DDWFTTW Turntable Test: 5 Min Video - Is It Conclusive?

[vanesch]

Still 55 (now 54) posts to go to reach 1000... Hope we'll get there :shy:

 

[atyy]

Still 55 (now 54) posts to go to reach 1000... Hope we'll get there :shy:

Ok, here's a little help. I probably missed it since your equations were spread out over many posts. What is the justification that 0<k<1 physically exists?

 

[swerdna]

I put my TT and cart together again to show a visiting friend and made a video with the TT running at a slower speed for those that want to compare calculations at different speeds (as suggested by mender post #940). I have also replaced the “large” tether arm with a thin bar. Are there any other tests anyone wants done while it’s together again? (that don’t involve me having to buy tachometers).

 

[vanesch]

Ok, here's a little help. I probably missed it since your equations were spread out over many posts. What is the justification that 0<k<1 physically exists?

Thanks

K is a design choice. It comes in v_out = K v_cart

v_cart determines the rotation speed of the wheels, and through some gearing, the rotation speed of the propeller, and the propeller has a pitch. So with a certain rotation speed of the propeller (and hence, rotation speed of the wheels, and hence, speed of the cart on the surface) corresponds a certain velocity of the outgoing air flow.
You can make K as big or as small as you want by changing the gear ratio between the wheel and the propeller, by changing the diameter of the wheel, or by changing the pitch of the propeller.

Note that v_out = K v_cart is an approximative model of a propeller, because v_out might
1) be influenced by the incoming velocity v_in
2) the relationship might be somewhat non-linear (in that case, the model v_out = K v_cart is still useful, but as a local linear approximation, and K can vary with the working point).

For a turbine in a closed tube, the relationship v_out = K v_cart would be much more exact (there's only one velocity that "gets through" the turbine without hitting the blades).
v_in will change the amount of work that needs to be done but it won't influence (much) the final velocity. I don't know in how much this applies to an "open" propeller.

The point was just to have a plausible model that shows that the device can work in principle, not really to get numerically very accurate outcomes. Given that there are large margins, a small model change won't change the qualitative conclusion.

By lowering the gearing ratio, you can make the propeller run as slowly as you like, and hence make K as small as you like. Actually, the relationship 0 < K < 1 is too severe. You can have K values outside of that range and still have the thing working. But if K really is too large (say, K = 5), then the device will not work. It is as if Atom Man was throwing his molecules too fast. The propeller would then require more work than can be delivered with a drag force on the wheels smaller than the trust by the propeller ; in other words, the overall force flips sign.

 

[vanesch]

I put my TT and cart together again to show a visiting friend and made a video with the TT running at a slower speed for those that want to compare calculations at different speeds (as suggested by mender post #940). I have also replaced the “large” tether arm with a thin bar. Are there any other tests anyone wants done while it’s together again? (that don’t involve me having to buy tachometers).

Nice ! I don't know if it is just changing a switch or if this involves more work, but a whole set of TT speeds would be nice (from very slow where the thing probably doesn't work, to whatever you consider reasonable). To be able to exclude all the zeros of the whole family of hypergeometric functions
(or, who knows, to find a "resonance" peak... :rofl:)

A few other (silly) experiments would be to disconnect the propeller, and see how the thing behaves without it (haha). You could also place a sail on it, to have an idea of the actual "wind speed" (maybe some air gets dragged along the table).

Finally, you could maybe place a visible dot on the small wheel so that we can see it turn and make a close up image of when the cart comes by (at low speed so that the video can capture it).

 

[mender]

Thanks, Ynot, that helps to have another set of data. I get 10.2 ft/s for the turntable in one direction and 2.1 ft/s for the cart going the other way just before the end of the video. Did the cart speed up much from that point?

That's 12.3 for the cart, 10.2 for the turntable and a ratio of 1.21 - another coincidence? 11 x 11? How often does that number pop up? Of course that's just a number.

Ynot, could you try it again with some fresh lube on the cable and any other appropriate spots? According to shroder's theory, a small change in friction shouldn't be enough to upset a null but according to everyone else, it should result in an increase in speed, providing it does reduce the drag a bit.

 

[vanesch]

That's 12.3 for the cart, 10.2 for the turntable and a ratio of 1.21 - another coincidence?

1.21 GigoWatt (sic) was the power needed for the car in Back to the Future, no ?

OMG, swerdna, be careful, you might just be projected in another era ! :rofl:

 

[swerdna]

I think the cart had reached terminal speed before the end of the video but maybe not. I try to keep the videos short because uploading to Youtube takes forever.

Wish it was as simple as changing a switch but it involves having to take the drill drive apart and fit a different size wheel each time. Would it be okay if I just fitted a different size wheel to the cart? If the prop wasn’t in the way I could just shorten the length of the tether arm.

Before slowing the TT down I filmed the cart with the same TT speed as this video -

Not sure if it was just more “run in” or because I re-washed the bearings but the cart is running more efficiently in this video -

In the first video it takes about one and a third revolutions of the cart before it “hovers” while in the second video it takes less than one revolution. You should find the TT speed is the same in both videos. The terminal speed in the second also seems much faster to me but I haven‘t measured it.

 

[vanesch]

Would it be okay if I just fitted a different size wheel to the cart?

That's even better, because that changes the effective "gear ratio".

 

[swerdna]

That's even better, because that changes the effective "gear ratio".

Do the videos have to show the start-up period or can I just film when the cart is up to speed?

 

[spork]

Would it be okay if I just fitted a different size wheel to the cart?

That's a good set of data to get, but it's very different from running the TT at different speeds. Changing the size of the wheel changes the cart's advance ratio. The advance ratio is the primary design feature that governs the carts theoretical speed relative to the wind. As the advance ratio approaches 1.0 the cart tries to go an infinite multiple of the wind's speed, but will fail to work at all if the real world losses don't become incredibly small.

When the advance ratio goes above 1.0 it becomes an upwind cart. That would be a great experiment to show.

 

[ThinAirDesign]

Do the videos have to show the start-up period or can I just film when the cart is up to speed?

If it were me and uploading were a problem I wouldn't show startup --- just a long enough clip of each different test to be able to time the TT revs to the cart revs.

JB

 

[mender]

I agree with spork and jb, for the first set of tests different speeds would be best with just the final steady state speeds shown. The next round could be with different wheels though.

My tests showed a different break even speed for different advance ratios, so a different size wheel should also take the cart out of the "null" ratio.

And thanks again for building your turntable and doing tests. I still plan on doing one but I plan a lot of things!

 

[spork]

My tests showed a different break even speed for different advance ratios, so a different size wheel should also take the cart out of the "null" ratio.

Yup, I think you can expect higher minimum turntable speeds as the advance ratio gets closer to 1.0. The extra energy is required for the effectively higher "leverage".

 

[schroder]

Not sure if it was just more “run in” or because I re-washed the bearings but the cart is running more efficiently in this video -

In the first video it takes about one and a third revolutions of the cart before it “hovers” while in the second video it takes less than one revolution. You should find the TT speed is the same in both videos. The terminal speed in the second also seems much faster to me but I haven‘t measured it.

You are back to a perfect 2.4 again! In the first video after putting the TT back together again, it is obvious that you are not getting a clean drop out of the forward revolution of the cart. This is a perfect analogy to a partial carrier drop out and the ratio can be almost anything at all. You need a clean and complete drop out of the CW rotation of the cart, a sharp transition, as we see in this last video. A very nice mechanical heterodyne!
Can you please give me the distance from the center of the TT to the center of the track of the wheel as well as the diameter of the small wheel? Thanks!

 

[spork]

A very nice mechanical heterodyne!

I can't for the life of me figure out why you're trying to come up with these bizarre and exotic explanations for something that has been explained using everyday classical physics. Even if you managed to determine this was a mechanical heterodyne, you'd still have to then come up with the mechanism that allows it to go faster than the belt, wind, or TT that's pushing it. Why not simply accept the well proven conclusion from the people who've designed, built, and tested them? Seriously?

 

[tsig]

Me:


Tsig responds:


It matters not how "loosely coupled" the other relationships are -- that's the entire point of the example; there's a solid relationship between the deck and the turbine. The deck moves and the turbine spins.

It doesn't matter that the sun shone and the photosynthesis caused plants to grow which were eaten by herbivores which were then eaten by the carnivores which died and became crude which was refined and burned to make the steam to drive the turbine which moved the freakin' deck. The only relevant point is ... power the deck however you wish and in the end as long as the deck moves, the turbine can't tell the difference.



No you don't. To analyze the wind turbine you need not look any farther than what the turbine can see -- the wind. It matters not what creates it.

To analyze the DDWFTTW cart, you need not look any farther than what the turbine can see -- the wind. It matters not what creates it.

JB

Just take it outside in the wind see if it moves, Why do you not want to test it in the wind?

 

[tsig]

To see what?

Where the power is coming from.

 

[vanesch]

Where the power is coming from.

From the slowing down of the wind behind the cart (in the reference frame of the surface, in other words, in the reference frame in which we have "wind").

 

[tsig]

No, you can't. Now that would take an over unit device. His point about the cart working is that it does not care where it gets its energy from. There is a lot of energy in the wind that could be harvested to power the cart. There is also a lot of energy from the treadmill producing a relative wind that can power the cart. A lot less energy is harvested by the cart than there is in the actual system.

JB, I know a way that a sail cart could beat the prop cart, we just don't limit the cart to directly downwind. Of course if it is a directly downwind race the cart would win hands down.

How are you going to harvest the energy when you are going at wind speed? There is no relative energy.

 

[tsig]

The problem is that even the notion "relative velocity" is distorted by schroder. Some posts back, when I asked him if he disputed the claim that if a cart was going 2 m/s to the left, and a tread was going 10 m/s to the right, the velocity of the cart wrt the tread was 12 m/s, and for sure he disputed that (see post 755). He claimed that the relative velocity was 8 m/s. (ok, it might have been mph instead of m/s). At that point, I still thought that there might be a misunderstanding about the actual setup - or that he was just trolling.

But it becomes more and more clear that it was not a misunderstanding concerning the setup.

Schroder doesn't understand what it means "relative velocity", or how to obtain it when you have the individual velocities, as he confuses this with mixing frequencies of 2 and 10 (in other words, he gives himself the liberty to alter signs at will in the velocity composition).

I have never met anyone who has such a profound confusion. It is a remarkable phenomenon, and a true challenge to find out how to tackle it, pedagogically. Have you EVER met anybody who disputed such an elementary claim with such vehemence ?
(especially somebody who claims to be an engineer ?)

The cart is producing more energy than is put into it.

 

[A.T.]

Where the power is coming from.

From the wind (relative movement between air and ground). Explained many times in this thread, just read back.

The cart is producing more energy than is put into it.

Proove it! No it isn't:
https://www.physicsforums.com/showpost.php?p=2063418&postcount=917

 

[vanesch]

How are you going to harvest the energy when you are going at wind speed? There is no relative energy.

Because when you are going at wind speed (and consider that the AIR is not moving), the floor is moving. And when you say that the floor is not moving (in the floor frame), the AIR is moving.

I don't know what the concept "relative energy" is, btw. I know what "relative velocity" is.

You should consider the following elements:

- the car is not "delivering energy" to anything once it is up to speed. At most it is dissipating some energy

- the wind (in the ground frame) is moving slower because of the action of the car than if it weren't. In other words, the wind has lost energy in the process (and that's the energy that is dissipated by the cart).

- the reasoning in the "frame of the car" will have different energy terms than the reasoning in the "frame of the ground". That's always the case when we do a frame transformation.

- in the frame of the car, a simple calculation which has been presented under several different aspects already shows easily that, under conservation of energy, we can have net forward force (the trust by the propeller working on the air being larger than the drag necessary on the wheel to provide for the power).

If you think that there is "free energy", tell us how you think you could extract it, in principle. (think of Silly Man's tragic story...)

EDIT: more to the point, could you go through a step-by-step calculation as there have been many in this thread, and tell us what step exactly doesn't work ?

 

[schroder]

I can't for the life of me figure out why you're trying to come up with these bizarre and exotic explanations for something that has been explained using everyday classical physics. Even if you managed to determine this was a mechanical heterodyne, you'd still have to then come up with the mechanism that allows it to go faster than the belt, wind, or TT that's pushing it. Why not simply accept the well proven conclusion from the people who've designed, built, and tested them? Seriously?

Because, spork, you have it all wrong! The way I see it, the original “inventor” of this cart did it as a joke, a spoof, and he himself admitted that it will not work. The original outdoor video is a hoax, as the propeller is turning as a wind turbine. The only chance to see the actual direction of the propeller turning comes right at the end of the video, when the cart slows down. It would be hard to doctor the video at that point, and have the propeller reverse direction, so they did the next best thing; have the cart go off camera until it is stopped, and then pan back on it showing the prop spinning as a prop! It is so obviously a hoax that it really is a joke! The reason why I am interested is because of what is happening on the turntable. It is a really beautiful example of mechanical heterodyning and it is not to be ignored. This cannot and does not happen outdoors, so why do you insist it does? You have been playing around with these carts for years now, and if anyone is in a position to know this is a hoax, it is you!

 

[schroder]

- in the frame of the car, a simple calculation which has been presented under several different aspects already shows easily that, under conservation of energy, we can have net forward force (the trust by the propeller working on the air being larger than the drag necessary on the wheel to provide for the power).


EDIT: more to the point, could you go through a step-by-step calculation as there have been many in this thread, and tell us what step exactly doesn't work ?

Once the cart (if ever) exceeds the velocity of the wind, it is going against a headwind! Saying that you can extract energy from the headwind, in order to move against the headwind, is nonsense. The next time I do my weight training, maybe I will use that same principle: extract energy from the weights I am lifting in order to lift even more weights! Anyone with a normal functioning brain can see this is nonsense!
I have pointed out the step where the calculation is wrong. It is where Silly Atom Man “DECIDES” to extract energy from the force of the propeller, to drive the propeller!

 

[ThinAirDesign]

Saying that you can extract energy from the headwind, in order to move against the headwind, is nonsense.

Yeah, it's "nonsense" -- 'cause a sailboat could NEVER to anything like that.

Perhaps you should also tell that to this organization where they give out prizes to whoever can win wind powered races *directly* into the wind:

http://www.nextenergynews.com/news08/next-energy-news8.29.08b.html

Current winner over a 3km *directly into the wind course* -- 64% of windspeed.

I just have to hear you say this and make a total fool of yourself again:

Saying that you can extract energy from the headwind, in order to move against the headwind, is nonsense.

You crack me up schroder: the lengths you will go to, the simplest physics principles that you will deny, all to keep from admitting that you are just flat wrong. LOL

JB

 

[spork]

Just take it outside in the wind see if it moves, Why do you not want to test it in the wind?

Where the power is coming from.

How are you going to harvest the energy when you are going at wind speed? There is no relative energy.

The cart is producing more energy than is put into it.

FAIL.

Because, spork, you have it all wrong!

Double FAIL.

The way I see it, the original “inventor” of this cart did it as a joke, a spoof, and he himself admitted that it will not work.

To the best of my knowledge no one alive knows who the original inventor was. Certainly none of the folks that have built and documented these have done it as a hoax.

The original outdoor video is a hoax, as the propeller is turning as a wind turbine. The only chance to see the actual direction of the propeller turning comes right at the end of the video, when the cart slows down. It would be hard to doctor the video at that point, and have the propeller reverse direction, so they did the next best thing; have the cart go off camera until it is stopped, and then pan back on it showing the prop spinning as a prop! It is so obviously a hoax that it really is a joke!

The reason why I am interested is because of what is happening on the turntable. It is a really beautiful example of mechanical heterodyning and it is not to be ignored. This cannot and does not happen outdoors, so why do you insist it does? You have been playing around with these carts for years now, and if anyone is in a position to know this is a hoax, it is you!

no.

Once the cart (if ever) exceeds the velocity of the wind, it is going against a headwind! Saying that you can extract energy from the headwind, in order to move against the headwind, is nonsense. The next time I do my weight training, maybe I will use that same principle: extract energy from the weights I am lifting in order to lift even more weights!

no.

Anyone with a normal functioning brain can see this is nonsense!

You're in no position to make such an assessment.

I have pointed out the step where the calculation is wrong. It is where Silly Atom Man “DECIDES” to extract energy from the force of the propeller, to drive the propeller!

I presume that's the same step that explain why sailboats are a hoax. You certainly can't extract energy from the force on the sail to drive the sail forward.

 

[vanesch]

It is where Silly Atom Man “DECIDES” to extract energy from the force of the propeller, to drive the propeller!

The energy is not "extracted from the propeller to drive the propeller", but is extracted from the WHEELS to drive the propeller (in the cart frame).

It is amazing that you stopped your correct calculation (namely, the kinetic energy of the thrown balls = 500 W to throw out 10 times a 1 kg mass per second with a velocity of 10 m/s, with which everybody here agrees, and the correct thrust that this gives, namely 100 N) when you had to calculate the drag force that a generator driven by the WHEELS will induce to produce 500 W when it is going 10 m/s. It is amazing that you were capable of such a feat while at the same time maintaining the blatant elementary errors (the famous 10 m/s left and 2 m/s right gives you 8 m/s relative - that's a real gem, but also the fact that the wheel slows down when the arm starts to get out of sync with the turntable, and other very elementary mistakes which you defended here). So some part of your brain seems to know some mechanics. Some part of your brain seems to know how to calculate the necessary power to throw 10 1kg balls out at 10 m/s per second. Some part of your brain is capable of calculating the thrust that this will give.

Having a generator produce 500 W when you go 10 m/s gives you a drag of 50 N. Having brakes which give you a drag of 50 N when you go 10 m/s will dissipate 500 W.
I'm pretty sure that the same part of your brain is capable of calculating the drag force that a generator, extracting 500 W, at 10 m/s, will cause. But suddenly, that part of your brain is shut off from the fingers that type posts here on PF, and another part of your brain, the one in denial, takes over to write just about any blatant nonsense in order to avoid the over-evident conclusion: *you are dead wrong on this*.

Because you're only two lines away from that evident conclusion. The first line is:
extracting 500 W (you know, the 500 W that will be FED INTO the propeller which the propeller will USE to get its thrust of 100 N) on a wheel running at 10 m/s induces a drag of:

500 W / 10m/s = 50 N

The second line of this embarrassing reasoning (that that shut-off part of your brain must be trying to yell in there) is that 100 N of thrust, and 50 N of drag, result in a net trust of 50 N.

But here, the emergency shutters have locked up and you seem to be incapable of admitting this.

Now, I understand where your difficulty comes from (apart from psychological factors such as an over-inflated ego). It comes from the "obvious" fact that we "drive the propeller from the wheels" but that if there is any "source of energy" it must be the "wind". This is an elementary although understandable error for a beginning student in mechanics (although for an established engineer, especially a "rocket scientist" it is rather embarrassing), and it is the point I've illustrated several times: energy balances are not the same in different reference frames. It is a known, elementary error of students.

In the cart frame, where it is easy to do the FORCE calculation, the energies are not the same than in the ground frame. In the cart frame, the ground is moving, and can deliver power but the air receives power. In the ground frame, the ground is not moving, and the air is delivering power. The whole "intuitive reason" why one thinks that one cannot go "faster than the wind" is that one looks upon two different energy balances at the same time and mixes up the terms. It is as if one were doing a bookkeeping in US dollar and in pound sterling, mixing up different entries.

In the ground frame, the air is just loosing speed through an interaction with the cart, and that will give it a forward thrust, which is partly offset by a drag of the wheels. In the cart frame, the air is gaining speed, and will result in exactly the same forward thrust which will just as well be partly offset by the drag of the wheels, only in this frame it is easy to calculate this drag force by using conservation of energy internally to the cart.

In the ground frame, the air is loosing energy. That's the ultimate "energy source" (in the ground frame). Going into the cart frame is only done to study the inner workings of the cart (from which we can derive the drag force).

 

[Subductionzon]

tsig as far as going into a headwind and still being able to extract energy from it I suggest you check out some sailing sites.Since it is so everyday people ignore the idea of a boat tacking into the wind. By doing so the boat actually increases the relative headwind it is running against. An iceboat can also run faster downwind faster than the wind when it is sailing on a broad reach. I would suggest you do your own Googling for these since you probably won't believe links supplied by us. So here we have two cases of boats that are able to sail into a headwind that is created by the boat itself and yet it still advances, granted it is not directly downwind in the second case but that is besides the point. Since the prop is geared directly to the wheels it can still extract energy from the wind even when running at wind speed. The blades are doing the equivalent of sailing on a broad reach.

 

[mender]

The reason why I am interested is because of what is happening on the turntable. It is a really beautiful example of mechanical heterodyning and it is not to be ignored. This cannot and does not happen outdoors, so why do you insist it does? You have been playing around with these carts for years now, and if anyone is in a position to know this is a hoax, it is you!

Hilarious, shroder - you are parodying yourself right? The "mechanical heterodyne" thing? So obviously something that you are making up and are exclaiming loudly that everything points to it! Good joke, to try and reverse that and distract by saying that everyone else is in a conspiracy to discredit you and that only a fool would believe any different.

Of course, I could be wrong and you are self deluded enough to believe your line of reasoning. Tell me, what kind of proof would it take to dissuade you of this "theory"? Can you make predictions regarding specific speeds that the cart should travel at rather than just blurting out, "See, it fits again, I was right!"? And if by chance (or more specifically reality) the cart doesn't do what you predict, will you accept that evidence with the same surety that you proclaim the present data to be undeniable proof?

No need to look for complex harmonics that just aren't there. For one thing, the construction of the turntable would dampen any harmonics before they reached any significant magnitude. You also haven't explained to us (and probably not to yourself either) how harmonics could "drive" the cart so much faster than the turntable. If you can, then it can be tested and either proven or disproven with some more testing. If you are truly honest you will have no trouble setting out a test program that will disprove your theory. Forcing a conclusion proves nothing; finding out "bad news" does. That's the way I test my theories, I try to find ways to prove myself wrong. Can you do that?

The cart is connected to the wind at all times because it is always immersed in the moving air mass no matter how fast or which direction it is traveling in. The cart is merely a way to gear up the wind speed. Get yourself a planetary gear set and turn it by hand. Think of one hand as air and one hand as ground as you move two of the three parts of the gear set. By moving the various parts at different speeds you can get underdrive (which is what you claim the cart is geared at), overdrive (which the cart is really geared at) and reverse (which is what an upwind cart would be geared at).

 

[The Dagda]

I must admit I don't even understand what application the word heterodyne has to this? Perhaps I'm just not as awesomely clever as Schroder?

 

[spork]

I must admit I don't even understand what application the word heterodyne has to this?

I think you do. The answer is NONE. This has nothing whatever to do with a heterodyne - mechanical or otherwise.

 

[The Dagda]

I think you do. The answer is NONE. This has nothing whatever to do with a heterodyne - mechanical or otherwise.

You got me I was being ironic, anyway it's a fascinating insight into classical mechanics if nothing else.

I've now learned what heterodyne means too, just goes to show.

 

[swerdna]

You are back to a perfect 2.4 again! In the first video after putting the TT back together again, it is obvious that you are not getting a clean drop out of the forward revolution of the cart. This is a perfect analogy to a partial carrier drop out and the ratio can be almost anything at all. You need a clean and complete drop out of the CW rotation of the cart, a sharp transition, as we see in this last video. A very nice mechanical heterodyne!
Can you please give me the distance from the center of the TT to the center of the track of the wheel as well as the diameter of the small wheel? Thanks!

Good to see you’re still “with us”. Don’t see how two videos where everything is the same except the efficiency of the cart can give the same mathematical results when the observed results are so different.

Wheel running Radius of TT = 60cm. Wheel diameter = 8cm.

 

[swerdna]

Here’s a video of a crude, smaller, tiered TT to change the relative speeds. It was put together very quickly so “never mind the quality, feel the width”. It shows you don’t need to build a big TT to observe the effect. It’s so unbalanced I think any mechanical heterodyne vibrations should be well and truly nullified.