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Old 05-13-2015, 07:58 PM   #226
jedidia
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Well, with that kind of setup any results could come from practically anywhere, so it wouldn't add much to the current process... still cool seeing people get involved.
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Old 05-13-2015, 08:27 PM   #227
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Quote:
Originally Posted by jedidia View Post
 Well, with that kind of setup any results could come from practically anywhere, so it wouldn't add much to the current process... still cool seeing people get involved.
Right! Some wind blowing through your house could show easily 0.001 N already...

Unfortunately the guy did not set up any control experiments to see if the scale is capable of actually measuring milli and micronewtons. Blowing on the machine would have been enough already...
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Old 05-14-2015, 08:55 AM   #228
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The guy cites Shawyer's claim that the effect shows 20 seconds after powering the gizmo on. That's odd. Assuming that the gizmo operates via electrogravitic coupling, the effect should have been immediate. On the other hand, 20 seconds is what I would expect if thermal effects were somehow involved.

Also, I don't remember any mention of this in NASA experiments, nor can I see this in their interferometry FFT.
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Old 05-14-2015, 10:59 AM   #229
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Time will tell, I guess.

My money is still on this being some measurement error. And I have good odds on it
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Old 05-14-2015, 09:05 PM   #230
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Old 05-14-2015, 11:02 PM   #231
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Yawn. The maker of this video should first educate himself about the subject.

1. The current working hypothesis does not involve violation of Newton's third law, any more than orbital precession of Mercury does.

2. EagleWorks does not work on the warp drive, except it has a rig called "warp field interferometer". Go figure.

3. Elaborating on the fact that the thrust is "only" 30uN misses the point, because the thrust should be zero. That's precisely what the whole brouhaha is about.

4. Further, complaining that the test rig can only measure from 15uN upwards also misses the point, because 30-50uN is 2-3 times the minimum force of the rig, so yes, it can be measured. Further, if this guy bothered to look at original results, he would have seen that the signal is clearly above the noise level. So the force is there, the controversy is about where it comes from.

5. And, of course, no discussion of interferometry results.
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Old 05-22-2015, 08:18 AM   #232
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"Facebook science", anyone? http://www.masinaelectrica.com/emdri...ependent-test/
He also claims to have thrust readings from his home-made EM drive.

I guess we'll soon have people with the "EMdrive-syndrom", suffering from inner tissue burning and eye-sight loses, if they all start to mess around with magnetrons.
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Old 05-22-2015, 12:05 PM   #233
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He's getting thrust, but his readings are highly inconsistent...

No thrust at first, small thrust when pointing down, even less thrust when pointing up.

There's also a delayed reaction between when he switches the power on to when the thrust is produced. But I can't tell if that's from the scale reacting too slowly or from air inside heating up and expanding, then being pushed out in the direction of the larger plate, through a leak somewhere.

There's some discussion in there that maybe the force up and down are expected to be different because "it's fighting against gravity instead of being helped". That's simply not true. The thrust in any direction should be the same.
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Old 05-22-2015, 01:08 PM   #234
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Quote:
Originally Posted by RisingFury View Post
 He's getting thrust, but his readings are highly inconsistent...

No thrust at first, small thrust when pointing down, even less thrust when pointing up.

There's also a delayed reaction between when he switches the power on to when the thrust is produced. But I can't tell if that's from the scale reacting too slowly or from air inside heating up and expanding, then being pushed out in the direction of the larger plate, through a leak somewhere.

There's some discussion in there that maybe the force up and down are expected to be different because "it's fighting against gravity instead of being helped". That's simply not true. The thrust in any direction should be the same.
Let's be fair here.

At first he had it hanging from the door frame in a kind of pendulum configuration, trying to measure displacement visually. No wonder he had no results with this.

Then he measured it pointing upwards mounted on a spring loaded lever, essentially measuring the weight on the lever using the proportional force ratio due to closer pivot point placement (aka small force created by device on the long leg, great force measured by the scale on the short leg). Here he got some readings.

People argued that it might be a simple hot air balloon effect causing the upward force, so he rotated the device to have it point down in the same configuration. Then the scale reflected a reading in the downward direction, but much smaller. The theory was that the hot air balloon effect is actually true and as such effectively creating a null-point offset.

The delayed reaction is indeed interesting. If you listen in to the videos, you'll notice that a low volume "fizzle" can be heard, supposedly produced by the cavity as soon as the magnetron is on full output power. Once this "fizzle" is heard, the scale immediately shows a reading. So the argument there is that the magnetron simply takes some time to create the microwaves.

Personally, I think those readings are due to magnetic field interactions on lever/spring/shield/scale that simply create forces by pushing/pulling on the structures.

I guess this mystery will go on until someone puts it into space and observes no movement at all (besides spinning wildly). Until then people will boost microwave vendors business a bit.
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Old 05-23-2015, 12:42 AM   #235
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Ok, so I did some math given his numbers.

I will give numbers, but have neglected the margins for error deliberately.

The volume of the device is

V = 8.69 \cdot 10^{-3} m^3

Buoyancy of an object is calculated as the weight of the gas it displaces. However, as the object fills with gas that is less dense, it still has a weight of its own.

Gas becomes less dense as it heats up and the same is true for air. I'm using the ideal gas law to describe air.

p \cdot V = \frac{m}{M} \cdot R \cdot  T

The quantities are
p - air pressure
V - chamber volume
m - mass of air
M - molar mass of air
R - gas constant
T - air temperature

I assumed an air pressure of p = 10^5 Pa and took gas constant R = 8314 \frac{J}{kmol}. Molar mas is M = 29 \frac{kg}{kmol}.

Rearranging the equation to find air density \rho

\rho = \frac{p \cdot M}{R \cdot T} = \frac{K}{T}

with K = \frac{p \cdot M}{R} = 348.8 \frac{kg}{m^3}.


Thus the change of force felt by the lever caused by buoyancy is given by

\Delta F = V \cdot g \cdot (\rho(T_1) - \rho(T_2))

I made the first estimate using ambient air temperature of [LaTeX Error: Syntax error] and in-chamber temperature given in measurement 1 as [LaTeX Error: Syntax error]. The temperature T_2 is actually the temperature of magnetron, but it'll do as a fair estimate.

Under that assumption, the change of force felt by the lever is \Delta F = 0.0122 N.

The scale, however, feels a force about 2.89 times greater, so \Delta F' = 0.0352 N.

The scale should then show a mass change of \Delta m = 3.59 g. The scale shows a mass of change of about 1.2 g once it settles. So obviously the temperature inside the chamber doesn't quite reach [LaTeX Error: Syntax error] or at least not in all places.

I don't know how he measured the temperature and what effect the microwaves might have on his measuring device.


How high is the temperature?

The power of the device is given as P = 800 W, but it takes more than 5 seconds for the scale to go from 0 to the initial jolt of 1.2 and a total of 10 seconds before the device settles.

We can find how by how much the temperature of air would change in that time.

The input of energy is
Q = P \cdot t

with
Q - heat
t - time it takes to settle

The change of temperature is given as
Q = m \cdot C \cdot \Delta T

with
C - heat capacity of air
\Delta T - change of temperature

The heat capacity of air isn't trivially easy to get. For dry air it's
C = 1 \frac{kJ}{kg \cdot K}

However, for 50% humid air, it increase because the water vapor in the air needs to be heated as well. The fraction of mass of water in the air is small and the water is vapor, not liquid, so its heat capacity is lower. So overall, the heat capacity doubles.

C = 2 \frac{kJ}{kg \cdot K}

The change of temperature is then
\Delta T = \frac{P \cdot t}{V \cdot \rho(T_1) \cdot C} = 387 K

This would imply that the temperature of air inside can change VERY quickly and that most of the power doesn't go towards heating the air, but heating the metal.

So what about the shifting of the null point?

The mass change up is about \Delta m = -1.2 g and down is \Delta m = 0.25 g. If the buoyancy and the other unaccounted for force are the same in both cases, buoyancy accounts for 0.27 g and the other force about 0.72 g.

Both number are given for the scale and are 2.89 times smaller.


However, given how much energy is pumped into the machine and how much of a role air plays, I still think air has more contributions.

I've thought of one more contribution that can lift the machine and offset the null point:

If the metal heats up, it transfers heat to the surrounding air. Air on the top plate can rise, but air on the bottom plate can get trapped and pushes the machine up.

If the bottom plate is larger, more air will be trapped below it and the upward force will be larger.

In the other case, with the bottom plate smaller, less force will be contributed up.

However, the net effect in test No. 4 was still down. That means that whatever force is unaccounted for is still greater than buoyancy and lift.


I'm still skeptical, though. None of the explanations I've seen would even come close to the number we're seeing here. I think it's a measurement error from something that's unaccounted for.


EDIT:

Could you see any force on test 1 and 2, with the pendulum? Yes and no. If we assume mass of the device of about 1 kg and a length of the wire of 1 m, the movement would be in the 0.1 to 1 mm range. The device might begin to swing, but nothing conclusive...

Last edited by RisingFury; 05-23-2015 at 12:53 AM.
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Old 05-23-2015, 06:34 PM   #236
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Another replication attempt for your bookmarks: https://hackaday.io/project/5596-em-drive

Of note is that these people will work at 24GHz.
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Old 05-23-2015, 06:55 PM   #237
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Quote:
Originally Posted by kamaz View Post
 Of note is that these people will work at 24GHz.
Not sure if the wavelength is really important except in the scale of the device, since the size and the wavelength have to be fine-tuned.

But 24 GHz (1.2 cm band) is something amateurs can easily use with little legal trouble and little problems to organize wave generators, since it is a common frequency for radio amateurs.
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Old 05-26-2015, 05:21 PM   #238
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Alternative theory of operation: http://physicsfromtheedge.blogspot.c...ce-motion.html
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Old 05-26-2015, 05:40 PM   #239
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Quote:
Originally Posted by kamaz View Post
I somehow still like the hypothesis more that the noise of this device is scaring the invisible pink unicorns away on one side of the thruster and thus produces a local unicorn vacuum.
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Old 05-26-2015, 08:06 PM   #240
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Quote:
Originally Posted by Urwumpe View Post
 I somehow still like the hypothesis more that the noise of this device is scaring the invisible pink unicorns away on one side of the thruster and thus produces a local unicorn vacuum.
Yes, because physics as we now it today must be final.
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