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#700 by MazonDel on 28 Mar, 2016 21:59
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Hey Monomorphic (and technically any other DIY builders),
I have, from an unfortunately failed robotics project, a surplus of crazy large capacity Li-Poly batteries. A link to the batteries at the end of the post. But they are 5000mah 8s batteries capable of some hefty discharge rates if desired. I would be willing to sell these batteries and their chargers at a (to be discussed if interested) discounted rate.
In September I shall be going to England for a year or so for grad school (woo!) and I find myself both in need of some extra funds, as well as in despair over the fate of these wonderful batteries (the only real equipment I have that can expire if left untouched).
So for those builders that are looking for a battery solution for your power system, feel free to send me a message.
http://www.hobbyking.com/hobbyking/store/__19158__Turnigy_nano_tech_5000mah_8S_65_130C_Lipo_Pack.html
-Mazon -
#701 by otlski on 29 Mar, 2016 03:04
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Been lurking for a while and now posting for the first time. I work for a company that makes air bearings as standalone test apparatus, and as components in our own very sensitive CG and MOI measurement equipment. I have personally made hundreds of air bearings as well as specify purchasing them from companies like Nelson. There is a lot to say on the subject, as well as how to design, build, and test sensitive force measurement mechanisms, and I hope to contribute in this small way. I wish i could follow the physics but I guess that's what you all do, so I'll try to learn.
First, as someone earlier posted, the weight of the sled can deflect the air tubes - naturally depending on wall thickness, length, and load. Whether it matters or not depends on the breakaway friction. In the case demonstrated in the video, this friction is not negligible otherwise the sled would have moved upon application of air. Dr Rodel is proper when he suggests measuring it. I would also add to use work-reversal as part of the this measurement and as part of all future thrust tests. The other three points made in the earlier post are also relevant.
Given that the level is not exacting (nor will it ever be) the non-parallelism will contribute on the same way. Natural undulations in the flatness of the tubes will give the bearing a preferred position. I am short on time but more will follow. Suffice to say that if this were a perfectly designed and executed bearing, all these error sources would corrupt the measurement as well as the previously mentioned flow impingement on the track. Make no mistake, the case presented is a very good try but we simply need to be aware of how sensitive these bearings can be.
For informational purposes, even a described "perfect bearing" is not frictionless. There are three terms that take turns dominating the friction calculation. They are: coulomb (breakaway of air molecules), viscous (due to orifice flow and sled motion), and turbulent (which is not viable at the sled but can be in the air gap depending on how large the fly height is. I will suppose that in the video's case none of this matters because all the other sources mentioned in earlier posts are dominating but are still not enough to overcome whatever is causing the friction. Here's a different thought, maybe it is actually performing quite well and he did not wait long enough for the sled to move on its own.
I hope to check/post each night but the next two weeks will be tough. till' tomorrow. -
#702 by meberbs on 29 Mar, 2016 04:34
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...
I will suppose that in the video's case none of this matters because all the other sources mentioned in earlier posts are dominating but are still not enough to overcome whatever is causing the friction. Here's a different thought, maybe it is actually performing quite well and he did not wait long enough for the sled to move on its own.
Good first post.
I just want to point out that I believe the drive is not active yet, and the video was just testing to make sure that it moved smoothly on the track from a gentle push. The lack of movement before the push indicates the the tracks are level to within the amount of friction present. (Although I would want to watch it sitting still for more than the short length of the video to be sure. I trust this is the case by Monomorphic's statements) -
#703 by SeeShells on 29 Mar, 2016 14:35
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Don't forget there's an interferometer going in later this week. That is what I will use to detect very small displacement.
This is from real world testing of air bearings. We used air bearings in our dicing machines on the X and Y axis. The carriages were floated on a flat aluminum bar and had sides and bottom bars that were adjustable to set the capture area.
They were extraordinary sensitive to any misalignment when allowed to just float free and a Z axis misalignment of just 25um on the air bearing beam of 800mm in length would cause the carriage to slowly move to the lowest end.
Dr. Rodal had a great suggestion in profiling the carriage by measuring the Z axis by using a screw... and the first post by otlski was brilliantly appropriate. Good post otlski and I look forward to hearing from you again.
Shell
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#704 by Monomorphic on 30 Mar, 2016 01:29
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First interferometer image. Major construction completed! It's way out of alignment/focus, but I can work on that tomorrow. The sorbothane pads arrived today. Those will be placed under each leg for vibration dampening.
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#705 by rfmwguy on 30 Mar, 2016 02:33
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Looking good jamie...nice visual. Congratulations on a first class diy experiment sofar.
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#706 by RotoSequence on 30 Mar, 2016 04:48
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First interferometer image. Major construction completed! It's way out of alignment/focus, but I can work on that tomorrow. The sorbothane pads arrived today. Those will be placed under each leg for vibration dampening.
Looking good! What equipment and time step interval will you be able to capture data with? Will the testing and observation equipment be shielded? -
#707 by Monomorphic on 30 Mar, 2016 12:51
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Looking good! What equipment and time step interval will you be able to capture data with? Will the testing and observation equipment be shielded?
For data capture I will probably use a camera (240 FPS) to watch the fringe patterns in real time as they move. As for shielding, the only component that may need shielding will be the camera. I do not think the laser needs to be shielded. -
#708 by TheTraveller on 30 Mar, 2016 15:53
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...The sorbothane pads arrived today. Those will be placed under each leg for vibration dampening.
Please note the following:
http://www.emdrive.com/EmDriveForceMeasurement.pdfQuoteA number of methods have been used in the UK, the US and China
to measure the forces produced by an EmDrive thruster.
In each successful case, the EmDrive force data has been superimposed
on an increasing or decreasing background force, generated by the test
equipment itself.
Indeed, in the UK when the background force changes were eliminated,
in an effort to improve force measurement resolution, no EmDrive force
was measured. -
#709 by Rodal on 30 Mar, 2016 16:00
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...The sorbothane pads arrived today. Those will be placed under each leg for vibration dampening.
Please note the following:
http://www.emdrive.com/EmDriveForceMeasurement.pdfQuoteA number of methods have been used in the UK, the US and China
to measure the forces produced by an EmDrive thruster.
In each successful case, the EmDrive force data has been superimposed
on an increasing or decreasing background force, generated by the test
equipment itself.
Indeed, in the UK when the background force changes were eliminated,
in an effort to improve force measurement resolution, no EmDrive force
was measured.
For an EM Drive in outer space there is no such thing as a "background force". Taking the following quotation literally:QuoteIndeed, in the UK when the background force changes were eliminated,
in an effort to improve force measurement resolution, no EmDrive force
was measured.
one would surmise that there is no "Shawyer EM Drive" force to be measured for a Shawyer EM Drive device in outer space, according to that quotation. Hence no outer space propulsion ?
There are no reported "UK measurements" of the EM Drive "force" in vacuum. Were measurements in vacuum ever attempted by SPR Ltd.? Or were they attempted and no force was measured by SPR Ltd. in vacuum? -
#710 by TheTraveller on 30 Mar, 2016 19:26
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...The sorbothane pads arrived today. Those will be placed under each leg for vibration dampening.
Please note the following:
http://www.emdrive.com/EmDriveForceMeasurement.pdfQuoteA number of methods have been used in the UK, the US and China
to measure the forces produced by an EmDrive thruster.
In each successful case, the EmDrive force data has been superimposed
on an increasing or decreasing background force, generated by the test
equipment itself.
Indeed, in the UK when the background force changes were eliminated,
in an effort to improve force measurement resolution, no EmDrive force
was measured.
For an EM Drive in outer space there is no such thing as a "background force". Taking the following quotation literally:QuoteIndeed, in the UK when the background force changes were eliminated,
in an effort to improve force measurement resolution, no EmDrive force
was measured.
one would surmise that there is no "Shawyer EM Drive" force to be measured for a Shawyer EM Drive device in outer space, according to that quotation. Hence no outer space propulsion ?
There are no reported "UK measurements" of the EM Drive "force" in vacuum. Were measurements in vacuum ever attempted by SPR Ltd.? Or were they attempted and no force was measured by SPR Ltd. in vacuum?
The advise is based on experimental data. Ignore it at your peril.
As for space, there will need to be some level of background vibration to trigger what Roger calls Motor mode. This has been discussed many times before.
Doesn't matter if you believe Roger's explination of why this is necessary or not. That this occurs is an experimental fact & ignoring it could result in no force generation. -
#711 by Monomorphic on 30 Mar, 2016 19:36
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there will need to be some level of background vibration to trigger what Roger calls Motor mode. This has been discussed many times before.
The sorbothane is to isolate the interferometer. I have noticed the high-voltage transformer hums when operating. This should supply plenty of background vibration. I'm even considering isolating the transformer, but can run tests without doing so. -
#712 by Rodal on 30 Mar, 2016 20:11
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THE PROBLEM WITH TEETER-TOTTER MEASUREMENTS TO MEASURE EM-DRIVE anomalous forces
QUESTION: What is one trying to measure ?
ANSWER : Propulsion forces from microNewtons to milliNewtons
These types of measurements for space propulsion are not unusual. For example, I am acquainted with such measurements at the Aeronautics and Astronautics Department of MIT, which has conducted research in electric/magnetic thrusters since at least the 1950's.
So, there is more than half-a-century of know-how on how to best measure such thrust at Universities engaging in Aerospace Engineering and at NASA, JPL, etc..
The consensus (at NASA, JPL, Aerospace Departments in major Universities) is that torsional methods: torsional balances or the Cavendish pendulum are the most appropriate measurements for micro-thruster measurements . (See: https://forum.nasaspaceflight.com/index.php?topic=39772.msg1508898#msg1508898 ).
Why is it that torsional methods like the Cavendish pendulum (first tested by Cavendish more than 200 years ago) have been found out to be the best, and teeter-totters are not ?
INDEPENDENCE OF THRUSTER'S MASS: a torsional balance rotational axis is parallel to the force of gravity direction, making its response independent of thruster mass. This is critical to measure thruster's that may be changing in mass during the test. (The EM Drive's mass may change for example, when the power source is located outside the testing device, or for other reasons). By contrast, the movement of a Teeter-Totter is obviously highly affected by a change in mass of a hanging EM-Drive at one end.
LOW ENVIRONMENTAL NOISE SENSITIVITY: by contrast, Teeter-Totters have much higher environmental noise sensitivity, including air convection, etc. This follows trivially from the equations of motion governing the Teeter-Totter motion.
MINIMUM SENSITIVITY TO THERMAL EXPANSION: by contrast, Teeter-Totters are highly affected by differential thermal expansion
HIGH MEASUREMENT SENSITIVITY : torsional methods are well characterized by the torsional stiffness. Hence, in steady state, the measured displacement (after the transient is damped) is simply x = F/k where k is the stiffness. The torsional stiffness is usually due to a metal's stiffness, metals used have a modulus of elasticity practically insensitive (from room temperature to a few hundred degrees above it or below it) to temperature. By contrast, the response of a perfect Teeter-Totter's steady-state force to a constant force is a velocity = Force/(damping constant). The damping is usually provided for example by a liquid whose damping constant is much more sensitive to temperature changes, and the force/damping constitutive relationship is not as simple as the force/displacement relationship for an elastic material like a metal and certainly not as well characterized. Moreover, some Teeter-Totter's that have been used for EM Drive experiments have additional moments of inertia that are not well characterized (acting to stabilize or stabilize the rotation) including the EM Drive itself, usually hanging from it. These additional moments of inertia results in a displacement x = F L/g where "L" is an effective length. This results in a changing (due to thermal expansion) moment of inertia and response.
RETURN TO ORIGINAL CONFIGURATION UPON UNLOADING: Torsional methods (relying on torsional stiffness) return to their original configuration when unloading, due to a well-characterized torsional stiffness of the metal torsional stiffness (an elastic material). This is not necessarily the case for Teeter-Totters. This is very important to properly characterize the response, for example to a step-force (constant force for a given amount of time, followed by unloading to zero).
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#713 by SeeShells on 30 Mar, 2016 20:15
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Also your carriage will be isolated from any direct contact of the beam by an air gap and provide additional isolation from the outside environment. Air bearing isolating is used extensively in industry to isolate vibration.there will need to be some level of background vibration to trigger what Roger calls Motor mode. This has been discussed many times before.
The sorbothane is to isolate the interferometer. I have noticed the high-voltage transformer hums when operating. This should supply plenty of background vibration. I'm even considering isolating the transformer, but can run tests without doing so.
As a matter of fact I'm waiting for delivery of car inner tubes that I'll be using on the bottom of my test bed legs. I'm just attaching a piece of plywood to the top of the tube that the test rig will set on and the bottom of the tube will sit on the floor. I can see my Great Pyrenees walking on the other side of the house through the laser target and these will isolate those outside vibrations.
Shell
added:http://london.ucdavis.edu/~reu/REU09/trips09.html
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#714 by rfmwguy on 30 Mar, 2016 20:48
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I admire the ideal test stand advice and concede that airtracks and teeter totters are less than ideal, but we might be getting ahead of ourselves. DIY test stands are certainly budget constrained, but believe what most DIY experimenters are striving for are personal Observational Results as opposed to a high-level institutional replication. In many cases, DIYers neither have the locale, equipment nor the budget; so my point is that any test stand that provides Observed results is useful.
Once the Observations are logged, DIYers have the ability to offer their devices to any lab that has the Cavendish or Torsion experiments (and vacuum chamber) for independent verification.
If a lab is not interested or wants to charge for the tests...too bad (from my perspective). -
#715 by SeeShells on 30 Mar, 2016 21:26
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I admire the ideal test stand advice and concede that airtracks and teeter totters are less than ideal, but we might be getting ahead of ourselves. DIY test stands are certainly budget constrained, but believe what most DIY experimenters are striving for are personal Observational Results as opposed to a high-level institutional replication. In many cases, DIYers neither have the locale, equipment nor the budget; so my point is that any test stand that provides Observed results is useful.
Once the Observations are logged, DIYers have the ability to offer their devices to any lab that has the Cavendish or Torsion experiments (and vacuum chamber) for independent verification.
If a lab is not interested or wants to charge for the tests...too bad (from my perspective).
My goal with constants is to eliminate as many error sources within my budget, to do less is to invite more criticism and provide a less validating test.
Shell
~25 Bucks.
http://www.ebay.com/itm/2-KR-14-15-INNER-TUBES-FITS-14-AND15-INCH-INNER-TUBE-Pair-of-2-Tubes-Heavy-Duty-/151064506376?hash=item232c257008:g:9YMAAOSwqxdTq6WA&vxp=mtr -
#716 by Rodal on 30 Mar, 2016 21:32
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My experience at MIT is that MIT students build their own instruments, many times with very low budgets.
For example, personally, from the time that I was a freshman, I was machining (under UROP: Undergraduate Research Opportunity Program at MIT) the nozzles for a research project with a hybrid rocket engine (nozzles machined from solid graphite, hybrid rocket solid was simply a "Lexan" polycarbonate thick cylinder). MIT had a huge number of lathes and other equipment to fabricate instruments and experiments. The MIT "mens et manus" philosophy is definitely not to go out and buy an expensive instrument, but instead to make your own scientific instrument, just as Cavendish designed his own instrument.
Concerning a budget, a torsional pendulum (a Cavendish pendulum) is not more expensive than any of the Teeter-Totter instruments featured in these threads by DIY.
For the reasons discussed here: https://forum.nasaspaceflight.com/index.php?topic=39772.msg1509734#msg1509734 such a torsional pendulum is a better instrument to measure micro-thrust of an electromagnetic thruster.
Actually the Cavendish pendulum fabricated by Brito, Marini and Galian in remote Argentina is cheaper, and requires an even lower budget. See how simple and low budget it is to make such a torsional pendulum:
This shows that it is incorrect to say that a Teeter-Totter is more inexpensive than a Cavendish torsional pendulum.
Such an experimental method was used by Brito, Marini and Galian to nullify a battery-powered "Mach Lorentz" electromagnetic propellant-less thruster:
Null Findings on Electromagnetic Inertia Thruster Experiments using a Torsion Pendulum
45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, 2 - 5 August 2009, Denver, Colorado
and by Marini and Galian in their peer-reviewed article in the AIAA Journal of Propulsion and Power:
Ricardo L. Marini and Eugenio S. Galian. "Torsion Pendulum Investigation of Electromagnetic Inertia Manipulation Thrusting", Journal of Propulsion and Power, Vol. 26, No. 6 (2010), pp. 1283-1290.
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#717 by Monomorphic on 30 Mar, 2016 21:42
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Some of the best thrust stands for microthrusters are tortion bars used with interferometers. This is similar to what I am going for. http://photonicassociates.com/ISBEP4-2.pdf
Tomorrow I get the aluminum support piece that runs along the top of the stand that the emdrive will hang from.
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#718 by MazonDel on 30 Mar, 2016 21:45
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As a matter of fact I'm waiting for delivery of car inner tubes that I'll be using on the bottom of my test bed legs. I'm just attaching a piece of plywood to the top of the tube that the test rig will set on and the bottom of the tube will sit on the floor. I can see my Great Pyrenees walking on the other side of the house through the laser target and these will isolate those outside vibrations.
Shell
That should work quite well. There was a story I read some time ago about a child (in middle/high school I believe) that wanted to make his own electron microscope. He placed his entire rig on something like 3-5 tires and this worked well enough for him to get the images he was looking for.
In fact, for him the hardest part was getting the piezo-electric components he needed cheaply enough. When he was visiting a nearby college that had a professional electron microscope, when the grad student who was operating it heard what he was missing, he opened up a drawer and gave the kid a handful of them! Perhaps not the most reliable of DIY funding sources, but results are what counts.
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#719 by Rodal on 30 Mar, 2016 21:46
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Moreover it does not follow that <<any test stand that provides Observed results is useful.>> (It may be useful if one carefully solve the equations of motion for the testing device and carefully analyzes the significance of what is measured).
As I discussed, Teeter-Totter instruments may provide false readings, as is known and documented, and as discussed here: https://forum.nasaspaceflight.com/index.php?topic=39772.msg1509734#msg1509734
It is noteworthy that, among DIY:
* Mulletron was the first DIY. Mulletron built a simple pendulum. No results reported.
* RFPlumber used a simple pendulum (not a torsional pendulum !) and obtained NULL results
See his published report: http://vixra.org/abs/1603.0153
* When Berca used a simple pendulum he also obtained NULL results.
Berca only obtained "results" when he hanged the EM Drive from one end of a teeter-totter beam and measured the movement of the opposite end with a scale.
* The lowest measured anomalous force were obtained by:
a) NASA Eagleworks using a torsional pendulum
b) Tajmar using a torsional pendulum
