DDWFTTW - Tests.

[ynot]

This is the opposite of science. If it's true that you were aware of this flaw you're simply guilty of intentionally misleading the people to whom you're presenting your results and your argument. But I suspect the statement is simply a lie. You were obviously aware that the turntable wasn't powered, but you were somehow not aware that this would completely invalidate your results - or if you were, you hoped no one would notice or ask the question. You certainly ignored the question enough times.

You might note that we have done our best to outline the parameters of our tests in each video. That IS science.

Don't see how you conclude that I'm "guilty of intentionally misleading" when the OP presents no "results" and makes no "argument". I simply posted a video of a very quick experiment with a marble on a turntable. I said I shouldn't have called it a test. "Suspect" I'm a liar all you like it really doesn't bother me. Your "science" seems to be more interested in attempting to discredit people that don't agree with you with personal insults rather than intelligent debate. Perhaps you're miffed that you didn't "spot the flaw". I will ignore any future insults and will only respond to comments that address the issue. What you choose to do is up to you.

 

[ynot]

Double post

 

[ynot]

fredricks & John Freestone - (in laymans terms) How the cart moves relative to the moving surface is a "battle" between propeller thrust (combined with whatever amount of KE the cart develops) and rolling resistance. When the cart is "active" on the moving surface it has a "received" amount of energy and is continuously gaining energy from the moving surface at the same time as it is continuously losing energy to rolling resistance. Whether the received/continuously gained energy is sustainable against the continuous loss of energy to rolling resistance or not is what I hope to establish by testing on a turntable. If the battle is lost to rolling resistance then I believe it is far more gradually and slow than most people realise. An endless turntable is better to use for this testing than treadmill.

 

[spork]

Don't see how you conclude that I'm "guilty of intentionally misleading"

Let's look at your quote:

Yes, the turntable was spun up by hand and was gradually slowing in the video. I was always fully aware of the consequences of this but I didn't mention it as I wanted to see if anyone would "spot the flaw"

Your "science" seems to be more interested in attempting to discredit people that don't agree with you...

My "science" seeks to discredit voodoo and those that propose or practice it.

 

[ynot]

Let's look at your quote:

It's hardly possible to conduct a spot the flaw test by revealing the flaw. Besides, I didn't provide any information about anything in the video, not just whether the turntable was constantly powered or not. As I said earlier, I did more testing than was shown on the video and the rate of slowing of the turntable didn't make and noticeable difference to it being constantly powered or sped up. My next turntable will be powered at a constant speed and all relevant information that I can think of will be fully revealed.

 

[ynot]

The opposite-side carts design is an interesting touch, ynot, which is intuitively appealing to 'balance' the forces, but I wonder if it does that significantly in practice. The centrifugal force of the single cart moving in a circle would be balanced at the central bearing, but it probably wouldn't be rotating very fast (unless you get a really efficient design) - windspeed, of course, being when it is at rest w.r.t. the ground - so the force won't be very great. However, the fact that you have doubled the motive force by having two mechanisms with two props, your twin cart should have twice the power, even if none of the losses are offset by better balanced bearing forces.

The turntable cart I made had two props so I think the power would be much the same as two sided cart I will be building. I think this design will also be very easy to construct. I was surprised at the speed my cart achieved against the rotation of the turntable. One of the reasons I want to have a balanced cart is that the initial "unbalanced" cart seized up when the turntable was spinning very fast. The cart spinning around at the same speed as the turntable was a very unbalanced scenario and a potentially very dangerous bucking bronco. Both the cart and turntable were badly damaged and was one of the reasons I couldn't do more testing. When I rebuild the turntable and new cart design I will post videos and invite comments and critiques (I also expect a few insults ;-).

 

[spork]

It's hardly possible to conduct a spot the flaw test by revealing the flaw...

And it's not much of a "spot the flaw" test if it's passed off as a valid experiment and you refuse to answer the direct question about the turntable being powered - because you're hoping people will simply let the issue die.

You're welcome to peddle that "explanation" and see if it flies with anyone else. Personally, it tells me not to pay too much attention to any experimental results you post.

 

[Dan O.]

The change in rotation of the flywheel is visible in the video itself. It doesn't appear to be a significant factor. As the marble looses energy, it starts to move in an orbit (in the same direction as the rotation of the flywheel). If the disk didn't have a hole in the center, the marble's orbit would end up going around the rotation axis and then it would be clear to everybody that the marble is traveling slower than the disk.

 

[ynot]

The change in rotation of the flywheel is visible in the video itself. It doesn't appear to be a significant factor. As the marble looses energy, it starts to move in an orbit (in the same direction as the rotation of the flywheel). If the disk didn't have a hole in the center, the marble's orbit would end up going around the rotation axis and then it would be clear to everybody that the marble is traveling slower than the disk.

By "flywheel" you are obviously referring to the turntable. Using a heavier, better balanced and rounded metal ball bearing gave a better demonstration. The ball rolled much more smoothly, circled less and lost energy more slowly. It became a far more dangerous projectile however when it occasionally fell in to the spokes.

 

[Dan O.]

Using a heavier, better balanced and rounded metal ball bearing gave a better demonstration. The ball rolled much more smoothly, circled less and lost energy more slowly.

That's pretty much what I predicted back in post 10.

 

[sol invictus]

By "flywheel" you are obviously referring to the turntable. Using a heavier, better balanced and rounded metal ball bearing gave a better demonstration. The ball rolled much more smoothly, circled less and lost energy more slowly. It became a far more dangerous projectile however when it occasionally fell in to the spokes.

The ball behaved as expected - I don't understand what you think it shows that's at all interesting. It doesn't matter very much that the turntable wasn't powered, so long as it wasn't slowing down too rapidly.

This whole debate has gotten increasingly mysterious to me - we understand perfectly what are the forces acting on the cart either on the treadmill or in the wind. We understand why it goes DDWFFTW, and why a marble won't. It's obvious that this is nothing to do with "stored energy", because that alone cannot make the cart accelerate from wind speed to FTTW.

All of this stuff follows from Newton's laws, and it agrees with all the evidence. So really - what more is there to discuss?

 

[ynot]

The ball behaved as expected - I don't understand what you think it shows that's at all interesting.

I think it's an interesting effect to observe and not what not what some people may have expected (as they have commented). It is not so impressive that a cart with a propeller can hover on a treadmill when a ball can be seen doing almost the same on a turntable (or treadmill). Of course the ball can never travel faster than the overall speed of the moving surface because it doesn't have the facility to do this. A cart does in the form of a propeller.

It doesn't matter very much that the turntable wasn't powered, so long as it wasn't slowing down too rapidly.

I agree. Spork seems to be the only one that has an issue with it. I suspect that he will say that the issue is that I'm a liar, and an incompetent one at that.

This whole debate has gotten increasingly mysterious to me - we understand perfectly what are the forces acting on the cart either on the treadmill or in the wind. We understand why it goes DDWFFTW, and why a marble won't. It's obvious that this is nothing to do with "stored energy", because that alone cannot make the cart accelerate from wind speed to FTTW.

All of this stuff follows from Newton's laws, and it agrees with all the evidence. So really - what more is there to discuss?

Perhaps "achieved or developed energy" would be a better term than "stored energy". If the prop was sufficiently highly geared to the wheels and the speed of the treadmill was fast enough I imagine the cart could be made to fly vertically with the thrust of the prop. This doesn't mean it could do this continuously however. I have seen my cart both hover and progress against the turntable. My main question is can it do this continuously? If it can I don't currently see any reason why this doesn't mean it can travel DDFTTW. I am more interested in physically testing than discussing this.

 

[Michael C]

I have seen my cart both hover and progress against the turntable. My main question is can it do this continuously? If it can I don't currently see any reason why this doesn't mean it can travel DDFTTW. I am more interested in physically testing than discussing this.

Questions:

1. - How long did the cart keep progressing against the turntable?
2. - What was the speed of the turntable when the cart progressed against it?
3. - At this point, did you keep the turntable going at a constant speed, or was it freely spinning, so that it was gradually slowing down?

In order to test if the cart can progress continuously against the turntable, you need to have the means of keeping the turntable going for an indefinite time at a given speed. For any DDWFTTW cart, there will be a certain wind speed at which the cart will run exactly at the speed of the wind, that is to say it will "hover" on the turntable. At this speed the forward thrust from the propeller is just enough to overcome the losses due to friction. If the wind speed drops lower than this level, the cart will lose speed. For the cart to go faster than the wind, the wind speed must be above this level. For the cart to keep going faster than the wind, the wind speed must stay above this level.

 

[fredriks]

Ynot, the difference is in having a cart going at the same speed as the turntable or a cart that start to go faster than the turntable. It can look like the first one happen for some time with stored energy and low friction. The second cant simple happen with stored energy and low friction unless you change the cart after you release it with for example a gear box.

Take a wheel and go out to a road. Roll the wheel to some speed (the wheel in contact with road) and release the wheel. The wheel is definitely not going to accelerate but might be at almost the same speed for some time due to inertia.

The importance are the acceleration or force from gravity that we can see on the treadmill.

 

[spork]

This whole debate has gotten increasingly mysterious to me - we understand perfectly what are the forces acting on the cart either on the treadmill or in the wind. We understand why it goes DDWFFTW, and why a marble won't. It's obvious that this is nothing to do with "stored energy", because that alone cannot make the cart accelerate from wind speed to FTTW.

Actually, ynot has explained several times that he doesn't buy any of this.

All of this stuff follows from Newton's laws, and it agrees with all the evidence. So really - what more is there to discuss?

For those that understand and accept Newton's laws - nothing.

Spork seems to be the only one that has an issue with it.

Wrong. Several people asked whether it was powered, and you refused to answer.

I suspect that he will say that the issue is that I'm a liar, and an incompetent one at that.

That's not "the issue" - but happens to be the case.

I am more interested in physically testing than discussing this.

It seems you're more interested in bitching that JB and I won't do your testing for you. So go do your testing. Then come back and report your results. Feel free to leave out any important data such as using magnets or strings to make your cart do as you'd like to see it do.

 

[Dan O.]

I am more interested in physically testing than discussing this.

The discussion can help the testing. The Wright brothers didn't just slap together an airplane and try to fly like all the yahoos before them. They first developed the physics they needed so they would know what was required to make the plane work.

One of the most critical aspects for the cart is the propeller efficiency. If your propeller is not over 50% efficient, your cart cannot go faster than the wind. I posted a sketch of a simple gig to measure propeller efficiency in the other thread. Each propeller will have a speed where it achieves maximum efficiency. If you know what this is it will help you design the rest of the cart for the best performance.

 

[spork]

If your propeller is not over 50% efficient, your cart cannot go faster than the wind.

This depends on the advance ratio and efficiencies of the drive-train etc. I'm pretty sure it is possible to build a DDWFTTW cart whose prop efficiency is less than 50%.

 

[ynot]

By saying "I am more interested in physically testing than discussing this" I didn't mean I don't see a value in pre-test discussions and I'm very happy to do so. Here is my current test thinking and any constructive comments and suggestions are welcome . . . Build a turntable that can be run at a constant speed with an electric motor. Gear the motor to the turntable so different speeds can be tested. Build a balanced, double sided two prop cart. Hold the cart against the motion of the spinning turntable until it can progress against it with the thrust of the props and whatever KE is involved. Let it run unrestricted for a reasonably long period to see if it retains the ability to progress against the turntable or not. Rinse and repeat.

Having a balanced double sided cart helps ensure that the cart is not adversely affected by any lack of perfect leveling of the turntable. It also allows a test to be conducted where the cart and turntable are started together from scratch with no restriction on the cart and without having the whole thing turning in to a violent bucking bronco.

The tests I did before my first cart self-destructed displayed that the cart could easily be made to hover and progress against the turntable. I think a cart on a turntable may work more efficiently than one on a treadmill because as the cart turns the prop is continuously thrusting against "new" still air and not moving prop-wash air as it is on the treadmill. As long as the cart can be made to move against the motion of the surface that powers it then it should be able to retain the ability to do it indefinitely if it's energy is not being gradually lost to rolling resistance.

 

[ynot]

Questions:

1. - How long did the cart keep progressing against the turntable?
2. - What was the speed of the turntable when the cart progressed against it?
3. - At this point, did you keep the turntable going at a constant speed, or was it freely spinning, so that it was gradually slowing down?

In order to test if the cart can progress continuously against the turntable, you need to have the means of keeping the turntable going for an indefinite time at a given speed. For any DDWFTTW cart, there will be a certain wind speed at which the cart will run exactly at the speed of the wind, that is to say it will "hover" on the turntable. At this speed the forward thrust from the propeller is just enough to overcome the losses due to friction. If the wind speed drops lower than this level, the cart will lose speed. For the cart to go faster than the wind, the wind speed must be above this level. For the cart to keep going faster than the wind, the wind speed must stay above this level.

1. - Not long enough in my opinion to tell if the cart's energy was being gradually lost to rolling resistance. As I have said earlier I don't think the cart was good enough to use for credible testing. Hopefully the next one I build will be as I will have much more time to work on it.

2. - Fast enough for the cart to hover and progress against the turntable.

3. - Before the whole thing violently self-destructed I was able to briefly test with the turntable gradually slowing, being turned by hand at a relatively constant speed and being sped up. None of the testing was good enough to take seriously as the gears on the cart kept briefly binding and eventually locked up completely.

 

[ynot]

Ynot, the difference is in having a cart going at the same speed as the turntable or a cart that start to go faster than the turntable. It can look like the first one happen for some time with stored energy and low friction. The second cant simple happen with stored energy and low friction unless you change the cart after you release it with for example a gear box.

Take a wheel and go out to a road. Roll the wheel to some speed (the wheel in contact with road) and release the wheel. The wheel is definitely not going to accelerate but might be at almost the same speed for some time due to inertia.

The importance are the acceleration or force from gravity that we can see on the treadmill.

As different parts of a turntable surface travel at different speeds (slower toward the centre) it's obviously important that the cart always travels only on a particular circumferal (hope that's the correct word) path. This easy to achieve with a rigid tether to the centre. I will start by testing with the cart gradually progressing against the turntable but will test at several speeds including whether the cart can sustain a hover.