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#2620
by
Monomorphic
on 20 May, 2016 01:38
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But, I've run a simulation with 50,000 reflections (flat endplates) for a given initial beam trajectory, and counted the number of reflections on small end, big end and sidewalls:
One cannot have equal big-end and small-end reflections without a concave-convex cavity with side-walls, as far as I can tell. Flat end-plates do not work in the long-run. I have a number of sims that show this. Will find a couple and share them tomorrow.
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#2621
by
Tellmeagain
on 20 May, 2016 04:37
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A friend asked me to review this manuscript by gustavo Colheri Uchida. Attached please find my review report. Thanks!
Thank you for posting your review,
It is for sure of a great value to my revisions
For the case of the cylinder where thrust is zero, I've looked in the solution matrix. There is something happening. Thrust is oscillating when the beam hits the ends, as can be seen in image attatched. The column 4 is z component of force in collision point, column 5 is the resulting sum of thrust in all collision points because we are considering a continuous beam.
For cylinder case, depending on where the beam finishes its trajectory, a resulting thrust is observed. This should be considered in my paper.
However, thrust has not significantly changed with your expression for radiation pressure. Conservation of momentum is still been violated. And, when considering a perfect mirror, the (1-η) turns to zero, and the expressions returns to the form I've written.
Frankly I do not know why the truncated cone is resulting in thrust.
Thank you! I like your response so I spent some hours to debug your code. Yes I found the bug. Now I have updated my review as attached. Good luck!
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#2622
by
SeeShells
on 20 May, 2016 04:45
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Got the beam laid out with the threaded side rods that will be used for balance as well as the center tube pivot on the torsion wire. I'll be using a thinner wire for the real tests and using a slip knot on the wire underneath the tube to secure the balance beam onto the wire. The slip knot will slide into the bottom of the alignment tube to make sure the wire twists correctly for testing.
This is set using a tissue on a set of vice grips to see the basic balance. Which is surprisingly good for the first time.
Also worked on the electronics box.
Shell
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#2623
by
Tellmeagain
on 20 May, 2016 04:55
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A friend asked me to review this manuscript by gustavo Colheri Uchida. Attached please find my review report. Thanks!
Thank you for posting your review,
It is for sure of a great value to my revisions
For the case of the cylinder where thrust is zero, I've looked in the solution matrix. There is something happening. Thrust is oscillating when the beam hits the ends, as can be seen in image attatched. The column 4 is z component of force in collision point, column 5 is the resulting sum of thrust in all collision points because we are considering a continuous beam.
For cylinder case, depending on where the beam finishes its trajectory, a resulting thrust is observed. This should be considered in my paper.
However, thrust has not significantly changed with your expression for radiation pressure. Conservation of momentum is still been violated. And, when considering a perfect mirror, the (1-η) turns to zero, and the expressions returns to the form I've written.
Frankly I do not know why the truncated cone is resulting in thrust.
Thank you! I like your response so I spent some hours to debug your code. Yes I found the bug. Now I have updated my review as attached. Good luck!
For those who want to try gustavo's simulation, you can download free software "octave" to run his MatLab code. I do that all the time. I attach the debugged code below which can run directly by octave. All copy rights go to Fustavo. Fustavo, If you want me to remove the file please let me know. I made the following modifications, 1. initiated parameters; 2. added one step to vector normalization; 3. modified the Fi formula. Thank you!
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#2624
by
meberbs
on 20 May, 2016 04:59
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A friend asked me to review this manuscript by gustavo Colheri Uchida. Attached please find my review report. Thanks!
Thank you for posting your review,
It is for sure of a great value to my revisions
For the case of the cylinder where thrust is zero, I've looked in the solution matrix. There is something happening. Thrust is oscillating when the beam hits the ends, as can be seen in image attatched. The column 4 is z component of force in collision point, column 5 is the resulting sum of thrust in all collision points because we are considering a continuous beam.
For cylinder case, depending on where the beam finishes its trajectory, a resulting thrust is observed. This should be considered in my paper.
However, thrust has not significantly changed with your expression for radiation pressure. Conservation of momentum is still been violated. And, when considering a perfect mirror, the (1-η) turns to zero, and the expressions returns to the form I've written.
Frankly I do not know why the truncated cone is resulting in thrust.
Thank you! I like your response so I spent some hours to debug your code. Yes I found the bug. Now I have updated my review as attached. Good luck!
Good job finding that issue, it is often really easy to miss a detail like that. Also, good job to gustavo as well, coding a simulation like this from scratch is not trivial, and there are always mistakes on the first pass. This is why scientists use peer reviews, to at least try and catch mistakes like this.
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#2625
by
TheTraveller
on 20 May, 2016 07:20
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So the English speaking science fair team is reporting 14.7mN of thrust. Do we have any more information on their build? I think the first question that needs to be answered is did they measure 14.7 mN in a DOWNWARD direction. I note that this result seem consistent with TT's observations of 20 mN/kilowatt.
My data is 8mN at 95W forward power or 84mN/kW.
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#2626
by
sghill
on 20 May, 2016 12:49
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Got the beam laid out with the threaded side rods that will be used for balance as well as the center tube pivot on the torsion wire. I'll be using a thinner wire for the real tests and using a slip knot on the wire underneath the tube to secure the balance beam onto the wire. The slip knot will slide into the bottom of the alignment tube to make sure the wire twists correctly for testing.
This is set using a tissue on a set of vice grips to see the basic balance. Which is surprisingly good for the first time.
Also worked on the electronics box.
Shell
Shells,
Forgive me for forgetting by now, but you are using torsion displacement to measure thrust correct? May I suggest assembling the whole thing and measuring any torsion over a 24 hour period with the thing turned off? I bring it up because the we're discussing forces are so weak, the earth's spin and magnetic field may produce some movement over a whole day.
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#2627
by
Monomorphic
on 20 May, 2016 14:07
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This comment/question is for Shell and Dave - but anyone else feel free to chime in.
Dampening. I've noticed that my tortional pendulum is sensitive to me moving around in the room or opening a door. Fortunately my workshop can be completely sealed off. But even so, it takes 15 or 30 minutes for the pendulum to come to a near stop. Entering the room to start the laser and other equipment starts the pendulum oscillating again.
The way I see it I have two options. I can dampen the pendulum with oil, but that adds complexity and will decrease sensitivity. Or I could rig up webcams, wireless switches and extension cords for the laser and other equipment - and perform the experiment from another room in the house.
Any thoughts on which way you plan on going?
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#2628
by
Monomorphic
on 20 May, 2016 14:31
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I assume Shell will enclose her build with plexiglass. I could always build something similar around mine. So that's a third option.
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#2629
by
SeeShells
on 20 May, 2016 15:13
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Got the beam laid out with the threaded side rods that will be used for balance as well as the center tube pivot on the torsion wire. I'll be using a thinner wire for the real tests and using a slip knot on the wire underneath the tube to secure the balance beam onto the wire. The slip knot will slide into the bottom of the alignment tube to make sure the wire twists correctly for testing.
This is set using a tissue on a set of vice grips to see the basic balance. Which is surprisingly good for the first time.
Also worked on the electronics box.
Shell
Shells,
Forgive me for forgetting by now, but you are using torsion displacement to measure thrust correct? May I suggest assembling the whole thing and measuring any torsion over a 24 hour period with the thing turned off? I bring it up because the we're discussing forces are so weak, the earth's spin and magnetic field may produce some movement over a whole day.
sghill,
I'm glad you brought this up as it's a critical issue with a free hanging wire.
I am using a vertical torsional wire displacement to measure thrusts although it's slightly different. You've pointed one of the issues with just hanging it from one point. When I lived in Southern California we had weights hung on piano wires of differing lengths to watch seismic movements and they would ALWAYS move and oscillate around and surprisingly quite sensitive.
A torsional pendulum to measure thrusts hanging off one wire and one point can and will suffer these same effects and also what your gif shows in osculations as the earth moves beneath it.
If I'm going to use only the torsional aspects of a wire to measure thrusts I need to negate the other movements and this is why I've captured the top and bottom of the wire and ran the wire through a hollow tube with small holes in the ends that the wire slides through.
On the beam you'll see two threaded rods projecting horizontally out from the beam that are used for a counter balance weights as well as a counter balance on the end of the beam.
Capturing the two ends of the wire and setting the tension on the wire allows just the torsional characteristics of the wire to measure not other effects.
Shell
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#2630
by
TheTraveller
on 20 May, 2016 15:21
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Just a comment to my magnetron based EmDrive builder associates.
Roger is a very experienced microwave engineer and would have had, before building his 1st Experimental" EmDrive very significant experience working with magnetrons and would have known the issues of magnetron frequency splatter. Plus I very highly doubt he worked with kitchen oven magnetrons and their badly regulated, high ripple power supplies.
What I suspect is from day one he knew he needed to tune the freq and have a very stable freq output. Being from the high end of the microwave industry (aerospace) no doubt he had access to high quality tunable magnetrons and their associated highly regulated, almost not ripple power supplies that could also vary / eliminate filament current to further reduce frequence splatter.
While I do believe kitchen oven magnetron powered EmDrives can be made to work, I would not expect to see the thrust levels Roger obtained from those units. What is nice is to see thrust at many times the noise level. So what Paul Stansell achieved 9-11mN and what the Google team achieved is probably around the target for kitchen magnetron Diyers to shoot for.
Of course Shell is going down the Roger aerospace / high quality pathway and designing in a highly regulated and very low ripple power supply as well as the ability to drop and then eliminate magnetron filament current to reduce maggie freq splatter to as low as possible.
So be careful Dave, too high a Q (too narrow a bandwidth), may be a disadvantage if the centre of the maggie freq splatter is not aligned to the centre of the VNA rtn loss peak dip.
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#2631
by
SeeShells
on 20 May, 2016 15:22
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This comment/question is for Shell and Dave - but anyone else feel free to chime in.
Dampening. I've noticed that my tortional pendulum is sensitive to me moving around in the room or opening a door. Fortunately my workshop can be completely sealed off. But even so, it takes 15 or 30 minutes for the pendulum to come to a near stop. Entering the room to start the laser and other equipment starts the pendulum oscillating again.
The way I see it I have two options. I can dampen the pendulum with oil, but that adds complexity and will decrease sensitivity. Or I could rig up webcams, wireless switches and extension cords for the laser and other equipment - and perform the experiment from another room in the house.
Any thoughts on which way you plan on going?
See my post
http://forum.nasaspaceflight.com/index.php?topic=39772.msg1536886#msg1536886Also I'm covering the sides of the cage with a Faraday cage and clear plastic to keep any air flow from disturbing the DUT.
I'll only have horizontal movements to worry about and I can if needed physically re-position it and let it settle before the next test.
Shell
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#2632
by
SeeShells
on 20 May, 2016 15:30
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I assume Shell will enclose her build with plexiglass. I could always build something similar around mine. So that's a third option.
Close.
Using .010" PETG clear sheet over a wire mesh Faraday cage.
Shell
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#2633
by
dustinthewind
on 20 May, 2016 17:17
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This comment/question is for Shell and Dave - but anyone else feel free to chime in.
Dampening. I've noticed that my tortional pendulum is sensitive to me moving around in the room or opening a door. Fortunately my workshop can be completely sealed off. But even so, it takes 15 or 30 minutes for the pendulum to come to a near stop. Entering the room to start the laser and other equipment starts the pendulum oscillating again.
The way I see it I have two options. I can dampen the pendulum with oil, but that adds complexity and will decrease sensitivity. Or I could rig up webcams, wireless switches and extension cords for the laser and other equipment - and perform the experiment from another room in the house.
Any thoughts on which way you plan on going?
It looks like shell has a covering around hers already and is what I was thinking to protect from breezes. If static charge were a problem shielding may help. The beam holding the pendulum could be dampened with rubber stoppers or some other method.
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#2634
by
SeeShells
on 20 May, 2016 19:50
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Hope nobody minds that I'm detailing out this build, I was asked politely to maybe post a little more.
Back from testing the test stand torsional wire. It's quite stable and very sensitive even with the thicker wire I'm using for pretesting, although it still wants to exhibit oscillations that will potentially add error to the readings. I think I'm going to extend the hollow tube to the ends of the wire like in my drawing and keep the circular osculations to a minimum. It will still be highly sensitive with the thin piano wire <.008" through the brass end caps with .010 holes and keep the jiggling (scientific term
) to a minimum.
Shell
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#2635
by
zen-in
on 20 May, 2016 20:07
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Hope nobody minds that I'm detailing out this build, I was asked politely to maybe post a little more.
Back from testing the test stand torsional wire. It's quite stable and very sensitive even with the thicker wire I'm using for pretesting, although it still wants to exhibit oscillations that will potentially add error to the readings. I think I'm going to extend the hollow tube to the ends of the wire like in my drawing and keep the circular osculations to a minimum. It will still be highly sensitive with the thin piano wire <.008" through the brass end caps with .010 holes and keep the jiggling (scientific term ) to a minimum.
Shell
Is the purpose of the tubes to stop the beam from rolling? I added a graphic of an airplane to define roll, yaw, etc. If the Center of Mass of the beam is below the attachment point of the wire there will be less tendency for the beam to want to roll or pitch. Any yaw oscillation can be damped with an eddy current device. You would need to have a thick Copper or Aluminum disk mounted to the beam, with the wire going through its center. The magnet could be on an arm and fixed to the frame. There may be interactions with your cables.
To clamp the wire you could use a short length of Aluminum tubing. Just drill a hole through it and tap it for a 4-40 screw. Run the cable through the tube and tighten the screw. When you are happy with the setup, put some Locktite on the threads.
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#2636
by
SeeShells
on 20 May, 2016 20:49
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Hope nobody minds that I'm detailing out this build, I was asked politely to maybe post a little more.
Back from testing the test stand torsional wire. It's quite stable and very sensitive even with the thicker wire I'm using for pretesting, although it still wants to exhibit oscillations that will potentially add error to the readings. I think I'm going to extend the hollow tube to the ends of the wire like in my drawing and keep the circular osculations to a minimum. It will still be highly sensitive with the thin piano wire <.008" through the brass end caps with .010 holes and keep the jiggling (scientific term ) to a minimum.
Shell
Is the purpose of the tubes to stop the beam from rolling? I added a graphic of an airplane to define roll, yaw, etc. If the Center of Mass of the beam is below the attachment point of the wire there will be less tendency for the beam to want to roll or pitch. Any yaw oscillation can be damped with an eddy current device. You would need to have a thick Copper or Aluminum disk mounted to the beam, with the wire going through its center. The magnet could be on an arm and fixed to the frame. There may be interactions with your cables.
To clamp the wire you could use a short length of Aluminum tubing. Just drill a hole through it and tap it for a 4-40 screw. Run the cable through the tube and tighten the screw. When you are happy with the setup, put some Locktite on the threads.
If I run the wire through the top and bottom I'll remove the center captured osculations like I videoed. Right?
Shell
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#2637
by
rq3
on 20 May, 2016 21:32
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Hope nobody minds that I'm detailing out this build, I was asked politely to maybe post a little more.
Back from testing the test stand torsional wire. It's quite stable and very sensitive even with the thicker wire I'm using for pretesting, although it still wants to exhibit oscillations that will potentially add error to the readings. I think I'm going to extend the hollow tube to the ends of the wire like in my drawing and keep the circular osculations to a minimum. It will still be highly sensitive with the thin piano wire <.008" through the brass end caps with .010 holes and keep the jiggling (scientific term ) to a minimum.
Shell
Is the purpose of the tubes to stop the beam from rolling? I added a graphic of an airplane to define roll, yaw, etc. If the Center of Mass of the beam is below the attachment point of the wire there will be less tendency for the beam to want to roll or pitch. Any yaw oscillation can be damped with an eddy current device. You would need to have a thick Copper or Aluminum disk mounted to the beam, with the wire going through its center. The magnet could be on an arm and fixed to the frame. There may be interactions with your cables.
To clamp the wire you could use a short length of Aluminum tubing. Just drill a hole through it and tap it for a 4-40 screw. Run the cable through the tube and tighten the screw. When you are happy with the setup, put some Locktite on the threads.
Careful with eddy current damping on magnetron driven devices! As I illustrated in a previous post, just ONE magnetron magnet can result in 30 degree rotation of a torsion pendulum as it seeks orientation with the Earth's magnetic field.
Clamping music wire is a bit tricky. It's a bit like clamping a glass fiber. The slightest nick severely compromises the tensile strength of the wire, which is why I suggested pin vises in an earlier post. Shell's method of using a guitar tuner is excellent, as the wire is wrapped around a large radius bend, not clamped. The downside is losing some control of the wire axis. It needs to be pretty darn vertical (relative to local gravity).
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#2638
by
rq3
on 20 May, 2016 21:48
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Hope nobody minds that I'm detailing out this build, I was asked politely to maybe post a little more.
Back from testing the test stand torsional wire. It's quite stable and very sensitive even with the thicker wire I'm using for pretesting, although it still wants to exhibit oscillations that will potentially add error to the readings. I think I'm going to extend the hollow tube to the ends of the wire like in my drawing and keep the circular osculations to a minimum. It will still be highly sensitive with the thin piano wire <.008" through the brass end caps with .010 holes and keep the jiggling (scientific term ) to a minimum.
Shell
Is the purpose of the tubes to stop the beam from rolling? I added a graphic of an airplane to define roll, yaw, etc. If the Center of Mass of the beam is below the attachment point of the wire there will be less tendency for the beam to want to roll or pitch. Any yaw oscillation can be damped with an eddy current device. You would need to have a thick Copper or Aluminum disk mounted to the beam, with the wire going through its center. The magnet could be on an arm and fixed to the frame. There may be interactions with your cables.
To clamp the wire you could use a short length of Aluminum tubing. Just drill a hole through it and tap it for a 4-40 screw. Run the cable through the tube and tighten the screw. When you are happy with the setup, put some Locktite on the threads.
If I run the wire through the top and bottom I'll remove the center captured osculations like I videoed. Right?
Shell
Shell, just a thought. The wire rotates through the maximum number of degrees per unit "thrust" at its center. The ends don't move at all, as they are physically clamped. The tubing with tiny holes that your wire runs through can only add friction.
Physically, the center of gravity of the pendulum "bob" should be at the middle of the length of wire, and the wire should be tensioned to negate "side to side wobble". It's nerve wracking, but a visit to your local music store with a request that they tune a 12 string guitar to open G tuning might help. The 0.008 inch diameter G string is tensioned to high D, and it's just under the breaking point. There are free, or very cheap, guitar tuning "apps" for iPhones and the like that would let you take that "note" back to the lab. Then you could tune your wire to match.
This is a lot less expensive than a precision force gauge. I own one. It cost about $800. The musical note method is extremely repeatable, even as the wire relaxes with time and temperature, and can easily be used to verify wire tension between runs. You might even pick up a tuning fork for the correct tension while at the music store.
It will be a LOT tighter than you think. If you are a guitar player, ignore the above!
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#2639
by
Monomorphic
on 20 May, 2016 21:48
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If I run the wire through the top and bottom I'll remove the center captured osculations like I videoed. Right?
Those oscillations will be greatly reduced once you load your beam with frustum and counterweight. Then it just takes time for it to settle down. It's not a problem once you stop touching it. The pendulum will only swing a few cm or so when testing, so the exaggerated movements you made with your hand just won't happen.
) to a minimum.