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#740 by otlski on 31 Mar, 2016 02:07
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How to measure this is quite an interesting problem. I do agree with the way a torsion pendulum mitigates issues found with see saws. I do worry that the large MOI of the batteries and counterweights (if required) would serve to mask any torque created. This would be especially concerning if the EM drive could not power for very long without burning something out. With tens of micronewtons of expected force at small distance, and a large MOI, how small would the angular acceleration be and how long would it take to notice (measure) it? Furthermore the ability to measure impulses due to rapid on/off cycles would disappear.
If money were no object than a good solution might be a linear air bearing coupled to a tuning fork based laboratory balance such as the ones made by Vibra. These balances have the dynamic range of a force restoration scale but without the magnetic penalty. Note: strain gauge load cells are not sensitive enough. A direct measurement of this type from a static instrument has lots of advantages; impulse response being chief among them. The static nature would tare out out-of-level, deflections, out of parallel, orifice air flow impingement, and more. But alas, it is said that motion is required for some reason so perhaps this wouldn't work.
The rotary air bearing would have the same sort of advantages as the torsion pendulum but the continuous rotation would give ample evidence of long term thrust when the rotation rate was analysed. This is also providing that that Em drive could be left on for long periods. Motoring (or turbine effect) would have to be dealt with via work reversal. The lack of response to impulses still prevails though; and the relevant MOI would likely be larger than the torsion pendulum.
So in the end, I don't see a perfect device. My preference would be the air-bearing/tuning-fork scale if it weren't for that pesky "motion requirement". Do you all accept the motion requirement part? (he asks innocently) -
#741 by Tellmeagain on 31 Mar, 2016 02:11
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but that doesn't necessarily follow either (see the picture of Brito, Marini and Galian's inexpensive torsional pendulum built in Argentina: https://forum.nasaspaceflight.com/index.php?topic=39772.msg1509771#msg1509771 ). A torsional pendulum is not more expensive than a Teeter-Totter. Concerning "the locale", it is actually the Teeter-Totter that takes more room (if a long Teeter-Totter is used as by rfmwguy).
Did your torsional pendulum require a much larger budget, not affordable by a DIY than the Teeter-Totter used by rfmwguy ? Or did your torsional pendulum require a special locale not available to a DIY ?
Dr. Rodal,
The cost was a $7.27 Ebay piano wire of diameter 0.009" and a $16.27 home depot aluminum square tube. The wood frame is a sidewalk found bar stool on top of a DIY bare wood table with a hole. For other DIY's who need to support heavier equipment, a thicker wire may be needed.
Tellmeagain
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#742 by Rodal on 31 Mar, 2016 02:17
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How to measure this is quite an interesting problem. I do agree with the way a torsion pendulum mitigates issues found with see saws. I do worry that the large MOI of the batteries and counterweights (if required) would serve to mask any torque created. This would be especially concerning if the EM drive could not power for very long without burning something out. With tens of micronewtons of expected force at small distance, and a large MOI, how small would the angular acceleration be and how long would it take to notice (measure) it? Furthermore the ability to measure impulses due to rapid on/off cycles would disappear.
If money were no object than a good solution might be a linear air bearing coupled to a tuning fork based laboratory balance such as the ones made by Vibra. These balances have the dynamic range of a force restoration scale but without the magnetic penalty. Note: strain gauge load cells are not sensitive enough. A direct measurement of this type from a static instrument has lots of advantages; impulse response being chief among them. The static nature would tare out out-of-level, deflections, out of parallel, orifice air flow impingement, and more. But alas, it is said that motion is required for some reason so perhaps this wouldn't work.
The rotary air bearing would have the same sort of advantages as the torsion pendulum but the continuous rotation would give ample evidence of long term thrust when the rotation rate was analysed. This is also providing that that Em drive could be left on for long periods. Motoring (or turbine effect) would have to be dealt with via work reversal. The lack of response to impulses still prevails though; and the relevant MOI would likely be larger than the torsion pendulum.
So in the end, I don't see a perfect device. My preference would be the air-bearing/tuning-fork scale if it weren't for that pesky "motion requirement". Do you all accept the motion requirement part? (he asks innocently)
There is no perfect device, but there are some instruments that are better than others.
As I carefully went over in this post: https://forum.nasaspaceflight.com/index.php?topic=39772.msg1509734#msg1509734. This has been carefully analyzed and tested over a space of 50 years of many experiments and Ph.D. dissertations.
I came over this conclusion again during the past few days upon analyzing the discrepancy between the torsional pendulum experiments of Tajmar and his teeter totter experiments and the fact that all torsional pendulum results have given much smaller thrust forces for the EM Drive:
I have analyzed the equations of motion of the teeter totter and found dependence on thermal expansion of the EM Drive itself (this motivated my post). Thus, a teeter-totter may give false readings (due to thermal expansion rather than thrust).
Concerning your question about the duration of the transient effect on a torsional pendulum, it all depends on specific values of the moment of inertia, the dimensions, and foremost the damping/mass ratio and the stiffness/mass ratio. One is not able to make a general statement of course without specific numbers (dimensions, mass, damping, stiffness), but let me remark that:
1) The practical feasibility (with batteries in the torsional pendulum) has already been demonstrated in the peer-reviewed paper by Marini and Galian in the AIAA Journal of Propulsion and Power.
2) The data from NASA (without batteries) shows the transient gone even during the small duration of their experiments
3) The amount of power necessary (and thus the size of the batteries) is questionable: NASA conducted tests at only 2 watts. Other NASA's test were conducted at 30 and 50 watts. RFPlumber conducted his experiments using only 30 watts.
I have not analyzed the equations of motion of the air bearings you are discussing, but the issue I see with air bearings is a lack of stiffness in the equations of motion. This should lead to dynamics governed by damping and mass. It may not have as many issues as the teeter-totter ?, but I cannot go further than that without an analysis. I didn't realize all the problems with the teeter-totter arrangement until I analyzed carefully the teeter totter that that has been posted in these EM Drive threads. Also, one can say that no air-track instrument is used to measure micro-thrust rocket electromagnetic propulsion at MIT's Aero & Astro or at most of NASA and JPL (as far as I know). And they have been measuring electromagnetic propulsion devices for half a century. -
#743 by rfmwguy on 31 Mar, 2016 02:50
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Dr rodal, I do not understand how thermal expansion would be an issue on a balance beam measuring vertical deflection of a symetric device. There would be no center of mass change causing a deflection. Since a teeter totter is not as prone to a primarily horizontal lorentz force, the main problem is thermal current mitigation, not thermal expansion nor lorentz compassing.
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#744 by Rodal on 31 Mar, 2016 03:00
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Dr rodal, I do not understand how thermal expansion would be an issue on a balance beam measuring vertical deflection of a symetric device. There would be no center of mass change causing a deflection. Since a teeter totter is not as prone to a primarily horizontal lorentz force, the main problem is thermal current mitigation, not thermal expansion nor lorentz compassing.
The reason has to do with the fact that you don't have a simple beam supported by a knife edge, but you also have the EM Drive supported at one end. Thus you have to analyze the equations of motion of the whole thing with the EM Drive at one end (which is subject to thermal expansion due to induction heating). It is not justified to disregard the equation of motion of the EM Drive itself. The EM Drive itself is moving, accelerating. Its inertia cannot be disregarded.
The mistake in your discussion above is that you are not taking into account the equation of motion of your whole structure, including the supported EM Drive, which has its own inertia, and you are only conceptualizing the motion of "an ideal rigid beam as a teeter-totter ". It is more complicated describing the whole system. You must take into account the inertia of the EM Drive.
Your setup has a number of other issues: the mast (sticking "up" from the initially horizontal beam) you used to support with wires the initially horizontal beam acts as a superposed inverted pendulum with its own MOI. But since your teeter-totter is on a knife-edge, that mast is an inverted pendulum without stiffness at its rotational point (which leads to some instability for large enough motions). The brackets that you used as weights at one end (sticking "down" from the initially horizontal beam) have additional MOI as attached small pendulums. Etc.
Your setup is not just a horizontal rigid beam. Just conceptualize what happens for example when the beam rotates towards one side (and compare your setup with a simple teeter-totter). Conceptualize what happens when you apply an impulsive load.
The dynamic motion of your experiment was so complicated that the only analysis that could find a "force" was a statistical analysis. -
#745 by Tellmeagain on 31 Mar, 2016 03:15
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Dr rodal, I do not understand how thermal expansion would be an issue on a balance beam measuring vertical deflection of a symetric device. There would be no center of mass change causing a deflection. Since a teeter totter is not as prone to a primarily horizontal lorentz force, the main problem is thermal current mitigation, not thermal expansion nor lorentz compassing.
frmwguy, Lorentz force is not necessarily primarily horizontal. It all depends on how you arrange your circuit. It can be primarily horizontal, primarily vertical, or any other angle, or be insignificant if it is correctly countered. We have talked about this in an earlier post. -
#746 by Tellmeagain on 31 Mar, 2016 03:39
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...
So in the end, I don't see a perfect device. My preference would be the air-bearing/tuning-fork scale if it weren't for that pesky "motion requirement". Do you all accept the motion requirement part? (he asks innocently)
No, I do not accept the motion requirement. I think it is (mis-) made by Mr. Shawyer from his observation of his own experiment. In this post https://forum.nasaspaceflight.com/index.php?topic=39004.msg1471694#msg1471694 (read also quoted text there) we discussed that. I think Mr. Shawyer observed that only when his device was in motion could he observe the EmDrive "effect". -
#747 by Rodal on 31 Mar, 2016 03:44
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As an (admittedly) extreme example that a teeter-totter horizontal beam ceases to be a simple teeter-totter when one places a central mast and hanging things from it, here is something to watch.
A Teeter-Totter with a central mast and two hanging devices exhibiting chaos when submitted to large motions
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#748 by oyzw on 31 Mar, 2016 04:26
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Moreover it does not follow that <<any test stand that provides Observed results is useful.>> (It may be useful if one carefully solve the equations of motion for the testing device and carefully analyzes the significance of what is measured).
RFPlumber‘s cavity resonator antenna design is not reasonable.Power is hard to feed into the cavity.According to the S11 map, I think cavity leakage is very serious.In a word, his cavity may be unable to run normally.
As I discussed, Teeter-Totter instruments may provide false readings, as is known and documented, and as discussed here: https://forum.nasaspaceflight.com/index.php?topic=39772.msg1509734#msg1509734
It is noteworthy that, among DIY:
* Mulletron was the first DIY. Mulletron built a simple pendulum. No results reported.
* RFPlumber used a simple pendulum (not a torsional pendulum !) and obtained NULL results
See his published report: http://vixra.org/abs/1603.0153
* When Berca used a simple pendulum he also obtained NULL results.
Berca only obtained "results" when he hanged the EM Drive from one end of a teeter-totter beam and measured the movement of the opposite end with a scale.
* The lowest measured anomalous force were obtained by:
a) NASA Eagleworks using a torsional pendulum
b) Tajmar using a torsional pendulum -
#749 by SeeShells on 31 Mar, 2016 04:31
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As an (admittedly) extreme example that a teeter-totter horizontal beam ceases to be a simple teeter-totter when one places a central mast and hanging things from it, here is something to watch.
A Teeter-Totter with a central mast and two hanging devices exhibiting chaos when submitted to large motions
Well Dr. Rodal if anyone gets that level of rotational spin, then they have made a monumental discovery. 
The issues with beams, balances and air bearings, Lorentz or thermal, becomes one where your measurements of expected and maybe measured thrusts move out of your error envelope created by these devices.
I saw where the pressure profiles I measure and the acceleration curves can be overlapped to reduce the error envelope or at least define it with finer margins. This is what defined the test bed.
I like air bearings and I believe you could do both pressure measurements as well as an acceleration profile. It was one option I considered but providing power levels to the frustum became the deciding point. Power to the air bearing would require it to be battery driven and at reduced power, whereas the beam I still could do pressure and acceleration with high power delivered to the frustum.
It was all a trade off in a low powered frustum vs high powered frustum of 50W vs 1000W.
Shell -
#750 by meberbs on 31 Mar, 2016 04:58
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Keep in mind that the emDrive having any effect at all isn't an experimental fact yet, since there is no conclusive data available.
Keep in mind that is your opinion. To others there are conclusive data available.
If you read Roger's papers, he makes it very clear a stationary EmDrive needs to experience some slight acceleration, big end to small end, to tigger Motor mode & further self acceleration.
The lack of conclusive experimental data is not an opinion. When scientists call something conclusive, it has a specific meaning. For many studies, it is defined by a pre-determined confidence value such as 95%. Eagleworks, Tajmar, etc. have too small of thrust measurements relative to potential error sources to be conclusive. The large measurements from Yang and Shawyer do not include enough information to allow repetition of their experiments or determination of error sources. Shawyer and Yang themselves have shown difficulties with simple physics, so even if they had confidence intervals, they would need to provide the data that went into determining the confidence level so that their determined level could be validated.
I have read Shawyer's papers before. He does not state anything clearly. After careful reading, I usually find basic mistakes within the first couple pages that make the entire rest of the paper entirely meaningless.
For one relevant example here is an excerpt from my post about the force measurement paper you posted recently.
If you are going to respond to this post, please either explain how that statement from the paper makes sense, or provide some actual information on how to put an emdrive into "motor mode". (This means quantifying the force/vibration, how it is applied, etc. Not just providing a description of how to deal with an experimental setup with too much static friction) This would be useful, since your statements so far aren't specific enough for the experimenters to incorporate this into their designs.Quote from: SPRThis internal force F is measured by an outside observer as the Thrust T, a force acting against the observer in the direction shown.
This statement is completely nonsensical. The outside observer would see the device accelerate with acceleration a. Why would the observer feel a force on them? You don't feel a force just from looking at an accelerating object. -
#751 by A_M_Swallow on 31 Mar, 2016 09:46
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Keep in mind that the emDrive having any effect at all isn't an experimental fact yet, since there is no conclusive data available.
Keep in mind that is your opinion. To others there are conclusive data available.
If you read Roger's papers, he makes it very clear a stationary EmDrive needs to experience some slight acceleration, big end to small end, to tigger Motor mode & further self acceleration.
Adding a solenoid as starter motor is not hard. Is it just the one push at start up or does it need repeating?
Control tests with no push, no power to the EmDrive and 'wrong' frequency are needed to show the effect of the starter motor. -
#752 by francesco nicoli on 31 Mar, 2016 09:57
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Keep in mind that the emDrive having any effect at all isn't an experimental fact yet, since there is no conclusive data available.
Keep in mind that is your opinion. To others there are conclusive data available.
If you read Roger's papers, he makes it very clear a stationary EmDrive needs to experience some slight acceleration, big end to small end, to tigger Motor mode & further self acceleration.
There are no conclusive data until a major peer-reviewed paper with full disclosure of the experimental setting is out. And, AFAIK, it is not. Keep in mind that if you believe that pink unicorns live in the oceans under Europa, it's up to you to prove it, not the opposite. So far, no proof of the EmDrive has been provided, meaning by proof the only thing that the scientific community, and by extension the world at large, considers such: a major, fully-disclosed, peer-reviewed paper.
You might have mistrust in the scientific community approach to science, that's fine but that's you. for what concerns the great majority of the world, there are some little hints that eventually pink unicorns of some form might swin in Europa's Oceans, but really, nothing like a proof (or even small evidence without error margins) is out there.
We all want to believe. but as a scientist, believing is not nearly enough. -
#753 by Tellmeagain on 31 Mar, 2016 12:21
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otlski's method can solve problem 1,2,3 by using a measure to measure the horizontal pressure of the air lifted cartridge, http://forum.nasaspaceflight.com/index.php?topic=39772.msg1509863#msg1509863
My opinion is that this air track idea is not good from beginning. A lot of things can be wrong. I list just a few problems that are difficult to deal with, especially when you are measuring tens of micro newton forces.
1. The air track is hard to be leveled properly for measuring 10 micro newton forces;
2. The air track beam can be de-shaped by the weight of the vehicle to make small slopes that may be too large for measuring 10 micro newton forces;
3. air escaped from the holes and seam can hit surrounding things and be re-directed to generate unwanted forces;
4. Any force that tilts the vehicle will generate linear force along the track direction. Just imaging the case when one end of the air seam is narrower than the other end. This may be too much for measuring 10 micro newton forces. How do you differentiate such a force from a true linear force?
You have to address all 4 problems in the "method" section of your paper to convince people about your measurement.
Just problem 4 is still outstanding.
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#754 by Rodal on 31 Mar, 2016 12:35
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Yes,As an (admittedly) extreme example that a teeter-totter horizontal beam ceases to be a simple teeter-totter when one places a central mast and hanging things from it, here is something to watch.
A Teeter-Totter with a central mast and two hanging devices exhibiting chaos when submitted to large motions
Well Dr. Rodal if anyone gets that level of rotational spin, then they have made a monumental discovery.
The issues with beams, balances and air bearings, Lorentz or thermal, becomes one where your measurements of expected and maybe measured thrusts move out of your error envelope created by these devices. ... , the purpose of the <<(admittedly) extreme example>> from the video was to get people using teeter-totter-like devices to think about their instrument: is it really behaving as an ideal teeter-totter ?. A simple rigid-teeter totter when rotated to a large angle does not exhibit a chaotic motion. On the other hand, the teeter-totter with a central mast and hanging pendulums exhibits a different response: a chaotic motion. What is responsible for the difference in behavior ?. In companies making a product, we need to "know your product". As experimenters, we need to "know your instrument". Can you neglect the influence of the mast and the influence of the hanging pendulum ?
Now, if you are further interested in discussing the subject of <<measurements of expected and maybe measured thrusts move out of your error envelope >>, let's contemplate that what one is trying to measure is, ideally, a constant applied force.
So, the question regarding "measured force within error envelope" is:
1) what is the measured output displacement vs. time for your instrument (your "teeter-totter" with a mast, brackets and hanging device) , when a constant force is applied at one end ?
(not asking for the output for the powered EM Drive, but asking about the output of the instrument for an applied force (by other known means of applying a constant force) of similar magnitude, that is constant vs. time.)
2) what is the measured output displacement vs. time for your instrument (your "teeter-totter" with a mast, brackets and hanging device) , when a constant force is applied at one end for a period of time t, and after that time t is reached, the force is fully unloaded ?
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#755 by rfmwguy on 31 Mar, 2016 14:08
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Lots of good discussion on teeter totter setups, although I think the complex motions stated are insignificant in my setup. The mast and stiff supporting wire would affect balance, but being lightweight, doesn't contribute much to natural beam resonance which is sub 1 Hz. I could detect no resonance of the wires themselves.
The oil dampener is on a stiff aluminum rod and a tight pivot point, meaning there is no significant, if any oscillation in x, y or z vectors. Counterweights are clamped tight.
The variable is the emdrive hanging from a 4 point harness on stainless steel wires, which have insignificant stretching. x, y, and z oscillations are possible, especially with thermal plumes and air currents. Which leads me to my next point which some may not like:
A torsion experiment is highly vulnerable to horizontal air currents, especially when there is a large vertical cross-section of the overall experiment. How I know this is simple. As I approached the beam, the air turbulence I created was mainly horizontal, yet I did have significant beam instability due to some vertical component of air (wake) turbulence.
This observation lead me to believe that a torsion device which exposes a significant vertical cross-section of not only the emdrive, but the support beam and counterweights to horizontal air currents. So in effect, each test stand has its positives and negatives.
I am not here to try and convince others to use a teeter totter or the shortcomings of a torsion setup. I do believe a teeter totter test stand is a useful way for observational tests once thermal pluming is mitigated. This...I have a plan and the parts are ordered. Should be fun. -
#756 by Mulletron on 31 Mar, 2016 14:21
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"Trigger" the "Motor mode"?
Trigger and mode imply some kind of composite mechanism, like a firearm or mouse-trap. May I elaborate? I'm reluctant, as I doubt it will or perhaps can be appreciated, having tried before, and suspecting the cherished hopes of new-physics and elaborate theories being dashed is unbearable to some. Nevertheless...
Once upon a time I blurted out: http://forum.nasaspaceflight.com/index.php?topic=39004.msg1484276#msg1484276which featured this illustration:
and the document http://arxiv.org/abs/1303.0733 from whence it came.
If a piston separates high pressure from low pressure gas in a cylinder, or a rocket nozzle, force and acceleration may result.
In photonic damping (cooling) and amplification, there is the "density of states" (tuning) and damping/loss in the optical cavity (see below)
If there is no acceleration/vibration induced doppler shift, there will be no imbalance of radiation pressure. In space or free-fall, there will be no external damping to stop it BUT if the frustrum is flimsy, I suspect some acoustic mode may start vibrating the frustrum and dissipate energy from the desired acceleration.
The frustrum is both a photonic/microwave cavity filled with radiation pressure, and a mechanical "resonator" of sorts, in its inertial frame. Ideally it would continuously accelerate, but in practice it will be electrically pulsed and mechanically vibrated against a ballast for a couple reasons. Similar to what Woodward intends.
Oh I forgot to add, Peltier coolers, which have electron-dispersive junctions similar to the microwave dispersive frustrum, and pump heat like the photonic cooler, have been reported to produce exhaust-less thrust (heat notwithstanding), similar to the EM drive.
FWIW, YMMV.
Thanks for bringing up reports of anomalous thrust from Peltier coolers. I missed where you had talked about it back in thread 5. https://forum.nasaspaceflight.com/index.php?topic=38577.msg1441654#msg1441654
I've been thinking about using a Peltier (or two of them) to create a cold small end and hot large end of my frustum. My last post links to a paper which got me thinking about trying this approach to see if it's important or not to thrust. I haven't worked out the details yet. It would be nice if I could keep the two end plates thermally isolated from each other somehow. Copper is such a good conductor of heat though. I wonder if this anomalous thrust from Peltiers has anything to do with the info about breaking Newton's Third Law mentioned here? http://forum.nasaspaceflight.com/index.php?topic=39004.msg1495024#msg1495024 -
#757 by Rodal on 31 Mar, 2016 14:24
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Lots of good discussion on teeter totter setups, although I think the complex motions stated are insignificant in my setup. The mast and stiff supporting wire would affect balance, but being lightweight, doesn't contribute much to natural beam resonance which is sub 1 Hz. I could detect no resonance of the wires themselves.
what I have been discussing does not have anything to do with:
The oil dampener is on a stiff aluminum rod and a tight pivot point, meaning there is no significant, if any oscillation in x, y or z vectors. Counterweights are clamped tight.
The variable is the emdrive hanging from a 4 point harness on stainless steel wires, which have insignificant stretching. x, y, and z oscillations are possible, especially with thermal plumes and air currents. Which leads me to my next point which some may not like:
A torsion experiment is highly vulnerable to horizontal air currents, especially when there is a large vertical cross-section of the overall experiment. How I know this is simple. As I approached the beam, the air turbulence I created was mainly horizontal, yet I did have significant beam instability due to some vertical component of air (wake) turbulence.
This observation lead me to believe that a torsion device which exposes a significant vertical cross-section of not only the emdrive, but the support beam and counterweights to horizontal air currents. So in effect, each test stand has its positives and negatives.
I am not here to try and convince others to use a teeter totter or the shortcomings of a torsion setup. I do believe a teeter totter test stand is a useful way for observational tests once thermal pluming is mitigated. This...I have a plan and the parts are ordered. Should be fun.
* natural beam resonance
* effect of supporting wire on resonance
* air "turbulence" (really aerodynamics: fluid mechanics involved in the motion)
discussed in your above response, rather, it has to do with the MOI of the brackets and the mast, and the EM Drive hanging from one end. It has to do with the fact that your instrument is not a simple teeter-totter.
If you are interested in discussing the subject of <<measurements of expected and maybe measured thrusts move out of your error envelope >>, let's contemplate that what one is trying to measure is, ideally, a constant applied force.
So, if you are really interested in investigating whether there are complex motions in your setup, you have to look at the displacement vs. time for your setup, which is shown in your video.
If interested in discussing this, then the questions are:
1) what is the measured output displacement vs. time for your instrument (your "teeter-totter" with a mast, brackets and hanging device) , when a constant force is applied at one end ?
(not asking for the output for the powered EM Drive, but asking about the output of the instrument for an applied force (by other known means of applying a constant force) of similar magnitude, that is constant vs. time.)
2) what is the measured output displacement vs. time for your instrument (your "teeter-totter" with a mast, brackets and hanging device) , when a constant force is applied at one end for a period of time t, and after that time t is reached, the force is fully unloaded ?
We can then compare your results of 1) and 2) with what a simple horizontal teeter-totter would show for a constant force input. We can then proceed to compare the repeatability of your output response to further characterize the instrument. And we can compare the response with other devices.
If you are not interested in assessing this, of course you can continue doing what you are doing, as I am also certainly not trying to convince you of anything or trying to change anything you are doing.
The purpose of my posts on this subject was instead to show the people reading this thread, why is it that NASA, JPL, and major universities use a torsional pendulum instead of teeter-totters to measure micro-thrust of electromagnetic drives, for over half a century.
The purpose of my post was also to show that different instruments will show different response to the same input, and that the reader must carefully take into account the response of the instrument when assessing the significance of the measurement.
And therefore to understand why the lowest anomalous forces were measured by NASA and Tajmar using torsional pendulums.
Such a superior torsional instrument (a Cavendish pendulum) can be made with an even smaller budget than a teeter-totter, as shown by Mr. Li and as used by Brito, Marini and Galian. See: https://forum.nasaspaceflight.com/index.php?topic=39772.msg1509865#msg1509865 ($7 for piano wire) -
#758 by TheTraveller on 31 Mar, 2016 14:33
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Keep in mind that the emDrive having any effect at all isn't an experimental fact yet, since there is no conclusive data available.
Keep in mind that is your opinion. To others there are conclusive data available.
If you read Roger's papers, he makes it very clear a stationary EmDrive needs to experience some slight acceleration, big end to small end, to tigger Motor mode & further self acceleration.
There are no conclusive data until a major peer-reviewed paper with full disclosure of the experimental setting is out. And, AFAIK, it is not. Keep in mind that if you believe that pink unicorns live in the oceans under Europa, it's up to you to prove it, not the opposite. So far, no proof of the EmDrive has been provided, meaning by proof the only thing that the scientific community, and by extension the world at large, considers such: a major, fully-disclosed, peer-reviewed paper.
You might have mistrust in the scientific community approach to science, that's fine but that's you. for what concerns the great majority of the world, there are some little hints that eventually pink unicorns of some form might swin in Europa's Oceans, but really, nothing like a proof (or even small evidence without error margins) is out there.
We all want to believe. but as a scientist, believing is not nearly enough.
I guess you missed I have measured 8mN of reaction force at ~94Wrf? Build is as close to Shawyer Flight Thruster as possible.
Now spending $5k to build a very high quality, very high Q spherical end plate, silver then gold plated & polished frustum & drive it with 4 x 250Wrf close coupled modules using automatic best freq tracking. Expected reaction force is >= 0.4N (400mN / ~40g). When LN2 cooled expect ~1.2N (1,200mN / ~120g) of reaction force to be generated.
2016 will be a very bad year for deniers & the year skeptics need to get off the fence. -
#759 by SeeShells on 31 Mar, 2016 14:53
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I do not have a central mast it is just a composite carbon fiber beam on a knife edge. Yes, it can be set up to provide a vertical displacement by removing the digital scales or it can also be used pre-loading the scales to 50 micro-grams with metered weights. Any oscillatory movements in the beam and setup will have a + and - deviation because of the oscillatory mechanisms you mentioned and being data logged and profiled after multiple runs harmonics can be extracted.
Yes,As an (admittedly) extreme example that a teeter-totter horizontal beam ceases to be a simple teeter-totter when one places a central mast and hanging things from it, here is something to watch.
A Teeter-Totter with a central mast and two hanging devices exhibiting chaos when submitted to large motions
Well Dr. Rodal if anyone gets that level of rotational spin, then they have made a monumental discovery.
The issues with beams, balances and air bearings, Lorentz or thermal, becomes one where your measurements of expected and maybe measured thrusts move out of your error envelope created by these devices. ... , the purpose of the <<(admittedly) extreme example>> from the video was to get people using teeter-totter-like devices to think about their instrument: is it really behaving as an ideal teeter-totter ?. A simple rigid-teeter totter when rotated to a large angle does not exhibit a chaotic motion. On the other hand, the teeter-totter with a central mast and hanging pendulums exhibits a different response: a chaotic motion. What is responsible for the difference in behavior ?. In companies making a product, we need to "know your product". As experimenters, we need to "know your instrument". Can you neglect the influence of the mast and the influence of the hanging pendulum ?
Now, if you are further interested in discussing the subject of <<measurements of expected and maybe measured thrusts move out of your error envelope >>, let's contemplate that what one is trying to measure is, ideally, a constant applied force.
So, the question regarding "measured force within error envelope" is:
1) what is the measured output displacement vs. time for your instrument (your "teeter-totter" with a mast, brackets and hanging device) , when a constant force is applied at one end ?
(not asking for the output for the powered EM Drive, but asking about the output of the instrument for an applied force (by other known means of applying a constant force) of similar magnitude, that is constant vs. time.)
2) what is the measured output displacement vs. time for your instrument (your "teeter-totter" with a mast, brackets and hanging device) , when a constant force is applied at one end for a period of time t, and after that time t is reached, the force is fully unloaded ?
You are correct, in the runs I've done I have seen oscillations of accelerated free frustum movement and oscillations deviate from the center line in pressure measurements or when doing acceleration profiles. I attribute this to several factors.
1. Mode locking and unlocking creating "bumps in pressures" on the beam which show up as a oscillatory harmonic of the DUT, beam and counterweights. These were caused by the heating of the magnetron shifting frequencies and changes in the thermal heating of the frustum.
2. Thermal heating of the frustum causing the frustum to change buoyancy. The beam being carbon fiber exhibits a zero thermal expansion.
3. Minor Lorentz deviations as the frustum VSWR as currents on the wires fluctuate and resonance varies.
It is critical to do profiling of the beam using the exact setup without power using measured weights in both modes pressure and acceleration.
Regardless if a pendulum is used or a beam teeter todder or a rope from a shower curtain they all can be profiled and with that profiling, data extracted.
I don't think there is one method test bed that's much better than another if you do not know your DUT or test bed deviations in a static and operational modes. The data gathered for profiling your test bed is as critical as determining you have seen real thrust.
Shell
