...Why is all research so focussed on the powered thrust, rather than on the increasing opposite-direction acceleration ...
Quote from: frobnicat on 04/27/2015 03:44 pmFrom this post, how do we interpret the "RF Dissipated Power" in the central caption of this slide ?bigger..."How do we interpret the "RF Dissipated Power" in the central caption of this slide ? Is it the (DC) power input to RF amplifier ? Or the difference of RF power input to frustum minus reflected power back to amplifier ? "Simple, it's the forward RF power being dissipated in the RF load AKA resonant cavity, minus the reflected power being dissipated back in the RF amplifier's 50 ohm isolator load. We measure it with two Mini-Circuit -50dBm to +20dBm RF power modules attached to the forward and reflected ports on a -40dB down bidirectional coupler.
From this post, how do we interpret the "RF Dissipated Power" in the central caption of this slide ?bigger...
"What is horizontal scale, is the != 0 part 16.5s long like the power-on period of the thrust chart ? The LabView RF power meter graphics has a scrolling data logging output with time on the horizontal x-axis and RF power level on the y-axis. Since a full frame of the time axis takes about 3.5 minutes to scroll from right to left, there are no time units appended.
"Why this particular profile with initial spike and 2 plateaus ?"Because I was manually controlling the VCO frequency to maintain the minimum VSWR, which at times is a bit jerky, being that my control servo loops are not as good as they used to be. "Why don't we see a corresponding 3x magnitude "step" on the thrust chart at half the excitation time ?"Overcoming the Inertia of the torque pendulum load which is close to 10 kg.
Hi clever people So, we'll have our article on the EM Drive - expertly and patiently built by Dr. Rodal and subedited by my assistant editor Chris Gebhardt - published on Wednesday. We'll link in this thread and also have a standalone thread (the latter allowing people to get up to speed - an entry level thread as such, before braving this 104 page, 470,000 viewed thread). I've been following this thread the best I can and I have to say that while I'm proud I know my way around a RS-25 engine, this thread has proven I probably didn't pay as much attention in class as I should have! The encouraging thing is, while NASA has become somewhat "social media fluffy" and has lost a lot some of its focus of late, there's obviously less publicized areas, such as Eagleworks, that are the true essence of Bruce Willis' line in Armageddon, where he claims "You're NASA, you're geniuses. I bet you've got a room of people just thinking *stuff* up, and people backing them up!"
Quote from: Dmytry on 04/28/2015 05:09 pm...Why is all research so focussed on the powered thrust, rather than on the increasing opposite-direction acceleration ...We need to clarify this point. My understanding is that NASA Eagleworks calls "thrust" the force occurring in the same direction as the acceleration.Now, what does "thrust force" mean in this context? For NASA Eagleworks it means the measured displacement, that can be converted to a rotational angle of the torsional balance, and hence to a torque (knowing the torsional stiffness of the torsional balance). Or simply, force=displacement*stiffness . Like in a spring, for example. Now, this is a tautology, as the "thrust force" is entirely based on the displacement, and hence it is not surprising that the displacement should be in the same direction as the acceleration (the second order derivative of the displacement with respect to time). (And yes, forces are never directly measured, they are an intuitive and theoretical concept, what we do is measure displacements and obtain forces if we know the stiffness, or we measure accelerations and we obtain forces using F=m*a)I am aware that Roger Shawyer has written that the thrust force and the displacement in his measurements occur in different directions, and that the EM Drive must be already in motion (or something to that effect), but frankly what he wrote in this regard is not comprehensible to me (and from what I recall was not comprehensible to @frobnicat either). Apparently it was not comprehensible to other people either, as his latest report http://www.emdrive.com/EmDriveForceMeasurement.pdf addresses this (I find his latest report just as difficult to reconcile).In the chart below, he even refers to a "force direction" which can be in the same direction as what he calls "thust" or what he calls "reaction" occurring in the opposite direction to what he calls "thrust".For his Demonstrator engine, he claims (in the chart below) that he measured "forces" in opposite directions for this same device. (It this was due to placing a dielectric at opposite ends or due to running the device in different mode shapes at different frequencies, I don't know.)
Thing is, the pendulum arm with its 10kg is usually not that shy of steep responses (on µm scale) from steep excitations, typically below 3s time constant. So this is strange that we don't see a corresponding step in thrust to the step from plateau to plateau of power (each during almost 8s). Why change of excitation power would deserve more "inertial smoothing" than on/off power steps ?Also this thrust chart happens to be very clean, with low noise. There is a slight inflection at ~2/3 of excitation time but it's quite clear there's nothing as dramatic as the usual responses to excitation steps. Such a weak response when going from 1W to 3W compared to when going to or from 0W would indicate strong non linearities... Or that what counts is not the net dissipated power in frustum (forward minus bounced back) but only forward power (regardless of what is bounced back). How could that be ?
What I was referring to is how in most of your graphs, after you turn your test article off, the graph shows a rising force acting in the opposite direction to the force you got when the device was turned on.edit: to clarify, this:
When a mirror reflects light, it experiences a slight push. This radiation pressure can be increased considerably with the help of a small superconducting island. This was revealed by the joint research done in the Aalto University and the Universities of Jyväskylä and Oulu. The finding paves a way for the studies of mechanical oscillations at the level of a single photon, the quantum of light. The results of the research were published in Nature Communications in April.
Coupling electromagnetic waves in a cavity and mechanical vibrations via the radiation pressure of photons is a promising platform for investigations of quantummechanical properties of motion. A drawback is that the effect of one photon tends to be tiny, and hence one of the pressing challenges is to substantially increase the interaction strength. A novel scenario is to introduce into the setup a quantum two-level system (qubit), which, besides strengthening the coupling, allows for rich physics via strongly enhanced nonlinearities. Here we present a design of cavity optomechanics in the microwave frequency regime involving a Josephson junction qubit. We demonstrate boosting of the radiationpressure interaction by six orders of magnitude, allowing to approach the strong coupling regime. We observe nonlinear phenomena at single-photon energies, such as an enhanced damping attributed to the qubit. This work opens up nonlinear cavity optomechanics as a plausible tool for the study of quantum properties of motion.
...What I was referring to is how in most of your graphs, after you turn your test article off, the graph shows a rising force acting in the opposite direction to the force you got when the device was turned on.edit: to clarify, this:
We found that this slope change after the test article and RF amplifer were turned on for 10-to-20 seconds was apprently due to IR radiation from the amplifier's heatsink that is mounted on the back side of the torque penlulum on an 8" square platform was affecting the top C-flex bearing more than the lower one. We tried aluminum shielding the top bearing assembly from the heatsink IR source and managed to reverse the metioned thermal slope in the thrust plots, but after shielding the bottom one we could reduce it but still coundn't completely get rid of this thremal drift artifact. Currently we are just living with it.
Quote from: Dmytry on 04/28/2015 07:39 pmWhat I was referring to is how in most of your graphs, after you turn your test article off, the graph shows a rising force acting in the opposite direction to the force you got when the device was turned on.edit: to clarify, this:You are referring to a drifting baseline for the measured displacement. It is addressed (succintly) in the "Anomalous..." report text in reference to thermal effects, and in multiple posts of @Star-Drive, @frobnicat and @zen-in in the EM Drive threads 1 and 2.
More problematic than those long lasting slow drifts in rest position after power on/off, is the fact that there seem to exist a continuum of situations in between slowly evolving charts (in response to excitation steps) and steep responses that serve as proof of real thrusts on the argument of their steepness (sorry for the poor wording). For instance, the rise and decay of the chart below (obtained in vacuum) show a very different time constant to reach and leave the "thrust" plateau than with the electrostatic calibration pulses with their clean square force(t) profile. The smoothed rise could be explained by change of tuning (effective received power) of the cavity, needing a "warm-up". But the smoothed decay is really a showdown. Off is off, there is no "warm-down" time to speak of for EM radiation to disappear (on the order of µs, given size and Q factor), and no electromagnetic/quantum theory could explain such a delay unless the vacuum is as heavy and viscous as oil or water. This lag in the decay, most visible in this particular chart, was already noticed by other contributors (sorry, can't remember).biggerfrom this post
Well, I have to admit I was being rather cheeky.
...What bothers me the most about this research is that there is a perfectly simple and rather cheap way to screen out most of such effects. The test article needs to be powered off a battery, run from a timer, and be enclosed in a conductive box with permalloy shielding; hanging off a very very Cavendish style torsion pendulum (which is fairly insensitive to shifts in CoM as well, by the way). ...
Well, one shouldn't even see a drift the size of the measured force, when it's not even sub-micronewton range.If one is heating metal, one is probably heating it unevenly, and it bends as long as heat is applied (the hotter material expands more), with a fairly short time constant (because the temperatures will equalize quickly once the heat source is off). Then the heat gets slowly conducted to another structural element, and that structural element happens to bend in a way that influences the experiment in the other direction. How much each structural element will bend will depend to how tight the screws are tightened, what stresses are already in the metal, and so on and so forth; it's essentially impossible to account for.
The issue for analyzing thermal structural effects (and other effects) for the EM Drive project at NASA Eagleworks is not a matter of present ability to be analyzed but is, instead, a matter of scarcity of project resources (money, time, and personnel) to analyze them. For example, NASA's EM Drive truncated cone was made by Paul March himself in Paul March's wife dining room. NO TAXPAYER's tax $$$ involved in its construction.