EM Drive Developments - related to space flight applications - Thread 7

[zellerium]

I propose that a common-sense tolerance for EM Drive thickness that DIY testing people should use for their frustums is the thickness of a commercial waveguide with similar diameter.

In this case, a common sense tolerance is that DIY people should use a thickness of waveguides with a diameter of 0.28 m to be used at ~2 GHz

I don't understand your reasoning Dr. Rodal, commercial waveguides are designed to transmit power, not resonate, as I'm sure you're well aware of. I would expect the amount of conductive heat dissipation required by a transmission line (with a typical .5 dB loss per meter) is significantly less than a resonator with no output.

Why not create the thickest frustum possible within price constraints so that the steady state temperature is lower?

It is a question of logical consistency:

1) Shawyer/TheTraveller regularly use open waveguide explanations to explain the EM Drive  (please refer to Shawyer's paper).  For example, the cutoff frequency concept only applies to open waveguides.

2) In the post above SeeShells argues that <<It's the endplates that set the resonance and Q. >>.  Rfmwguy is polishing the end plates to look like a  mirror.  Both of these arguments run contrary to standing wave resonance inside a cavity:   for the eigenmodes and eigenfrequencies in a cavity, the conical walls are just as important as the end plates.

3) I am not discussing anything to do with heat dissipation or thermal effects.  I am just arguing dimensional tolerance.

4) You write <<Commercial waveguides are designed to transmit power, not resonate>>.  That is not strictlly correct.  Commercial waveguides "resonate" only in the cross-dimensional direction: that is what TE01 for example means.  The mode shapes for waveguides are the result of solving the eigenvalue problem.

Here are the first "resonant" eigenmodes "mode shapes" for a waveguide with circular cross-section:



  It is important for a waveguide to have certain tolerances in their cross-section, in order to maintain a given mode shape.

5) The question here is to justify the 1 mm thickness being used by DIY.  Where did that come from?  How is that justified?

6) It is not logical to say that only longitudinal resonance matters: that only the "p" matters in TEmnp for example.

7) How can people say that tight tolerances are needed in the longitudinal direction for "p" but not in the cross-section for "mn".

How could one say that the endplates need to look like a mirror (for 2.45 GHz frequency with wavelength of several cm) and that it is OK for example for the cross section  to look like a star instead of circular

Okay I jumped in without fully reading the context. Thank you for reiterating what the discussion is all about.

Looking at the waveguide solutions presented in "Electromagnetic Fields and Waves" by Iskander, its clear that the broad dimensions determine the resonant frequency and dominant mode. A third resonance (in the z direction) will probably replace the exp(-j*beta*z) with a sin or cos function.

Therefore I would assume all dimensions should be designed to the highest tolerance possible and all of them will combine to produce a certain quality. Polishing the end plates surely wouldn't hurt but I'd polish the whole inner surface if possible.

But if the cavity is going to warp from thermal effects then you probably can't high quality resonance no matter how well it's polished... unless it was designed to be the perfect dimensions when thermally expanded if that's even feasible.

And then we're back to the problem of measuring uN-mN from a cavity radiating, convecting and conducting heat in all directions asymmetrically.  As many have brought up many many times, the heat is a major theme of all EM Drive experiments and has yet to be fully addressed.

And Dr. Rodal, I for one very much appreciate your feedback in all regards. But I have to wonder, why is it you are such a knowledgable top contributer on the topic but have yet to attempt an experiment?

[rfmwguy]

Where do a couple of posters get the impression that sidewall tolerances are as important as endplate tolerances? If someone has an emdrive theory, please share it.
In addition, what is driving the assumption that sidewall deformations are not being addressed by builders?
Look at it this way, the reported emdrive force is perpendicular to the endplates, not the sidewalls. Seems like endplates are where precision is most needed. Just my build ideas...I'm not trying to tell anyone else what needs to be done...nor should anyone.

[Rodal]

...And Dr. Rodal, I for one very much appreciate your feedback in all regards. But I have to wonder, why is it you are such a knowledgable top contributer on the topic but have yet to attempt an experiment?

Because there is no need for me to duplicate the work that Dr. White's team is conducting at NASA, and because there are other new, unique, promising experiments for me to spend my time on.

[WhatAFeynDay]

Dr rodal, you seem to be bothered by diy methodology. I suggest no diyer has a correct methodology and neither do you. This topic has advanced well beyond being a roger shawyer comment thread to diy and theory beyond one person. My advice is to build one yourself and show others where errors are being made. Either that or publish a diy guide you would recommend to new diyers.

I think I'm really misunderstanding the discussion here, because your comment has me very confused.

We have this device that Roger Shawyer has claimed makes thrust. He's the reason this thread exists, and has been (apparently) contributing advice to DIY experimenters. In that regard, TheTraveller has been kind enough to pass along the advice and specifications that the inventor, Shawyer, claims are required for the device to create thrust.

Among that advice is a tolerance of 13um.

If I'm understanding Dr. Rodal correctly, he is pointing out that your sidewall thickness of 1mm is susceptible to deformation which will cause its Q to be reduced significantly. Furthermore, there's an apparent contradiction between being concerned enough about these tolerances to polish the endcaps to a mirror finish, and yet not having any concerns about possible deformation of the frustum.

So, in light of that apparent contradiction, it's been suggested that DIY builders come to a consensus as to whether or not Shawyer's 13um tolerance is what should be adhered to, or if it should be some other number as yet to be determined.

I thought it was an attempt at solving an apparent fly in the ointment. I'd really like to know how DIY builders are going to reconcile these types of discrepancies, especially if we're ever going to prove this device works as claimed.

I think I'm just missing something here, forgive me.

[Rodal]

Dr rodal, you seem to be bothered by diy methodology. I suggest no diyer has a correct methodology and neither do you. This topic has advanced well beyond being a roger shawyer comment thread to diy and theory beyond one person. My advice is to build one yourself and show others where errors are being made. Either that or publish a diy guide you would recommend to new diyers.

I think I'm really misunderstanding the discussion here, because your comment has me very confused.

We have this device that Roger Shawyer has claimed makes thrust. He's the reason this thread exists, and has been (apparently) contributing advice to DIY experimenters. In that regard, TheTraveller has been kind enough to pass along the advice and specifications that the inventor, Shawyer, claims are required for the device to create thrust.

Among that advice is a tolerance of 13um.

If I'm understanding Dr. Rodal correctly, he is pointing out that your sidewall thickness of 1mm is susceptible to deformation which will cause its Q to be reduced significantly. Furthermore, there's an apparent contradiction between being concerned enough about these tolerances to polish the endcaps to a mirror finish, and yet not having any concerns about possible deformation of the frustum.

So, in light of that apparent contradiction, it's been suggested that DIY builders come to a consensus as to whether or not Shawyer's 13um tolerance is what should be adhered to, or if it should be some other number as yet to be determined.

I thought it was an attempt at solving an apparent fly in the ointment. I'd really like to know how DIY builders are going to reconcile these types of discrepancies, especially if we're ever going to prove this device works as claimed.

I think I'm just missing something here, forgive me.

I'm glad to see that you understood very well what I posted 

This saves me the time to try to find another way to explain this again. 

Good night to all.

[meberbs]

"Number of bounces" has limited meaning in this context....

Put an E field sensor through one end plate plus a lot of attenuation so it doesn't add significant load to the cavity.

Set up to measure the unloaded cavity Q and the number of positive peak events in the E field during 5 TCs of the cavity discharge time.

Fill the cavity with resonant Rf.

Stop the Rf input just as the Rf crosses zero.

Measure the time until the E field probe says there is no more Rf energy inside the cavity. Should be 5x TC.

Count the number of E field positive peak events during the 5 x TC time period (should occur at the rate of the Rf resonant freq). Should be the indicated end plate reflection count number.

Emphasis mine.

You are ignoring the sidewalls again. The radiation is reflecting off all of the surfaces. If you didn't have the side walls (for safety, please don't do this) the radiation would be going in all sorts of directions and would not stay neatly confined.

Also, 5 times TC as stated by others before is the time to get to about 0.7% of the maximum energy that was in the cavity. It is an exponential decay, and will take quite a while to get to truly 0 (the last single photon gets absorbed - although black body radiation would instead cause an equilibrium at some point). You are describing an experiment as if each photon could last a fixed number of bounces, that in itself is not true. If you were to do an experiment bouncing single photons between mirrors, somehow counting the bounces, you would find each individual photon is absorbed after a random number of bounces, with distribution based on the reflectivity of the mirrors.

There is good discussion going on right now about things more meaningful for the experiments (effect of tolerances, surface finish, machining errors, and thermal expansion on Q). I don't want to sidetrack too much from that, so this discussion can be taken to another thread or PM if you still disagree.

[Amestad]

Yes, the cone is not cut yet.

What thickness copper side walls? The 1/8 or sticking with 1mm?

1mm sidewalls. Was going to to spin thicker copper but no spinners responded with decent prices. A fully funded institutional project could spin then polish. A user here also suggested a lost wax pocess.

It is not going to be possible to have a high Q (quality of resonance) close to theoretical with 1 mm walls: very compliant (the opposite of stiff).  For a length of 0.26 meters and diameter of 0.28 meters, a 1 mm wall thickness is easy to deform out of shape just by applying hand pressure, and hence difficult to maintain geometrical tolerance.

If expansion due to thin sidewalls is an issue then reinforce the sidewalls.. There was talk about this previously, but personally I'd always take a "KISS" approach....

This assumes RFM's build technique so the frustum is formed and sealed with the endplates large than the truncated cone ends. Basically take the sealed frustum and stick in in a bucket slightly larger than the end plates then pour in a batch of concrete (any low expansion co-efficient, low melting point / setting point material..). Adds thermal mass to reduce rapid heating effects and limits expansion.

Or take a much more complicated and I think not yet thought of approach?
I've read much of these threads but I may have forgotten.

Follow RFM's build process (any process really as long as the frustum is sealed to the end plates) only this time ensuring the endplates are the same diameter.
Once formed the frustum could be inserted into a cylinder.. Let's think heavy duty steel casing..  and the external volume between endplates now becomes a separate internal volume of the cylinder.

Attach valves / ports to the  flange of the end plates and now you have a way to inject some form of fluid in to the annular space around the exterior of the frustum sealed by the end plates and cylinder walls.

This could either be done simply under a one way valve to inhibit expansion of the side walls (liquids don't compress easily) or add a second valve/port and with appropriate pressure regulation you also now have an active cooling fluid chamber and expansion inhibition control.
You could still do side wall injection by running all the feeds through appropriately sealed holes in the flange. Add threaded rods between flanges to control and inhibit expansion in the Z axis of the frustum / cylinder.. all sealed and cooled in the cylinder.

I think this is all quite well within the reach of the builders here and really doesn't take much to do....

granted you need to tune your source to the frustrum but seems like that's on the cards anyways..

Ok this might be tricky to visualise.. when I read it back, I fudged up a drawing in Ppt.

If you can't see it.. (this is my like third post) let me know and i'll do a imagehost link

Cheers
Amestad

Modified for typos





 



 

[Amestad]

Another method would be to actually wind something around the frustum. Material choice here is much more difficult... but in essence winding it around the frustum walls like cotton on a reel would provide significant inhibition to expansion. I think this has been discussed previously in any case.

Using the fluid filled cylinder method described above allows controlled deformation of the frustum if desired so it ticks many more boxes.

[ThinkerX]

To me, the degree of fine machining called for by Shawyer sounds like the sort of precision found in the cylinders of automotive engines.  I also note these cylinders tend to be set in thick metal blocks. 

On the one hand, it sound insane, almost like adding another barrier. 

On the other hand, at least with automotive cylinder work, if you DON'T attain that kind of precision, then the vehicle either won't run, or will run poorly at best. 

Given a frustum of the proper thickness, maybe a professional engine rebuild guy could attain the precision Shawyer claims is needed? 

[FattyLumpkin]

Machining of cylinders in internal combustion engines (cars) involves 1000ths not 10s of 1000ths---so I suspect Shawyer is referring to the "finish" of the material (mirror like). The roundness that Dr. Rodal is referring to is difficult to achieve, but possible ...one way is by using male and female mandrels, and relaxing of the material being molded by heating it to a certain extent prior to pressing in the said mandrels. There are also other different methods. I'd go with .125" thick all the way around irrespective of cost. A system of heat rejection could also be put into place by soldering thin (inexpensive) strips of copper radially, perpendicularly all about the frustum.  Nothing like radiator fins to save the day.
While I didn't get EM resonance right I do still know my fabrication.  Ciao!  , F L 

[TheTraveller]

Also, 5 times TC as stated by others before is the time to get to about 0.7% of the maximum energy that was in the cavity.

This statement is wrong. Suggest you talk to any EE that has experience with charge & discharge rates of any electronics element that stores energy.

Here is a TC driven energy charge curve. Flip it vertically to get the discharge curve. 5x TC is what EEs use to determine effective full charge/discharge of energy storage electronic elements. And yes it also applies to Rf resonant cavities.

At 5 x TC, a cavity energy is discharged 99.3% (as attached), which as an EE I would consider as being, in practical terms, totally discharged.

[rfmwguy]

Dr rodal, you seem to be bothered by diy methodology. I suggest no diyer has a correct methodology and neither do you. This topic has advanced well beyond being a roger shawyer comment thread to diy and theory beyond one person. My advice is to build one yourself and show others where errors are being made. Either that or publish a diy guide you would recommend to new diyers.

I think I'm really misunderstanding the discussion here, because your comment has me very confused.

We have this device that Roger Shawyer has claimed makes thrust. He's the reason this thread exists, and has been (apparently) contributing advice to DIY experimenters. In that regard, TheTraveller has been kind enough to pass along the advice and specifications that the inventor, Shawyer, claims are required for the device to create thrust.

Among that advice is a tolerance of 13um.

If I'm understanding Dr. Rodal correctly, he is pointing out that your sidewall thickness of 1mm is susceptible to deformation which will cause its Q to be reduced significantly. Furthermore, there's an apparent contradiction between being concerned enough about these tolerances to polish the endcaps to a mirror finish, and yet not having any concerns about possible deformation of the frustum.

So, in light of that apparent contradiction, it's been suggested that DIY builders come to a consensus as to whether or not Shawyer's 13um tolerance is what should be adhered to, or if it should be some other number as yet to be determined.

I thought it was an attempt at solving an apparent fly in the ointment. I'd really like to know how DIY builders are going to reconcile these types of discrepancies, especially if we're ever going to prove this device works as claimed.

I think I'm just missing something here, forgive me.

Easy to clarify when you do the math: 2.450000 GHz has a wavelength of 122364.2685714 micrometers. A +/- 13 micrometer variation is 2.449739739248 GHz to 2.450260316059 GHz or 0.000520576811 GHz or 520.576811 (+/- 250) kHz. Its +/- 125 kHz if you consider +/- 6.5 micrometers for a total of 13 micrometers.

Magnetrons do not have this type of stability. A signal source would need +/- 0.005% accuracy at 2.45 GHz.

[rfmwguy]

To me, the degree of fine machining called for by Shawyer sounds like the sort of precision found in the cylinders of automotive engines.  I also note these cylinders tend to be set in thick metal blocks. 

On the one hand, it sound insane, almost like adding another barrier. 

On the other hand, at least with automotive cylinder work, if you DON'T attain that kind of precision, then the vehicle either won't run, or will run poorly at best. 

Given a frustum of the proper thickness, maybe a professional engine rebuild guy could attain the precision Shawyer claims is needed?

The endplates are easy to fabricate for 13 micrometer tolerance. I did this by hand with a lapping plate and wheel. I estimate about 8-9 micrometers worst-case flatness. The sidewalls are a different story. I believe it is overkill to design for 13 micrometers on the sidewalls given the signal source stability we have to work with. Only reason I prepped the endplates is they were relatively easy to do and I learned a new skill...AKA fun.

High-end mechanical precision is a latter-stage development AFTER people get consistent results at less precision. IOW, its likely a way to scale the emdrive effect up in power once people demonstrate its repeatability. We're still not there yet IMHO.

[SeeShells]

Where do a couple of posters get the impression that sidewall tolerances are as important as endplate tolerances? If someone has an emdrive theory, please share it.
In addition, what is driving the assumption that sidewall deformations are not being addressed by builders?
Look at it this way, the reported emdrive force is perpendicular to the endplates, not the sidewalls. Seems like endplates are where precision is most needed. Just my build ideas...I'm not trying to tell anyone else what needs to be done...nor should anyone.

All I'm saying is that the influence of the endplate quality is seen as a action through the entire length of the frustum through all of the frustum modes, whereas a sidewall deformation is only seen in that local cross sectional area.

This isn't to say that the build should be as good as you can get for a DYIer.

Shell

[SeeShells]

Dr rodal, you seem to be bothered by diy methodology. I suggest no diyer has a correct methodology and neither do you. This topic has advanced well beyond being a roger shawyer comment thread to diy and theory beyond one person. My advice is to build one yourself and show others where errors are being made. Either that or publish a diy guide you would recommend to new diyers.

I think I'm really misunderstanding the discussion here, because your comment has me very confused.

We have this device that Roger Shawyer has claimed makes thrust. He's the reason this thread exists, and has been (apparently) contributing advice to DIY experimenters. In that regard, TheTraveller has been kind enough to pass along the advice and specifications that the inventor, Shawyer, claims are required for the device to create thrust.

Among that advice is a tolerance of 13um.

If I'm understanding Dr. Rodal correctly, he is pointing out that your sidewall thickness of 1mm is susceptible to deformation which will cause its Q to be reduced significantly. Furthermore, there's an apparent contradiction between being concerned enough about these tolerances to polish the endcaps to a mirror finish, and yet not having any concerns about possible deformation of the frustum.

So, in light of that apparent contradiction, it's been suggested that DIY builders come to a consensus as to whether or not Shawyer's 13um tolerance is what should be adhered to, or if it should be some other number as yet to be determined.

I thought it was an attempt at solving an apparent fly in the ointment. I'd really like to know how DIY builders are going to reconcile these types of discrepancies, especially if we're ever going to prove this device works as claimed.

I think I'm just missing something here, forgive me.

Obi Wan would say: Fly in the ointment you're not.

<quoted from a past post>
Yes, I'm using ceramic plates <.05um flatness, they provide these very critical build and design points.

Force the endplate flat. The copper 101 O2 free .032" from the factory is better then .3um flat. (best I can measure) When bonded I don't need to do extreme lapping to get high flatness and plus it makes it easier to lap.

Keep deformations to a minimum even during a build from soldering or handling.

They maintain the flatness of the plates during cavity heating.

They make sure the plates stay together via the Quartz rod during tune and maintain parallelism during runs and thermal heating.

Allow the sidewalls expand up and past the small endplate which isn't captured but has a beryllium gasket.

Makes a stiffer overall frustum.

Shell
<end>

[rfmwguy]

Where do a couple of posters get the impression that sidewall tolerances are as important as endplate tolerances? If someone has an emdrive theory, please share it.
In addition, what is driving the assumption that sidewall deformations are not being addressed by builders?
Look at it this way, the reported emdrive force is perpendicular to the endplates, not the sidewalls. Seems like endplates are where precision is most needed. Just my build ideas...I'm not trying to tell anyone else what needs to be done...nor should anyone.

All I'm saying is that the influence of the endplate quality is seen as a action through the entire length of the frustum through all of the frustum modes, whereas a sidewall deformation is only seen in that local cross sectional area.

This isn't to say that the build should be as good as you can get for a DYIer.

Shell

Its not you Shell. Think you've got the idea. Oh, guess I'll share my conical conformity "trick" from my post on January 8th:

Take your pick: http://tinyurl.com/h9ju53q

[TheTraveller]

Oh, guess I'll share my conical conformity "trick" from my post on January 8th:

Can confirm, Dave's hoop idea does work.

[meberbs]

Also, 5 times TC as stated by others before is the time to get to about 0.7% of the maximum energy that was in the cavity.

This statement is wrong. Suggest you talk to any EE that has experience with charge & discharge rates of any electronics element that stores energy.

Here is a TC driven energy charge curve. Flip it vertically to get the discharge curve. 5x TC is what EEs use to determine effective full charge/discharge of energy storage electronic elements. And yes it also applies to Rf resonant cavities.

At 5 x TC, a cavity energy is discharged 99.3% (as attached), which as an EE I would consider as being, in practical terms, totally discharged.

Did you even read the rest of my post?
Also you said I'm wrong and then posted information that confirms what I said (100% minus 99.3% discharged equals 0.7% remaining)

Again 5 TCs is an arbitrary number. It is "good enough" for many applications, but you keep treating it like an absolute, which it isn't. If the starting point is 1 MJ, there would still be 7kJ left, so you might want to wait a few more TCs before sticking your hand inside.

[TheTraveller]

Also, 5 times TC as stated by others before is the time to get to about 0.7% of the maximum energy that was in the cavity.

This statement is wrong. Suggest you talk to any EE that has experience with charge & discharge rates of any electronics element that stores energy.

Here is a TC driven energy charge curve. Flip it vertically to get the discharge curve. 5x TC is what EEs use to determine effective full charge/discharge of energy storage electronic elements. And yes it also applies to Rf resonant cavities.

At 5 x TC, a cavity energy is discharged 99.3% (as attached), which as an EE I would consider as being, in practical terms, totally discharged.

Did you even read the rest of my post?
Also you said I'm wrong and then posted information that confirms what I said (100% minus 99.3% discharged equals 0.7% remaining)

Again 5 TCs is an arbitrary number. It is "good enough" for many applications, but you keep treating it like an absolute, which it isn't. If the starting point is 1 MJ, there would still be 7kJ left, so you might want to wait a few more TCs before sticking your hand inside.

Apologies. Read your 0.7% as 70%.

Never stated 5x was absolute. Did use approx & ~ when quoting levels.

You may be interested to know forward power, into a empty cavity follows the same curve. In fact it is possible to measure unloaded cavity Q by simply measuring how long it takes forward power to climb from 0W at cavity fill start to 63.2% of the final fully charged value. Knowing that time, it is then possible to calc unloaded Q & never need to use a VNA to measure -3dB bandwidth, which only gives you loaded Q.

[SeeShells]

Currently this site hosts half a dozen builders of EMDrives. Some are on their first or second or third  build (some are keeping quiet and just building), but the common thread throughout it all is the quality of the build has increased dramatically in the last year.  This is due to no small part by the mass contributions of so many here pushing the envelope of theory, creativity, and DYI quality. I never could have made it this far if it wasn't for the contributions and guidance and the heartfelt giving of others.

We need to thank those who offer their time, their expertise and encouragement to quantify whether this drive will be a curiosity in the annals of time or reinventing fire for humanity.

Thank You.


Shell