I was able to confirm that it is RFI affecting the scale causing the apparent changes in force. I used a rubber duck antenna suspended above the scale and was able to reproduce the ~30mg change with 30mw of net power, which seems like a plausible leakage value from the adjustable end which is not well sealed. That end is closest to the scale in the "Up" orientation that produced the largest force changes.
As I've mentioned here before, one of the best devices for measurement is the Mettler H20, a miracle of Swiss engineering, fully mechanical, available from time to time on eBay for a not unreasonable sum, and gets you 0.1 microNewton force resolution (10 microgram-weight). A friend of mine has automated it using a laser position measuring device, and gets even better resolution plus electronic data logging capability.The downside of the Mettler is that it takes a maximum of 200 gm.
Is the MEEP model's finite difference grid fine enough and the MEEP eigensolution HarmInv well-conditioned enough to successfully predict the frequencies measured by NASA and other experimenters, using their geometrical dimensions?@ RodalDon't you mean, "The frequencies that COMSOL indicated that they should use? And the answer is that Harminv only comes close. And would you care to give an error bound on the measured (stated) dimensions of the cavities and the sensitivity of resonance to those measurements? I don't expect Harminv to reproduce the COMSOL numbers even if I do input the same numbers and precision used but we don't know what was used, do we. As for the experimental data, we have the same problems in spades. So if you could tell me what the resonance frequency sensitivities to small diameter and length are, that would be very helpful. Then we could estimate probable measurement errors and see if they are realistic. And if you can't tell me what the sensitivities are, then I can tell you, by using numerical data.I doubt that Paul made a measurement error by as much as a tenth of an inch but unless he used a large micrometer to measure the height, he could have. And even with a micrometer, unless he was very very careful he could have introduced a slight angle to his measurement. My point is that you know as well as I that my computer is not up to running high resolution in 3D but Harminv does do much better in 3D than it ever did in 2D or cylindrical coordinates.And just so you will know, over the last nearly 10 years, meep has been downloaded over 10,000 times. Some, if not most of the downloaders used meep, and many of them conducted and published peer reviewed research papers based on meep results. Meep is still widely used and does not have a reputation for frequency errors. The one thing those users may have had access to that I don't yet have is a powerful computer. Mine is a good home desk-top but at 5 years old, it is not a supercomputer. Go ahead and knock my computer all you want but please lay off of meep.And to answer your question as asked, "Yes, Meep absolutely does have the capability to measure resonance frequencies as well or better than other tools. I just do not have the needed tools installed. Harminv, not so much."To install MPB and recent meep upgrades, I need to compile, link and load from C++ source code. That code is available but I am not a computer systems administrator or a professional C++ programmer and I do not want to stop producing some helpful results to produce nothing for the time it will take me to become knowledgeable enough to do that. Then take the time to learn to use the newly installed and upgraded program features. And then only to have my results flawed my my own modelling errors with many more potential sources of error. My system does what it does and if someone doesn't like it they can choose not to consider it.And to the other 1,499,999 readers of this thread, I apologize for my rant.
I find this fascination with simulation rather curious, given the fact that all simulators seek to follow Maxwell's equations as accurately as their computational methods allow, and that Maxwell's equations predict zero thrust for the EmDrive. So what is it precisely that's so interesting about simulating the fields inside the cavity?
Frankly, between the proposal that the EM Drive somehow "knows" its velocity so that it cannot become a free-energy machine and this proposal that the EM Drive has to have an unspecified level of vibration amplitude and frequency to exert a force... well I better stop here.
Quote from: rfmwguy on 06/25/2015 02:34 amQuote from: aero on 06/25/2015 12:45 am@rfmwguy - some images https://drive.google.com/folderview?id=0B1XizxEfB23tfmcxbUxsM0lVTGVkemVTX1RaMlZJb001NHVaUDRvYUtjS0lIbjdIcUNkX0k&usp=sharinganyone who has the link can view?I had trouble finding resonance and basically failed. My excuse is that I ran out of daylight.Driving at 2.45 GHz I got Q's of 145 at both 2.40189260E+009 and 2.64320588E+009 Hz.Driving at the 2.40 GHz I got a Q of 100 and no other resonancesDriving at 2.64 GHz I got Q = 2000 at 2.40 GHz so I switched back to that number but the resonance went away.So these images are from the cavity driven at 2.64 Ghz and so perhaps not meaningful. I did use the full 15 digits computed, not the 3 digits used here. I probably need to play some more and decrease the bandwidth of the search for resonance. Maybe I'll try that ... later.These images are twice as dense as before. Ten images per cycle instead of five.Thanks aero, well done. Unfortunately I am stuck at driving at 2.45 ghz and not 2.64...fortunately I have yet to cut the frustum, meaning I can tweak the small and big diameters from 6.25 and 11.01. Is it easy to plug in the slightly larger diameters for 2.45 ghz resonance?. Not wanting to load u down, but 2k Q is better than 100. 6.735 in small diameter and 11.864 in large diameter, length can stay the same. Just wanting to know if resonance occurs...no pics needed. Thanks in advance...last favor to ask as I am meepless A clarification on my previous suggestion: I had suggested to use MEEP to look at optimal antenna placement, but not to make a decision at what frequency there is resonance. Not until the MEEP finite difference model has been verified vs. experimentally measured frequencies. Is the MEEP model's finite difference grid fine enough and the MEEP eigensolution HarmInv well-conditioned enough to successfully predict the frequencies measured by NASA and other experimenters, using their geometrical dimensions?
Quote from: aero on 06/25/2015 12:45 am@rfmwguy - some images https://drive.google.com/folderview?id=0B1XizxEfB23tfmcxbUxsM0lVTGVkemVTX1RaMlZJb001NHVaUDRvYUtjS0lIbjdIcUNkX0k&usp=sharinganyone who has the link can view?I had trouble finding resonance and basically failed. My excuse is that I ran out of daylight.Driving at 2.45 GHz I got Q's of 145 at both 2.40189260E+009 and 2.64320588E+009 Hz.Driving at the 2.40 GHz I got a Q of 100 and no other resonancesDriving at 2.64 GHz I got Q = 2000 at 2.40 GHz so I switched back to that number but the resonance went away.So these images are from the cavity driven at 2.64 Ghz and so perhaps not meaningful. I did use the full 15 digits computed, not the 3 digits used here. I probably need to play some more and decrease the bandwidth of the search for resonance. Maybe I'll try that ... later.These images are twice as dense as before. Ten images per cycle instead of five.Thanks aero, well done. Unfortunately I am stuck at driving at 2.45 ghz and not 2.64...fortunately I have yet to cut the frustum, meaning I can tweak the small and big diameters from 6.25 and 11.01. Is it easy to plug in the slightly larger diameters for 2.45 ghz resonance?. Not wanting to load u down, but 2k Q is better than 100. 6.735 in small diameter and 11.864 in large diameter, length can stay the same. Just wanting to know if resonance occurs...no pics needed. Thanks in advance...last favor to ask as I am meepless
@rfmwguy - some images https://drive.google.com/folderview?id=0B1XizxEfB23tfmcxbUxsM0lVTGVkemVTX1RaMlZJb001NHVaUDRvYUtjS0lIbjdIcUNkX0k&usp=sharinganyone who has the link can view?I had trouble finding resonance and basically failed. My excuse is that I ran out of daylight.Driving at 2.45 GHz I got Q's of 145 at both 2.40189260E+009 and 2.64320588E+009 Hz.Driving at the 2.40 GHz I got a Q of 100 and no other resonancesDriving at 2.64 GHz I got Q = 2000 at 2.40 GHz so I switched back to that number but the resonance went away.So these images are from the cavity driven at 2.64 Ghz and so perhaps not meaningful. I did use the full 15 digits computed, not the 3 digits used here. I probably need to play some more and decrease the bandwidth of the search for resonance. Maybe I'll try that ... later.These images are twice as dense as before. Ten images per cycle instead of five.
So, to summarize: EM drive works, but I am afraid that we won't be able to replicate it, simply because we lack some important (undisclosed) bits of information (the devil is in the details), and we may never find them, except if someone else discovers it by accident and make public (unlikely).
I found this article from May 2015. Roger Shawyer answers there on some interesting questions. I did not see the link to the article so far on the forum, so here it is.It seems his cooperation with the private companies and development of the second generation EmDrive is alive and well. It fact, he is very sure about the progress. So, make a coffee, tea or your favourite poison and read it http://www.ibtimes.co.uk/nasa-validates-emdrive-roger-shawyer-says-aerospace-industry-needs-watch-out-1499141I really can not wait to see the coming paper from him. I also noticed that media are starting to pay more attention to him.
SECOND GENERATION EMDRIVE PROPULSION APPLIED TO SSTO LAUNCHER AND INTERSTELLAR PROBERoger Shawyer C.Eng.MIET.FRAeSSPR Ltd, United Kingdom[email protected]ABSTRACTIn an IAC13 paper the dynamic operation of a second generation superconducting EmDrive thruster was described.A mathematical model was developed, and in this paper, that model is used to extend the performance envelope of the technology.Three engine designs are evaluated. One is used as a lift engine for a launch vehicle, another as an orbital engine for the launcher, and a third as the main engine for an interstellar probe.The engines are based on YBCO superconducting cavities, and performance is predicted on the basis of the test data obtained in earlier experimental programmes.The Q values range from 8 x 10^7 to 2 x 10^8 and provide high specific thrusts over a range of accelerations from 0.4 m/s^2 to 6 m/s^2.The launch vehicle is an “all-electric” single stage to orbit (SSTO) spaceplane, using a 900 MHz, eight cavity, fully gimballed lift engine.A 1.5 GHz fixed orbital engine provides the horizontal velocity component.Both engines use total loss liquid hydrogen cooling.Electrical power is provided by fuel cells, fed with gaseous hydrogen from the cooling system and liquid oxygen.A 2 Tonne payload, externally mounted, can be flown to Low Earth Orbit in a time of 27 minutes.The total launch mass is 10 Tonnes, with an airframe styled on the X37B, which allows aerobraking and a glide approach and landing.The full potential of EmDrive propulsion for deep space missions is illustrated by the performance of the interstellar probe.A multi-cavity, fixed 500 MHz engine is cooled by a closed cycle liquid nitrogen system.The refrigeration is carried out in a two stage reverse Brayton Cycle. Electrical power is provided by a 200 kWe nuclear generator.The 9 Tonne spacecraft, which includes a 1 Tonne science payload, will achieve a terminal velocity of 0.67c and cover a distance of 4 light years, over the 10 year propulsion period.The work reported in this paper has resulted in design studies for two Demonstrator spacecraft.The launcher will demonstrate the long-sought-for, low cost access to space, and also meet the mission requirements of the proposed DARPA XS-1 Spaceplane.The probe will enable the dream of an interstellar mission to be achieved within the next 20 years.
Quote from: Vix on 06/25/2015 11:38 amSo, to summarize: EM drive works, but I am afraid that we won't be able to replicate it, simply because we lack some important (undisclosed) bits of information (the devil is in the details), and we may never find them, except if someone else discovers it by accident and make public (unlikely).Sorry, but pfft. Between the math-heads trying to get a wrap around this in one direction, and the builders who are actually making these things, the amount of knowledge regarding how EMDrives function has gone up tremendously in just the last few months. The biggest problem isn't that somebody else has a 'special sauce' that the people here can't figure out the recipe to. I don't think that *anybody* yet has a solid grasp on why an EMDrive appears to do what it does. There's nothing accidental going on here; lots of theory and serious science is. And yes, the skeptics are as much a part of that process as the DIYers, the people developing software models, etc. I wonder how many papers have been written now as a result of this exploration/experimentation In the end it could be nothing more than an interesting artifact that can be used to make thrust that is better than photons, but not as effective as something else. Or it could open up new avenues in understanding the dual nature of wave/particles and their interaction with 'regular' matter. Either way; patience. Data is coming.
Quote from: deltaMass on 06/25/2015 09:04 amI find this fascination with simulation rather curious, given the fact that all simulators seek to follow Maxwell's equations as accurately as their computational methods allow, and that Maxwell's equations predict zero thrust for the EmDrive. So what is it precisely that's so interesting about simulating the fields inside the cavity?The main interest lies in precisely predicting the natural frequency and mode shape of a resonating cavity.A secondary interest is in finding the optimal location for the RF Feed, for resonance.Here is a comparison of natural frequencies and mode shapes for truncated cone cavities: http://forum.nasaspaceflight.com/index.php?topic=37642.msg1393872#msg1393872The people in this thread that are interested in making their own cavities are interested in knowing at what frequency and mode shape will their cavities resonate. The solution of Maxwell's equations for a conical frustum are non-trivial. If you know of other ways to solve Maxwell's equations to predict the natural frequency and modes shapes of a truncated cone cavity (other than by using numerical methods or by using exact solutions) please let us know.
...Several hundred quotes ago you, Thetraveler and a host of others joined in to do some not so simple calculations for a truncated cone. they all kind of worked and you all agreed to disagree, and now we have meep telling us something else...And don't feel bad about spread sheets or formulas calculating the variable geometries giving you exact harmonic frequencies, look at it as a clue. ...