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Re: Using many cheap accelerometers to reduce error

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The same reason that a mil-spec part had additional testing done on it.  
Cost.   higher class chips cost more, but not always due to hard  
internal differences so much as exceptional performance compared to the  
rest of the lot.

  Intel cpus still got sold when they exhibited too much heat ran at  
speced rate.  Ran slower.  Tag it with a different name, and sell it as  
a slower version.  The 486's that had failed math cos still got sold.
Intel die issues.  Have to keep to a minimum the number of failed units  
on a single platter.

Re: Using many cheap accelerometers to reduce error
wrote:

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sqrt(1000) is only 32. I'd expect the ring gyro to be vastly better
than a cheap MEMS or some such.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Using many cheap accelerometers to reduce error
On Saturday, February 9, 2019 at 6:13:07 PM UTC-5, John Larkin wrote:
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What if they charge more for the MEMS?  Does that make it more accurate?  

Rick C.  

Re: Using many cheap accelerometers to reduce error
snipped-for-privacy@gmail.com wrote in

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There are some pretty damned good MEMS based accelerometers out  
there.

  All of your basic quad rotor craft use pretty good 'cheap' models,  
so the high end is even more resolved.

Re: Using many cheap accelerometers to reduce error
On Sunday, February 10, 2019 at 1:13:07 AM UTC+2, John Larkin wrote:
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OK I did the sums. Based on the random walk of a laser ring gyro (0.0035 deg/sqrt-hour) and that of a MEMS accelerometer (2.25 deg/sqrt-hour) [1], you need about 400k MEMS accelerometers to approach the accuracy of a laser ring gyro.

It sounds like a lot of components to solder together but if done in a chip fab,  it should be possible.  

Is it possible to make a commercial accelerometer with no export restrictions by using such an array? Or will ITAR or the like be slapped on such a device once its accuracy is published in a brochure?

Refs:
[1] Honeywell GG1320AN Digital Laser Gyro brochure
[2] Error and Performance Analysis of MEMS-based Inertial Sensors with a Low-Cost GPS Receiver. Park, M & Gao, Y. [2008] Sensors Vol 8

Re: Using many cheap accelerometers to reduce error

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  What makes you think they need to be 'together'?  Simply on the  
same superstructure should be enough.
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  Is it possible to feesibly make such an array, cost, logistics,  
etc. at all?

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  ITAR restricts YOU the maker long before you go publishing product  
performance numbers.  If you make certain items, you 'learn' the  
restrictions (long) before you get past single proto stage.
  
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Perhaps they are an order of magnitude better since 2008.  The gear  
they based their numbers on was perhaps even older than that.

Re: Using many cheap accelerometers to reduce error
On Sunday, February 10, 2019 at 8:15:10 AM UTC+2, DecadentLinux...@decadenc
e.org wrote:
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Incorrect. On the same superstructure there will be additional structural v
ibrations whose amplitude and frequency are position-dependent. While these
 vibrations do not result in a net spatial or angular translation (you woul
d hope so!) for the math to work the accelerometers have to be at the same  
location, the closer the better, sampling the same thing.

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Within a chip yes.

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The accuracy is good enough, especially if the gyros are only used in porti
ons of the journey where other sensors (e.g. GPS) are unavailable, such as  
indoors or underground.

Re: Using many cheap accelerometers to reduce error
On 2/10/2019 12:35 AM, JS wrote:
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Which is why he is known as AlwaysWrong.

Re: Using many cheap accelerometers to reduce error
On Monday, February 11, 2019 at 9:43:30 AM UTC+11, John S wrote:
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dence.org wrote:
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al vibrations whose amplitude and frequency are position-dependent. While t
hese vibrations do not result in a net spatial or angular translation (you  
would hope so!) for the math to work the accelerometers have to be at the s
ame location, the closer the better, sampling the same thing.
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Not true. DecadentLinuxUserNumeroUno is called AlwaysWrong by krw because h
e's one of the many people who disagree with krw.

DLUNU can be irritating, and the name AlwaysWrong gets thrown at him from t
ime to time by other people when he's gotten more irritating than usual - I
've done it - but DLUNU is right some of the time, and more frequently righ
t than krw.

He's done some interesting stuff, but he's almost as likely to fly off the  
handle as Phil Allison.

--  
Bill Sloman, sydney

Re: Using many cheap accelerometers to reduce error
On Sunday, February 10, 2019 at 1:15:10 AM UTC-5, DecadentLinux...@decadenc
e.org wrote:
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Perhaps you are saying this in a tongue in cheek way, but ITAR is one of th
ose things where you are expected to know your device is restricted without
 anyone in the government telling you.  Not only are you required to not se
ll it to the wrong people, but you are supposed to know that the people you
 sell it to won't sell it to the wrong people.  

Rick C.

Re: Using many cheap accelerometers to reduce error

  MEMs have come a long way over the years.

  FOG and MEMS compete with ring laser gyros in many applications  
because at certain points increased accuracy yields no gain in  
performance for that particular application.

<https://www.analog.com/en/technical-articles/the-battle-between-mems-
and-fogs-for-precision-guidance.html>

Re: Using many cheap accelerometers to reduce error
snipped-for-privacy@decadence.org wrote in

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me

  Found a lot of good info in this pdf about position  
tagging/tracking/placement science.


<https://www.analog.com/media/en/technical-documentation/data-
sheets/ADIS16488A.pdf>

Re: Using many cheap accelerometers to reduce error
On 10/02/2019 05:58, JS wrote:
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It might be interesting to try out say 16 to see how much of an  
improvement is obtained and how much of it is systematic error.

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A 10 fold performance improvement with 100 or 128 might be worthwhile if  
they are cheap enough to fabricate in bulk.


--  
Regards,
Martin Brown

Re: Using many cheap accelerometers to reduce error
On Sunday, February 10, 2019 at 4:16:24 AM UTC-5, Martin Brown wrote:
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The problem is the square root relationship.  That means you need N^2 more units to get an N factor improvement which means a *lot* more units.  

Rick C.  

Re: Using many cheap accelerometers to reduce error
On 10/02/2019 09:16, Martin Brown wrote:
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A UK seismometer company did (does?) just this, 16 MEMS accelerometers  
per axis.  I don't know what the improvement is, but I'm certain they'd  
lie about it knowing the customer couldn't check.  [That's why I only  
stayed there a few months, shocking quality and shocking performance  
exaggeration.]

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Cheers
--  
Clive

Re: Using many cheap accelerometers to reduce error
wrote:

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If the MEMS parts use vibrating cantilevers, they would want to sync
up. I don't know if that is good or bad.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Using many cheap accelerometers to reduce error
On Sunday, February 10, 2019 at 10:57:41 AM UTC-5, John Larkin wrote:
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They might "want" to sync up, but I'm not sure they would.  If the platform has rotational acceleration there would be a difference in the acceleration on each device depending on it's distance from the center.  That would keep them out of sync.  

Rick C.

Re: Using many cheap accelerometers to reduce error
snipped-for-privacy@gmail.com wrote in

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  If the 'platform' it was mounted to was 'known' (by the software),  
the positions and differences from the center reference of any arc  
like motion of the platform would be part of it.

 Does anyone remember the guy whom all on his own developed little  
quad rotor 'birds' that would all act together in a swarm fashion?
He showed it off in an ice rink or such and they were extremely  
controllable and all knew exactly where they were in reference to  
each other.

  Pretty sure DARPA snatched him up.  They wanted his software and  
the algos he used.

Re: Using many cheap accelerometers to reduce error
On Sunday, February 10, 2019 at 6:55:35 PM UTC+2, DecadentLinux...@decadenc
e.org wrote:
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It is not just the bulk motion of the body which you have to take into acco
unt, but also all the structural vibrations and their harmonics if you want
 to do averaging of accelerometer values over a distributed space.  

For example, if you have three arrays of accelerometers on the nose, wing r
oot and tail, all three will experience and report different accelerations  
if the drone is buffeted by wind and its wings experience a momentary boost
 in lift. Thing is you don't even know what the wind pressure-space-time di
stribution is exactly so you can't account for it.  

It would take a supercomputing cluster to do a real-time dynamic analysis o
f all the accelerations from bulk + vibrational motion in your platform, ev
en IF you knew to a high degree of accuracy what all the forces acting on y
our platform are.

The very act of trying to correct for systematic errors in a distributed ac
celerometer array introduces new errors in terms of the accuracy of your ma
thematical models.

But your idea of a spatially distributed sensor network for navigation soun
ds interesting. Migratory birds for example are fascinating because of thei
r ability to fly intercontinentally and land in their previous destination  
last year, with great accuracy and no trial-and-error. I wonder if one bird
 would get lost whereas as the flock size increases, their likelihood of ge
tting lost decreases?

Re: Using many cheap accelerometers to reduce error
On Sunday, February 10, 2019 at 6:28:43 PM UTC+2, snipped-for-privacy@gmail.com w
rote:
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ample size), does having many accelerometers and then averaging their outpu
t therefore reduce their overall error?
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ers rather than one expensive one like a laser ring gyro?
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35 deg/sqrt-hour) and that of a MEMS accelerometer (2.25 deg/sqrt-hour) [1]
, you need about 400k MEMS accelerometers to approach the accuracy of a las
er ring gyro.
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 chip fab,  it should be possible.  
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ictions by using such an array? Or will ITAR or the like be slapped on such
 a device once its accuracy is published in a brochure?
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 a Low-Cost GPS Receiver. Park, M & Gao, Y. [2008] Sensors Vol 8
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rm has rotational acceleration there would be a difference in the accelerat
ion on each device depending on it's distance from the center.  That would  
keep them out of sync.  
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If the body is rigid then s = r*theta, and you can take the time derivati
ve twice for velocity and then acceleration.

Problem is that real life is not so easy. A long slender missile body for e
xample would have very different transient accelerations at the tip and the
 tail. After you double integrate the accelerations to get displacements, o
ver a distance of say 10 - 1000km range, your CEP becomes wide as the side  
of a barn.

The best thing really for such applications is to either locate all your ch
eap accelerometers into a small, rigid box, or use a more niche but higher  
accuracy accelerometer like a RLG.

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