Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1803503 times)

Online Rodal

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Re: New comment by Martin Tajmar
« Reply #5620 on: 07/29/2015 03:01 PM »
I just come across an article that was posted 60 minutes ago. IBT talked to Prof. Martin Tajmar and here are his comments. It does not sound encouraging for the enthusiast side of the spectrum  :( . I guess critics might celebrate their victory this or next year. I just hope they will at least be more polite than Mr. Sean Caroll.

Here is the extract and the link

http://www.ibtimes.co.uk/emdrive-dr-martin-tajmar-generates-thrust-test-controversial-space-propulsion-technology-1513151

"Next steps include better magnetic shielding, further vacuum tests and improved EmDrive models with higher Q factors and electronics that allow tuning for optimal operation. As a worst case we may find how to effectively shield thrust balances from magnetic fields."

Tajmar told IBTimes UK that he feels his EmDrive experiments are just a "work in progress" at the moment. "I believe there is no real news here yet. I specifically wrote in the abstract and conclusion of the paper that our measurements can not confirm or refute anything here regarding the EmDrive."

"After building our own setup we did indeed measure effects similar to what you would expect from an EmDrive - but also in directions where you would expect zero thrust. Our setup therefore produced a null effect within our measurement resolution which is on the order of the claimed thrust we did identify magnetic forces from the power cables that may still lead to a significant influence which must be assessed in future work."
That's why I had earmarked as the most important technical question to ask at the meeting the issue of the bloody big hole from the bloody big waveguide producing the extraneous side force.

It is unfortunate the Dr. Bb was not given a chance to ask questions.

For sure the skeptics are going to latch on to this fact.

But is a big weakness of Tajmar's study not to have properly addressed the issue of this bloody big waveguide on the side.  I also note the asymmetry in the therrmal camera view from above showing a clear asymmetry in the temperature around the circumference.
« Last Edit: 07/29/2015 03:04 PM by Rodal »

Offline aero

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You know that I am about as pro real thrust as it can get, but if its an artefact I want to find it. So I had a thought re. Tajmar's measured lingering thrust dissipating in seemingly correlation to the hot magnetron cooling.

Have the folks using magnetrons all used New magnetrons? That is, tubes that have not yet been burned in? If so then the inside of those things is likely be "dirty." Covered with a sheen of cleanser if not light oil. Not very dirty but what ever amount is burning off could travel down the waveguide to the cavity and leak out, or deposit on the inside of the relatively cool and polished copper.  EW didn't use a magnetron, and still got a force signal. Is there a sneak path for hot stuff to come out of the waveguide into the cavity in that case?
Just to be sure I understand your thesis here; the presence of this light oil, having trickled into the cavity, will cause the cavity temperature to maintain longer than if it were absent, due to the oil's heat capacity?

Maybe. But what is more salient for me than the cause of the thermal "run-on" is its magnitude and duration. It had magnitude comparable to the putative thrust, and a duration which roughly corresponded to the cooling time of the magnetron itself. The disturbing thing for me here is that, as a result of the magnitude of the thermal effects, the SNR was in the toilet. Which means the fidelity of the force measurement is in doubt. I say this knowing full well that the force signal had a prompt onset.

Not so much "trickled in" as being left over from the manufacturing process. As I understand it, the magnetron is in part a metal cavity with high surface area/volume. Manufacturing metal components often/usually involves machine oil lubricate the cutting/stamping process. Then the finished parts are dipped in a cleanser bath and air dried. (I don't know specifically for magnetrons.) But it was left over residue from this process that I was referring to. Of course they are somewhat "clean" as in microwave ovens, they couldn't be allowed to contaminate the food.

But "clean" is relative when detecting micro-Newtons of force.
Retired, working interesting problems

Offline deltaMass

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f + b = 620 uN
-f + b = 390 uN
so force f = 115 uN, buoyancy etc. b = 505 uN

As pointed out, SNR is in the toilet.

Online Rodal

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f + b = 620 uN
-f + b = 390 uN
so force f = 115 uN, buoyancy etc. b = 505 uN

As pointed out, SNR is in the toilet.
As expected with a ridiculously low Q below 50

Iulian Berca conducted a better experiment than Tajmar !

In Iulian Berca's experiment, the EM Drive went up when the small diameter was pointed upwards, and down (from the neutral position) when pointed downwards (just not as much, due to buoyancy).  In Tajmar's the buoyancy overwhelms the EM Drive force.

The (buoyancy force)/thrust was smaller for Iulian Berca

To continue with the experiments Tajmar could aim for an even lower Q=2

A Q=2 will ensure to increase the SNR and could be used as a better nullification

Also he could try using a bigger waveguide and a smaller EM Drive cavity, that will maximize the side force even further.  :)
« Last Edit: 07/29/2015 03:27 PM by Rodal »

Offline WarpTech

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...Hold on, it's not just the scale. Tajmar says his scale and setup was capable of measuring forces < 1uN. This must require that the restoring-force of the scale that is coupled to his balance is << 1uN. We are used to seeing real-world forces, where scales "snap-back" to zero very quickly because the internal spring mechanism or whatever supplies the restoring force is strong. Here, the restoring force is necessary weaker than the EM drive thrust. Such a tiny restoring force "should" take a long time to restore the balance to equilibrium once the thrust is removed. If he had a setup where the balance quickly went back to zero, it would not be able to measure such small forces accurately.

The DIY's using balance beams should consider that if it's oscillating, it will have a very slow oscillation before it comes to a complete stop. How slow? Could it take minutes to settle? I'm sure it could if the restoring force is << 1uN!
Todd

That's correct.  It is not just the scale itself but the beam balance mechanics that are very much at play here.

I think the point here is: The graphs that show thrust are probably labeled incorrectly. The correct labeling should be "displacement". When the EM drive is on, there is definitely thrust because the displacement is growing. When the power is turned off, the displacement doesn't just suddenly go back to it's starting location. The displacement would be,

z(t) = z0 + .5*(F/M)*t2

When power is on, F is the thrust of the EM drive. When the power is off, F = -1uN is the restoring force. The If it takes 15 sec. to accumulate this displacement with the EM drive on, it will take much, much longer to restore it to z0 with the EM drive off. So I was wrong, the persistence has nothing to do with stored energy inside the frustum, and everything to do with the "very weak" restoring forces acting when the power is turned off.
Todd


Offline deltaMass

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The displacement would be,

z(t) = z0 + .5*(F/M)*t2
That's the first equation you've posted that I a) understand and b) agree with  ;D

Offline deltaMass

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I have trouble with this Q-multiplier for the force.
Neglecting constants like design factors, and finessing the group/phase velocity issue, in broad terms people like to write, for an EmDrive force model
F = P*Q/c

A big Q gives great superiority over the esteemed photon rocket. This is a big part of the magic and I believe it's a mistake. It's apparently a free lunch.

Let's recalibrate using Bae as an example, who bounces lasers between parallel mirrors and gets thrust multiplication that way. His scheme is conventional - there are no overunity issues there. And yet he too has a factor Q in his equations.

Is there a physicist here who can disavow me of the suspicion that he too is cheating? If you are pumping power into a Bae "extended laser" then at equilibrium you cannot extract power faster than P - not at Q*P, or at least not for long. What gives?

Offline deltaMass

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When power is on, F is the thrust of the EM drive. When the power is off, F = -1uN is the restoring force. The If it takes 15 sec. to accumulate this displacement with the EM drive on, it will take much, much longer to restore it to z0 with the EM drive off. So I was wrong, the persistence has nothing to do with stored energy inside the frustum, and everything to do with the "very weak" restoring forces acting when the power is turned off.
Todd
This is the classic "ballistic galvanometer" from days of yore.

Online SeeShells

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A couple of observations on the Dresden cavity. One is the plasma arcing in the cavity. I'm wondering why it was so extreme. This is not much different than the Tomak trying to sustain a plasma in a cavity. When the plasma that has built up from being generated with microwaves producing a very high Q discharges most or all of the energy bleeds off. If your goal is to maintain a high Q you don't want it to be shunting to ground via a gap in the containment fields.

Their design goals to excite the lowest mode was a good one and using a waveguide to directly couple to the frustum trying to assure the maximum transfer of RF was smart. But where it shows that it all falls apart is in the fact that it created a very unstable mode generation in the very asymmetrical cavity leading to plasma discharges that lowered the Q and dissipated the mode generation they were trying to maintain.

While you might be able to pump more RF through a waveguide if you create a unstable mode generation it throws a monkey wrench into your test  when using just one waveguide into the side.

I'm thinking he would have been better off to use 2 magnetrons, one on each side with matching waveguides to inject.   Making them symmetrical in the same plane to each other. The magnetrons would lock onto each other generating the TE mode in the cavity without the asymmetrical issues of using one.  I remember asking when I first joined the group had anyone had done this. ElizabethGreen commented one time that you could use 2 phase locked magnetrons locked in the same waveguide and they would self lock. I would have popped the mini EMDrive cavity right in the center of the two and avoided what I have seen with the Dresden tests.

Or just use one if that's all you have but use matching waveguides to insert on either side of a cavity maintaining the symmetry of your mode generation.

Morning coffee thoughts.

Shell

 

Offline zellerium

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I think the point here is: The graphs that show thrust are probably labeled incorrectly. The correct labeling should be "displacement". When the EM drive is on, there is definitely thrust because the displacement is growing. When the power is turned off, the displacement doesn't just suddenly go back to it's starting location. The displacement would be,

z(t) = z0 + .5*(F/M)*t2

When power is on, F is the thrust of the EM drive. When the power is off, F = -1uN is the restoring force. The If it takes 15 sec. to accumulate this displacement with the EM drive on, it will take much, much longer to restore it to z0 with the EM drive off. So I was wrong, the persistence has nothing to do with stored energy inside the frustum, and everything to do with the "very weak" restoring forces acting when the power is turned off.
Todd

I like this idea, but it sparked a few questions:
Do you think it just a coincidence that the restoring force and temperature are ~ proportional?
Why is the restoring force not constant in all thruster orientations?

What supplies the restoring force?


Offline deltaMass

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If he is still using the ARC balance, then it uses special "C-flexural" bearings. These come with an intrinsic restoring force and prevent the balance from acting like a ballistic galvanometer.
http://c-flex.com/

These bearings are now beloved these many years by Woodward. As a matter of fact, right after the "null result report" by Tajmar and Buldrini re. a Woodward Effect experiment they reported upon at STAIF2006, Tom Mahood (an ex-student of Woodward whose M.Sc. thesis was on the Woodward Effect) went off to his well-equipped home workshop and ran up the "ARClite", which Woodward has used ever since. It was a copy of the Buldrini design.

Therefore, it is most likely that this persistent measured force is a real force and really is persistent.
« Last Edit: 07/29/2015 04:12 PM by deltaMass »

Offline deltaMass

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Here are my suggestions to Prof. Tajmar.

Put everything on the thrust measuring apparatus - that's the entire drive with batteries and electronics. Lithium Ion batteries should give you over 30 minutes continuous power. There should be no wires trailing out of the apparatus, because these can cause spurious thrust measurements.

Enclose the apparatus in a hermetically sealed box with stout walls, so that ballooning due to heating is not excessive. It is important to do thorough testing of the seals when operational, at maximum temperature. If this is not done correctly, outgassing can occur in an unpredictable way, which will look like thrust. A 48 hour bake-out at 50 - 65 oC before an experimental run is recommended.

Because accumulation of charge may occur on the outside surface of the enclosure, the outside surface should be conductive to eliminate charge patches, which can cause spurious pseudo-thrusts. It should be grounded through the measurement system. It is prudent to check that the grounding current is small enough that it cannot be expected to generate pseudo-thrust via the Lorentz force. As a precaution here, the ambient DC magnetic field should be checked so as to rule out Lorentz forces due to currents on the outside surfaces.

The apparatus is commanded on and off via a photodiode mounted and sealed into the enclosure wall. This should be mounted orthogonal to the thrust axis so as to minimise the effect of any possible outgassing.

Data recording is best done inside the box and inspected at the end of the experimental run. However, so long as a good antenna seal can be had, WiFi would also work and provide realtime data monitoring and recording.
One more thing - the centre of gravity might shift during power on due to thermal effects. It is important to check that such shifts do not result in a change in the measured weight, by thermally cycling and monitoring the measured weight for various orientations of the box.

At least one other bleeding edge researcher I know about fell afoul of this particular problem.

Offline WarpTech

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If he is still using the ARC balance, then it uses special "C-flexural" bearings. These come with an intrinsic restoring force and prevent the balance from acting like a ballistic galvanometer.
http://c-flex.com/

These bearings are now beloved these many years by Woodward. As a matter of fact, right after the "null result report" by Tajmar and Buldrini re. a Woodward Effect experiment they reported upon at STAIF2006, Tom Mahood (an ex-student of Woodward whose M.Sc. thesis was on the Woodward Effect) went off to his well-equipped home workshop and ran up the "ARClite", which Woodward has used ever since. It was a copy of the Buldrini design.

Therefore, it is most likely that this persistent measured force is a real force and really is persistent.

He says he used a knife edge balance, which is what's shown in the photo. There is no bearing. The only restoring force is gravity acting on the counter weight. He's counter-balanced the EM drive to the resolution of 1 uN of force. Which means, the restoring force must be < 1 uN. I would agree that IF there were a bearing with a restoring force, then to persist in the displaced position would require a continuous force. But given that it was simply a knife edge, there is nothing but gravity to restore the displacement back to the origin.

A good control test would've been to displace the EM drive to this level of displacement with the power off, and then determine how long it takes to restore the displacement back to the origin.

IMO, the correlation with temperature is a red herring. Both are slow to change and he didn't do anything to investigate if they are or are not correlated.
Todd

Offline zen-in

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Tajmars' tests are similar to the Eagleworks' tests except with more power and a larger vacuum chamber.   The similarities between these two vacuum tests is interesting.   The Eaglework's thrust waveform, after reducing the magnetic interaction is shown below.    The quick 9 uN response after the power is switched on is, I believe a residual magnetic effect.   Then there is a slow climb which I believe is a thermal effect.  Tajmar's vacuum tests also have this slow climb after the RF is switched on (second graph).   It was suggested earlier that this could be from a change in center of mass because of thermal expansion.    The last graph is also from Tajmar's paper and shows his thrust measurements in air using a fluid damper.    I don't see any evidence of an em-drive thrust.

Offline LasJayhawk

If I am to presume that I can get thrust out of this thing by exciting modes in the microwave band, I'm forced to assume the same thing could happen in the infrared band.

In that case the residual heat could be stimulating the EM drive effect (assuming it exists, or course) :)

Offline JasonAW3

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Welp,

     Looks like either there really is something to this EM Drive or as CalTech physicist Sean Carroll says,
My insight is that the EMDrive is complete crap and a waste of time...

http://io9.com/no-german-scientists-have-not-confirmed-the-impossibl-1720573809

     An old saying is that, when a scientist says something is impossible, then he is most assuridly wrong.


My God!  It's full of universes!

Offline aceshigh

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Thanks to Dr Tajmar for his paper and willingness to dip into a controversial area.

its not as if Dr Tajmar was a stranger to "dipping into controversial areas", considering he is known for research into anti-gravity...

I remember some 6-7 years ago there was a lot of talk about a propellantless engine arising from the theories of German Physicist Burkhardt Heim (Heim Theory), and if I am not mistaken, somehow Tajmar got involved in it too, as it seems his anti-gravity results matched the possible equations of Burkhardt Heim (which were all in german and notoriously hard to follow)
« Last Edit: 07/29/2015 05:22 PM by aceshigh »

Offline deltaMass

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If he is still using the ARC balance, then it uses special "C-flexural" bearings. These come with an intrinsic restoring force and prevent the balance from acting like a ballistic galvanometer.
http://c-flex.com/

These bearings are now beloved these many years by Woodward. As a matter of fact, right after the "null result report" by Tajmar and Buldrini re. a Woodward Effect experiment they reported upon at STAIF2006, Tom Mahood (an ex-student of Woodward whose M.Sc. thesis was on the Woodward Effect) went off to his well-equipped home workshop and ran up the "ARClite", which Woodward has used ever since. It was a copy of the Buldrini design.

Therefore, it is most likely that this persistent measured force is a real force and really is persistent.

He says he used a knife edge balance, which is what's shown in the photo. There is no bearing. The only restoring force is gravity acting on the counter weight. He's counter-balanced the EM drive to the resolution of 1 uN of force. Which means, the restoring force must be < 1 uN. I would agree that IF there were a bearing with a restoring force, then to persist in the displaced position would require a continuous force. But given that it was simply a knife edge, there is nothing but gravity to restore the displacement back to the origin.

A good control test would've been to displace the EM drive to this level of displacement with the power off, and then determine how long it takes to restore the displacement back to the origin.

IMO, the correlation with temperature is a red herring. Both are slow to change and he didn't do anything to investigate if they are or are not correlated.
Todd
Thanks for the correction. I had seen a reference to "ARC" in the report, but that's an institution name (Austrian Research something). It is indeed a knife edge. And as you point out, calibration data and control experiment data is sadly lacking in Tajmar's paper.

Offline rfmwguy

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Welp,

     Looks like either there really is something to this EM Drive or as CalTech physicist Sean Carroll says,
My insight is that the EMDrive is complete crap and a waste of time...

http://io9.com/no-german-scientists-have-not-confirmed-the-impossibl-1720573809

     An old saying is that, when a scientist says something is impossible, then he is most assuridly wrong.
OK, here's the "physicist" with the not-so-well thought out response (couldn't remember, thks). Caltech as well...nice. I bet he is an inspiration to all his students and institution.

Its taken me a couple of days to analyze and read the most recent test results; months, overall to figure out what the story is. This guy spouts off within hours indicates his "insight" is not 20/20.

Regardless, he'd best read NSF for analysis of potential problems with the recent test plus improvements that can be made. Critics without solutions or real efforts are simply wasting bandwidth...IOW, a very low Q factor ;)

Offline deltaMass

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If I am to presume that I can get thrust out of this thing by exciting modes in the microwave band, I'm forced to assume the same thing could happen in the infrared band.

In that case the residual heat could be stimulating the EM drive effect (assuming it exists, or course) :)
That's assuming an infrared reflector is in place in the apparatus. I don't think so.

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