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#3420 by otlski on 01 Jul, 2016 19:13
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1) What is the period of oscillation of rfmwguy's torsional pendulum ?
Thanks
The oscillation period is approximately one minute (estimate from before reworking the umbilical). Perhaps changed by less than 10% after rework. -
#3421 by Rodal on 01 Jul, 2016 21:09
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1) What is the period of oscillation of rfmwguy's torsional pendulum ?
Thanks
The oscillation period is approximately one minute (estimate from before reworking the umbilical). Perhaps changed by less than 10% after rework.
Mmmm. Are you sure? If the fundamental period of oscillation of his pendulum is a short as 1 minute, then those oscillations have a much, much longer period and are not due to the dynamics of the pendulum. Those oscillations then have a period of many minutes, they cannot be due to electromagnetic effects either, particularly when the magnetron is off.
And rfmwguy wrote that the "magnetron-power-on" cycles (marked by red bars) are 1.5 minutes each?:Quote from: rfmwguy4 cycles of 50% power at about 1.5 minutes each
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#3422 by dustinthewind on 01 Jul, 2016 21:52
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...
Sigh, never mind this post. While indeed there is a force on the antenna at magnetic maximum, this induces cancellation of one of the two counter propagating light waves. It turns out, if the force on the antenna is up then the light canceled is the light traveling up. The light traveling down at a later time, dt=lambda/2c, strikes the cavity, canceling the push the antenna got.
Having the antenna out of position slightly does induce a force on the antenna but also the cavity such that the over all force cancels. (or should cancel.) -
#3423 by otlski on 01 Jul, 2016 23:14
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1) What is the period of oscillation of rfmwguy's torsional pendulum ?
Thanks
The oscillation period is approximately one minute (estimate from before reworking the umbilical). Perhaps changed by less than 10% after rework.
Mmmm. Are you sure? If the fundamental period of oscillation of his pendulum is a short as 1 minute, then those oscillations have a much, much longer period and are not due to the dynamics of the pendulum. Those oscillations then have a period of many minutes, they cannot be due to electromagnetic effects either, particularly when the magnetron is off.
And rfmwguy wrote that the "magnetron-power-on" cycles (marked by red bars) are 1.5 minutes each?:Quote from: rfmwguy4 cycles of 50% power at about 1.5 minutes each
Am I sure? No. not anymore. I did see a few weeks ago that his calibration sample rate was 1 Hz. Using that rate, I had determined that the natural frequency (in our axis of interest) of his apparatus was one minute; he confirmed it was one minute. Now, upon closer examination and assuming the same sample rate, I see that for this posting the period looks closer to two minutes. He has moved his umbilical. Moving his umbilical must contribute a torsion rate almost equally to that of the wire and oil damper combination. I have not read anywhere where he might have changed his sample rate. -
#3424 by Rodal on 01 Jul, 2016 23:22
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OK, thanks.
1) What is the period of oscillation of rfmwguy's torsional pendulum ?
Thanks
The oscillation period is approximately one minute (estimate from before reworking the umbilical). Perhaps changed by less than 10% after rework.
Mmmm. Are you sure? If the fundamental period of oscillation of his pendulum is a short as 1 minute, then those oscillations have a much, much longer period and are not due to the dynamics of the pendulum. Those oscillations then have a period of many minutes, they cannot be due to electromagnetic effects either, particularly when the magnetron is off.
And rfmwguy wrote that the "magnetron-power-on" cycles (marked by red bars) are 1.5 minutes each?:Quote from: rfmwguy4 cycles of 50% power at about 1.5 minutes each
Am I sure? No. not anymore. I did see a few weeks ago that his calibration sample rate was 1 Hz. Using that rate, I had determined that the natural frequency (in our axis of interest) of his apparatus was one minute; he confirmed it was one minute. Now, upon closer examination and assuming the same sample rate, I see that for this posting the period looks closer to two minutes. He has moved his umbilical. Moving his umbilical must contribute a torsion rate almost equally to that of the wire and oil damper combination. I have not read anywhere where he might have changed his sample rate.
So even if the period is now 2 minutes, those oscillations that take place after he powers completely off have a much longer period.
None of that can be electromagnetic.
How can one end up with a much longer period ? did he add mass to the pendulum ? (that would decrease the natural frequency, hence increase the corresponding period)
Or something else is producing a forcing function, even when the power is off, that has much longer period duration than the period of the pendulum? -
#3425 by Tcarey on 02 Jul, 2016 03:18
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...And it is evident from rfmguy's picture that at the moment he can have no idea of what mode shape (if any) is being excited...
Dave's VNA S11 rtn loss scan shows a very high Q dip where TE013 resonance would be expected. But his antenna placement can't excite TE013 but can excite TM113 which exists at the same resonant freq as TE013.
He also knows the cold maggie freq is above this resonant freq and that his maggie needs to warm up a bit, to drop it's freq to get pull lock with the high Q frustum, which can be seen on his 1st test run as attached.
Please note in this zoomed in image, AC filament current and DC anode current flowed over the feed wires for approx 30 sec, until the maggie warmed, freq dropped enough to get lock and force was generated. If you look close you can see a very slight drop in the cold base line as DC anode current flowed and probably generated a very small Lorentz force.
Should also add that over those 1st 30 seconds, there was 900Wrf being injected into the frustum by a maggie antenna INSIDE the frustum, yet there is no sign of any movement of the base line as the frustum heated up prior to achieving freq lock and generating a "Shawyer Effect" thrust output.
At lease in those 1st 30 secs, starting with a ambient temp maggie,, there doesn't appear to be any significant Lorentz or thermal forces active as the base line is flat.
TT. I'd like you comments on rfmwguys results with an eye towards something you posted earlier that the frequency bandwidth that generates thrust is smaller than the overall possible resonance bandwidth of the system. What I am wondering about is the frequency drift and splatter that the maggie produces when driven with the type power supply being used. It would seem to me that two things might be happening, first the splatter makes it more likely that the thrust producing frequency will be hit and second, when it is hit there will be a lot less power at the frequency resulting in less thrust.
Your thoughts please? -
#3426 by SeeShells on 02 Jul, 2016 03:44
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https://www.reddit.com/r/QThruster/comments/4qvcwd/1701a_longer_duration_dataset_for_return_to/
Looks like around 16+mN on this run. Seems to be near max whether at 1 or 2 minute power duration. Pretty sure the 18.4mN is about max for this design. Slow return with air turbulence more likely than mechanical stickiness but not ready to make that call until more testing is done. -rfmwguy -
#3427 by dustinthewind on 02 Jul, 2016 05:10
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...And it is evident from rfmguy's picture that at the moment he can have no idea of what mode shape (if any) is being excited...
Dave's VNA S11 rtn loss scan shows a very high Q dip where TE013 resonance would be expected. But his antenna placement can't excite TE013 but can excite TM113 which exists at the same resonant freq as TE013.
He also knows the cold maggie freq is above this resonant freq and that his maggie needs to warm up a bit, to drop it's freq to get pull lock with the high Q frustum, which can be seen on his 1st test run as attached.
Please note in this zoomed in image, AC filament current and DC anode current flowed over the feed wires for approx 30 sec, until the maggie warmed, freq dropped enough to get lock and force was generated. If you look close you can see a very slight drop in the cold base line as DC anode current flowed and probably generated a very small Lorentz force.
Should also add that over those 1st 30 seconds, there was 900Wrf being injected into the frustum by a maggie antenna INSIDE the frustum, yet there is no sign of any movement of the base line as the frustum heated up prior to achieving freq lock and generating a "Shawyer Effect" thrust output.
At lease in those 1st 30 secs, starting with a ambient temp maggie,, there doesn't appear to be any significant Lorentz or thermal forces active as the base line is flat.
TT. I'd like you comments on rfmwguys results with an eye towards something you posted earlier that the frequency bandwidth that generates thrust is smaller than the overall possible resonance bandwidth of the system. What I am wondering about is the frequency drift and splatter that the maggie produces when driven with the type power supply being used. It would seem to me that two things might be happening, first the splatter makes it more likely that the thrust producing frequency will be hit and second, when it is hit there will be a lot less power at the frequency resulting in less thrust.
Your thoughts please?
I am curious about this also. Doesn't the narrow end approaching cut off frequency for a wave guide imply some maximum wavelength that can fit in the narrow region. Isn't this region what is stretching out the wavelength in the narrow end? Wouldn't this suggest a very specific frequency, where it is barely, but not quite cut off from reflecting from the end plate. Am I mistaken that this is the goal? -
#3428 by TheTraveller on 02 Jul, 2016 07:18
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...And it is evident from rfmguy's picture that at the moment he can have no idea of what mode shape (if any) is being excited...
Dave's VNA S11 rtn loss scan shows a very high Q dip where TE013 resonance would be expected. But his antenna placement can't excite TE013 but can excite TM113 which exists at the same resonant freq as TE013.
He also knows the cold maggie freq is above this resonant freq and that his maggie needs to warm up a bit, to drop it's freq to get pull lock with the high Q frustum, which can be seen on his 1st test run as attached.
Please note in this zoomed in image, AC filament current and DC anode current flowed over the feed wires for approx 30 sec, until the maggie warmed, freq dropped enough to get lock and force was generated. If you look close you can see a very slight drop in the cold base line as DC anode current flowed and probably generated a very small Lorentz force.
Should also add that over those 1st 30 seconds, there was 900Wrf being injected into the frustum by a maggie antenna INSIDE the frustum, yet there is no sign of any movement of the base line as the frustum heated up prior to achieving freq lock and generating a "Shawyer Effect" thrust output.
At lease in those 1st 30 secs, starting with a ambient temp maggie,, there doesn't appear to be any significant Lorentz or thermal forces active as the base line is flat.
TT. I'd like you comments on rfmwguys results with an eye towards something you posted earlier that the frequency bandwidth that generates thrust is smaller than the overall possible resonance bandwidth of the system. What I am wondering about is the frequency drift and splatter that the maggie produces when driven with the type power supply being used. It would seem to me that two things might be happening, first the splatter makes it more likely that the thrust producing frequency will be hit and second, when it is hit there will be a lot less power at the frequency resulting in less thrust.
Your thoughts please?
The natural maggie freq splatter can be pulled into the bandwidth of a high Q load. However the pulling introduces forward power losses versus the amount of pulling. Most maggie data sheets have a pulling chart.
So it is complex, well maybe almost impossible to calculate the energy versus freq splatter that can form resonance.
Dave has done external leakage spectrum analysis, which visually shows the unlocked freq splatter becoming locked and actually painting the frustum bandwidth on the screen. I'll find an image of that and post.
Commercial maggie are cooled and operational temperature controlled to stop freq drift lower as the maggie heats. Then the anode current is highly regulated to stop freq pushing drift from anode current variance. Next, after a few seconds, filament current us backed down to zero to further eliminate freq splatter. Have seen maggie output spectrums with +-5kHz bandwidth.
Dave's measured S11 VNA resonance is a, I think, around 50MHz below the maggie cold output and via spectrum scanner there is no freq pulled lock as it is too far above the narrow frustum bandwidth. But as the maggie warms and the freq drops, you can see the maggie freq splatter being pulled into the frustum's bandwidth. He has videos of this happening.
So while Dave's maggie & frustum can only engage in a short lock, the effect of the lock is VERY clear. -
#3429 by TheTraveller on 02 Jul, 2016 07:30
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...And it is evident from rfmguy's picture that at the moment he can have no idea of what mode shape (if any) is being excited...
Dave's VNA S11 rtn loss scan shows a very high Q dip where TE013 resonance would be expected. But his antenna placement can't excite TE013 but can excite TM113 which exists at the same resonant freq as TE013.
He also knows the cold maggie freq is above this resonant freq and that his maggie needs to warm up a bit, to drop it's freq to get pull lock with the high Q frustum, which can be seen on his 1st test run as attached.
Please note in this zoomed in image, AC filament current and DC anode current flowed over the feed wires for approx 30 sec, until the maggie warmed, freq dropped enough to get lock and force was generated. If you look close you can see a very slight drop in the cold base line as DC anode current flowed and probably generated a very small Lorentz force.
Should also add that over those 1st 30 seconds, there was 900Wrf being injected into the frustum by a maggie antenna INSIDE the frustum, yet there is no sign of any movement of the base line as the frustum heated up prior to achieving freq lock and generating a "Shawyer Effect" thrust output.
At lease in those 1st 30 secs, starting with a ambient temp maggie,, there doesn't appear to be any significant Lorentz or thermal forces active as the base line is flat.
TT. I'd like you comments on rfmwguys results with an eye towards something you posted earlier that the frequency bandwidth that generates thrust is smaller than the overall possible resonance bandwidth of the system. What I am wondering about is the frequency drift and splatter that the maggie produces when driven with the type power supply being used. It would seem to me that two things might be happening, first the splatter makes it more likely that the thrust producing frequency will be hit and second, when it is hit there will be a lot less power at the frequency resulting in less thrust.
Your thoughts please?
I am curious about this also. Doesn't the narrow end approaching cut off frequency for a wave guide imply some maximum wavelength that can fit in the narrow region. Isn't this region what is stretching out the wavelength in the narrow end? Wouldn't this suggest a very specific frequency, where it is barely, but not quite cut off from reflecting from the end plate. Am I mistaken that this is the goal?
Roger developed a Df or Design factor that deals with the way the big and small ends behave. It is part of his thrust equation F = (2 Qu Pwr Df) / c. As the small end diameter decreases, the guide wavelength increases and the Df increases. As the big end diameter increases, the guide wavelength decreases and the Df increases. Max Df = 1. When small end is at or below cutoff diameter, the Df = 0. Design goal is to make the small end diameter as small as possible while operating just above cutoff diameter and for the big end diameter to be as big as possible. -
#3430 by TheTraveller on 02 Jul, 2016 10:47
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https://www.reddit.com/r/QThruster/comments/4qvcwd/1701a_longer_duration_dataset_for_return_to/
Looks like around 16+mN on this run. Seems to be near max whether at 1 or 2 minute power duration. Pretty sure the 18.4mN is about max for this design. Slow return with air turbulence more likely than mechanical stickiness but not ready to make that call until more testing is done. -rfmwguy
Hi Shell,
Attached is my rate of change plot (current mm deflection - last mm deflection) with the Beam rotation vertical axis in mm. The displayed rate of change is not directly related to the mm deflection scale on the left side and was adjusted to obtain good visibility on the chart.
Note the max rate of change occurs at approx the same time, in each of the 3 power on events, shortly after maggie power is applied. The rate of change then drops as torsion beam wire twist increases and slows EmDrive acceleration. Additionally the rate of change analysis amplifies the oscillatory nature of the beam return to home after maggie power is switched off.
I suspect as the EmDrive thrust is tangential, it pulls the centre of mass of the system off axis and introduces an additional pendulum motion to the torsion beam's natural oscillatory return to home action.
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#3431 by Rodal on 02 Jul, 2016 10:50
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https://www.reddit.com/r/QThruster/comments/4qvcwd/1701a_longer_duration_dataset_for_return_to/
If the " Slow return with air turbulence" with oscillations having a period that is multiple times of the period of the torsional pendulum, with the power off, hence not due to the pendulum dynamics and not due to anything electromagnetic, and clearly admitted to be due to "air turbulence"
Looks like around 16+mN on this run. Seems to be near max whether at 1 or 2 minute power duration. Pretty sure the 18.4mN is about max for this design. Slow return with air turbulence more likely than mechanical stickiness but not ready to make that call until more testing is done. -rfmwguy
....
why is it that the measured force is not also ascribed to heating of the air by the magnetron generating thermal convection? Hence the very slow rise with time. The test is being performed in air and hence it is subject to all the known issues with trying to measure electromagnetic radiation pressure in air. Ever since Maxwell first explained electromagnetic radiation in the 1800's. It was not until 1900 that radiation pressure could be measured by Lebedev...
QUESTION: How did Lebedev in 1900 finally experimentally proved the existence of electromagnetic radiation pressure?
ANSWER: by performing the experiment in a partial vacuum.
-------------------------------
Pyotr Lebedev was the first to measure the pressure of light on a solid body in 1899. The discovery was announced at the World Physics Congress in Paris in 1900, and became the first quantitative confirmation of Maxwell's theory of electromagnetism. The lunar crater Lebedev on the far side of the Moon is named after him.
Pictures of his experiment announced in 1900:
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#3432 by SeeShells on 02 Jul, 2016 13:03
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Hmmm. Not quite what he saidhttps://www.reddit.com/r/QThruster/comments/4qvcwd/1701a_longer_duration_dataset_for_return_to/
If the " Slow return with air turbulence" with oscillations having a period that is multiple times of the period of the torsional pendulum, with the power off, hence not due to the pendulum dynamics and not due to anything electromagnetic, and clearly admitted to be due to "air turbulence"
Looks like around 16+mN on this run. Seems to be near max whether at 1 or 2 minute power duration. Pretty sure the 18.4mN is about max for this design. Slow return with air turbulence more likely than mechanical stickiness but not ready to make that call until more testing is done. -rfmwguy
....
why is it that the measured force is not also ascribed to heating of the air by the magnetron generating thermal convection? Hence the very slow rise with time. The test is being performed in air and hence it is subject to all the known issues with trying to measure electromagnetic radiation pressure in air. Ever since Maxwell first explained electromagnetic radiation in the 1800's. It was not until 1900 that radiation pressure could be measured by Lebedev...
QUESTION: How did Lebedev in 1900 finally experimentally proved the existence of electromagnetic radiation pressure?
ANSWER: by performing the experiment in a partial vacuum.
-------------------------------
Pyotr Lebedev was the first to measure the pressure of light on a solid body in 1899. The discovery was announced at the World Physics Congress in Paris in 1900, and became the first quantitative confirmation of Maxwell's theory of electromagnetism. The lunar crater Lebedev on the far side of the Moon is named after him.
Pictures of his experiment announced in 1900:QuoteSlow return with air turbulence more likely than mechanical stickines
but that's not the point.
You both are jumping to a conclusion that may not be the culprit for the small osculations after a magnetron power off. Maybe I can offer a few thoughts.
It could be the twisted power leads that are loosing their heat. The twisted power leads will "stiffen" up as power is applied through them and then relax as they power is removed and this also could show up as a cyclic component in the beams displacements.
It also could be an effect of a rocking of the beam on the torsional wire as it settles back to "zero". (note: It was one reason I captured both ends of my torsional wire).
If I was Dave I'd set up a test when I would displace the beam the same amount without power and monitor the osculations with the beam returning to zero.
Also the magnetron with induce a torsional component trying to rotate the drive that the beam could pick up and then settle back when the power is removed.
It also could be the thermals from the heated magnetron and cavity after power off causing a rocking showing up on the scales.
Heck it would even be the vibrations of Dave moving around added in after a test to setup another one.
It's not just "air" he needs to define and quantify and it doesn't need the "must be running it in a vacuum" clause that's posted here, not yet, because there are many other things to do even before you go there.
Shell -
#3433 by Monomorphic on 02 Jul, 2016 13:19
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Dr. Rodal, I have a question about the magnetic B-Fields extending outside the magnetron. I have confirmed with a simple compass that these fields extend out several feet. My question is, do those exterior B-fields change with the interaction of the stream of electrons and cavity resonators? Surely this external B-field is warped or otherwise distorted during operation vs power off?
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#3434 by SeeShells on 02 Jul, 2016 13:27
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Dr. Rodal, I have a question about the magnetic B-Fields extending outside the magnetron. I have confirmed with a simple compass that these fields extend out several feet. My question is, do those exterior B-fields change with the interaction of the stream of electrons and cavity resonators? Surely this external B-field is warped or otherwise distorted during operation vs power off?
B fields.
I'll let Dr. Rodal carry on since you asked him but it needs to be covered.
Shell -
#3435 by Monomorphic on 02 Jul, 2016 13:39
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Now, rfmwguy had the magnetron outside the cavity, inserted in a hole on the big end, as I recall. Are you discussing the internal microwave fields escaping and interacting through the magnetron itself ?
I'm referring to the magnetic field from the permanent magnets inside the magnetron. How are those affected by the magnetron running vs power off? Those are green in the image and have been confirmed with a magnetic compass.
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#3436 by Rodal on 02 Jul, 2016 13:43
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...Also the magnetron with induce a torsional component trying to rotate the drive that the beam could pick up and then settle back when the power is removed....
As I said, that is negated by the fact that the period of the torsional pendulum was reported to be from 1 to 2 minutes, while the settling down you are discussing is much, much longer than that, and the oscillations taking place obviously have a period much exceeding the reported period of the torsional pendulum.... it doesn't need the "must be running it in a vacuum" clause that's posted here, not yet, because there are many other things to do even before you go there.
Why is rfmwguy running this test with a magnetron outside the cavity, fully exposed to the air, heating the air around it?
Shell
How hot does the magnetron get? What does the magnetron do to the air around it?
Is the magnetron acting as a very inefficient heater of the air?
Has rfmwguy tried to correlate what he is measuring with the temperature of the magnetron ?
It appears that the air around the big end of the EM Drive is hotter than the air around the small end because of the magnetron.
This sets an asymmetric gradient of heat in the air.
The fact that the pendulum does not return to its original position within the period of the pendulum (1 to 2 minutes) but continues meandering down slowly as if following the cool down of the magnetron when powered off, seems to indicate that this is a thermal drive that relies on thermal convection of the air. -
#3437 by Tellmeagain on 02 Jul, 2016 14:07
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Now, rfmwguy had the magnetron outside the cavity, inserted in a hole on the big end, as I recall. Are you discussing the internal microwave fields escaping and interacting through the magnetron itself ?
I'm referring to the magnetic field from the permanent magnets inside the magnetron. How are those affected by the magnetron running vs power off? Those are green in the image and have been confirmed with a magnetic compass.
The magnetron's two permanent magnets generate permanent static magnetic field. This field, because is static, penetrates the magnetron's thick copper wall into the magnetron's slotted cavity and interacts with electrons there. This interaction will attempt to modulate the magnetic field outside of the magnetron cavity. But since the magnetron's cavity has thick copper walls, Eddy current will be generated on the inner surface of the walls to counteract with the attempt. Thus the static magnetic field outside of the magnetron's cavity will not change, from an engineer's point of view; or will not change much, from a scientist's point of view. Most of such change, if strong enough to be detectable, will be detected as leaked microwave. I do not know whether there will be rectification effect. Usually from an engineer's point of view, that's it. Because for an engineer, good enough is enough. But from a scientist's point of view, proper control experiments need to be done to control the suspected effect. -
#3438 by SeeShells on 02 Jul, 2016 14:22
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The Torsional Pendulum is mainly a horizontal rotational test bed that was done to try to negate out the many vibrational harmonics in a teeter todder balance beam but it doesn't entirely.... it doesn't need the "must be running it in a vacuum" clause that's posted here, not yet, because there are many other things to do even before you go there.
Why is rfmwguy running this test with a magnetron outside the cavity, fully exposed to the air, heating the air around it?
Shell
How hot does the magnetron get? What does the magnetron do to the air around it?
Is the magnetron acting as a very inefficient heater of the air?
Has rfmwguy tried to correlate what he is measuring with the temperature of the magnetron ?
Let's take my build as an example.
with even both ends of the torsional wire captured, oscillations can still be seen that are not horizontal in nature.
Depending on the way the beam is measured you might see this as part of beam settling back to zero.
With a hanging torsional pendulum not secured on the bottom you will see increased osculations that are not horizontal in nature and that will show up in the data.
I propose that is what we are seeing in rfmwguy's free hanging torsional pendulum wire test stand.
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#3439 by Rodal on 02 Jul, 2016 14:27
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The Torsional Pendulum is mainly a horizontal rotational test bed that was done to try to negate out the many vibrational harmonics in a teeter todder balance beam but it doesn't entirely.... it doesn't need the "must be running it in a vacuum" clause that's posted here, not yet, because there are many other things to do even before you go there.
Why is rfmwguy running this test with a magnetron outside the cavity, fully exposed to the air, heating the air around it?
Shell
How hot does the magnetron get? What does the magnetron do to the air around it?
Is the magnetron acting as a very inefficient heater of the air?
Has rfmwguy tried to correlate what he is measuring with the temperature of the magnetron ?
Let's take my build as an example. with even both ends of the torsional wire captured, oscillations can still be seen that are not horizontal in nature.
Depending on the way the beam is measured you might see this as part of beam settling back to zero.
With a hanging torsional pendulum not secured on the bottom you will see increased osculations that are not horizontal in nature and that will show up in the data.
I propose that is what we are seeing in rfmwguy's free hanging torsional pendulum wire test stand.
OK, those are called swinging oscillations of the pendulum (to differentiate them from the torsional oscillations). Their period is easy to calculate, particularly if rfmwguy's pendulum is free-hanging and not also supported at the bottom.
Anyway, experimenters measure, has rfmwguy measured the period of swinging oscillation for his pendulum?
It is trivial to measure the period of swinging oscillation. All it takes is a watch.
What is the swinging pendulum's period for rfmwguy's pendulum?