Thanks guys !So I have data for everything except the mode(s), and temp size for the flight cone.I need to use X numbers of 21, 26, and 77, respectively, for the proto, demo and flight cones to get those numbers. (w/o dielectric that is)What that means is TBD of course. There may be another variable involved, in or out of favor of a real effect.

I wonder if the following effect has been quantitatively assessed :if a thermal displacement (again) of a part of significant mass relative to the fixation point can occur, this will change the torque seen by the balance arm around the x axis. (See attached picture for naming conventions). While the flexure bearings make for a very stiff reaction around x and y axis (compared to the natural rotation around z) no stiffness is infinite. Likewise, the Faztek beam could twist a little around the x axis. Since the distance reported in the charts is measured (along the y axis) from a plate below the beam, any increased rotation clockwise would increase this distance.Contrary to dynamical recoil effects that needs constant acceleration to mimic sustained force, it suffices the deformation is kept at constant position (relative to fixation point) to yield an apparent long lasting force reading. As for the orientation, in this hypothesis one would have to explain a displacement of some mass to the right (relative to fixation point) to get an upward reading (corresponding to a leftward force interpretation). Expansion of frustum's copper walls alone would shift some mass to the left relative to fixation point, so would run contrary to the observed directions. Expansion of a left wall (small end) glued dielectric would go in the right direction, but Paul March reported of a try with the dielectric on the right wall (big end) and the apparent thrust haven't inverted or even reduced...So, this is on shaky ground on orientations considerations alone, but I'd be curious to know the amount of rotation stiffness around the x axis, maybe that was discussed already ?Side note : I'm trying to know the exact model of flexure bearings used. From this post we know that <<The Riverhawk C-flex torsion bearing's spring constant is a nominal 0.007 in-Lb/deg.>> but that doesn't add up with the vertical readings in the charts (from calibration pulses, between 0.033µm and 0.1µm per µN on vertical scale, with still unexplained disparity from chart to chart).

.... Earlier I proposed this same effect to explain the negative slope in the baseline of the thrust waveform. It appears to have a long time constant so may be from a thermally induced change in CoM.

Quote from: Notsosureofit on 02/28/2015 11:49 pmThanks guys !So I have data for everything except the mode(s), and temp size for the flight cone.I need to use X numbers of 21, 26, and 77, respectively, for the proto, demo and flight cones to get those numbers. (w/o dielectric that is)What that means is TBD of course. There may be another variable involved, in or out of favor of a real effect.Realized this morning I'd been missing something after rereading Shawer's flight paper and the Magnetron "lock" time.Kicking myself for not recognizing a "Q multiplier circuit" (I've used enough of them) The long lock time (time constant) is the tip-off if this is what he's doing and the results are real. The trade off in that case is spectral purity vs the frequency stability of the oscillator since you track the cavity.Needs only a modest *10 for the proto and demo cases. The flight system needs *100 which is not out of the question at all.Again, this is pure speculation on my part w/o confirmation from Shawyer, but it puts the mode back in a reasonable range.

Quote from: frobnicat on 03/01/2015 11:19 amI wonder if the following effect has been quantitatively assessed :if a thermal displacement (again) of a part of significant mass relative to the fixation point can occur, this will change the torque seen by the balance arm around the x axis. (See attached picture for naming conventions). While the flexure bearings make for a very stiff reaction around x and y axis (compared to the natural rotation around z) no stiffness is infinite. Likewise, the Faztek beam could twist a little around the x axis. Since the distance reported in the charts is measured (along the y axis) from a plate below the beam, any increased rotation clockwise would increase this distance.Contrary to dynamical recoil effects that needs constant acceleration to mimic sustained force, it suffices the deformation is kept at constant position (relative to fixation point) to yield an apparent long lasting force reading. As for the orientation, in this hypothesis one would have to explain a displacement of some mass to the right (relative to fixation point) to get an upward reading (corresponding to a leftward force interpretation). Expansion of frustum's copper walls alone would shift some mass to the left relative to fixation point, so would run contrary to the observed directions. Expansion of a left wall (small end) glued dielectric would go in the right direction, but Paul March reported of a try with the dielectric on the right wall (big end) and the apparent thrust haven't inverted or even reduced...So, this is on shaky ground on orientations considerations alone, but I'd be curious to know the amount of rotation stiffness around the x axis, maybe that was discussed already ?Side note : I'm trying to know the exact model of flexure bearings used. From this post we know that <<The Riverhawk C-flex torsion bearing's spring constant is a nominal 0.007 in-Lb/deg.>> but that doesn't add up with the vertical readings in the charts (from calibration pulses, between 0.033µm and 0.1µm per µN on vertical scale, with still unexplained disparity from chart to chart).My very first post on this forum was motivated by the rotation produced by the change in location of the center of mass: http://forum.nasaspaceflight.com/index.php?topic=29276.msg1252386#msg1252386This rotation results in nonlinear coupling of degrees of freedom. I solved the nonlinear coupled differential equations using Mathematica. The coupling is very small because the rotational stiffness for the motion you are considering is much stiffer than the torsional stiffness of Eagleworks torsional pendulum around the vertical axis perpendicular to the ground.

The Riverhawk C-flex torsion bearing's spring constant is a nominal 0.007 in-Lb/deg., but that varies with the mass load mounted on the torque pendulum arm and selected balance point of the test article mass and its counterbalance mass on the other end of the pendulum arm relative to the torque pendulum’s center of rotation. Each bearing block is rated for ~25.0 Lb of vertical mass load, so we nominally restrict ourselves to a 25 pound total load limit on the torque pendulum arm to give ourselves a 100% support mass margin.

Quote from: Rodal on 03/01/2015 03:10 pmQuote from: frobnicat on 03/01/2015 11:19 amI wonder if the following effect has been quantitatively assessed :if a thermal displacement (again) of a part of significant mass relative to the fixation point can occur, this will change the torque seen by the balance arm around the x axis. (See attached picture for naming conventions). While the flexure bearings make for a very stiff reaction around x and y axis (compared to the natural rotation around z) no stiffness is infinite. Likewise, the Faztek beam could twist a little around the x axis. Since the distance reported in the charts is measured (along the y axis) from a plate below the beam, any increased rotation clockwise would increase this distance.Contrary to dynamical recoil effects that needs constant acceleration to mimic sustained force, it suffices the deformation is kept at constant position (relative to fixation point) to yield an apparent long lasting force reading. As for the orientation, in this hypothesis one would have to explain a displacement of some mass to the right (relative to fixation point) to get an upward reading (corresponding to a leftward force interpretation). Expansion of frustum's copper walls alone would shift some mass to the left relative to fixation point, so would run contrary to the observed directions. Expansion of a left wall (small end) glued dielectric would go in the right direction, but Paul March reported of a try with the dielectric on the right wall (big end) and the apparent thrust haven't inverted or even reduced...So, this is on shaky ground on orientations considerations alone, but I'd be curious to know the amount of rotation stiffness around the x axis, maybe that was discussed already ?Side note : I'm trying to know the exact model of flexure bearings used. From this post we know that <<The Riverhawk C-flex torsion bearing's spring constant is a nominal 0.007 in-Lb/deg.>> but that doesn't add up with the vertical readings in the charts (from calibration pulses, between 0.033µm and 0.1µm per µN on vertical scale, with still unexplained disparity from chart to chart).My very first post on this forum was motivated by the rotation produced by the change in location of the center of mass: http://forum.nasaspaceflight.com/index.php?topic=29276.msg1252386#msg1252386This rotation results in nonlinear coupling of degrees of freedom. I solved the nonlinear coupled differential equations using Mathematica. The coupling is very small because the rotational stiffness for the motion you are considering is much stiffer than the torsional stiffness of Eagleworks torsional pendulum around the vertical axis perpendicular to the ground.Yes I recall that, but can't find the values you used, don't remember if you published or just PM to someone asking. At the moment my concern is not that much on coupling, but on absolute stiffness around the x axis (as seen from torque around x applied 10'' from the z axis). Do you know or have derived the exact flexure bearing model ? Is it a tandem of 2 C-Flex E-10 or B-20 at .0037 Lb-in/degree each as found there http://www.c-flex.com/companyproducts.pdf or a tandem of 2 RiveHawk like 5005-600 (.0035) or 5006-660 (.0037) or 5010-800 (.0036).From this post :Quote from: Star-DriveThe Riverhawk C-flex torsion bearing's spring constant is a nominal 0.007 in-Lb/deg., but that varies with the mass load mounted on the torque pendulum arm and selected balance point of the test article mass and its counterbalance mass on the other end of the pendulum arm relative to the torque pendulum’s center of rotation. Each bearing block is rated for ~25.0 Lb of vertical mass load, so we nominally restrict ourselves to a 25 pound total load limit on the torque pendulum arm to give ourselves a 100% support mass margin.Have we anything more specific ?For vertical mass load (ie. axial load) E-10 is rated 36.48 Lb, B-20 is 19.6 Lb (page 11 C-Flew spec sheet). From axial load indication could be A-30 or C-20, A-30 is too stiff...Nearest fit (if 0.007 in-Lb/deg is for each) would then be C-20 : 0.0060 in-Lb/deg and 27.90 Lb axialFor RiverHawk I don't find axial load ratings, neither at here nor there.Anyhow, even if we have 2 times .007 in-Lb/deg. that's 9.06e-2 Nm/rad (please check as I'm not used to imperial units) and a 29.1µN (calibration pulse) at 10'' from z axis is 7.39e-6 Nm, so we should have 8.16e-5 rad, that is 20.7 µm deviation (at 10'' from z axis, LDS is a bit further so it should be even a bit more).Yet we see on the charts that the calibration pulses give between 1 to 2.5 µm deviation on the vertical scale. We don't know why this should be varying from chart to chart, and there is one order of magnitude difference with the given stiffness. So maybe the indicated vertical scale is irrelevant... but then it becomes difficult to model the system. Looks like the flexure bearing are stiffer than 0.007 in-Lb/deg. (around z).

Quote from: Notsosureofit on 03/01/2015 01:27 pmQuote from: Notsosureofit on 02/28/2015 11:49 pmThanks guys !So I have data for everything except the mode(s), and temp size for the flight cone.I need to use X numbers of 21, 26, and 77, respectively, for the proto, demo and flight cones to get those numbers. (w/o dielectric that is)What that means is TBD of course. There may be another variable involved, in or out of favor of a real effect.Realized this morning I'd been missing something after rereading Shawer's flight paper and the Magnetron "lock" time.Kicking myself for not recognizing a "Q multiplier circuit" (I've used enough of them) The long lock time (time constant) is the tip-off if this is what he's doing and the results are real. The trade off in that case is spectral purity vs the frequency stability of the oscillator since you track the cavity.Needs only a modest *10 for the proto and demo cases. The flight system needs *100 which is not out of the question at all.Again, this is pure speculation on my part w/o confirmation from Shawyer, but it puts the mode back in a reasonable range.Notsosureofit:Could you describe to me how one goes about building a "Q-multiplier Circuit" for a 1.90 GHz RF amplifier circuit? I've used the old Heathkit QF-1 Q-Multiplier for my old shortwave radio receiver back in high school, see: http://tubularelectronics.com/Heath_Manual_Collection/Heath_Manuals_O-RX/QF-1/QF-1.pdf , but I've never thought to use one to enhance the Q-Factor of a microwave frustum cavity before...Best, Paul M.

Dr. Rodal & Crew:The Eagleworks team has already build a 6061 aluminum frustum cavity with 1/4" thick walls and O-ring end caps meant to hold a 1 Bar pressure differential with internal nickel/copper/silver/gold plating system on all interior surfaces with plating thickness of 10-to-15 microns for the first three layers and 0.5 microns for exposed to the RF gold layer. Sadly the gold layer was just as thick as the rest of the plated layers and textured as well, so as far as the applied ~2.0 GHz RF was concerned it was only interacting with the rough gold layer. This had the effect of cutting the resonant Q-factor for this aluminum frustum by almost a factor of three over our copper frustum for the resonances of interest. At the same time we also tried using a smaller volume, higher-K (e-r=~40) ceramic dielectric resonator discs in the Al cavity mounted at its small OD end, while driving it at its TE011 mode if memory serves. Bottom line was that this configuration was a total bust in regards to thrust production in our torque pendulum system running at this resonant mode. This aluminum frustum design also turned out to be ~4X times the mass of the thin walled copper cavity even while using lower density aluminum for its construction. This exercise was a tribute to the fact that one should never ASSUME that you know what you are doing until proven otherwise! And oh yes, and only try one variation in the design at a time or one will get lost, fast!Best, Paul M.

...These thermally induced actions to the left requires the torque pendulum's arm to move to the right to maintain the balance of the torque pendulum's arm in the lab's 1.0 gee gravity field, since we also use the Earth's g-field to help null the pendulum's movements....

DIYFAN:Once the test series we are working on is finished, I will suggest to Dr. White that we try the use of the more readily available NiFeCo mu-metal from McMaster-Carr (See: http://www.mcmaster.com/#mu-metal-foil/=w4hfa3 ) for such a test. However I think we will have to copper plate the side of the mu-metal facing the interior of the cavity with about 10 microns of copper or silver to keep this large OD end-cap from greatly reducing the Q-Factor of the copper frustum. Mu-metal resistivity is much higher than copper...Best, Paul M.

Dr. March,I'm trying to model various aspects of the whole system to put upper bounds on thermal effects, and possibly also reconstruct the thrust(t) original signal from the distance(t) given in the charts. It would be a nice boost to this (amateur level) effort if you could confirm either :- That the flexure bearings have a stiffness of 0.007 in-Lb/deg ? Each ? Both together ? Do you know the exact model reference ?- That the vertical scale in the charts (indicated in µm, around 500) are relevant or not relevant.I ask this question because I find a contradiction between the stiffness around the vertical axis and the recorded deviation from the 30µN calibration pulses (at .007 in-Lb/deg the deviation of the linear displacement sensor would be above 40µm, at .014 in-Lb/deg still above 20µm). The readings amount for between 1 to 2.5 µm for the 30µN calibration pulses. So I'm stuck.While I'm at it : is the plane in which the arm rotates kept as horizontal as possible (ie the axis of rotation as vertical as possible) or is there a small slope voluntarily introduced leading to some pendulum effect against g (for stabilisation or tuning purpose) ? That could explain the varying deviation (in µm) for the same calibration pulses thrusts. Also wondered if this is what was implied in this post :Quote from: Star-Drive...These thermally induced actions to the left requires the torque pendulum's arm to move to the right to maintain the balance of the torque pendulum's arm in the lab's 1.0 gee gravity field, since we also use the Earth's g-field to help null the pendulum's movements....Thanks