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Newton's third law problem.
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electrodacus:

--- Quote from: Nominal Animal on November 22, 2022, 01:02:32 am ---
This is why I show the CAD model of the exact vehicle I built and verified works as I described –– and Electrodacus claims is impossible ––: so that you can examine it and build it or your own version of it, and prove it yourself.  There is absolutely no trickery here.

--- End quote ---

I want to first mention that I appreciate your long description and I read it at least twice.

I do not need to build the vehicle you mentioned to know it will work and never claimed your device or mine works as shown in many videos.
The question is not if it works or not but how it works.

Both my simpler belt model and your use the same principle is just simple to explain how it works on the model that is easier to visualize.
It is not possible to get rid of energy storage so saying that the string you used is not elastic will not be true as all stings will have elasticity it will just be less elastic than the rubber belt I used.
It is also very likely that the string is not even the energy storage used for your vehicle or not the main one.
For example on the geared vehicle I used (gears instead of the belt) the actual frame of the vehicle was the part that stores most of the energy and you could see how the vehicle body deforms with a regular patterns as energy was charged and discharged.

So the question is the same and in the simplest form I can think of it looks like this


I did not added the force pairs related to gravity as they are not relevant.
In this case the applied force is F1 and all the resulting forces are added in the diagram.
Now if you prefer you can reverse the direction of the treadmill so F1 faces away from F2 to be more similar to your vehicle setup but nothing else will actually change.

So question is in what circumstances the F2 can be larger than F1 to allow the vehicle to be accelerated in the opposite direction the F1 is applied.
The only solution I can see is energy storage so it can be the orange string that is stretched or it can be the green body that is compressed or even a combination of both.
This storing of energy alone will not be sufficient as the energy should be discharged in order to move the vehicle and for that to happen something will need to slip and it is also important that there is a delta between the force needed to slip and the one needed to stick so that energy can be charged and discharged repeatedly.

I actually showed video evidence of what I'm describing but the critique was that vehicle is just not build great and that observed behavior is just some sort of coincidence and not needed.
One thing that can be done is to measure the force needed to move the vehicle and show that is exactly the force needed for the front wheel to slip.
fourfathom:
While this is an interesting topic (originally "downwind faster than the wind"), I am skipping this discussion because we have already discussed it to death with electrodacus here: https://www.eevblog.com/forum/chat/mess-with-your-minds-a-wind-powered-craft-going-faster-than-a-tail-wind-speed/ and here: https://www.eevblog.com/forum/chat/veritasium-wrong-about-faster-than-wind-direct-down-wind/.  Don't bother trying to explain it to him, unless you enjoy repeatedly banging your head against a brick wall.
Nominal Animal:

--- Quote from: IanB on November 22, 2022, 02:27:22 am ---
--- Quote from: Nominal Animal on November 22, 2022, 02:11:39 am ---It is one thing to argue with math and diagrams and even animations, but a completely different thing to show a model one can build and examine, and build the proof with their own hands.
--- End quote ---

Someone built a model before, but Electrodacus simply rejected it and said it couldn't possibly work without including energy storage in the explanation.

--- End quote ---
Oh, I missed that.

This one, with a worm and a pinion, eliminates the energy storage argument.  The worm can turn the pinion, but the pinion cannot turn the worm at all: it immediately locks up.  Any energy storage would therefore have to be in the spool axis.  Because the spool stops turning immediately when you stop pulling on the thread (which also means the trike immediately stops), there is evidence of no energy storage.

Attached are couple of real-life photos of it.  (I removed the front black thread guide block for these, so you can see the structure better, but otherwise it matches the LeoCAD model.)


--- Quote from: electrodacus on November 22, 2022, 02:39:23 am ---Both my simpler belt model and your use the same principle
--- End quote ---
No, they absolutely do not.

Your model uses a gearing ratio which means no stable motion is possible.

This model uses a gearing ratio where stable motion is possible, and indeed, if you pull the thread at a constant velocity, the vehicle travels at a constant velocity as well.  If you relax the thread, the motion stops immediately.  There is no energy storage.  Even the forward momentum of the vehicle itself does not and cannot act as a energy storage, because of the worm-pinion gearing: the forward momentum and wheels cannot feed back energy to the worm.  Lego worm gear is steep, and immediately locks up if you try to back-drive the worm with the pinion gear.

Your model requires energy storage because of the inverse gearing ratio.  Mine works completely without any kind of energy storage, for the reasons I described earlier.


--- Quote from: electrodacus on November 22, 2022, 02:39:23 am ---It is not possible to get rid of energy storage
--- End quote ---
Yes, it is.  I described how, and implemented it in real life.  If you think about how a worm-pinion gearbox works, and demonstration shows the worm side (spool side) does not retain any energy, because as soon as you relax the thread, the spool stops turning, and that immediately stops the trike.

In particular, the vehicle does not move if you just repeatedly tug on the thread.  You need to pull consistently, without any oscillation, to make the vehicle move.

Because the spool, worm, and pinion are in a very rigid structure above the driving wheel axis, any flex in the rest of the structure is irrelevant.

You cannot consider the moment of inertia in the wheels as energy storage, because it cannot be back-fed over the worm-pinion.  It is just rotational inertia in the wheels.  To prove this, switch to smaller, more lightweight wheels (thus less rotational inertia), and the vehicle will move even easier!
(The rotational inertia in the driving wheels means you must pull consistently, as dropping the pull rate even slightly will lead to lockup, because the wheels will try to drive the worm via the pinion, which leads to the worm-pinion locking up.  With less rotational inertia, you can drop the pull rate slightly without lockup, because the wheels won't freewheel as much.)


--- Quote from: fourfathom on November 22, 2022, 03:08:38 am ---we have already discussed it to death with electrodacus here: https://www.eevblog.com/forum/chat/mess-with-your-minds-a-wind-powered-craft-going-faster-than-a-tail-wind-speed/ and here: https://www.eevblog.com/forum/chat/veritasium-wrong-about-faster-than-wind-direct-down-wind/.  Don't bother trying to explain it to him, unless you enjoy repeatedly banging your head against a brick wall.
--- End quote ---
Oh.  Thanks.  I avoided those threads, because I knew a physics view would be lost in the noise in such a thread.  And the physics view is that whenever there is wind with respect to the vehicle, energy can be extracted; and no Earthly wind is stable enough for the switchover (when vehicle goes exactly at downwind speed) to last for any appreciable time, so it is just a matter of efficiency and reducing losses.

It seems I was indeed trapped in a fool's errand, because I did not realize this thread is just a continuation or restatement of those.  :'(
Having played with Lego Technic extensively as a child, I discovered many non-intuitive powering mechanisms on my own, so I know how unintuitive many of them are; I spent many tens of hours just examining the mechanisms.  Here, I just didn't associate the treadmill or "providing linear mechanical power opposite to the desired movement" with the faster than tail wind stuff at all.  :palm:
bdunham7:

--- Quote from: Nominal Animal on November 22, 2022, 03:27:33 am ---And the physics view is that whenever there is wind with respect to the vehicle, energy can be extracted

--- End quote ---

Indeed that is what is apparent at first glance, but it isn't actually true, at least not if you mean with respect to the body of the vehicle.  What is actually needed is simply any reference (the ground in the actual vehicle) and a wind relative to that reference.  The point at which the wind speed equals the vehicle body speed isn't really that special at all because the action of the wind on the body is not the main event.
electrodacus:

--- Quote from: Nominal Animal on November 22, 2022, 03:27:33 am ---No, they absolutely do not.

Your model uses a gearing ratio which means no stable motion is possible.


Yes, it is.  I described how, and implemented it in real life.  If you think about how a worm-pinion gearbox works, and demonstration shows the worm side (spool side) does not retain any energy, because as soon as you relax the thread, the spool stops turning, and that immediately stops the trike.

In particular, the vehicle does not move if you just repeatedly tug on the thread.  You need to pull consistently, without any oscillation, to make the vehicle move.


--- End quote ---

Your vehicle is in no way different in functioning principle.
The gear ratio while larger on your machine it is not different.

On my vehicle the wheels with the smaller pulley is the generator wheel (input) and in your case the input is the spool.
If you can measure the tension in the thread (a small strain gauge load cell connected to an oscilloscope) you will be able to see the charge discharge cycles.
It will obviously look smooth the same way the vehicle I showed looks smooth in real life no slow down video and a bit higher speed when the vehicle kinetic energy storage smooths things same way as adding a capacitor in an electrical circuit will do.

Look at this zoomed in gear and slowed down video 120FPS using my soldering microscope https://odysee.com/@dacustemp:8/120fps24:9
See at around second 9 in the video the gear changing direction for a few video frames imperceptible with the naked eye.  That is the point the energy was discharged and that will repeat at regular intervals. The video is upside down but not relevant.


The point is that you are unable to explain how it works without energy storage and that is my main question. There are plenty of variants of this same vehicle and all of them work the same. For some strange reason you think that your vehicle is different than mine when it is not and no the gear ratio is not reversed as there is no such thing (you just rotate my vehicle 180 degree and it what you are asking witch is the same thing).
Also if I move the paper that is under the back wheels instead of the front the vehicle works exactly the same as it is irrelevant what surface moves relative to the other or in what direction.

In the case of your vehicle if you spool the thread in one direction you get the same vehicle I have and if you spool in the other direction you get the version I will have if I were to twist the belt like an infinity sign so no longer a locked gear and vehicle will move in the direction of the applied force.

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