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#3480 by Rodal on 03 Jul, 2016 20:11
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Build update: More work continues on the test stand. I purchased the same laser displacement sensor as Rfmwguy, thanks Dave for finding that sweet deal on ebay! I am in the process of integrating the sensor into the test stand.
I am also removing all ferromagnetic material from the vicinity of the emdrive. This includes replacing all zinc screws with brass. and moving the computer monitor to the far right.
I am also including an image of the test stand support with sorbothane pads.
Excellent build! I admire your workmanship. Brass is slightly diamagnetc while type 303 stainless steel has very low ferromagnetic properties. You should not see any magnetic attraction between 303 hardware and a strong magnet.
Make that many of us, that are extremely impressed by your craftmanship.
I notice the fact that in your build the length of the torsional pendulum's wire is much shorter than in rfmwguy's, as the period of swinging oscillations goes like the square root of the length
The period of swinging oscillation for your build should be shorter than the one for rfmwguy.
The period of rfmwguy's torsional oscillations has been reported as 1 to 2 minutes, so the oscillations after the power is turned off have a much longer duration than 1 to 2 minutes, and cannot be explained by torsional oscillations of his pendulum.
SeeShells thought that perhaps the very long period oscillations in rfmwguy's experiment are due to his pendulum's swinging oscillations. (see the oscillations in this image after the power is off, power on represented by the red bars, where the power-on bars have a width of 1.5 minutes each:
) To this date no information has been reported at NSF what is the period of swinging oscillation for rfmgwuy's build.
Alternatively, SeeShells shortened the period of oscillations in her build by constraining the pendulum at both the top and the bottom. That makes the analysis of her pendulum swinging oscillation more complex as it is not given by the simple pendulum formula shown above.
In this movie SeeShells what appears as coupling between the torsional oscillations and the swinging oscillations in her build (difficult to tell whether the coupling is due to the initial conditions due to the moments introduced by her hands):
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#3481 by ishik on 03 Jul, 2016 20:17
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Hi everyone. Long time silent reader, non-expert, avid fan. Thank you all for your incredible work.
An idea just popped into my head and, call it ignorance, thought to throw it out there.
Could there be any positive increase in thrust if the cavity (frustum/cannae etc.) were to be spinning along an appropriate axis at an appropriate frequency? for what triggered the thought.
AAA (apologies if absolutely absurd)
Ishik -
#3482 by Monomorphic on 03 Jul, 2016 22:28
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I have been working on mounting the laser displacement sensor to the test stand. All seems to be going well. I still need to wire everything into the Dataq. Will do that tomorrow.
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#3483 by JonathanD on 03 Jul, 2016 23:16
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Sorry for the total layman question. My understanding is that a torsional pendulum has a tension on it that pulls it back to zero, correct? So if there was was some force that caused it to move in a direction (be it the thus-far unknown Shawyer effect, thermal, Lorentz or otherwise), once the source/cause of the force was removed, it would then pull back to zero, and wobble around for a bit like a swing until it came to rest at zero again?
Thanks!
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#3484 by SeeShells on 03 Jul, 2016 23:45
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I have been working on mounting the laser displacement sensor to the test stand. All seems to be going well. I still need to wire everything into the Dataq. Will do that tomorrow.
Really nice work monomorphic! You have the engineering touch and common sense in your builds and it shows.
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#3485 by SeeShells on 03 Jul, 2016 23:50
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Sorry for the total layman question. My understanding is that a torsional pendulum has a tension on it that pulls it back to zero, correct? So if there was was some force that caused it to move in a direction (be it the thus-far unknown Shawyer effect, thermal, Lorentz or otherwise), once the source/cause of the force was removed, it would then pull back to zero, and wobble around for a bit like a swing until it came to rest at zero again?
Thanks!
Yes.
It's the twisting on the wire after rotating and that small twist will cause the DUT to rotate back to zero.
PDF... follows
http://www.colorado.edu/physics/phys1140/phys1140_sp05/Experiments/M4Fall04.pdf
Shell -
#3486 by FattyLumpkin on 04 Jul, 2016 00:19
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Monomorphic , can you disclose your antenna set-up for this sim that you performed? Thanks, FL
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#3487 by Monomorphic on 04 Jul, 2016 00:58
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Monomorphic , can you disclose your antenna set-up for this sim that you performed? Thanks, FL
It is a ~3cm monopole antenna connected using a wire port and voltage source.
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#3488 by FattyLumpkin on 04 Jul, 2016 01:08
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That is very helpful! Thank you! , Kevin
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#3489 by 1 on 04 Jul, 2016 01:13
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Upon some thought, I think it's unlikely that the long-period movement in Dave's setup would be caused by swinging oscillations. As mentioned above, the period for small angle displacements is proportional to the square of the length, specifically:
There are two approximations built into this equation. First, that the initial displacement of the oscillations is small such that the approximation sin θ ≈ θ is valid; and secondly that Mem-drive >> Mwire such that we can ignore the moment of inertia of the wire itself. Both approximations should be well and valid in the regime of the test setups being built.
Allowing such, plugging in a 120 second period into that formula yields an absurd pendulum length of ~3.5Km. Perhaps a massively overdamped system could appear to have such a long period, but in that case the system shouldn't "ring" as it appears to do in Dave's data.
Without knowing the details of Dave's build (and I welcome anyone to correct me on such) I would guess that what we're seeing is perhaps a coupling, perhaps a beat frequency between two different torsional oscillations. Even Shell's setup islikely to bemay be vulnerable to such coupling as the tension (read: torque constant) in the upper wire (which bears the weight of the most of the setup) is almost certainly a different value than the tension in the lower wire.*
Anyone know details on how Dave is damping parasitic oscillations?
*Edit: Think this would only manifest for Shell if the top and bottom wires have an initial angular displacement relative to one another, and that should be easy to prevent. Would very likely manifest if the bottom wire attached to a free hanging mass instead of anchored to the test setup. -
#3490 by rq3 on 04 Jul, 2016 01:35
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Build update: More work continues on the test stand. I purchased the same laser displacement sensor as Rfmwguy, thanks Dave for finding that sweet deal on ebay! I am in the process of integrating the sensor into the test stand.
I am also removing all ferromagnetic material from the vicinity of the emdrive. This includes replacing all zinc screws with brass. and moving the computer monitor to the far right.
I am also including an image of the test stand support with sorbothane pads.
Excellent build! I admire your workmanship. Brass is slightly diamagnetc while type 303 stainless steel has very low ferromagnetic properties. You should not see any magnetic attraction between 303 hardware and a strong magnet.
Make that many of us, that are extremely impressed by your craftmanship.
I notice the fact that in your build the length of the torsional pendulum's wire is much shorter than in rfmwguy's, as the period of swinging oscillations goes like the square root of the length
The period of swinging oscillation for your build should be shorter than the one for rfmwguy.
The period of rfmwguy's torsional oscillations has been reported as 1 to 2 minutes, so the oscillations after the power is turned off have a much longer duration than 1 to 2 minutes, and cannot be explained by torsional oscillations of his pendulum.
SeeShells thought that perhaps the very long period oscillations in rfmwguy's experiment are due to his pendulum's swinging oscillations. (see the oscillations in this image after the power is off, power on represented by the red bars, where the power-on bars have a width of 1.5 minutes each:
) To this date no information has been reported at NSF what is the period of swinging oscillation for rfmgwuy's build.
Alternatively, SeeShells shortened the period of oscillations in her build by constraining the pendulum at both the top and the bottom. That makes the analysis of her pendulum swinging oscillation more complex as it is not given by the simple pendulum formula shown above.
In this movie SeeShells what appears as coupling between the torsional oscillations and the swinging oscillations in her build (difficult to tell whether the coupling is due to the initial conditions due to the moments introduced by her hands):
That's because none are true torsion pendulums, which require that the suspension wire be under tension. Simply capturing the free end (SeaShells), or not capturing it at all (the two others), don't meet the definition of torsion pendulums. Tension the wire, please. Ideally, the wire should be as thin as possible for the load (vertical mass), and as stiff as possible (yield) for greatest sensitivity when stressed to just below yield (Poisson). This is old physics and mechanics. -
#3491 by SeeShells on 04 Jul, 2016 02:33
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Upon some thought, I think it's unlikely that the long-period movement in Dave's setup would be caused by swinging oscillations. As mentioned above, the period for small angle displacements is proportional to the square of the length, specifically:
The beam is 23" or 584.2mm long 6 pounds or 2.7 Kg.
There are two approximations built into this equation. First, that the initial displacement of the oscillations is small such that the approximation sin θ ≈ θ is valid; and secondly that Mem-drive >> Mwire such that we can ignore the moment of inertia of the wire itself. Both approximations should be well and valid in the regime of the test setups being built.
Allowing such, plugging in a 120 second period into that formula yields an absurd pendulum length of ~3.5Km. Perhaps a massively overdamped system could appear to have such a long period, but in that case the system shouldn't "ring" as it appears to do in Dave's data.
Without knowing the details of Dave's build (and I welcome anyone to correct me on such) I would guess that what we're seeing is perhaps a coupling, perhaps a beat frequency between two different torsional oscillations. Even Shell's setup islikely to bemay be vulnerable to such coupling as the tension (read: torque constant) in the upper wire (which bears the weight of the most of the setup) is almost certainly a different value than the tension in the lower wire.*
Anyone know details on how Dave is damping parasitic oscillations?
*Edit: Think this would only manifest for Shell if the top and bottom wires have an initial angular displacement relative to one another, and that should be easy to prevent. Would very likely manifest if the bottom wire attached to a free hanging mass instead of anchored to the test setup.
The wire with my current drive I'm using on this run is .028" or 0.71mm steel wire.
The wire has a torsion set on it of 19 pounds or 8.6Kg.
The wire is captured 1/2 way between top and bottom.
Shell
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#3492 by masterharper1082 on 04 Jul, 2016 02:54
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Notice that each of the power on durations is similar to the frequency of oscillation. Whatever is the cause of that natural frequency, it is getting forced by the power on time. What is preventing a longer power on Period? Inability to maintain torque-producing frequency lock? Overheating?Build update: More work continues on the test stand. I purchased the same laser displacement sensor as Rfmwguy, thanks Dave for finding that sweet deal on ebay! I am in the process of integrating the sensor into the test stand.
I am also removing all ferromagnetic material from the vicinity of the emdrive. This includes replacing all zinc screws with brass. and moving the computer monitor to the far right.
I am also including an image of the test stand support with sorbothane pads.
Excellent build! I admire your workmanship. Brass is slightly diamagnetc while type 303 stainless steel has very low ferromagnetic properties. You should not see any magnetic attraction between 303 hardware and a strong magnet.
Make that many of us, that are extremely impressed by your craftmanship.
I notice the fact that in your build the length of the torsional pendulum's wire is much shorter than in rfmwguy's, as the period of swinging oscillations goes like the square root of the length
The period of swinging oscillation for your build should be shorter than the one for rfmwguy.
The period of rfmwguy's torsional oscillations has been reported as 1 to 2 minutes, so the oscillations after the power is turned off have a much longer duration than 1 to 2 minutes, and cannot be explained by torsional oscillations of his pendulum.
SeeShells thought that perhaps the very long period oscillations in rfmwguy's experiment are due to his pendulum's swinging oscillations. (see the oscillations in this image after the power is off, power on represented by the red bars, where the power-on bars have a width of 1.5 minutes each:
) To this date no information has been reported at NSF what is the period of swinging oscillation for rfmgwuy's build.
Alternatively, SeeShells shortened the period of oscillations in her build by constraining the pendulum at both the top and the bottom. That makes the analysis of her pendulum swinging oscillation more complex as it is not given by the simple pendulum formula shown above.
In this movie SeeShells what appears as coupling between the torsional oscillations and the swinging oscillations in her build (difficult to tell whether the coupling is due to the initial conditions due to the moments introduced by her hands):
That's because none are true torsion pendulums, which require that the suspension wire be under tension. Simply capturing the free end (SeaShells), or not capturing it at all (the two others), don't meet the definition of torsion pendulums. Tension the wire, please. Ideally, the wire should be as thin as possible for the load (vertical mass), and as stiff as possible (yield) for greatest sensitivity when stressed to just below yield (Poisson). This is old physics and mechanics.
Sent from my SM-T710 using Tapatalk
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#3493 by Rodal on 04 Jul, 2016 02:55
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Upon some thought, I think it's unlikely that the long-period movement in Dave's setup would be caused by swinging oscillations. As mentioned above, the period for small angle displacements is proportional to the square of the length, specifically:
There are two approximations built into this equation. First, that the initial displacement of the oscillations is small such that the approximation sin θ ≈ θ is valid; and secondly that Mem-drive >> Mwire such that we can ignore the moment of inertia of the wire itself. Both approximations should be well and valid in the regime of the test setups being built.
Allowing such, plugging in a 120 second period into that formula yields an absurd pendulum length of ~3.5Km. Perhaps a massively overdamped system could appear to have such a long period, but in that case the system shouldn't "ring" as it appears to do in Dave's data.
Without knowing the details of Dave's build (and I welcome anyone to correct me on such) I would guess that what we're seeing is perhaps a coupling, perhaps a beat frequency between two different torsional oscillations. Even Shell's setup islikely to bemay be vulnerable to such coupling as the tension (read: torque constant) in the upper wire (which bears the weight of the most of the setup) is almost certainly a different value than the tension in the lower wire.*
Anyone know details on how Dave is damping parasitic oscillations?
*Edit: Think this would only manifest for Shell if the top and bottom wires have an initial angular displacement relative to one another, and that should be easy to prevent. Would very likely manifest if the bottom wire attached to a free hanging mass instead of anchored to the test setup.
Thank you for plugging the numbers and thereby show that if rfmwguy is performing his experiment on the Earth (*) and if his garage is not several km high, and if he is using a hanging pendulum, the swinging oscillations period of many, many minutes cannot be due to swinging oscillations.
The Socratic method (https://en.wikipedia.org/wiki/Socratic_method), as no amount of preaching is going to be as convincing. And criticizing is counterproductive.
I had remarked that they look like thermal oscillations to me.
rfmwguy has a magnetron at the big end that gets quite hot. (**)
That explains the "force" and it also explains why it takes so long to come back to the origin.
Also try to imagine the shape of the decaying force as a moving average, taking away the oscillations.
What does it look like?
Doesn't it look like a decaying exponential ? Just the kind of decay you would expect from thermal convection.
Even after a long, long, long time it still has not returned to its original position.
Some further calculations can show that it cannot be due to torsional-swinging coupling either (given the fact that it has been reported that the period of torsional oscillations is only 1 to 2 minutes: about the width of the red bars in the picture).
See: http://forum.nasaspaceflight.com/index.php?topic=39772.msg1556132#msg1556132
and
http://forum.nasaspaceflight.com/index.php?topic=39772.msg1556102#msg1556102
________________
(*) it would take a very low g indeed. By the way, this asteroid is spinning so fast, that things on its surface experience a negative acceleration: http://www.iflscience.com/physics/bizarre-asteroid-has-%E2%80%9Cnegative-gravity%E2%80%9D/
(**) notice that Monomorphic has it on the side
Since we know that the magnetron gets very hot it would be a good idea to try to minimize or eliminate its effect producing thermal convection.
(***) Ever wonder why the inventor (Shawyer) has been working with the EM Drive the longest and has never, ever, reported a single test in a partial vacuum ? (only NASA and TU Dresden. NASA uses a polymer insert -Woodward effect ?- and TU Dresden got extremely small levels of force/input power) -
#3494 by FattyLumpkin on 04 Jul, 2016 03:22
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So moving forward with an "onboard" solid state RF/power pack should eliminate these thermal effects? As I understand, this will be a few months in coming, but is planned (for).
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#3495 by otlski on 04 Jul, 2016 03:24
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Anyone know details on how Dave is damping parasitic oscillations?
He is using a pool of oil and an immersed paddle. -
#3496 by rfmwguy on 04 Jul, 2016 05:15
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Build update: More work continues on the test stand. I purchased the same laser displacement sensor as Rfmwguy, thanks Dave for finding that sweet deal on ebay! I am in the process of integrating the sensor into the test stand.
You are welcome Jamie...rock on!
I am also removing all ferromagnetic material from the vicinity of the emdrive. This includes replacing all zinc screws with brass. and moving the computer monitor to the far right.
I am also including an image of the test stand support with sorbothane pads. -
#3497 by Tcarey on 04 Jul, 2016 06:55
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RFMWGUY. I was looking at your walkaround trying to understand the deflection plots you have been posting and I have a few questions about something I saw. The vertical rod going from the beam down to the weight in the oil bath caught my eye. How is that rod fastened to the beam? It didn't look like like it was a rigid coupling, but the video didn't show that very clearly. Also the long length of that rod going into the oil bath should impart a small twisting motion to the beam as it transfers energy to the oil bath. I was wondering if that might be some of the wiggles in the plots. I have no feel for how that laser device would react to the target being moved in that manner. Congratulations on the progress you have been making.
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#3498 by frobnicat on 04 Jul, 2016 09:25
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.../...
The period of rfmwguy's torsional oscillations has been reported as 1 to 2 minutes, so the oscillations after the power is turned off have a much longer duration than 1 to 2 minutes, and cannot be explained by torsional oscillations of his pendulum.
.../...
.../...
Loosely following but it seems to me that the principal oscillations (more chaotic on this particular plot, a bit more regular on previous ones) are on the order of 1 to 2 minutes. Isn't the horizontal axis simply labelled in seconds, as it is explicitly stated bottom of plot ? Where do you see a period much longer than 1 to 2 minutes ?
An electromagnet pulling on a bead of iron, soft iron preferably, let's say a small unplugged transformer core fixed on pendulum arm near test article, and an electromagnet fixed to fixed frame, at some distance from said iron (let's say 10 times the typical travelling distance of pendulum's arm at this point) pulling on it and excited with a 1 minute or 2 minutes clean square pulse (DC current off/on/off) would give a good idea of what would be expected from a square force and how the measured results depart from that. A rough estimation of needed current for simulated force can be made, vertically, with a scale in the gram range as I'm sure any DIY has already. The magnitude of force would vary a little bit with displacement so a bit imprecise, but this would be an assessment of expected dynamics roughly comparable to that performed by EagleWorks with their electrostatic calibration pulses, a huge improvement compared to nothing, and at little cost.
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#3499 by Rodal on 04 Jul, 2016 11:58
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.../...
The period of rfmwguy's torsional oscillations has been reported as 1 to 2 minutes, so the oscillations after the power is turned off have a much longer duration than 1 to 2 minutes, and cannot be explained by torsional oscillations of his pendulum.
.../...
.../...
Loosely following but it seems to me that the principal oscillations (more chaotic on this particular plot, a bit more regular on previous ones) are on the order of 1 to 2 minutes. Isn't the horizontal axis simply labelled in seconds, as it is explicitly stated bottom of plot ? Where do you see a period much longer than 1 to 2 minutes ?
....
DETAILED ANSWER
The discussion started previously, as discussed here, with this plot:
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
1) In that plot, the horizontal axis was not labeled with any time unit. It did not state "seconds". It stated UTC timestamp. Thus, we had to ascertain the time scale from other data:
2) the following information was given:Quote
The oscillation period is approximately one minute (estimate from before reworking the umbilical). Perhaps changed by less than 10% after rework.
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
And rfmwguy also stated in the above plot that the red bars were associated with power ON
3) By that, I interpreted that the width of each red bar in that figure was about 1.5 minutes, and that therefore the period of the oscillations afterwards were much, much longer than that (as clearly the period of the oscillations in the long time where the power is off, is significantly longer than the width of the red bars ! )
4) Thank you for pointing out that the latest figure has finally been labeled with the time axis unit (seconds).
So the information appears contradictory at first sight. If the labeling of this latest figure is correct, then perhaps the interpretation of rfmwguy's statementQuote4 cycles of 50% power at about 1.5 minutes each
is that he was not referring as a cycle to each red bar, but instead he was referring to a cycle being composed of the 4 bars?
What is the meaning of the red bar and the word cycles?
Is what rfmwguy meaning by a "cycle" is
cycle 1 Power ON/OFF/ON/OFF/ON/OFF/ON/OFF
then long time of no power
then
cycle 2 Power ON/OFF/ON/OFF/ON/OFF/ON/OFF
then long time of no power
cycle 3 Power ON/OFF/ON/OFF/ON/OFF/ON/OFF
then long time of no power
then
cycle 4 Power ON/OFF/ON/OFF/ON/OFF/ON/OFF
then long time of no power
cycle 5 Power ON/OFF/ON/OFF/ON/OFF/ON/OFF
then long time of no power
But there were 5 such "cycles" (not four) of 4 red bars?
Looking at the title we see it says "1 minute warmup and then 4 cycles".
So the the 1 minute warmup is the 5th cycle?
So perhaps this is what he meant ?
The meaning of a cycle seems to have changed in the latest plot, as the latest plot title states "3 cycles of 2 minutes @100% power"
Nothing being said about the first group of red bars being a "warm up" in the latest plot. So apparently in the latest plot all groups of red bars are counted as cycles. The number of red bars in each group is signficantly larger than in the first plot. And they are now a different duration. And they are now 100 power instead of 50% power.
SUMMARY
Anyway, difficult to read the tea leaves: at first the horizontal axis was not labeled with information as to whether it was a time unit like seconds or whether it was another number at which the data had been taken.
Had to resort to estimate the time from the information given about the red bars.
Meaning of cycle not clear. Stated meaning of red bar and cycle in the first plot and the label of the time axis in the latest plot seem to be in conflict with each other.
Perhaps it would have been clearer if the experimenter himself would be here discussing his data (the information instead was posted here by others). I am not a member of that site where rfmwguy is apparently posting more information if one signs up there.
I look forward to your analysis of rfmwguy's statement of 4 cycles 1.5 minutes each and of the time axis in the original picture and compare that information with the labeling of time in the latest picture.
It would be nice to be able to understand this information.
