poppi
 
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ynot said:
Sorry but the secret is actually in the vice grips - They have been sprinkled with fairy dust ;)

ETA - Hope people appreciate the danger involved with this test. I could have had my guts ripped open with the prop or my fingers torn off with the spokes. :eye-poppi
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It sounded like you did catch a finger on something.

Why didn't you spin the flywheel from below or use a disk mounted in a drill to spin the tire.



If you have ambitions to build a bigger rotating disk: http://www.astro.ubc.ca/lmt/lzt/gallery.html
 
John Freestone said:
I think this is the best proof provided so far in support of the DDWFTTW claim.
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Finally I can rest. I was on the edge of my seat wondering whether DDWFTTW really was possible. I figured all the existing analyses and experiments, both outdoors and with constant speed belts, were pretty sketchy.
 
spork said:
Finally I can rest. I was on the edge of my seat wondering whether DDWFTTW really was possible. I figured all the existing analyses and experiments, both outdoors and with constant speed belts, were pretty sketchy.
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spork, I don't understand. You quote me as saying "I think this is the best proof provided so far in support of the DDWFTTW claim.", and I'm sorry if this offends your studies and experiments, as well as those of others, so to check what I was on about, I clicked the link, and I can't find where I said it, if I did. If I did, and if I said it about ynot's turntable, I apologise and retract it. I think your and JB's treadmill tests are by far the best empirical proof for those who, like me, are crap at maths.

I'm not bothered about trawling through for an in-depth spork-gate, I just want to clarify my position. I think for those who feel that the magic plastic spork pushing your cart backwards causes a problem with steady-state (much as perhaps ynot had/has), the turntable removes such an objection, although it adds different ones, particularly if you don't have it moving at a known speed. As I think the record will attest, I have said that I think different experiments are good for people with different ways of thinking about the problem and different sources of doubt. For the frames-of-reference deniers, there's only going to be road tests, etc...

When it comes to proof of DDWFFTW so far, for those reasonably educated on the discoveries of the last 350 years, AFAIK, yous the daddy.
 
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Dan O. said:
The prop radius to wheel radius just changes the gearing. But that flex cable from the wheel to the prop... that's going to store a lot of energy like a spring. :)
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Hi Dan. Can you help me with this a bit more. I can't get it out of my head that somehow it is the same as having a differential windspeed - like putting your 'sail' up to a greater height than where the cart is meant to be going faster than the wind. But then, when I think "where is the cart?", I'm stuck, with this angular, rotating analogue. The 'cart' goes from the prop tip at its greatest radius (to clarify, we're meaning the turntable radius, not the radius of the prop or wheel itself here, yeah?) perhaps right to its fixing to the centre of the TT. It's natural to think of the wheel as being in the stream of wind equivalent to that in which a land cart would be, just because it is a wheel and is in contact with the surface, and the bits further in as only part of the experimental requirement to keep the vehicle in place. I presume that I'm at least right in saying that the equivalent windspeeds are different - right at the centre, there is zero windspeed whatever happens. If we extended that cable and frame and stuck the prop out at twice the radius of wheel position on the TT, doesn't that represent putting the prop of a landcart into an airstream twice that of the vehicle at wheel-level? Or is it in the end 'nominal' where we say the cart is, and we can define it as where its prop is?
 
The prop does see more effective wind the further out it is placed. But it is also equivalent to spinning the disk faster. It's probably easier to analyze by considering the position of the prop as fixed and varying everything else.

The "wind" at the prop is ωdp where ω is the angular speed of the disk (in radians per second) and dp is how far from the center the prop is placed.

[note: radians are just a unit for measuring angles to make the math easier. If the disk rotates 1 radian, a point on the disk at radius r moves a distance r around the circle.]

If the wheel is at distance dw from the center of the disk, the disk will move under the wheel ωdw (assuming that the wheel is moving at the speed of the "wind". The wheel (and the propeller) will therefore be rotating at ωdw/2πrw (where rw is the radius of the wheel (2πrw is the circumference)).

The gearing which is the ratio of the speed of the propeller to the speed of the cart is dw/dp * 1/2πrw].
 
ynot said:
In the previous video (and all other videos I've seen) the cart was held against the moving surface until it reached the speed of the surface. In other words it was forced to do so.
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All well and good, but that's not what you said the last time.

Above you say it was forced until it reaches "the speed of the surface". In the post I questioned you said "I couldn’t resist going to the next step and test if the cart would develop enough speed to travel against the turntable when it wasn’t forced to do so".

See the clear difference. Now you say it's forced to the same speed and previously you say it's forced to a faster speed. I couldn't understand why you were saying you had previously been forcing the device to go faster than the turntable. Now I understand.

We do force it to go the same speed as the belt when we place it there. We do not force it to go faster.

JB
 
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Here’s another video of the cart being powered only by the wind on a repaired and motor driven turntable (electric drill). The turntable is fairly level but looks to be on an angle because of the camera angle. The cart ran against the motion of the turntable at a constant speed for over 5 minutes (then the drill chuck came loose on the shaft).

http://www.youtube.com/watch?v=MCB1Jczysrk

I was thinking of doing another test where the cart is held in a set position on the spinning turntable (spinning with it) so it’s like a cart not moving on the ground in a wind. Then the cart would be released so the wind could move it. Would this test have any added value?
 
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Yes.

Maybe we can get humber to look at it and tell us how an orange can do the same thing!:D
 
mender said:
Yes.

Maybe we can get humber to look at it and tell us how an orange can do the same thing!:D
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Here tis - http://www.youtube.com/watch?v=k4owZkoeGAU

Things are moving a bit fast to see clearly what’s happening but the cart is held to the turntable with a block that is removed at about 3-4 second in (if you’re quick you can see it flying through the air on a string).

Surely not an orange . . . But how about a ball bearing? ;)
 
ynot said:
Here’s another video of the cart being powered only by the wind on a repaired and motor driven turntable (electric drill). The turntable is fairly level but looks to be on an angle because of the camera angle. The cart ran against the motion of the turntable at a constant speed for over 5 minutes (then the drill chuck came loose on the shaft).

http://www.youtube.com/watch?v=MCB1Jczysrk

I was thinking of doing another test where the cart is held in a set position on the spinning turntable (spinning with it) so it’s like a cart not moving on the ground in a wind. Then the cart would be released so the wind could move it. Would this test have any added value?
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Nice one. It looks like it's still accelerating by the end of the video, and is on its way towards 2x windspeed (rough guesstimate). I suppose this test, starting the TT with the cart free to do its thing, is just like 'a wind gradually getting up' when you're on the tarmac. The next one with the block, of course, demonstrates self-start in a constant wind.

I have to say that there is something very impressive about these TT tests. They combine the control of the treadmill with the ability to let the cart do its own thing, and it very clearly does not have any desire to hang about at that dawdling old windspeed, does it? The treadmill tests are great, but unfortunate in having to prod or retain the cart, or put the treadmill on a slope, which doesn't have quite the same emotional effect - or have I just forgotten how impressive that was; yes, that's certainly part of it. It was unbelievable to see it climbing a hill against the belt. I suppose people gawped at bicyles at one time. In a few years people might go "DDWFTTW, yeah, and?". Well done, ynot. Pity about all the wrangles, but I'm not going to take sides on this one.

Now, can you do that without the wheel slipping?:D
 
Dan O. said:
The prop does see more effective wind the further out it is placed. But it is also equivalent to spinning the disk faster. It's probably easier to analyze by considering the position of the prop as fixed and varying everything else.

The "wind" at the prop is ωdp where ω is the angular speed of the disk (in radians per second) and dp is how far from the center the prop is placed.

[note: radians are just a unit for measuring angles to make the math easier. If the disk rotates 1 radian, a point on the disk at radius r moves a distance r around the circle.]

If the wheel is at distance dw from the center of the disk, the disk will move under the wheel ωdw (assuming that the wheel is moving at the speed of the "wind". The wheel (and the propeller) will therefore be rotating at ωdw/2πrw (where rw is the radius of the wheel (2πrw is the circumference)).

The gearing which is the ratio of the speed of the propeller to the speed of the cart is dw/dp * 1/2πrw].
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Thanks Dan. I'm going to chew on that for a while, and probably should try harder to get my head round the basic math for the straight-line cart to help me understand it. It sounds like you're saying that there's no need to be concerned about that 'cheat' of having the prop in a faster effective wind than the wheel, though. And when I think about that again, it's clear that 'the cart' is beating the windspeed at the prop as well as the wheel.

It's a weird kind of model to compare with the land situation, like a perfectly uniform gradient of wind from the ground upwards, which continues even higher. Not absolutely unlike real conditions, just more perfectly like them. Similarly, if we had a cart body and wheels a centimeter high, with a prop raised to a metre, we're not going to measure whether it beat the wind at the 1cm height.
 
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