Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1837825 times)

Offline Rodal

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I saw that in your information. I used traveller's spreadsheet, which is the only working spreadsheet publicly released, (many thanks Mr T.) and it came up with 185 mg of gram-force with a Q of 50K. Not expecting to see that type of Q, I scaled it back to 10K. Plug some numbers into the spreadsheet and see where gram force comes out. Your numbers would be far too small for EMDIYers to validate. Let me know.

That is the problem I have been having. My calculated values, by using experimental data found on the emdrive wiki, are far to small to be measured by the EMDIYer. So, I am a bit stuck on what to expect.

I don't have that kind of space to create what you have, so I have to figure out a smaller way of testing this thing.

If I achieve null results using the shawer inspired spreadsheet, then I would conclude his position is irrelevant. Reason I chose to follow it was its the only public tool I am aware of and its within a diyers measurement capability. Should nasa cough up a designers tool, which I highly doubt, I would consider it provided it doesn't require NIST to test the results.
But then, to be consistent with Shawyer, you have to use his mode shapes, Shawyer uses transverse ELECTRIC TE01 modes, just like Yang.  So you should choose the dimensions that give TE013 at 2.45GHz instead of the dimensions that give the transverse magnetic TM212 mode (used by NASA) at 2.45 GHz.

////////////////////////////////

bigDiameter = 11.01 inches;
smallDiameter = 6.25 inches;
axialLength = 10.2 inches;  NOTICE 10.2 inches -- in this case

with FLAT ENDs with a TRANSVERSE ELECTRIC MODE.  It resonates at 2.45044 GHz with TE013



////////////////////////////////

It would be inconsistent for you to use the  dimensions that give the transverse magnetic TM212 mode (used by NASA) at 2.45 GHz
« Last Edit: 06/26/2015 02:20 AM by Rodal »

Offline rfmwguy

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(...)

Alright, I have watched the video and your setup looks great!

I must have typed it incorrectly, but I was referring to the laser terminus, not actual laser measurement. So, my fault on that.

Have you checked for linearity of distance to weight?

The NASA test around our power input of 8W is 0.05 mN which is roughly 0.005 mg. So, assuming you have a linear relationship  of 2.5 in/200 mg, the hypothetical thrust will cause a rise of about 0.0000625 inches.

Is that correct?

-I

I saw that in your information. I used traveller's spreadsheet, which is the only working spreadsheet publicly released, (many thanks Mr T.) and it came up with 185 mg of gram-force with a Q of 50K. Not expecting to see that type of Q, I scaled it back to 10K. Plug some numbers into the spreadsheet and see where gram force comes out. Your numbers would be far too small for EMDIYers to validate. Let me know.
Hey Dave,

take a gander at this table:  http://emdrive.wiki/Experimental_Results

in the rightmost columns labeled Force/PowerInput

the numbers from TheTraveller are based on Shawyer's formula: they are (rounding off) 100 to 1,000 times greater than NASA' findings with mode TM212.

So, if your Q is 5,000 instead of 50,000 and your force/PowerInput agrees with NASA (as Iulian Berca's did) then your force could be 10,000 (ten thousand times) smaller than what TheTraveller calculated.

Such is the disparity between what NASA and Shawyer have reported.  That's why many people in this forum have stated that NASA effectively nullified Shawyer's measurements (actually NASA got zero force without a dielectric).

See my reply to drbagelbites. Shawyers reported results were within reasonable measurement range. ew is working too near measurement noise levels for homeboy here. Consider my build a possible shawyer refutation, not an ew validation. if null, my expense has been low and I had a little build fun in the process...been a few years.

Offline DrBagelBites

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...

See my reply to drbagelbites. Shawyers reported results were within reasonable measurement range. ew is working too near measurement noise levels for homeboy here. Consider my build a possible shawyer refutation, not an ew validation. if null, my expense has been low and I had a little build fun in the process...been a few years.

You have plans for a different setup if null?

And agreed, building is the best part regardless if it works.

Offline SeeShells

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Good information and some sweet basic engineering. I also am going with the fulcrum. I've  started to laminate the beam I'm going to use.

Took a 100 mile RT today only to find that the very nice piece of copper with perforations sold this morning, they we supposed to hold it for me. grrrr. So I will be finding another supplier.

Shell

Wow! What a build! :D

How long of a beam are you using?

-I
Thanks. 12 foot.

Offline rfmwguy

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...

See my reply to drbagelbites. Shawyers reported results were within reasonable measurement range. ew is working too near measurement noise levels for homeboy here. Consider my build a possible shawyer refutation, not an ew validation. if null, my expense has been low and I had a little build fun in the process...been a few years.

You have plans for a different setup if null?

And agreed, building is the best part regardless if it works.

I will experiment with antennas, placement and possibly dielectrics or frustum tweaks, but not with power input. Others are doing that.

Offline frobnicat

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Something that at least @frobnicat will appreciate - can we build an overunity device (free energy, perpetual motion, you know the drill) with the current crop of EmDrives?

The answer is - maybe, but not on Earth; only in space.

A generous k-value looks like about 2*10-4 N/W.
That corresponds to a breakeven velocity of 10 Km/s.
That's a problem for a terrestrial rotator, I think. No - actually I know it is  8)

But in space we can make the radius arm as big as we like.
Let's say that we can engineer a complete EmDrive system to withstand 100 gee.
Then the breakeven radius is 100 Km.
That's pushing it, but not completely beyond the bounds of possibility.

The hub would be anchored at a mountain top on the Moon and the plane of rotation would be horizontal.

Isn't it necessary to have the same kind of stuff that would make a space elevator possible to reach tangential velocities at 10km/s ? Tangential velocity is limited by specific strength of materials... limit is around 2km/s tangential velocity for energy storage flywheels, regardless of radius. Might be extended a little bit with tapered schemes but this quickly becomes impractical.

Without unobtainium materials, I would go with two contra-rotating satellites sharing the same orbit. They both carry a coil (big loop) and a permanent magnet. Each time they cross at 2*7.8km/s = 15.6km/s relative velocity, the induced current (energy) is recovered. This slows the two satellite a little bit, but they use part of this energy to power an EMdrive to restore velocity, with a net excess to dispose of.

Assuming unleashed budget, make two contra-rotating orbital rings, filled with emdrives and inductor and induced coils (basically a gigantic generator). Spacing one EMdrive every metre makes for about 42 millions EM drives on each ring. Each one consumes 1kW(electric) and thrusts at 0.2 N : total consumption 84GW (for the two rings), total tangential thrust 8.4MN (Mega Newtons, for each ring). Recoverable mechanical power at constant velocity : P=Fv=131GW. Generators efficiencies of 95% are common, but maintaining small gaps at 15.6km/s relative velocities may be challenging, lets say 70% efficiency seems achievable : we have recovered about 92GW(electric), enough to feed the EM drives + a small net benefit of a few spare GW.

Nice point with this design is that it allows the EM drives to operate at 0g (off axis), unlike a wheel, and also that it suffices to have a massive and dense enough body to orbit to make any thrust/power EM drive slightly above photon rocket to generate net power benefit, without requiring solid materials of impossible specific strength. About 50µN for 50W as per Eagleworks results needs a relative velocity above 1000km/s. A body with a low orbit velocity of 1000km/s will allow 2000km/s relative speed, ample margin for limited efficiency in the feedback + net surplus. Just requires orbiting a white dwarf for instance...

Offline aero

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@Rodal,
Thanks for the correct dimensions. Using the 9.00 inch length, and narrowing the search bandwidth, Harminv calculates the resonant frequency to be 2.45163893E+009 which seems pretty close. Of course it helps to start with the solution.
I started with the search bandwidth = 0.1*drive frequency (your exact solution, 2.45032 GHz), got resonance at 2.45475327E+009, plugged that frequency back in with BW = 0.05, got 2.45163969E+009 Hz, then BW=0.04 gives 2.45163893E+009 Hz. This was with the "magnetic" antenna configured and located half wavelength from the small end.

I tried increasing the resolution but that doesn't seem to be the way to use Harminv. After 5 hr. 20 min at double the resolution, Harminv returned nothing. Counter intuitively, reducing the bandwidth increases the run time almost as much as increasing the resolution.

Anyway, if I'm reading your data correctly, that is a kind of verification of Harminv's capability to locate resonant frequency accurately in 3D. Now all I need to know is the answer and Harminv will converge to it.  ???

Oh, and the Q was extremely high, in the millions using the copper model for the cavity,

Now do I understand you that rfmwguy will use 10.2 inch length (TE013) instead of the 9 inch length (TM212)? That does seem like a good choice IMO.
Retired, working interesting problems

Offline SeeShells

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I've read as many theories for the why this cannot work as for the theories of why it does, makes one dizzy. And it matters not to me as I will build it and Damn the Theories Full Speed Ahead.

I believe something is happening within the cavity that we just can't grasp ... yet. I will be  open when the time comes to show all, bear my failure, or shout my success and just maybe we can whittle down the theories. I'm tired of being dizzy.

Shell

Offline SeeShells

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@Aero,

Been doing some numbers and I'll post new ones in the morning for you if you wouldn't mind and are still interested.

Shell

Offline SeeShells

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http://phys.org/news/2015-06-quantum-hall-effect-fundamental-property.html

"We had previously done work looking at evanescent electromagnetic waves," says Konstantin Bliokh, who led the research, "and we realized the remarkable properties we found, an unusual transverse spin—was a manifestation of the fact that free-space light exhibits an intrinsic quantum spin Hall effect, meaning that evanescent waves with opposite spins will travel in opposite directions along an interface between two media."
Evanescent waves propagate along the surface of materials, such as metals, at the interface with a vacuum, in the same way that ocean waves emerge at the interface between the air and the water, and they decay exponentially as they move away from the interface.
The quantum spin Hall effect for electrons allows for the existence of an unusual type of material—called a topological insulator—which conducts electricity on the surface but not through the bulk of the material. The team was intrigued to learn that an analogy for these can be found for photons. Though light does not propagate through metals, it is known that it can propagate along interfaces between a metal and vacuum, in the form of so-called surface plasmons involving evanescent light waves. The group was able to show that the unusual transverse spin they found in evanescent waves was actually caused by the intrinsic quantum Hall effect of photons, and their findings also explain recent experiments that have shown spin-controlled unidirectional propagation of surface optical modes.


Read more at: http://phys.org/news/2015-06-quantum-hall-effect-fundamental-property.html#jCp

Offline Rodal

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@Rodal,
Thanks for the correct dimensions. Using the 9.00 inch length, and narrowing the search bandwidth, Harminv calculates the resonant frequency to be 2.45163893E+009 which seems pretty close. Of course it helps to start with the solution.
I started with the search bandwidth = 0.1*drive frequency (your exact solution, 2.45032 GHz), got resonance at 2.45475327E+009, plugged that frequency back in with BW = 0.05, got 2.45163969E+009 Hz, then BW=0.04 gives 2.45163893E+009 Hz. This was with the "magnetic" antenna configured and located half wavelength from the small end.

I tried increasing the resolution but that doesn't seem to be the way to use Harminv. After 5 hr. 20 min at double the resolution, Harminv returned nothing. Counter intuitively, reducing the bandwidth increases the run time almost as much as increasing the resolution.

Anyway, if I'm reading your data correctly, that is a kind of verification of Harminv's capability to locate resonant frequency accurately in 3D. Now all I need to know is the answer and Harminv will converge to it.  ???

Oh, and the Q was extremely high, in the millions using the copper model for the cavity,

Now do I understand you that rfmwguy will use 10.2 inch length (TE013) instead of the 9 inch length (TM212)? That does seem like a good choice IMO.

That's excellent !!!!


Recall that the cavity with L=9 inches is the Brady cavity.

Recall that NASA's Frank Davis calculated that the Brady cavity L=9 inches, resonates at 2.4575 GHz with mode TM212.

So your Meep model with flat ends frequency 2.4516 GHz is very close to COMSOL's FEA frequency.

Both COMSOL's FEA and MEEP's FD frequencies are a little higher than what I calculate with the exact solution (2.45032 GHz).


COMSOL FEA =  2.4575 GHz  Mode TM212
MEEP FD       =  2.4516 GHz  Mode Shape ???
Exact            =  2.4503 GHz (but with flat ends modeled with approximate equation) Mode TM212

The small discrepancy could be due to the fact that both FEA and FD analysis are stiffer (higher frequency) than the exact solution because it would take an infinite number of finite elements, or an infinite number of finite difference grid points to converge to the solution, so a finite mesh is always stiffer (higher frequency) than the exact solution.  It could also be because my exact solution uses spherical ends, and to approximate a flat end I derived a formula to calculate the equivalent radius of a spherical end that mimics a flat end.  That formula is an approximation.

Anyway, my exact solution, COMSOL's FEA and MEEP's FD are in agreement to within less than 1%, which I think is very good.  It is interesting that MEEP is actually a little closer to the exact solution than to COMSOL FEA's but that may be within numerical noise.

The problem is that it appears that you need to give to HarmInv an initial value to search that is pretty close to the solution.  So, like you say, you have to "know the solution to converge to it".

This is typical of iterative solutions to problems that are difficult to converge to.

As to why it is difficult to converge to, we have to think about it.  My understanding is that your MEEP formulation uses linear equations (no nonlinear constitutive equations in your model). 

So the difficulty in converging has something to do with the inversion performed by HarmInv, it looks like the MEEP problem is numerically ill-conditioned.

HarmInv: given a discrete-time, finite-length signal that consists of a sum of finitely-many sinusoids (possibly exponentially decaying) in a given bandwidth, it determines the frequencies, decay constants, amplitudes, and phases of those sinusoids. 



It can, in principle, provide much better accuracy than straightforwardly extracting FFT peaks, essentially because it assumes a specific form for the signal. (Fourier transforms, in contrast, attempt to represent any data as a sum of sinusoidal components, and are thus limited by the uncertainty principle.) It is also often more robust than directly least-squares fitting the data (which can have problematic convergence), since it re-expresses the problem in terms of simply finding the eigenvalues of a small matrix.

In order to do this it has to invert a matrix. It looks like the matrix is ill-conditioned. It means that the diagonal eigenvalues in the matrix are small, in comparison to the magnitude of the off-diagonal components.

Why is it numerically ill-conditioned?  We will need to think more about it.

It can be due to:

a) the discretization model 
b) the boundary conditions
c) something inherent to the problem: evanescent waves? or the RF feed? , something that is "fighting against" the standing wave resonance.  We see this 'fighting" in the movie frames.  Most likely the RF feed "fights with the standing wave"

Both the exact solution and COMSOL's FEA do not have this problem because they are not solving the problem that way.  They are not using an excitation frequency, instead they are solving the eigenvalue problem of a cavity to find the natural frequencies.  This is not what MEEP is doing, in MEEP you are placing an antenna and finding the response.  HarmInv's eigenvalue problem is related to inverting the output signal from the FD analysis with a known excitation (instead of zero excitation).

Where did you place the antenna for the L=9 inch model to get resonance at 2.4516 GHz ??

Or is it simply due to the high Q, which doesn't allow you to get these solutions unless your initial guess is within the bandwidth frequency/Q ?
« Last Edit: 06/26/2015 02:49 PM by Rodal »

Offline A_M_Swallow

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I saw that in your information. I used traveller's spreadsheet, which is the only working spreadsheet publicly released, (many thanks Mr T.) and it came up with 185 mg of gram-force with a Q of 50K. Not expecting to see that type of Q, I scaled it back to 10K. Plug some numbers into the spreadsheet and see where gram force comes out. Your numbers would be far too small for EMDIYers to validate. Let me know.

That is the problem I have been having. My calculated values, by using experimental data found on the emdrive wiki, are far to small to be measured by the EMDIYer. So, I am a bit stuck on what to expect.

I don't have that kind of space to create what you have, so I have to figure out a smaller way of testing this thing.

The laser pointer does not have to be aimed directly at a white wall, you can bounce the light off a mirror or 3.

Offline DrBagelBites

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The laser pointer does not have to be aimed directly at a white wall, you can bounce the light off a mirror or 3.

Right, and I have definitely considered that as well as using convex mirrors to sort of "amplify" the effect of a shift. I might be changing my plan to use a fulcrum as well, mostly because it is cheap and easy to make. 

Offline OttO

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For the DIY

Take a look at the following paper, it seems to me that you could improve the Q factor by cooling the ends of the cone.


A high quality, efficiently coupled microwave cavity for trapping cold molecules
http://iopscience.iop.org/0953-4075/48/4/045001/article

"The Q-factor was measured as the cavity warmed up from 77 K to room temperature"
« Last Edit: 06/26/2015 01:19 PM by OttO »

Offline Rodal

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For the DIY

Take a look at the following paper, it seems to me that you could improve the Q factor by cooling the end of the cone.


A high quality, efficiently coupled microwave cavity for trapping cold molecules
http://iopscience.iop.org/0953-4075/48/4/045001/article

"The Q-factor was measured as the cavity warmed up from 77 K to room temperature"

Great paper.  They also find the hole size that maximizes the intra-cavity electric field. And they develop an analytical theory of the aperture-coupled cavity that agrees well with their measurements, with small deviations due to enhanced diffraction losses due to the opening.

In other words, this paper addresses a lot of what we are discussing: what is the best location for the RF feed? and for a coupled waveguide feed (like in Yang's experiments), what is the optimal aperture size for the RF feed?

For the modes to resonate, the wavefront at the mirror must match the mirror curvature, and this determines the Rayleigh parameter.

They find that the ideal location, for mode n=3, for this symmetric cavity, is the middle location along the length.  Which coincides with the location of maximum amplitude, as proposed here  http://forum.nasaspaceflight.com/index.php?topic=37642.msg1394232#msg1394232 and here http://forum.nasaspaceflight.com/index.php?topic=37642.msg1394326#msg1394326 , and without any "arm waving",  frobnicat ;)
« Last Edit: 06/26/2015 12:16 PM by Rodal »

Offline francesco nicoli

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it is sad that @thetraveller has disappeared. I would have much appreciated some clarifications on the nature of the "new" paper. If there are no replies, it seems to me that he/she will lose any credibility left.

Offline Rodal

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it is sad that @thetraveller has disappeared. I would have much appreciated some clarifications on the nature of the "new" paper. If there are no replies, it seems to me that he/she will lose any credibility left.

Francesco,

This is the problem with communications when people that don't use their real names indulge in promotion, claiming that they have special connections, that they are "in the know", "they know more and have better information",  that they have special access to unpublished reports and unaccessible information and special influence, discussing "programs that went dark", access to "proprietary secret information", claiming that they are "not the only active NSF member who has the paper": they can always come back under another monicker, since nobody knows who they really are.

There is no real credibility issue, because credibility is attached to a monicker instead of to a real name.  All they have to do is to change their monicker.  This is a great difference between communications in real life and communications in a forum.

JR
« Last Edit: 06/26/2015 01:39 PM by Rodal »

Offline Notsosureofit

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For the DIY

Take a look at the following paper, it seems to me that you could improve the Q factor by cooling the end of the cone.


A high quality, efficiently coupled microwave cavity for trapping cold molecules
http://iopscience.iop.org/0953-4075/48/4/045001/article

"The Q-factor was measured as the cavity warmed up from 77 K to room temperature"

It looks like that cavity solution can be "split" into two with the center division being a planar surface.  The walls in this case are not conical.  It would be interesting to see the rest of the mode structure in that case.

Offline Rodal

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For the DIY

Take a look at the following paper, it seems to me that you could improve the Q factor by cooling the end of the cone.


A high quality, efficiently coupled microwave cavity for trapping cold molecules
http://iopscience.iop.org/0953-4075/48/4/045001/article

"The Q-factor was measured as the cavity warmed up from 77 K to room temperature"

It looks like that cavity solution can be "split" into two with the center division being a planar surface.  The walls in this case are not conical.  It would be interesting to see the rest of the mode structure in that case.

I wonder whether a closed-form solution would be available for the non-symmetric case.  When no closed-form solutions are available, much less is known about the nature of the solution, as numerical solutions only allow very limited exploration of the whole state of affairs.

A lot is known for linear solutions of symmetric problems.  Much less is known for nonlinear problems. 
That chaos and randomness is possible to arise from simple systems of coupled nonlinear differential equations was only learnt relatively recently (mainly due to Poincare) and mainly after WWII: issues of parametric amplification, etc.  Chaotic solutions that are non-intuitive that arise in mundane systems leading to self-excited oscillations and chaotic motion.
« Last Edit: 06/26/2015 12:30 PM by Rodal »

Offline rfmwguy

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it is sad that @thetraveller has disappeared. I would have much appreciated some clarifications on the nature of the "new" paper. If there are no replies, it seems to me that he/she will lose any credibility left.

Francesco,

This is the problem with communications when people don't use their real names to  indulge in promotion, claiming that they have special connections, that they are "in the know", "they know more and have better information",  that they have special access to unpublished reports and unaccessible information and special influence, discussing "dark programs" and behavior in an Internet forum that they would be more careful to indulge in if they were using their real names: they can always come back under another monicker, since nobody knows who they really are when using monickers.

There is no real credibility issue, because credibility is attached to a monicker instead of to a real name.  All they have to do is to change their monicker.  This is a great difference between communications in real life and communications in a forum.

JR

While I enjoyed Mr Ts infectious enthusiasm, many posts were repeats and reminded me of advocacy posts. There is a growing marketing industry out there that pays people for position statements on social media; sponsored advertising in the 21st century if you will. Not saying Mr T is one, but posters should avoid these traps...it is transparent to many. And yes, nicknames are fine but real names on formal papers is a must.

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