Author Topic: EM Drive Developments - related to space flight applications - Thread 6  (Read 973893 times)

Offline FattyLumpkin

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Hi folks,
well now that we are on the subject of fabrication, I'd like to chime in with a few comments. Sorry if some of this might be superfluous as I am just coming in (new guy), that aside damn the torpedoes...!
Based on my studies of Emdrive one requirement is that the frustum cone and end pieces TOGETHER be in "resonance" or (oscillation) to function correctly, however minute the oscillations might be. ?

Assuming this is the case I would assert that the device must be constructed homogeneously: the end plates and frustum must be conjoined with the same material of/from which they are composed: copper. Solder would act as an oscillatory barrier and not translate oscillations from one separate piece of copper to another. Brazing is the way to go IMHO. Care should to be taken that excess "filler" not be left on the completed frustum/end plates assembly. Electric welding might also be an option. + there are more exotic ways.

Bolting of endplates to the frustum may also result in adequate surface union given the appropriate preparation of the surfaces to be conjoined. Numerous equal distant fasteners would be required and torqued/tightened to a high degree. Groove cutting and appropriate surface preparation to increase area exposer of one face to another is also an option.     
Hope I was correct in my initial assumption/assertion re resonance of an EM Drive assembly.   ,
                                                                                                                                            Fatty Lumpkin

Offline rfmwguy

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Brazing is the best, but the 1 mm or so sidewall thickness makes warping a real possibility at copper brazing temps. I looked into spinning copper meaning the large diameter would have the only seam. Alas, small budgets and few copper spinners was a roadblock.

Your idea is good, solder is not ideal but we work with what we have. Lost wax would make a solid piece but internal polishing would be near impossible. Keep thinking about new fab ideas and welcome to the forum.

Offline Rodal

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Hi folks,
well now that we are on the subject of fabrication, I'd like to chime in with a few comments. Sorry if some of this might be superfluous as I am just coming in (new guy), that aside damn the torpedoes...!
Based on my studies of Emdrive one requirement is that the frustum cone and end pieces TOGETHER be in "resonance" or (oscillation) to function correctly, however minute the oscillations might be. ?

Assuming this is the case I would assert that the device must be constructed homogeneously: the end plates and frustum must be conjoined with the same material of/from which they are composed: copper. Solder would act as an oscillatory barrier and not translate oscillations from one separate piece of copper to another. Brazing is the way to go IMHO. Care should to be taken that excess "filler" not be left on the completed frustum/end plates assembly. Electric welding might also be an option. + there are more exotic ways.

Bolting of endplates to the frustum may also result in adequate surface union given the appropriate preparation of the surfaces to be conjoined. Numerous equal distant fasteners would be required and torqued/tightened to a high degree. Groove cutting and appropriate surface preparation to increase area exposer of one face to another is also an option.     
Hope I was correct in my initial assumption/assertion re resonance of an EM Drive assembly.   ,
                                                                                                                                            Fatty Lumpkin

<<Based on my studies of Emdrive one requirement is that the frustum cone and end pieces TOGETHER be in "resonance" or (oscillation) to function correctly, however minute the oscillations might be. ?>>

No, sorry, the frustum cone and end pieces are not in "resonance" or (oscillation) in a resonant electromagnetic cavity.  This is not at all like a mechanical vibration problem whereby the metal copper would be oscillating. 
There is no oscillation of the frustum cone metal.  There is no oscillation of the frustum cone end.
There is no "resonance" or (oscillation) of the frustum cone and end pieces either separate or together.
That's not what happens in electromagnetic resonance of a cavity.  Instead what happens is that the electromagnetic fields oscillate inside the cavity much much faster than it is possible for the copper to move.  It is not physically possible for the copper metal to oscillate with any significant amplitude at GigaHertz frequency.  Any significant movement of the copper will necessarily be practically static compared to the photons that propagates at the speed of light.

No medium is necessary inside the cavity for this oscillation to take place: it will perfectly take place in an absolute vacuum.  The electromagnetic fields propagate perfectly fine in an absolute vacuum. 

Any movement of the copper actually degrades the quality of resonance Q  It has actually been a big problem with EM Drive experiments that the magnetic field is responsible for induction heating of the metal cavity, and this heating in turn results in thermal expansion and distortion of the cavity which reduces the quality of resonance.  It would be ideal for electromagnetic resonance if the metal in the cavity would stay perfectly rigid and not move at all. 

Concerning homogeneity of the cavity:  at 2.45 GHz the electromagnetic fields only penetrate (to a significant amplitude) the metal within a micrometer.  The copper thickness of these cavities is made significantly thicker than that in order to ensure rigidity of the cavity (as obviously a thin cavity would be easy to distort which would result in lowering of the Q).  According to most theories of the EM Drive (DeAquino, Dr. White's QV, McCulloch's, etc.) it would actually be better to have an asymmetry of material properties, just like there is an asymmetry of geometry.  There is no mandate that the cavity material must be homogeneous.  It has been proposed for example to have a ferromagnetic plate at one end of the EM Drive (instead of the diamagnetic copper used up to now) although nobody has reported such experiment, yet. And NASA has only reported significant anomalous force measurements by inserting a dielectric polymer at one end.   
« Last Edit: 03/10/2016 02:27 AM by Rodal »

Offline FattyLumpkin

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Doctor Rodal, thanks for the differential DX. I wasn't sure, but plunged in anyway. Prior to posting this, I reflected with another individual and ended the conversation by asking: "Or are the surfaces of the cavity considered to be fully rigid and resonance occurs by dint of specific design of the inside walls/barriers."
Thank you for your succinct and precise response!!! Are there any do's or don't's that you suggest re fabrication?
Any addition information would be greatly appreciated.   ,  Fatty Lumpkin

Offline ThinkerX

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Fatty, unless you are an expert machinist with the appropriate tools, you really should consider hiring out the actual frustum construction.  Multiple DIY posters here have run into issues with this.  Perhaps a musical instrument maker?

Offline FattyLumpkin

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ThinkerX, indeed, I have recommended to a few here on NSF to use a machine shop for cutting their copper sheet vis--vis laser or water jet, and brazing their frustums together. Seems I was in error where the joinery is concerned (now having received the input from Dr. Rodal re EM resonance). Thanks for your input!!!    F L

Offline TheTraveller

In regard to current dimensional build tolerance discussion, Roger advised me that max frustum dimensional build error, end plate alignment error & surface flatness should be max 10X skin depth plus all surfaces to have a oxidation free mirror like finish.

For my frustum that is +- ~13um tolerance or +- ~0.0005 inches. Tight but doable.
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Online Monomorphic

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For my frustum that is +- ~13um tolerance or +- ~0.0005 inches. Tight but doable.

I don't see how it is possible to DIY build a ~20cm copper frustum with a 13um tolerance. That's 1/1,300th of a cm. You would have to use a very large (and expensive) micrometer and a MEMS-like fabricating process.

I'm shooting for a tolerance of 1mm. Simulations I've run show there is vanishingly little change when altering dimensions at that scale.
« Last Edit: 03/10/2016 12:28 PM by Monomorphic »

Offline TheTraveller

For my frustum that is +- ~13um tolerance or +- ~0.0005 inches. Tight but doable.

I don't see how it is possible to DIY build a ~20cm copper frustum with a 13um tolerance. That's 1/1,300th of a cm. You would have to use a very large (and expensive) micrometer and a MEMS-like fabricating process.

I'm shooting for a tolerance of 1mm. Simulations I've run show there is vanishingly little change when altering dimensions at that scale.

+- 10X skin depth accuracy is what I'm advised is needed. My skin depth is 0.00000132m or 0.00132mm or 1.32um.

Here is what Roger advised:

Quote
The route to high Q is to achieve very high precision in the machining of cavity components and their alignment, together with mirror finish on the conducting surface (copper, silver or gold) of at least 10X skin depth. Maintaining this quality of finish also requires a clean dry environment. This is typical flight standard for space qualified microwave equipment, and is therefore expensive to achieve.

Best of luck with your build.
« Last Edit: 03/10/2016 12:56 PM by TheTraveller »
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Offline Rodal

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For my frustum that is +- ~13um tolerance or +- ~0.0005 inches. Tight but doable.

I don't see how it is possible to DIY build a ~20cm copper frustum with a 13um tolerance. That's 1/1,300th of a cm. You would have to use a very large (and expensive) micrometer and a MEMS-like fabricating process.

I'm shooting for a tolerance of 1mm. Simulations I've run show there is vanishingly little change when altering dimensions at that scale.
You are correct.  Furthermore, such precision would be irrational for any shell structure made of copper that is a very thin: mm thick compared to length and diameter of ~ 0.2 m (EM Drive thickness being used in many EM Drive experiments up to now), since, as it is trivial to show (using equations from shell theory routinely used in Aerospace Engineering), even if one would achieve such precision, such mm thick structure would be easy to permanently deform out of tolerance to 13um or more even just by using your own hands to compress the thin shell EM Drive structure !   ;)

Such a tolerance would only make sense for a metal cavity thick enough such that it could not be deformed out of tolerance during handling or operation. 
« Last Edit: 03/10/2016 01:30 PM by Rodal »

Online Monomorphic

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The route to high Q is to achieve very high precision in the machining of cavity components and their alignment, together with mirror finish on the conducting surface (copper, silver or gold) of at least 10X skin depth. Maintaining this quality of finish also requires a clean dry environment. This is typical flight standard for space qualified microwave equipment, and is therefore expensive to achieve.

The hard part from what i've seen is getting the frustum side wall seam to align perfectly. I will use a micrometer that measures 100ths of a cm for the first build (so my tolerance will be much better than 1mm!). That's about as good as I can get with a DIY budget.
« Last Edit: 03/10/2016 01:06 PM by Monomorphic »

Offline TheTraveller

The route to high Q is to achieve very high precision in the machining of cavity components and their alignment, together with mirror finish on the conducting surface (copper, silver or gold) of at least 10X skin depth. Maintaining this quality of finish also requires a clean dry environment. This is typical flight standard for space qualified microwave equipment, and is therefore expensive to achieve.

The hard part from what i've seen is getting the frustum side wall seam to align perfectly. I will use a micrometer that measures 100ths of a cm for the first build (so my tolerance will be much better than 1mm!). That's about as good as I can get with a DIY budget.

It is my belief that all 3 frustums Roger built were sidewall seamless and had at least 2mm thick side walls. Have no proof of that other than photos, gut feel & experience.

Note all 3 frustums used thick side wall end flanges & multi bolt end plate compression to side wall attachment system. I would bet the individual end plate bolt tensions were adjusted while monitoring VNA rtn loss in real time to achieve optimal end plate alignment & highest Q. The end plates were not soldered or brazed to the side wall.

Also note the long external bolts on the Experimental & Demonstrator EmDrive, possibility used to distort the frustum to achieve optimal end plate alignment.

Sure building a frustum this way is difficult, slow & expensive. I now know, from experience, there is no quick & easy way to do this. Please review the images of Roger's 3 builds on the emdrive web site.
« Last Edit: 03/10/2016 01:38 PM by TheTraveller »
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Offline Rodal

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The route to high Q is to achieve very high precision in the machining of cavity components and their alignment, together with mirror finish on the conducting surface (copper, silver or gold) of at least 10X skin depth. Maintaining this quality of finish also requires a clean dry environment. This is typical flight standard for space qualified microwave equipment, and is therefore expensive to achieve.

The hard part from what i've seen is getting the frustum side wall seam to align perfectly. I will use a micrometer that measures 100ths of a cm for the first build (so my tolerance will be much better than 1mm!). That's about as good as I can get with a DIY budget.

It is my belief that all 3 frustums Roger built were sidewall seamless and had at least 2mm thick side walls. Have no proof of that other than photos, gut feel & experience.

Note all 3 frustums used thick side wall end flanges & multi bolt end plate compression to side wall attachment system. I would bet the individual end plate bolt tensions were adjusted while monitoring VNA rtn loss in real time to achieve optimal end plate alignment & highest Q. The end plates were not soldered or brazed to the side wall.

Sure building a frustum this way is difficult, slow & expensive. I now know, from experience, there is no quick & easy way to do this. Please review the images of Roger's 3 builds on the emdrive web site.

It is trivial  to show (with equations routinely used by Aerospace Engineers to design thin shell structures for rockets and spacecraft) that a shell structure made of copper 2 mm thick and 0.2 m length and diameter, would be easy to deform by more than 13 micrometers just by handling.  (Several DIY reported early on that they could change the natural frequency of their EM Drive DIY just by squeezing the EM Drive with their hands).

So, if Shawyer really means that a tolerance of 13 micrometers is necessary, he must have used much thicker (than 2 mm) copper shell structure for the Flight Thruster.

If anything even close to 13 micrometers tolerance is needed, it is easy to show that the thickness of copper used by rfmwguy, SeeShells, Berca,  NASA and others for the EM Drive conical walls are way too thin.
« Last Edit: 03/10/2016 01:52 PM by Rodal »

Offline TheTraveller

So, if Shawyer really means that a tolerance of 13 micrometers is necessary, he must have used substantially thicker (than 2 mm) copper shell structure for the Flight Thruster.

The Flight Thruster is quoted at 2.92kg. I believe it was alum based with multiple layers of internal and external coating.

We know the approx internal dimensions.

BD: 0.2314m
SD: 0.1257m
Len: 0.1386m
RFreq: 3.85GHz.

http://www.emdrive.com/flightprogramme.html

Believe the Flight Thruster side walls are thicker than 2mm. Also believe the Experimental & Demonstrator may have been externally manually "tuned" for max Q, by adjusting the nuts on the external rods, between runs. Again no proof, just gut feel & experience playing with my frustum.

Those external side rods are there for a purpose and are very strong versus the frustum.
« Last Edit: 03/10/2016 01:59 PM by TheTraveller »
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Offline rfmwguy

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Thought about this a lot. Incidental reflections off the side wall don't seem nearly as critical as the endplate reflections. For me, just as in optics, the flatness, thickness and parallel alignment of the endplates is the critical factor.

Of course, I'm 1 DIYer and the beauty of this thing is there is no wrong way to build it; as the right way has not yet been formally disclosed...just hinted at.

Offline rfmwguy

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What a great thread T6 has been!

With well over 400K views and approaching 200 pages, its time we kickoff

THREAD 7

See you there: http://forum.nasaspaceflight.com/index.php?topic=39772.0

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