Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1800309 times)

Offline kml

I assume small end was leading as thrust comes out the back(large end)

In the youtube video the large end is leading.    The spacing of the screws is different on each end and the feedline is closest to the small end.   It's not clear whether that video represented the "prograde" direction or not.

If the guided wavelength model is correct then the large end should lead when there is no dielectric present, as appears to be the case with this design.   If there was a thin dielectric on the small end the curves would reverse and the small end would lead, and with higher thrust.    Move the (resized) dielectric to the large end and the large end would again lead and with the highest thrust of the three configurations, adjusting for net power and Q.

Offline Prunesquallor

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Here's a slightly clearer picture of the Hackaday.io graph.

I downloaded their spreadsheet.  For those interested, it looks like their sample rate was 16 Hz.  The ordinate axis is rpm.
<edit>  The ordinate axis data is LABELED as RPM which is probably not right, unless this was spinning VERY fast.
« Last Edit: 06/11/2015 02:22 AM by Prunesquallor »
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Online Rodal

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...If the guided wavelength model is correct then the large end should lead when there is no dielectric present, as appears to be the case with this design.   If there was a thin dielectric on the small end the curves would reverse and the small end would lead, and with higher thrust.    ...

1) What is the guided wavelength model? Is that Shawyer's model?

I have found Shawyer's diagrams of thrust force pointing towards the big end and the reaction movement pointing towards the small end confusing (because the "thrust force" is not something ever measured but appears to be something conceived to try to explain conservation of momentum) but:

2) My recollection is that in Shawyer's tests the frustum moves pointing towards the small end (instead of the large end) for the Demonstrator (no dielectric present).

3) My recollection is that  in NASA's tests, the truncated cone moves in the direction of the small end (same as in Shawyer's Demonstrator).  NASA' truncated cone has a dielectric insert at the small end.

So my recollection is that the movement is always towards the small end.

« Last Edit: 06/11/2015 02:27 AM by Rodal »

Offline cej

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Here's a slightly clearer picture of the Hackaday.io graph.

I downloaded their spreadsheet.  For those interested, it looks like their sample rate was 16 Hz.  The ordinate axis is rpm.
<edit>  The ordinate axis data is LABELED as RPM which is probably not right, unless this was spinning VERY fast.

Sorry! I failed to mention in my initial post that it is NOT the original data. I attached the spreadsheet so that anyone can adjust the data points and play with the trend lines. Also, the units in the spreadsheet are complete guesses (based on the experimenter saying, "to get the proper time, devide X by 16," which seems like it could be in seconds).
« Last Edit: 06/11/2015 02:43 AM by cej »

Offline vulture4

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If the theory is that the thrust is due to radiation pressure, then it cannot exceed the total radiation pressure on the large end of the frustrum. It is essential to record the microwave power level in the resonator.This would provide a clear indication of the maximum possible force that could be generated from photon momentum. It is essential to measure the frequency at both ends of the resonator as well. If the frequency is different, then we need to figure out why. If the frequency is the same, then the momentum of incident photons will also be the same, regardless of their group velocity, and differential radiation pressure will not occur.

Getting more accurate laboratory data would at least provide some opportunity to determine what forces the device is producing and whether they actually result from electromagnetic interactions or from artifactual (probably air/thermal) processes. Tests under more complex conditions, with the device in motion, floating on air or water, or in space introduce additional complexities which make any meaningful analysis even more difficult. Experiments in space will be so much more expensive that the amount of actual data that can be collected will be vastly reduced.
« Last Edit: 06/11/2015 03:23 AM by vulture4 »

Maybe we are not at rest in our own frame inside earths gravity well with respect to space. 
Are you suspecting the microwave resonance behaves like a gyroscope which interacts with a moving spacetime around us?

Offline vulture4

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Shades of the Michelson-Morley experiments for Aether. 
The experiments were very precise and performed in the simplest, most stable, and most carefully controlled environment possible. They showed no evidence of a preferred frame of reference. There is no moving spacetime. The speed of light was exactly the same to the limit of measurement regardless of its direction with respect to the Earth's motion.

We should strive to be equally precise.
« Last Edit: 06/11/2015 03:22 AM by vulture4 »

Online dustinthewind

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Maybe we are not at rest in our own frame inside earths gravity well with respect to space. 
Are you suspecting the microwave resonance behaves like a gyroscope which interacts with a moving spacetime around us?

I am not sure how you are suggesting a gyroscope interacts with moving space-time.  What I was thinking is that if you eliminate buoyancy, thermal convection, and and pressure gradients from expanding heated air and what you get is a thrust that appears to behave differently with respect to direction and that thrust was dependent on pushing off a moving medium then maybe thrust would be less one way compared to another. 

On the other hand the speed of light measured "locally" should not be influenced by the motion of this medium (via the Lorentz contraction of rulers) except for the perception of a 3rd person removed from the gravitational well.  The way to measure something non-locally is to send it in (maybe to a black hole), let its path be bent and come back and I would guess you should observer the difference in the passage of time.  Am I wrong here? (E.g. this goes back to the engineers use of a varying k = dielectric constant of space to explain relativity near gravitational wells.)  This paper seems to suggests a possibility of flowing space time, "http://arxiv.org/abs/physics/9902029".

Of course maybe there is some other reason for this non-symetry and is why I made reference to the unusual measurement of the capacitor in my last post.  ( http://forum.nasaspaceflight.com/index.php?topic=37642.msg1387736#msg1387736 ) The question being why in that case I would observe non-symetric emf in the capacitor by reversing the polarity of the magnetic field of the solenoid and also why the voltage would be constant as long as the DC magnetic field was there.  That is I would have thought it would be -dB/dt that would push the electrons away from the solenoid not a constant magnetic field.  The EMF was always in the same direction regardless of the magnetic field and maybe it was the para-magnetism of aluminum but still the non-symmetry of that. 
« Last Edit: 06/11/2015 03:54 AM by dustinthewind »

Offline TMEubanks

Everyone check out Hackaday.io! Results are up and data is looking good.

Maybe I am missing something, but what is exciting about having the device spin slower in both prograde and retrograde configuration? Are we sure that's not just friction? Have they tried to spin it up?
Excited that, instead of copying the same dimensions used by Shawyer, Yang and NASA, Aachen fellows miniaturized it, and instead of running at 2.45 GHz they went 10 times higher to 24 GHz in unexplored territory, and that after taking these big risks they are reporting seeing a thrust signal.   :)

Having said that, the signal-to-noise ratio is, shall we say, Ahem, unexciting ?   :)

Disturbing to se the EM Drive's strange preference of one direction vs. another (reminds me of the issue with NASA turning it around by 180 degrees). 

Hope that they continue, that they check whether they are in resonance (? never heard anything about Q, what mode shape they have, etc.) that they show null curves and they do lots more testing, and perhaps they can also try filling it with Ammonia gas (it emits at 24 GHz) ? and looking forward to vacuum testing as well...

I agree fully - while the SNR is unimpressive, these drives are just the size needed for a test in space.

Offline WarpTech

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I've been working on the EM Drive attenuation factor, and the design equations for a "better" thruster. I'm not quite there yet, but what I have just found is interesting, I think.

Shawyer's design criteria calls for the small end to be (half?) the cut-off wavelength, equal to (half?) the wavelength in free space, such that "his" wave velocity goes to zero. I've coined the analogy that this is like falling into a black hole, the energy is attenuated asymmetrically.

What I've determined is, with this design it's more like the waves are reflecting off the event horizon, not falling through it where they are attenuated. In order for the waves to be attenuated, there is a time constant on the order of;

tau = lambda0/c,

Where, lambda0 is the free space wavelength, and c is light speed in free space. In an exponentially decaying function, 1 time constant will only allow 2/3 of the energy to be attenuated. The other 1/3 can take several more time constants. The frustum is not even 1 wavelength long, so the attenuation is severely limited.

Based on this it would seem to me that, to maximize thrust one would want to extend the frustum out another 1/2 wavelength or more, until the small end is 1/2 it's current value. Why?

Well, the damping factor is the attenuation/frequency, and this is lambda0/lambdacutoff. The current design sets this to 1. It should be set to 2, the Q will be relatively low, but that is because more of the stored-energy is being attenuated as thrust.

It has nothing to do with what is flowing in on the wires, that is just charging the LC oscillator, and nothing is required to thrust out the back. AFTER the energy is stored, the rate of attenuation is asymmetrical and that is what generates the thrust. The faster the rate, the more force will be exerted, due to phase cancellation inside. With a low Q, less energy will be stored, but more thrust will be achieved. I'd be willing to wager!

We are "guessing" what Yang did with her design and @Rodal suggested she followed Shawyer's DF making the small end equal to (half?) the input wavelength. I'd be surprised if it wasn't 50% smaller than that, given her thrust measurements and low Q values.

Todd
« Last Edit: 06/11/2015 04:44 AM by WarpTech »

Offline deltaMass

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I thought I might try to deduce the N/W figure from the data, and the first issue is modelling the friction. It looks like the simplest model would work quite well - a constant frictional force opposed to the motion, independent of the angular velocity. Anything more complex produces an exponential decay, and we don't see that.
« Last Edit: 06/11/2015 04:46 AM by deltaMass »

Offline kml

...If the guided wavelength model is correct then the large end should lead when there is no dielectric present, as appears to be the case with this design.   If there was a thin dielectric on the small end the curves would reverse and the small end would lead, and with higher thrust.    ...

1) What is the guided wavelength model? Is that Shawyer's model?

I have found Shawyer's diagrams of thrust force pointing towards the big end and the reaction movement pointing towards the small end confusing (because the "thrust force" is not something ever measured but appears to be something conceived to try to explain conservation of momentum) but:

2) My recollection is that in Shawyer's tests the frustum moves pointing towards the small end (instead of the large end) for the Demonstrator (no dielectric present).

3) My recollection is that  in NASA's tests, the truncated cone moves in the direction of the small end (same as in Shawyer's Demonstrator).  NASA' truncated cone has a dielectric insert at the small end.

So my recollection is that the movement is always towards the small end.

1) It is Shawyer's model (at least the part of it I understand), but derived and explained in a more straightforward way.

In the "guided wavelength" model photon momentum transfer is proportional to Lambda0 / Lambdag.  Which is  equation 7 in Shawyer's theory paper but not ignoring permittivity and permeability of media in calculating guided wavelength.    I haven't tried to make sense of his later formulas where he adds back the previously ignored dielectric effects in an unnecessarily confusing way.    If you calculate guided wavelength at each end using industry standard formulas that include permittivity and permeability then Shawyer's equation 7 (plus Q) equals this model.

the simplest explanation of the model is that the energy of a photon is always based on it's frequency:

 E = h c / Lambda0

but the momentum of a photon, at least for these interactions, depends on it's actual in media wavelength:

 p = h / Lambdag.

So:
 
 P0 = n h c / Lambda0    (Power = number of photons per second * energy per photon)

 n = P0 Lambda0 / h c     (rearranging for n)

 F = 2 n h / Lambdag     (Force = 2 * number of photons per second * momentum per photon)

Thus the force transferred in a perfect reflection is:

 F = 2 P0 Lambda0 / c Lambdag

And thrust equals:

  T = (2 P0 Q  / c)  * (Lambda0 / Lambdag1 - Lambda0 / Lambdag2)   (Shawyer's formula 7 with Q)

Since the guided wavelength of a tapered resonator without dielectric is longer at the small end, there should be less force on the small end and the large end should lead.     The presence of a dielectric usually overrides the effect tapering so the dielectric end (large or small) should lead when present.    This is of course very different from a group velocity model which would have the small end lead in an empty tapered resonator. 

2) The demonstrator in the video is leading small end forward which would contradict this model if there is no dielectric or high permeability media in the small end and the rotation is due to emdrive thrust and not mechanical effects. 

3) In one of the Eagleworks tests the thrust did decrease and reverse towards the large end when the dielectric separated which is in agreement with this model.  The other tests all accelerated dielectric end first in agreement with the model.

I like the simplicity of this model as it says momentum transfer only depends on actual wavelength. A photon with a 1m wavelength in air transfers the same momentum as a lower freqency photon in media with a guided wavelength of 1m.    Whether or not the change in momentum in media is offset elsewhere is not addressed here :)

I have a spreadsheet that models this for rectangular resonators like the one I'm building.  It handles tapering in a very crude way. For straight resonators with dielectrics of the correct size/shape for the mode used (TE vs TM) it should be good.  It could easily be adapted for specific circular modes.

http://kl.net/emdrive/kml-emdrive-latest.xls
« Last Edit: 06/11/2015 05:27 AM by kml »

Offline PaulF

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Disturbing to se the EM Drive's strange preference of one direction vs. another (reminds me of the issue with NASA turning it around by 180 degrees). 


I have been wondering if a preferred frame means that there is a specific velocity at which it appears one should be at rest.  I would suspect that this might be so.  Far away from a gravity well, maybe we can assume space is stationary, and light speed is about the same in any direction from a 3rd observer displaced from all gravity.  Inside a gravity well however, lets assume space time is moving into the gravity well.  With a black hole, at the event horizon lets say, space is moving in at the speed of light.  At that point light cant escape because space is moving in at the same speed it propagates.  Maybe we are not at rest in our own frame inside earths gravity well with respect to space. 

I once during an experiment encountered some non-symmetry that also baffled me.  We had a high resistance volt meter connected to a capacitor that was outside and concentric around a large solenoid.  It had, I think around 180 picofarads and was aluminum.  I could apply DC current through the solenoid in one direction and the voltage would rise on the capacitor and stay that way but decay as charge flowed off slowly.  If I discharged it then reversed the voltage wires so current flowed the other way through the Edit:(solenoid) then give it current the magnitude of increase in the voltage on the capacitor was about an order less.
While reading this, I asked myself the following:

How is that, as spacetime expands, the matter in our universe is dragged outward along with it (or is this my misconception?) and that the invisible part is receding from us at greater than the speed of light (Vgalaxies + Vspacetime), while with a black hole spacetime is dragged in, and acceleration toward the black hole is solely due to gravity. Vmax = c, not c + speed of dragged spacetime. Why is that? Due to time dilation / length compression? Is this a proprietary property of a black hole, being able to stretch spacetime into itself without dragging in matter at V > c ?

Can anyone clear this up for me with a good explanation?

-PS maybe a better question is: Why can expanding spacetime without gravity well expell matter from "us"at V>c while a blackhole with it's monster gravity can suck in spacetime so brutally but fail to suck in matter at V>c ?
« Last Edit: 06/11/2015 05:50 AM by PaulF »

Offline deltaMass

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I'm trying to deduce the thrust from the Baby Emdrive data, and failing.

Let q represent dw/dt or the angular acceleration (always < 0), where
q0 is the acceleration with the drive off = -29.408
q+ is the acceleration with the drive prograde (impeding decay) = -24.987
q- is the acceleration with the drive retrograde (assisting decay) = -35.007
where the numbers have been read off from the interpolated graphical slopes.

Let b = the constant frictional force acting against the motion (Newtons)
Let F = the drive force (Newtons)
Let a = I/R, so that a*q is also in Newtons (torque = moment of inertia * dw/dt)

Then we have 3 equations in 3 unknowns:
1. a q0 = -b
2. a q+ = -b + F
3. a q- = -b - F

For consistency we are forced to have
2 q0 = q+ + q-
and from the interpolated graphical slopes, this is quite nicely the case (58.82 vs. 59.99).

However, we cannot solve for F independently of a or b.
Bummer. Or am I being stupid?


« Last Edit: 06/11/2015 07:24 AM by deltaMass »

Offline TheTraveller

I've been working on the EM Drive attenuation factor, and the design equations for a "better" thruster. I'm not quite there yet, but what I have just found is interesting, I think.

Shawyer's design criteria calls for the small end to be (half?) the cut-off wavelength, equal to (half?) the wavelength in free space, such that "his" wave velocity goes to zero. I've coined the analogy that this is like falling into a black hole, the energy is attenuated asymmetrically.

What I've determined is, with this design it's more like the waves are reflecting off the event horizon, not falling through it where they are attenuated. In order for the waves to be attenuated, there is a time constant on the order of;

tau = lambda0/c,

Where, lambda0 is the free space wavelength, and c is light speed in free space. In an exponentially decaying function, 1 time constant will only allow 2/3 of the energy to be attenuated. The other 1/3 can take several more time constants. The frustum is not even 1 wavelength long, so the attenuation is severely limited.

Based on this it would seem to me that, to maximize thrust one would want to extend the frustum out another 1/2 wavelength or more, until the small end is 1/2 it's current value. Why?

Well, the damping factor is the attenuation/frequency, and this is lambda0/lambdacutoff. The current design sets this to 1. It should be set to 2, the Q will be relatively low, but that is because more of the stored-energy is being attenuated as thrust.

It has nothing to do with what is flowing in on the wires, that is just charging the LC oscillator, and nothing is required to thrust out the back. AFTER the energy is stored, the rate of attenuation is asymmetrical and that is what generates the thrust. The faster the rate, the more force will be exerted, due to phase cancellation inside. With a low Q, less energy will be stored, but more thrust will be achieved. I'd be willing to wager!

We are "guessing" what Yang did with her design and @Rodal suggested she followed Shawyer's DF making the small end equal to (half?) the input wavelength. I'd be surprised if it wasn't 50% smaller than that, given her thrust measurements and low Q values.

Todd

What Shawyer suggest for the small end is it should operate just ABOVE cutoff, defined as Guide Wavelength at small end still above zero. That way there is an EM wave to bounce back off the small end plate

That gives max Df as either small end diameter, excitation mode or input frequency will need to be adjusted / chosen to obtain that result.

Next he suggests getting big end as big as possible while obtaining desired internal 1/2 wave multiples of the effective overall guide wavelength to fit inside end plate spacing.
« Last Edit: 06/11/2015 06:41 AM by TheTraveller »
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Offline deltaMass

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I'm trying to deduce the thrust from the Baby Emdrive data, and failing.

Let q represent dw/dt or the angular acceleration (always < 0), where
q0 is the acceleration with the drive off = -29.408
q+ is the acceleration with the drive prograde (impeding decay) = -24.987
q- is the acceleration with the drive retrograde (assisting decay) = -35.007
where the numbers have been read off from the interpolated graphical slopes.

Let b = the constant frictional force acting against the motion (Newtons)
Let F = the drive force (Newtons)
Let a = I/R, so that a*q is also in Newtons (torque = moment of inertia * dw/dt)

Then we have 3 equations in 3 unknowns:
1. a q0 = -b
2. a q+ = -b + F
3. a q- = -b - F

For consistency we are forced to have
2 q0 = q+ + q-
and from the interpolated graphical slopes, this is quite nicely the case (58.82 vs. 59.99).

However, we cannot solve for F independently of a or b.
Bummer. Or am I being stupid?
I think that's quite sensible so I'm not dropping the ball.
In order to get the value of F, either the friction needs be known (which is the value 'b'), or the moment of inertia of the cavity and its lever arm needs be known (which yields the value 'a').

Note that the numerical values used for q are not yet in the correct (SI) units at this point.
« Last Edit: 06/11/2015 07:29 AM by deltaMass »

Online dustinthewind

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Disturbing to se the EM Drive's strange preference of one direction vs. another (reminds me of the issue with NASA turning it around by 180 degrees). 


I have been wondering if a preferred frame means that there is a specific velocity at which it appears one should be at rest.  I would suspect that this might be so.  Far away from a gravity well, maybe we can assume space is stationary, and light speed is about the same in any direction from a 3rd observer displaced from all gravity.  Inside a gravity well however, lets assume space time is moving into the gravity well.  With a black hole, at the event horizon lets say, space is moving in at the speed of light.  At that point light cant escape because space is moving in at the same speed it propagates.  Maybe we are not at rest in our own frame inside earths gravity well with respect to space. 
...
While reading this, I asked myself the following:

How is that, as spacetime expands, the matter in our universe is dragged outward along with it (or is this my misconception?) and that the invisible part is receding from us at greater than the speed of light (Vgalaxies + Vspacetime), while with a black hole spacetime is dragged in, and acceleration toward the black hole is solely due to gravity. Vmax = c, not c + speed of dragged spacetime. Why is that? Due to time dilation / length compression? Is this a proprietary property of a black hole, being able to stretch spacetime into itself without dragging in matter at V > c ?

Can anyone clear this up for me with a good explanation?

-PS maybe a better question is: Why can expanding spacetime without gravity well expell matter from "us"at V>c while a blackhole with it's monster gravity can suck in spacetime so brutally but fail to suck in matter at V>c ?

This article kind of helped me with your question.  Here is a quote, "how we could possibly see a galaxy that is moving away from us faster than the speed of light! The answer is that the motion of the galaxy now has no effect whatsoever on the light that it emitted billions of years ago. The light doesn't care what the galaxy is doing; it just cares about the stretching of space between its current location and us. So we can easily imagine a situation where the galaxy was not moving faster than the speed of light at the moment the light was emitted; therefore, the light was able to "outrun" the expansion of space and move towards us, "

http://curious.astro.cornell.edu/about-us/104-the-universe/cosmology-and-the-big-bang/expansion-of-the-universe/616-is-the-universe-expanding-faster-than-the-speed-of-light-intermediate

So in a sense I think that when the light was emitted the velocity of the space it passed through never went above the speed of light so it made it to us but was still stretched due to the expansion (red shifted).  This seems to imply that if the space light passes through does go above the speed of light then the light doesn't reach us and may be similar to a black hole but with an event horizon that surrounds us.  In a sense everything freezes at the event horizon and time stops so it doesn't go above light speed but then maybe the universe does that to hide anything that does go above c. 

It is an interesting subject in that it seems to suggest space is moving and dragging us with it. 
« Last Edit: 06/11/2015 08:14 AM by dustinthewind »

Offline Flyby

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The observation that the supposedly generated forces are unable to overcome the deceleration, due to air resistance, when oriented with the rotation direction, ....well.... i find that very worrying and not something to be overly ecstatic about... Or is that just me?

we'll be talking about N here instead of mN...

And with such minute forces at play, then the same dreadful monster emerges :...doubt....
 "wasn't it due to other residual forces?"

This test does not solve the question whether or not the EMdrive produces thrust.

It still splits people into believers or not believers (and a few skeptics).
However, science isn't about believing or not believing, but about reproducible experiments and data validation...

We really need 720mN (or something alike) to validate the EMdrive or else the discussions/debate will never draw to a conclusion...
« Last Edit: 06/11/2015 08:14 AM by Flyby »

Offline deltaMass

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That 720 mN came from about 1 KW of power. The Baby EmDrive uses not kilowatts, not Watts, but milliwatts. You need to adjust your expectations accordingly.

Offline Vix

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We really need 720mN (or something alike) to validate the EMdrive or else the discussions/debate will never draw to a conclusion...

That's why I consider that Baby EM drives are not the way to go. We should build a "Monster EM" instead. Not trivial, I know....

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