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#3260 by zen-in on 16 Nov, 2014 03:01
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So I need a copper cavity. Those aren't easy to come by and I'm too lazy to buy copper sheet to build my own and I'd probably build it like crap anyway. But I remembered that I can get my hands on a little brass bell just about anywhere. Look in your Christmas decorations. Once a suitable bell is found, it is a straight forward exercise to drill a hole in it to mount an rf connector, fabricate a suitable loop probe and solder it into the rf connector cup, glue some dielectric material in it, and then cut out a copper sheet and solder the thing shut. A quick and dirty resonant cavity on the cheap.
For the cavity itself, metal 3d printing is now ubiquitous and affordable.
http://gpiprototype.com/services/metal-3d-printing.html
https://www.solidconcepts.com/technologies/direct-metal-laser-sintering-dmls/?gclid=CMCy2rWzmMECFQqCfgod3A4AXw
(and many others)
A simple CAD design and a submission to a 3d printing company can yield a well-formed prototype cavity within 1-2 weeks. The prototype can be formed of a variety of metals. The prototype could be tested in a non-superconducting configuration first to get a baseline. Then, the inner portion of the cavity could be lined with YBCO film, cooled to liquid nitrogen temperatures, and tested in a superconducting configuration.
It even appears that some universities have access to 3d printers that are capable of printing using superconducting materials. Perhaps this would make a good senior project or thesis for an ambitious student. I always wished I'd taken more advantage of my university's resources when I had the chance.
http://www.tamuk.edu/engineering/departments/mien/3D%20Printers/index.html
I would be interested in learning more about this 3-D printer for superconductors. They are difficult to work with. Low temperature superconducting resonant cavities have been machined from Niobium. It would be very impractical to make one from pieces of high temperature superconductor because there is no way of connecting the pieces electrically so that everything together is superconductive. Also HTS is anisotropic for the most part. It is difficult to measure small forces on an article when lN2 is boiling off. The escaping gas produces its own thrust. Pure Silver or Copper have been used to produce high Q cavities. Other alloys are too lossy. One source for Copper is VHF cavities. I have some with a Dia of 18" and 3' high made from 16 gauge. They are VHF reject cavities. It would be a simple matter for someone skilled in metal smithing to make a cone out of one. -
#3261 by JohnFornaro on 16 Nov, 2014 13:13
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...it is the DIY vs. the Institutional mindset. I remember my high school teacher using liquid nitrogen in the classroom near students to freeze and smash banana peels into bits.
I dunno what that faux respect is all about, since the other guy just said that a $2k budget is insufficient. Intuitively, $2M is far too high a price to posit for conducting a DIY experiment.
I do share the happy memory of our physics teacher hammering frozen banannas in the actual classroom, and all of us actual students were dressed in actual street clothes. Now you see, in educational promotional materials, staged fotographs of "happy", "smiling" students with absolutely clear eye protection, gathered around a voltmeter, being safer that could be possibly imagined. But anyhow....... it would be more a matter of making sure the test article doesn't take off.
I'm sure you realize that this has not been the problem. -
#3262 by Rodal on 16 Nov, 2014 15:55
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I received the following message from Robert Ludwick answering Ron Stahl's comments:
From: Robert Ludwick
Sent: Friday, November 14, 2014 6:15 PM
To: Dr. J. Rodal
Subject: Testing the EmDrive
Hello Dr. Rodal,
This is in response to Ron Stahl's comments:Quote from: Ron StahlI think he’s right. He doesn’t understand. This is a very high Q resonator. The higher the Q, the narrower the bandwidth it can resonate at. Without resonance the Q will drop off to between 1/100 and1/10,000 what it is normally. The resonator needs to resonate. You cannot simply sweep a resonator and think you are changing the frequency only, when the Q is only for small bandwidths of specific frequencies.
Of course the higher the Q the narrower the bandwidth. Actually, Bandwidth=(resonant frequency)/Q ,so if we are talking frequencies of 1-2 Ghz and Q’s of (using Ron’s numbers above) 10,000 it implies a bandwidth of 100-200 KHz, which is NOT particularly narrow. Shawyer is talking superconducting thrusters with Q’s in the vicinity of 1e9. That would imply bandwidths of 1-2 Hz at the frequencies of the thrusters tested to date.
The test procedure I provided ASSUMED that a network analyzer had been used to identify the resonant frequencies and bandwidths of interest PRIOR to the start of the actual thrust test, so that the operator would be able to select appropriate start and stop frequencies, guaranteeing that the testing starts and stops well outside the high Q region and steps at the appropriate increment to ensure that there will be multiple thrust tests across the actual bandwidth of highest Q. The procedure ENSURES that the thruster is tested at the frequency of maximum Q, and thus, per theory, the frequency of maximum thrust. If any.
Then Ron Stahl states this:Quote from: Ron StahlSince Eagle has a PLL resonance matching circuit, there is little trouble with this except that you need to note you have not one but two variables as you have changed the amount of active mass.
First, please tell me that a lab set up to evaluate ‘Propellant-Less (exotic physics) Drives’ is NOT using a Mini-Circuits VCO, stabilized by a home brew Phase Locked Loop (PLL), as their lab signal source.
Concerning Ron's statementQuote from: Ron Stahl….you need to note that you have not one but two variables, as you have changed the amount of active mass.
If you identify the frequency of maximum Q, then step the signal generator frequency through the frequency of maximum Q, holding the amplifier power constant, making sure you start well below the frequency of peak Q and stop well above it, using frequency steps small enough to ensure that at least 10 (and in the case of Q’s as low as 10,000, as many as 100) test frequencies are within the resonant bandwidth, and wait after each frequency step long enough for the mechanical system to stabilize before taking a thrust reading, how is that 'changing the active mass’ (using the definition of mass generally accepted in academia) ? If they are changing the internals of the thruster between tests, it would be necessary to put the thruster on the network analyzer after every ‘change of guts’ to identify the new resonant frequencies / bandwidths, but otherwise it would seem to me that the test as described would work just fine, and would only involve changing one factor: test frequency. Power and thus amplifier current would remain constant for the duration of the test. The purpose of the test is to discover if thrust is generated under any conditions and whether the thrust is related to the thruster Q at the drive frequency.
Then Ron Stahl states this:Quote from: Ron StahlThis is much more difficult and much more expensive than you understand. Just the high speed auto matcher used up at George Hathaway’s lab cost $150k. And make no mistake, it is the power equipment that one presumes should be easy enough to build that costs so much. It was a big breakthrough for Eagle to get their PLL circuit in place and this is something that Woodward has never been able to do.
I have no idea what a ‘high speed auto matcher' is in this context, what function it performs, or why it is required to measure the thrust of an EmDrive. As for the PLL circuit is their need for something uniquely different from the standard use of PLL’s, which is to provide precisely controlled, stable outputs from an oscillator ?. And the ‘power equipment that costs so much’?? Again, what I have seen on the forum refers to amplifiers in the 1-3 GHz range that output a few tens of watts. THOSE are NOT expensive. So what is the super expensive ‘power equipment’ that Ron is talking about?
My simple minded interpretation of the commentary leads me to believe that Eagleworks could use some decent test equipment, such as signal sources, network analyzers, power meters, power amplifiers etc.
It is obvious from the over 200 pages of commentary on this subject I am not the only one excited about the claims about EM Drives. These folks need to get off the dime and get this thing going (or prove conclusively that there ain’t no there there, so I can relax and forget it).
Bob Ludwick
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#3263 by Mulletron on 16 Nov, 2014 17:04
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You've all seen this presentation before, more than likely:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140000851.pdf
I broke out two slides, which were pretty small in the presentation (had to zoom in a lot) about Shawyer's and Fetta's design and highlighted some neat information. One such thing is that it says Darpa got the Cannae through the door at Eagleworks. Indeed Fetta's design does look like a node from superconducting linear accelerator resonant cavities I've seen presented. See below.. The rest is circled in the slides.
Hightlights: The Cannae slide shows an actual photo of the dewar. Looks like it's in somebody's kitchen. It also states the cavity is asymmetric. The only asymmetry I see is the fact that one tube is longer than the other on the Cannae test article from Brady et al.
http://www.lepp.cornell.edu/~hoff/LECTURES/10USPAS/notes10.pdf
http://uspas.fnal.gov/materials/09UNM/Unit_4_Lecture_9_RF_Cavities.pdf
http://uspas.fnal.gov/materials/09UNM/ResonantCavities.pdf
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#3264 by DIYFAN on 16 Nov, 2014 17:30
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If a resonant frequency can be found with a small superconducting test article, it won't be a matter of detecting tiny force measurements on a delicate balance. If Shawyer type predicted forces bear out, then it would be more a matter of making sure the test article doesn't take off.
I should note too, that YBCO's superconductivity is highly frequency dependent. I don't think it works past low VHF. Certainly not microwave.
The conclusions of the authors of the attached IEEE paper entitled "Microwave Properties of YBCO Thin Films" seem to contradict your thoughts on YBCO's superconductivity not working past low VHF. To the contrary, the authors conclude:
"All techniques are capable of producing high quality thin films with excellent microwave properties. The patterned films exhibit low surface resistance values at 8GHz down to 25µΩ and 120µΩ at 13K and 77K, respectively which is comparable with the best reported values in the literature. . . . Furthermore, the results suggest that there is insignificant degradation of the microwave properties of the films due to patterning. . . . demonstrates the excellent power performance of these YBCO thin films which is essential for practical applications."
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#3265 by Rodal on 16 Nov, 2014 17:41
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Lol yes. I know what I'm doing. Radars and satcom are what I do. The biggest issue here is trying to couple rf from a 40 pound sweep generator to the test article because of the cable strain. Rf cables are heavy and rigid and using them would screw everything up. If I can't figure this out, I'm not doing it. I'd rather have a small rf generator balanced right there on the thing, running on batteries, but I'm not spending money buying one. I want to use an actual sweep generator so I can tune it and provide an rf sweep. But the cable issue is daunting. I'm thinking of using an xbee pro or putting an old wifi access point in CW mode. I have those. The best I can get in any case is +20dbm, so the test article needs to be small and light. The low powers involved would mean keeping the thing running for hours or days to see if any rotation happens.QuoteHave you worked with microwave before?
Bob Ludwick sent me this response:
From: Robert Ludwick
Sent: Saturday, November 15, 2014 5:19 PM
To: Dr. J. Rodal
In order to stop worrying about how to install a signal cable from the 40 lb sig gen, plugged into the wall, to the amplifier driving the thruster, forget the cable. The sig gen, which puts out +10-+20 dBm, has plenty of beans to drive something like a standard gain horn transmit antenna, and get enough power across a short gap to a lightweight receive antenna on the test rig to drive the power amplifier to saturation. If not, a low power, low noise pre-amp can be hooked to the receive antenna to boost the power up enough to drive the power amp. Suitable preamps are readily available. And cheap.
If one chooses to run the system off a battery, one will be forced to choose between run time and drive power.
If one chooses to power the system through some sort of low drag contacts, then 20-30 watt amplifiers are readily available covering the range of frequencies that have been discussed/tested, and run time can be essentially infinite.
The devil is in the details, as always, but replacing the stiff RF cable with a short transmit/receive link will at least solve that problem.
Bob -
#3266 by Mulletron on 16 Nov, 2014 18:10
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Lol yes. I know what I'm doing. Radars and satcom are what I do. The biggest issue here is trying to couple rf from a 40 pound sweep generator to the test article because of the cable strain. Rf cables are heavy and rigid and using them would screw everything up. If I can't figure this out, I'm not doing it. I'd rather have a small rf generator balanced right there on the thing, running on batteries, but I'm not spending money buying one. I want to use an actual sweep generator so I can tune it and provide an rf sweep. But the cable issue is daunting. I'm thinking of using an xbee pro or putting an old wifi access point in CW mode. I have those. The best I can get in any case is +20dbm, so the test article needs to be small and light. The low powers involved would mean keeping the thing running for hours or days to see if any rotation happens.QuoteHave you worked with microwave before?
Bob Ludwick sent me this response:
From: Robert Ludwick
Sent: Saturday, November 15, 2014 5:19 PM
To: Dr. J. Rodal
In order to stop worrying about how to install a signal cable from the 40 lb sig gen, plugged into the wall, to the amplifier driving the thruster, forget the cable. The sig gen, which puts out +10-+20 dBm, has plenty of beans to drive something like a standard gain horn transmit antenna, and get enough power across a short gap to a lightweight receive antenna on the test rig to drive the power amplifier to saturation. If not, a low power, low noise pre-amp can be hooked to the receive antenna to boost the power up enough to drive the power amp. Suitable preamps are readily available. And cheap.
If one chooses to run the system off a battery, one will be forced to choose between run time and drive power.
If one chooses to power the system through some sort of low drag contacts, then 20-30 watt amplifiers are readily available covering the range of frequencies that have been discussed/tested, and run time can be essentially infinite.
The devil is in the details, as always, but replacing the stiff RF cable with a short transmit/receive link will at least solve that problem.
Bob
Funny you mentioned the horn antennas. I don't have any horn antennas, but I can build them.
Tonight I'm doing an experiment here at work using 2, 9dbi omnis (not the best choice because they radiate energy in every direction) I had laying around. They are all I have at the moment. I'm going to place them next to each other in the near field of each antenna. Inject a calibrated 0dbm into one and measure the rsl, thus the free space loss after the signal is picked up from the rx antenna. I think just wireless coupling the energy into the device is probably much easier than using liquid metal. If the omni test works okay, I'll invest in a couple yagis or build a horn setup to get rf into the cavity. I horn is definitely better because they have a wide bandwidth, yagis not so much. I really want to sweep a broad range of frequencies, so two horns are definitely the ticket.
Results:
6db loss at 2450mhz with the omnis. Max energy available, using unamplified sig gen max output of +15dbm(0.03 watts), after transmitted through antennas and picked again is +9dbm(0.008 watts). Better than I expected actually. This simply isn't enough power, even with an unattenuated +15dbm. An amp is a must, so are directional antennas. Time to get/make some directional antennas. Too bad I sold all my wifi parabolic and panel antennas years ago. -
#3267 by Mulletron on 17 Nov, 2014 00:21
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http://www.amazon.com/Copper-Tumbler-Healing-Ayurvedic-Product/dp/B00IDDZRNG/ref=sr_1_22?ie=UTF8&qid=1416187099&sr=8-22&keywords=copper+tumbler
This is why we can't have nice things....
http://www.fab-corp.com/product.php?productid=2026
I've spent a lot of money with fab corp. They're legit.
http://www.drivebywifiguide.com/TetraBrikHowTo.htm
http://www.turnpoint.net/wireless/cantennahowto.html
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#3268 by DIYFAN on 17 Nov, 2014 00:45
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Only one of the copper cups left in stock. Better snag it quick!
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#3269 by Mulletron on 17 Nov, 2014 01:06
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I think it is a little too small (higher frequency). I'm trying to stay between 2400-2500mhz.
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#3270 by DIYFAN on 17 Nov, 2014 02:10
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This one is 6 inches long, although the diameter is less.
http://www.ebay.com/itm/Ayurveda-Healing-Drinkware-Copper-Tumbler-Glasses-Set-of-2-personalized-gifts-/191305013772?_trksid=p2054897.l4275 -
#3271 by aero on 17 Nov, 2014 02:40
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I think it is a little too small (higher frequency). I'm trying to stay between 2400-2500mhz.
To bad your neighbor or good friend isn't a spinner. It would be straight forward to spin a cavity out of copper, making the mold is the expensive part with set-up second. Twenty years ago it was about $300 for a much more elaborate (parabolic) shape, and much larger mold (24 inches) turned out of hard wood. A soft wood mold is cheaper but won't last. But then you don't need to spin a lot of cavities.
There might be a neighborhood machine shop with a spinning lathe and the skills to use it. The commercial outfit I used did a really good job with surprisingly little by way of drawings. I gave them a hand drawn sketch and a list of reference distances, back plane to parabolic surface and lo - the mold maker turned it into a very nice, high fidelity product. Just make sure you include a mounting lip for the copper clad PC board around the large end but that should be easy, too.
I've reason to think that the PC board on the small end does not contribute because of the dielectric, but you can cut out the small end and attach a PC board if you think it is needed. -
#3272 by Mulletron on 17 Nov, 2014 04:58
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I gotta figure out how to explain to my boss why I really really need to borrow an expensive 83752B sweep generator for a science experiment in my basement. I did float him a hard copy of the "anomalous thrust" paper a few weeks ago so that might help.
My backup plan is to use wifi. I can get a CW (hacked) or wideband DSSS or OFDM 100mw signal out of those, not to mention access to dirt cheap 802.11 amplifiers. -
#3273 by frobnicat on 17 Nov, 2014 09:25
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I may have a very shallow grasp of what can be done or not with microwaves (at what practical efficiencies) but isn't it possible to use a hollow waveguide and interrupt it for 1mm or so, I mean a waveguide with a fixed part linked to wall plugged RF amp, and a mobile part (coaxial with rotation). Would the leak be too big ? Is a waveguide simply not appropriate for efficient power transmission ?
As I understand (weakly, feel free to educate me) RF is "transverse" (E and B orthogonal to propagation) so maybe any power RF wireless transmission scheme might show intrinsic torque between mobile part and fixed part (waveguide or antenna), no ? This could be mitigated by sampling at various relative orientations, or by having a freely rotating part (full 360°) to integrate and even out any orientation dependency ...
I wonder if a light enough "carousel" mounted on a sapphire cup bearing (near point like contact) could have low enough stiction to measure 10µN or so at ends of arm. See attached picture for the overall idea. Alternatively instead of a dry point like contact use a "floater bearing" in water (or liquid metal or low vapor pressure oil for vacuum compatibility). Probably high viscosity but no stiction.
Let it spin, measure thrust from acceleration profile first, then from equilibrium speed against viscosity. Check for periodic dependency of signal relative to angle of rotation (as "real" signal part wouldn't depend on that). Make the whole system as symmetric as possible around the axis (cylindrical walls around...).
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#3274 by JohnFornaro on 17 Nov, 2014 12:11
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I gotta figure out how to explain to my boss why I really really need to borrow an expensive 83752B sweep generator for a science experiment in my basement.
Pretty cool that Mulletron can chat with his boss like that. How expensive is that instrument anyway?I wonder if a light enough "carousel" mounted on a sapphire cup bearing...
I thought that the plan was to hang it from fishing filament...
But what do I know. Apparently I'm just a gamer. But hey: Don't miss any updates! -
#3275 by Ron Stahl on 17 Nov, 2014 13:47
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Shawyer discloses using YBCO film both in his patent application and in reported prototype testing, with positive results.
I'll be interested to learn about that, but you need to remember that he had full funding for many years, including those when he won his patent; and he was defunded by the UK because he doesn't have anything and because his notions betray a complete lack of understanding of what group velocity is all about. He is an engineer, not a physicist, and he does not have a real understanding of the concepts he based the device on. If it is working, it is working by mistake and for reasons other than what Shawyer hoped, since what he hoped for was a violation of conservation. -
#3276 by Ron Stahl on 17 Nov, 2014 14:07
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What is needed more than ever is additional confirmation of the effect.
You're all excited about the conference paper from Eagle, but validation does not require a bunch of home hobbyists look to produce results in the garage with chewing gum and duct tape. Validation requires real labs doing real lab work they understand and can demonstrate on command, on a reliable force sensor of some sort. When I write that the thruster itself is the smallest part of the challenge, and that the instrumentation first, then the power system and then the thruster cost more than will fit in a home hobby budget, I am not making this stuff up. People who say a superconducting chamber with cryogenics can be had for $2k don't know what they're talking about. Who here has ever put cryogenics in vacuum?
I confess I am surprised that someone tested YBCO at Ghz and found it to work. I'd note to you, it is not superconducting at those frequencies. It has real resistance so it is not a superconductor, but the resistance is in tenths of an ohm and it is carrying 10A/mm width which is impressive, so the stuff may work well inside the resonator.
In any event, with NASA devoting resources across three centers to this, whatever home hobbyists come up with will make no difference, IMHO. And I am not trying to be a wet blanket, as I have supported hobbyist work over the years. As I said, I built a whole series of thrusters for Woodward back in 2007. I'm just noting you can't skimp on the balance and vacuum and have people take your findings seriously. Paul March had propellantless thrust in his extra bedroom in 2003-4 and no one took it seriously because he had no vacuum.
As to vacuum, if you want to be satisfied with E-3T, I can recommend the Welch 1400 as I used to own one and they're a very cost effective. You can purchase them very cheap and rebuild them. The rebuild kit is cheap too. Really the most expensive part is the shipping. They're beasts.
http://www.ebay.com/itm/AS-IS-Welch-Duo-Seal-Vacuum-Pump-Model-1400-w-A-O-Smith-1-3HP-Motor-RS1030A-/361112493011?pt=BI_Pumps&hash=item5413fb5bd3
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#3277 by JohnFornaro on 17 Nov, 2014 17:49
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...validation does not require a bunch of home hobbyists look to produce results in the garage with chewing gum...
I don't recall them saying they'd be using gum. But what do I know? I'm a koi farmer. -
#3278 by Ron Stahl on 17 Nov, 2014 18:02
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There might be a neighborhood machine shop with a spinning lathe and the skills to use it.
http://www.nextlinemfg.com/metal-3d-printing/?gclid=Cj0KEQiA1qajBRC_6MO49cqDxbYBEiQAiCl5_Heanp4RYgtNQc2YiqRYHNw7cMHmySmZxFBOZzfMUD0aAiP78P8HAQ -
#3279 by zen-in on 18 Nov, 2014 05:29
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Shawyer discloses using YBCO film both in his patent application and in reported prototype testing, with positive results.
I'll be interested to learn about that, but you need to remember that he had full funding for many years, including those when he won his patent; and he was defunded by the UK because he doesn't have anything and because his notions betray a complete lack of understanding of what group velocity is all about. He is an engineer, not a physicist, and he does not have a real understanding of the concepts he based the device on. If it is working, it is working by mistake and for reasons other than what Shawyer hoped, since what he hoped for was a violation of conservation.
The same was said of Lee de Forest and his "audion" 100 years ago. However there was never any question his invention worked.
