Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1874336 times)

Offline Rodal

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...

Boy, that's going way back.  Seems we always looked at an antenna as a matching transformer between the line and the impedance of free space.  (the antennas on sounding rockets, we would try to match or measure the ionosphere)  Anyway, the reaction momentum would be to the last free carrier that acted as the radiation oscillator.  Goes back to Plank, I believe.

Sort of what I was thinking. The wave doesn't reflect off the impedance of free space (vacuum), it is the current flowing in the conductor that reflects from the end of the conductor.
But that would not constitute a TE011 resonance, the SWR standing wave is in the feed line instead of in the electromagnetic field in the waveguide: " it is the current flowing in the conductor that reflects from the end of the conductor." Do you agree?



« Last Edit: 06/28/2015 02:03 AM by Rodal »

Offline Notsosureofit

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Depends on what you define as an "antenna" I guess.  There certainly is a large variety.  A short open ended waveguide is often used as a non-critical "antenna" around the lab.  Bad match, so it probably has a resonant structure.  Then you have the addition of parasitic elements which are free-standing resonators in the near field, usually set slightly off frequency to adjust the phase pattern, it goes on and on, gets fussy real fast.
« Last Edit: 06/28/2015 01:12 AM by Notsosureofit »

Offline aero

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Well, rfmwguy's 9 inch cavity resonates at almost exactly the same frequency using a magnetic source (Hy) and axial antenna as it does when using an electric source (Ez) and lateral antenna. 200 Hz difference.

By the way, have I mentioned that I am now using the copper model instead of the perfect metal for the cavity? The dielectric constant for perfect metal is infinity, and the copper model uses a dielectric constant of 1. I still think we should use a dielectric constant (real part of permittivity) for copper somewhere between 6 and 18 but haven't any better data than that. In any case, it is much closer to 1 than to infinity.
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Offline Rodal

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Well, rfmwguy's 9 inch cavity resonates at almost exactly the same frequency using a magnetic source (Hy) and axial antenna as it does when using an electric source (Ez) and lateral antenna. 200 Hz difference.

By the way, have I mentioned that I am now using the copper model instead of the perfect metal for the cavity? The dielectric constant for perfect metal is infinity, and the copper model uses a dielectric constant of 1. I still think we should use a dielectric constant (real part of permittivity) for copper somewhere between 6 and 18 but haven't any better data than that. In any case, it is much closer to 1 than to infinity.
Is what you call "perfect metal" the perfect conductor choice under Meep? and is the dielectric constant of 1 what deltaMass told you to use? and what difference does it make in the results? and why do you want to use 6 to 18 and what difference would it make?
« Last Edit: 06/28/2015 01:29 AM by Rodal »

Offline rfmwguy

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257.5 g for frustum exoskeleton, simply tacked together. Will need stiffening, should come in well under 750 g. Weight budget for everything at 1.5 kg looks fine. Circle cutting 11.01 and 6.25 was a hassle. Probably less stiffening needed with thicker copper clad pcb, oh well. Mr. Whiskers supervising...

Edit...corrected gram weight...sheesh...sniffed too much solder smoke.
« Last Edit: 06/28/2015 02:13 PM by rfmwguy »

Offline deltaMass

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257.5 mg for frustum exoskeleton, simply tacked together. Will need stiffening, should come in well under 750 mg. Weight budget for everything at 1.5 kg looks fine. Circle cutting 11.01 and 6.25 was a hassle. Probably less stiffening needed with thicker copper clad pcb, oh well. Mr. Whiskers supervising...
I suspect that the cat will have matching issues :o

Offline rfmwguy

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Regarding resonant modes in the frustum. Would there still be resonant modes if;

1. the frustum were open on the big end only?

2. the frustum were open on both ends?

IF I understand these modes correctly, the TExx0 modes resonate with the pointing vector radial in/out-ward from the axis to the walls. It seems to me, that a cone that is open on both ends would still support the same TEnm modes, just not the p modes. Correct?

If it's closed at the small end, it should still support odd harmonics of p modes. Correct?

Thank you!
Todd
Todd,

This is another case where both size, and frequency do matter.

Even without any hole, both in a cylinder and in a truncated cone, modes that are high in azimuthal quantum number "m": for  TEmnp with high m have no central field.   The higher m, the more they start to look like a whispering-gallery mode. 

Pictures of whispering-gallery modes:



This is a picture of London's St.Paul's cathedral, which is associated with the whispering-gallery phenomenon.  Climb 259 steps inside the dome, stand on one side of the circular gallery and talk very quietly and your speech can be heard quite clearly on the other side some 30m away.  You can see deltaMass at the Cathedral whispering something about conservation of energy to frobnicat who is at the opposite end of the Cathedral listening to deltaMass musings:





you will notice that there is a hole in the center of the whispering gallery.

This picture shows the quadrapole for mode TM212 used by NASA Eagleworks, for the electric field:



and for the magnetic field:



You can see that even this low mode will support a small hole through the middle of the big base without affecting it.

See for example the octopole TE411 for NASA's Brady cavity in the attachment below, which will support a much larger hole.

As "m" increases, the hole supported in the middle can be bigger and bigger.

For these modes, you can actually make a hole through the central portion where there is no field, and it won't make a difference.

As "m" increases the mode looks more and more like a ring.  In the limit you can still have resonance with very high "m" and a very thin ring.

When the hole is such that it is flash with the internal surface of the cylinder, "m" is infinite and you have no resonance.

Ditto for the big diameter in a truncated cone: you can have resonance at ever increasing "m" until the hole is flash with the interior surface, at which point m is infinite and you have no more resonance.

////////////////

You can also have resonance with holes on both ends, as long as they are not flash with interior surface.  The resonance will be at a higher frequency as "m" increases.   The big diameter hole size is what matters most.  When the big diameter hole is flash with the interior surface "m" is infinite, the natural frequency is infinite and you no longer have resonance.

//////////////

To answer your unnumbered question requires more wording and I don't have a picture to explain it at the moment. So maybe tomorrow.
The whispering gallery pics reminded me of something I saw elsewhere...took me a while to remember...cannae drive cavity "vents" that ew claimed were of no significance:
:
http://www-tc.pbs.org/wgbh/nova/next/wp-content/uploads/2014/07/cannae-drive-schematic.jpg

Offline dustinthewind

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I was thinking of a few modifications.  One idea was to fill the cavity with barium titanate which I think slows down the propagation speed and allows us to move into the radio frequency range.  Maybe this is or isn't a bad idea? Edit: (Removed cheaper as I really have no idea) (less precision tolerance in construction though dielectric may counteract that.) Ok, never mind the barium titanate as it dosn't have an unusually large index of refraction like I thought it did. - not sure why I thought that.

Some of the talk about opening up one end of the cavity got me thinking and so we have a coil outside the cavity submersed in dielectric to keep the spacing 1/4 λ.  It is out of phase with the current in the bottom plate by 90 degrees to give the 0 and 180 degree phase relationship by time retardation sort of like a phase array antenna.  If I am right this should allow radiation to pass through the bottom cavity wall.  That is, if there is any thrust, and what is occurring is a form of this, then it may be a deliberate enhancement of the effect.  On the other hand, maybe not. 
« Last Edit: 06/28/2015 05:18 AM by dustinthewind »

Offline aero

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Well, rfmwguy's 9 inch cavity resonates at almost exactly the same frequency using a magnetic source (Hy) and axial antenna as it does when using an electric source (Ez) and lateral antenna. 200 Hz difference.

By the way, have I mentioned that I am now using the copper model instead of the perfect metal for the cavity? The dielectric constant for perfect metal is infinity, and the copper model uses a dielectric constant of 1. I still think we should use a dielectric constant (real part of permittivity) for copper somewhere between 6 and 18 but haven't any better data than that. In any case, it is much closer to 1 than to infinity.
Is what you call "perfect metal" the perfect conductor choice under Meep? and is the dielectric constant of 1 what deltaMass told you to use? and what difference does it make in the results? and why do you want to use 6 to 18 and what difference would it make?

Perfect metal is one of the meep default materials. The users are expected to design their own materials. The other meep defaults are vacuum, air and "nothing." ("nothing" material is used to cut through the structure.) The model we designed is e = e' + i e" and deltaMass designed mathematically developed the e" value then normalized it to e' using e'=1. Meep thinks that e' = the dielectric constant which is consistent with much of the literature. I am suggesting that instead of using 1, the dielectric constant of vacuum, we should normalize e" to e' = dielectric constant of copper which from my literature search looks like it is somewhere between 6 and 18. Some values:
Copper Catalyst 6.0 - 6.2
Copper Oleate (68 F) 2.8
Copper Oxide 18.1
But there is not agreement. Others claim that the dielectric constant of metals is very large, near infinity.  I suspect they may have something there but in any case it is the dielectric constant value that keeps energy contained within the cavity (or so it appears within Meep). DeltaMass had a very large value as I recall, before normalizing, perhaps that is the best value. If you look at the views I have posted you see that they show a lot of energy outside of the cavity and I don't think that is realistic. In particular, look at my latest uploads on Google Drive. And on further thought, 6 to 18 probably wouldn't make much difference, a large value is needed.

On another point, I have uploaded the x, y, and z views of Ex, Ey, Ez and Hx, Hy, Hz field components for rfmwguy's 9 inch cavity excited by a magnetic source with the antenna oriented axially. They use a constant range of Min/Max as you requested. And they are only for the last 14 frames, just more than the final full cycle, (10 frames/cycle).

I have also uploaded to Google Drive, the complete data sets for the Ex and Ey views of the previous case, June 26 data set. These also use a fixed Min/Max range over each data set. You can easily see why it is not visually satisfying to use these fixed range values over a lengthy time interval where energy is being added to the resonant cavity. It does eliminate the background color flickering, though.

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Offline SeeShells

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Offline deltaMass

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I dislike 200 lines of quote followed by a couple of lines of text, so two points, and you know who you are.

- Barium titanate at MHz has an extraordinarily high relative pemittivity. This translates (via sqrt) into a high refractive index.

- My calculations on the relative pemittivity of copper concerned its complex value. The real part is unity and the imaginary part about 1 million - I could tell you more exactly if this forum had a half-decent search function.

Offline Rodal

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...On another point, I have uploaded the x, y, and z views of Ex, Ey, Ez and Hx, Hy, Hz field components for rfmwguy's 9 inch cavity excited by a magnetic source with the antenna oriented axially. They use a constant range of Min/Max as you requested. And they are only for the last 14 frames, just more than the final full cycle, (10 frames/cycle).

I have also uploaded to Google Drive, the complete data sets for the Ex and Ey views of the previous case, June 26 data set. These also use a fixed Min/Max range over each data set. You can easily see why it is not visually satisfying to use these fixed range values over a lengthy time interval where energy is being added to the resonant cavity. It does eliminate the background color flickering, though.

[This is a discussion of the numerical results by aero, using Meep Finite Difference code, shown here:  https://drive.google.com/folderview?id=0B1XizxEfB23tfmcxbUxsM0lVTGVkemVTX1RaMlZJb001NHVaUDRvYUtjS0lIbjdIcUNkX0k&usp=sharing ]

Having a fixed range eliminated the nonsense:  the changing color background, the nonsense associated with fractal artifacts from the FD mesh, and the nonsense associated with amplifying by thousands of times transients that are really insignificant beyond their numerical accuracy.

For the magnetic excitation  (June 27 runs) you excited (based on Hy/y and Hy /z)

TM114   which according to my program has a natural frequency of 2.63 GHz


EDIT or it may be

TM212  which according to my program has a natural frequency of 2.45 GHz

but unfortunately the Cartesian axes are aligned along the two directions where this mode is zero, so all we can see is the quadrupole Hz -x

This would make a lot of sense, as TM114 is nearby and it is only a parasitic mode.  To see the fields for TM212 we would need views at an angle to the Cartesian axes.


For the June 26 "fixed color range" your Google Drive shows: Ez / x  and Ez /y , while your comment above reads:

<<the complete data sets for the Ex and Ey views of the previous case, June 26 data set. These also use a fixed Min/Max range over each data set.>>

I assume that you meant Ez / x  and Ez /y , since I cannot see Ey /x and Ey /y as well as other important fields, I reserve my judgement on that set :)

Below are my personal thoughts, based on decades of writing and using Finite Element and Finite Difference methods to model the transient nonlinear response of complex physical processes (of course, I don't pretend to have the sum total of knowledge in this regard, but having worked with numerical models for a long time, the audience will pardon my strong views on this subject):

///////////////////////////////////

My comment regarding <<You can easily see why it is not visually satisfying to use these fixed range values over a lengthy time interval where energy is being added to the resonant cavity.>> is that it is very satisfying  to me to have a fixed range because otherwise one is seeing a pseudo-random number generator:  if one artificially amplifies and shrinks in every frame by thousands of times the numerical answer from a numerical method that is in the range of numerical noise, what one sees is noise.

A movie of something changing vs time without numerical labels, should be presented such that every frame has the same max/min, so that one can see what happens vs time.  Otherwise, if every frame is modified by random artificial multipliers such that they all reach the same contours, what one gets is a confusing picture where one cannot tell what is going on.  If what is supposed to be 0.00000001 is displayed in one frame as 10,000 and what is supposed to be 10,000 is displayed in another frame as 10,000, it will look complicated and fascinating, but what one is looking at is numerical noise.

Now, some people (not you) , may find it satisfying to see fractals and weird looking images in a numerical response (yes it is artistically beautiful and it is intriguing to the mind), and they may think that they are looking at some new physical process dealing with the 10th dimension, but they are risking misinterpreting numerical noise for something real because these are numerical artifacts, and they represent nothing physical.

They need to know that what they are looking at is a movie where the magnitude of every frame is being altered by a large multiplier or shrinking factor, that changes from frame to frame, without their knowledge, and where this multiplier or shrinking factor is not associated with anything physical

They are the numerical analogue of what many people were criticizing about the EM Drive experiments: if one has experiments where what one outputs is plagued with noise, then it is nearly impossible to tell what is going on, and the scientific community is not going to take it seriously.  If we construct a movie of a process where the magnitude changes by orders of magnitude (as it should because of the high Q that eventually builds up) and instead of showing everything to the same final magnitude, we artificially change every frame so that it is amplified or shrunk by a random multiplier, we lose all sense of perspective and we cannot tell what is zero, what is insignificant numerical noise and what is significant.
« Last Edit: 06/28/2015 02:02 PM by Rodal »

Offline Tellmeagain

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I have not followed the thread recently. Regarding to the EM drive, I am interested in getting the answers to the following questions (I browsed the last few pages but did not find the answers). Are there new experiments or results from NASA after the wrap drive news in later May/ early June? Are there plans to publish the results so far in a peer-reviewed journal? Will there be new paper from NASA at the Joint Propulsion Conference of this year? Thanks!
« Last Edit: 06/28/2015 08:13 AM by Tellmeagain »

Offline Rodal

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I have not followed the thread recently. Regarding to the EM drive, I am interested in getting the answers to the following questions (I browsed the last few pages but did not find the answers). Are there new experiments or results from NASA after the wrap drive news in later May/ early June? Are there plans to publish the results so far in a peer-reviewed journal? Will there be new paper from NASA at the Joint Propulsion Conference of this year? Thanks!
NO

Offline Rodal

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...
The whispering gallery pics reminded me of something I saw elsewhere...took me a while to remember...cannae drive cavity "vents" that ew claimed were of no significance:
:
http://www-tc.pbs.org/wgbh/nova/next/wp-content/uploads/2014/07/cannae-drive-schematic.jpg
Thank you.

That is a very sharp observation.  I always wondered what Fetta had in mind with those machined vents.  He may indeed have found some high mode whispering-gallery mode in his numerical models, and maybe this is what he had in mind with those vents.   That also explains the strange-looking flying-saucer design of Fetta: to maximize such modes. 

If so, this also makes sense to me as to why they did not work in practice in the Eagleworks tests.  The reason is that these high "m" modes that show a whispering-gallery require a lot of numerical precision in the model that may be unrealistic to attain:  the results may not be robust.  A small change in input may result in a big change in output (both in the numerical model and in the physical system).   I expect that these whispering-gallery modes should be excitable at much higher frequencies than 2 GHz used by Eagleworks.    I wonder what is the natural frequency that Fetta had in mind for his design to work at

If Fetta designed his vents to work at a higher frequency than what Eagleworks tested his unit at, then of course his vents would be negated.  But that's the problem with such a design: it would work at a very specific narrow frequency range, if ever.
« Last Edit: 06/28/2015 09:04 AM by Rodal »

Offline rfmwguy

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...
The whispering gallery pics reminded me of something I saw elsewhere...took me a while to remember...cannae drive cavity "vents" that ew claimed were of no significance:
:
http://www-tc.pbs.org/wgbh/nova/next/wp-content/uploads/2014/07/cannae-drive-schematic.jpg
Thank you.

That is a very sharp observation.  I always wondered what Fetta had in mind with those machined vents.  He may indeed have found some high mode whispering-gallery mode in his numerical models, and maybe this is what he had in mind with those vents.   That also explains the strange-looking flying-saucer design of Fetta: to maximize such modes. 

If so, this also makes sense to me as to why they did not work in practice in the Eagleworks tests.  The reason is that these high "m" modes that show a whispering-gallery require a lot of numerical precision in the model that may be unrealistic to attain:  the results may not be robust.  A small change in input may result in a big change in output (both in the numerical model and in the physical system).   I expect that these whispering-gallery modes should be excitable at much higher frequencies than 2 GHz used by Eagleworks.    I wonder what is the natural frequency that Fetta had in mind for his design to work at

If Fetta designed his vents to work at a higher frequency than what Eagleworks tested his unit at, then of course his vents would be negated.  But that's the problem with such a design: it would work at a very specific narrow frequency range, if ever.
Thanks doc, also suspect the vents would be narrow band...slight freq offset and zero performance. My apologies to dm for multiline quotes, but thought all of that discussion a few pages ago was worth revisiting. Focused egress of energy from the frustum should be one of our topics imho.

Edit - cannae patent published 2014: http://www.google.com/patents/US20140013724

Note: wide band of operation, only a couple of freqs discussed, not sure which one vents were cut for but appears to be sub-1 ghz.
« Last Edit: 06/28/2015 02:05 PM by rfmwguy »

Offline Rodal

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Thanks so much for taking your valuable time to make this movie :)

Could you be so nice to make movies from these four sets also, please ?

 (https://drive.google.com/folderview?id=0B1XizxEfB23tfmcxbUxsM0lVTGVkemVTX1RaMlZJb001NHVaUDRvYUtjS0lIbjdIcUNkX0k&usp=sharing June 27 runs)

1)  rfmwguy- ez-xyz views June 27 views, Magnetic antenna, Hy views,    Hy-y

and

2)  rfmwguy- ez-xyz views June 27 views, Magnetic antenna, Hy views,    Hy -z

and

3) rfmwguy- ez-xyz views June 27 views, Magnetic antenna, Ex views,    Ex -y
and

4) rfmwguy- ez-xyz views June 27 views, Magnetic antenna, Hz views,    Hz -x

Thanks :)
« Last Edit: 06/28/2015 01:16 PM by Rodal »

Offline deuteragenie

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Uploading of 18x312 views of 9 inch cavity complete. Top level folder dated June 26, link is:
https://drive.google.com/folderview?id=0B1XizxEfB23tfmcxbUxsM0lVTGVkemVTX1RaMlZJb001NHVaUDRvYUtjS0lIbjdIcUNkX0k&usp=sharing

Very nice ! Thank you.

Looking at the result, it looks like the simulation becomes "mature" around t=200. 
You can then see that the patterns repeat with periodicity=5.

Presumably, you could win a lot of computing time by limiting the simulation to start at t=250 (to be sure), and last for t=10 (also to be sure that the periodic behavior is properly captured).

The step between frames, however, appear to be still too large.  The transition t307 and t308 for example is "dramatic".  I would think that at least 10 intermediary steps are needed to make the transition smooth and animate it without "jumps".

Which brings us to animation: in order for you to save a lot of time loading images, it would be much more efficient to create a .mp4 video and load it.
It is easy to create a high quality .mp4 from .pngs using ffmpeg for example:
https://trac.ffmpeg.org/wiki/Create%20a%20video%20slideshow%20from%20images
Creating a video of 100 frames (from t=250 to t=260, 10 steps), would take a few seconds.  Note that the video @ 30 fps only last a bit over 3 seconds, so better enable "repeat" 3 - 4 times, or add more steps and get even smoother transitions.   

As regards to measurements, I suggested earlier to use Meep "flux" function.

aero, could you load the .ctl file together with the images?
 





« Last Edit: 06/28/2015 02:10 PM by deuteragenie »

Offline SeeShells

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.

[This is a discussion of the numerical results by aero, using Meep Finite Difference code, shown here:  https://drive.google.com/folderview?id=0B1XizxEfB23tfmcxbUxsM0lVTGVkemVTX1RaMlZJb001NHVaUDRvYUtjS0lIbjdIcUNkX0k&usp=sharing ]

EDIT or it may be

TM212  which according to my program has a natural frequency of 2.45 GHz

but unfortunately the Cartesian axes are aligned along the two directions where this mode is zero, so all we can see is the quadrupole Hz -x

This would make a lot of sense, as TM114 is nearby and it is only a parasitic mode.  To see the fields for TM212 we would need views at an angle to the Cartesian axes.



Dr. Rodal and Aero...
I was writing to say about the same thing in what you edited on the mode of TM212, good observation Jose (you're good!).

What is confusing to me (and maybe others) are the multiple files and directories laid out seeing at random with descriptors that are hard to decipher.  I found myself digging through all of the directories and files trying to guess what was going on so I could post a gif that was important data. You two went through a lot of test runs and data that was not relevant, but now I feel you have done a great job at getting something that's useful.

One comment. Could we delete the useless files with the 60's motif?  And if google will allow it, rename them so we don't confuse everyone. (I'm so easily confused before my first cup of coffee in the morning anyway).

I'm grateful for both of you because if Aero hadn't taken hours and hours of time to learn meep and Rodal's decades of simulations I would would have had to try it myself and would now would be staring hypnotized at my monitor.

Shell

PS: The garden party was a huge success (at least to me) when the Bridge playing sisters asked... and what are you doing Shell?

When 44% of Americans think we lived with walked with Dinosaurs it's tough telling some the what and why of what your are doing, but I did ok, they honestly became excited and understood just a little. NASA has a tough sell and sometimes they are ridiculed for drawing pretty pictures, but they shouldn't be chastised considering so many in their audience that pays the bills want to ride a Velociraptor to work.

Offline SeeShells

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257.5 g for frustum exoskeleton, simply tacked together. Will need stiffening, should come in well under 750 g. Weight budget for everything at 1.5 kg looks fine. Circle cutting 11.01 and 6.25 was a hassle. Probably less stiffening needed with thicker copper clad pcb, oh well. Mr. Whiskers supervising...

Edit...corrected gram weight...sheesh...sniffed too much solder smoke.
This excites me to no end!!! Good for you and it looks like you do great work, clean edges and I like the way you supported the axis with the 4 standoffs. Smart man.

cute kitty!

Shell

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