[DeTomaso] Speedhut versus Autometer gauges help

gow2 at rc-tech.net gow2 at rc-tech.net
Sun Jan 20 16:49:19 EST 2013


Good Post Denny!



> Hi Gary,
>
> This is correct. It's now possible achieve 2--4 inch pass-by-pass accuracy
> through a field (repeatable). And all using commercially available GPS
> receivers. However, the cost is in the engineering that goes into the
> auto-steer control system, touch panel display, and the software to
> process
> GPS signals from multiple antennas to also provide orientation (i.e. roll,
> pitch, and yaw). The cost of the GPS unit is not what drives up the cost.
> I
> used to consulted for Norvariant from 1996 until 2004 (formally
> IntegriNautics) and went to school with the founders while at Stanford.
>
>   http://www.gpsfarm.com/Products/OnTrac2/tabid/112/Default.aspx
>   http://www.gpsfarm.com/Technology/PrecisionPosition/tabid/169/Default.aspx
>
> http://www.gpsfarm.com/Technology/AdvancedControlSystem/tabid/170/Default.aspx
>   http://www.gpsfarm.com/About/tabid/60/Default.aspx
>
> The current company is focused entirely on GPS farming and has removed
> almost all reference to the original company named IntegriNautics from
> their website. IntegriNautics patented the idea of using multiple antennas
> and calculating the phase angle of the two RF carrier frequencies (L1 and
> L2) for GPS as the signal passes over each antenna. With this technology
> they were able to achieve real-time centimeter-level accuracy plus
> orientation to a fraction of a degree by determining the position of
> multiple antennas. Here's the key patent describing this.
>
>
> http://www.sumobrain.com/patents/wipo/Multiple-antenna-multi-frequency-measurement/WO2003044556.html
>
> It is called Carrier-Phase Differential GPS. This was used in aircraft in
> the 1990s for auto-landing tests, including over 100 hands-free landings
> of
> a United 737. Note, this was before the government stopped degrading the
> accuracy of the civilian GPS signal. Searching the Internet about all I
> can
> find about this is on the website for the Gravity Probe-B NASA mission to
> test Einstein's General Theory of Relativity.
>
>   http://einstein.stanford.edu/highlights/hl_033106.html
>
> Search for Clark Cohen in this page and you can read the early history of
> the development of this technology. It was used on the the Gravity Probe
> spacecraft mission in a polar orbit 400 miles above the earth. Clark's
> Ph.D. thesis is
> here<http://waas.stanford.edu/~wwu/papers/gps/PDF/Thesis/ClarkCohenThesis92.pdf>.
> As an aside, the science gyros on-board Gravity Probe-B are the roundest
> man-made objects ever and are a million times more accurate than the best
> we have, which are those on the Hubble space telescope or possibly those
> on
> our nuclear powered subs. I consulted for Gravity Probe-B for 10 years and
> it was one of the most amazing projects I've worked on.
>
> As others have said there is no speed limitation on receivers using the
> civilian channel of the GPS signal. Now days the accuracy of the civilian
> and military signals are the same. However the military signal is
> broadcast
> on two carrier frequencies, which can be used to reduce the errors
> introduced by the ionosphere.
>
>   http://www.gps.gov/systems/gps/performance/accuracy/
>
> It's used for aircraft and spacecraft all the time. The primary things
> that
> affect the accuracy of a GPS based speedometer are the view of the sky for
> satellites, multi-path signals from bouncing off things like buildings in
> a
> city or canyon walls, location of the antenna, the number of channels in
> the GPS receiver, and the sample rate of the GPS position by the
> speedometer. Assuming good visibility of the sky and minimal multi-path,
> the sample rate of the signal will have the largest impact on accuracy and
> lag in the display. If the speedometer is only sampling every few seconds
> the speed measurement will lag quite a bit. There will be some low-pass
> filtering of the difference in the position measurements in order to keep
> the reading from jumping back and forth due to the errors in the GPS
> position measurement, which can be as much as +-10 feet without some type
> of differential reference signal. So I would expect a good speedometer to
> be sampling at least 1 times per second, which is the rate that nearly all
> smartphones can do. Faster sampling is better, so 5 to 10 times per second
> would be better. I've read some rumors that some of the new smartphones
> coming out will support 5 Hz GPS sampling.
>
> However, with additional sensors this could be improved quite a bit. All
> modern smartphones have accelerometers built into them. So if you are
> driving down a smooth flat road at a constant speed the accelerometers
> will
> show no change even though the GPS position may say that you jumped 1 foot
> to the right between the last measurement and this one. The accelerometer
> data can smooth all of this out. And if you are turning or accelerating
> the
> accelerometers will also tell you that. Not only that, the accelerometer
> data can carry you through a brief loss of GPS signal. So a great GPS
> speedometer would have a fast sample rate of the GPS signal as well as
> accelerometers.
>
> Cheers,
>
> Denny
> ----
>
>
> On Fri, Jan 18, 2013 at 3:09 PM, Gray Gregory <rgg at gregorycook.com> wrote:
>
>> The GPS units used to run the auto steering in big farm tractors are
>> very
>> accurate (to about 4" or less) but they do cost considerably more than
>> automotive units.
>>
>> Gray
>>
>> -----Original Message-----
>> From: detomaso-bounces at poca.com [mailto:detomaso-bounces at poca.com] On
>> Behalf Of gow2 at rc-tech.net
>> Sent: Friday, January 18, 2013 4:23 PM
>> To: Boyd Casey
>> Cc: Charles McCall; detomaso at poca.com; michael at michaelshortt.com; Ed
>> Mendez
>> Subject: Re: [DeTomaso] Speedhut versus Autometer gauges help
>>
>> There are a couple different reasons for Aircraft GPS being more
>> expensive. One is they typically require more satellites to confirm
>> navigation. They also notify you of accepted navigation levels because
>> of
>> available satellites and due to messages satellite give out about their
>> integrity.
>>
>> Anything not aviation just takes the signal they get and say here it is.
>>
>> Also, Aviation is certified to a high degree of scrutiny and lower
>> production then other GPS marketed for the general use. It means a high
>> price but not necessarily a better unit.
>>
>> GPS tracking is not that hard. Cheap devices doing computations will be
>> no
>> less accurate then expensive devices. They all read the same signal.
>>
>> As far as the sat moving, it is not about the movement of the sat
>> refference. That is minor or slow to the point it has no effect on the
>> accuracy of speed; only that the map is off.
>>
>>
>>
>>
>> > As  I said , I knew  a certain degree a certain degree of locational
>> > information was intentionally erronious. The speed information may
>> > have been urban legend or perhaps the unit in question was not  new
>> > enough or the GPS  being used was  a portable aviation unit. They make
>> > portable pilot  GPS thigh mounted  units that need to be able to meet
>> > the speed and altitude limits of aircraft the are intended to be used
>> > in. I believe the articcle I read refered to Automotive GPS units. The
>> > air craftgps devices are considerabelly more expensive. I picked up my
>> > last Tom Tom for $99 bucks. The gist of this article was "build a
>> > cruise  missle for  $1000 (or something along those lines.  I first
>> > read this article years ago and the last thing I remember about the
>> > whole subject the Government ( New Zealand or Austrailia) put the
>> > Kalashnikov on the whole thing. I believe they approached the author
>> > and warned him about " actions that were contrary to the "national
>> > security interests" and or the risk of being kidnapped by Al Queda or
>> > Iran etc. So that was that. Just now I searched and found this link.
>> >
>> > http://www.aardvark.co.nz/pjet/cruise.shtml
>> >
>> > On Friday, January 18, 2013, Ed Mendez wrote:
>> >
>> >> I appreciate the feedback on these gauges. The seam better than
>> >> Autometer then. So thanks.
>> >>
>> >> Can someone tell me the size of the factory tach and speed? 5" 4",
>> etc.
>> >>
>> >> Ed
>> >>
>> >>
>> >> On 18/01/2013, at 12:30 PM, Roland Jaeckel <pantera874 at t-online.de>
>> >> wrote:
>> >>
>> >> > Brake down and speed up and see then, how fast it follows. We tried
>> >> > it
>> >> on track and it couldn't show the speed at any time right.
>> >> > In town, the same situation.
>> >> >
>> >> > --------------------------------------------------
>> >> > From: "Charles McCall" <charlesmccall at gmail.com>
>> >> > Sent: Friday, January 18, 2013 8:23 PM
>> >> > To: "'Boyd Casey'" <boyd411 at gmail.com>; "'Roland Jaeckel'" <
>> >> pantera874 at t-online.de>
>> >> > Cc: <michael at michaelshortt.com>; "'Ed Mendez'" <edducati at mac.com>;
>> >> > <
>> >> detomaso at poca.com>
>> >> > Subject: RE: [DeTomaso] Speedhut versus Autometer gauges help
>> >> >
>> >> >> I turned an early-generation GPS receiver on once on a commercial
>> >> airplane
>> >> >> flight and it read perfectly well at 600mph so I think that the
>> >> maximum
>> >> >> speed thing is urban legend.
>> >> >>
>> >> >> The rest is true - a certain amount of error is built in for
>> >> >> security reasons. But I think that is more related to exact
>> >> >> location than your
>> >> speed.
>> >> >>
>> >> >>
>> >> >> On an open highway with no tall buildings, I get a fairly stable
>> >> >> gps
>> >> speed
>> >> >> on my TomTom and believe it to be more accurate than the stock
>> >> >> speedo
>> >> >>
>> >> >> Charles McCall
>> >> >> Raising Pantera Awareness Across Europe
>> >> >> 1985 DeTomaso Pantera #9375
>> >> >> http://www.poca.com/index.php/gallery/?g2_itemId=2323
>> >> >>
>> >> >>
>> >> >> -----Original Message-----
>> >> >> From: detomaso-bounces at poca.com [mailto:detomaso-bounces at poca.com]
>> >> >> On
>> >> Behalf
>> >> >> Of Boyd Casey
>> >> >> Sent: viernes, 18 de enero de 2013 20:16
>> >> >> To: Roland Jaeckel
>> >> >> Cc: michael at michaelshortt.com; Ed Mendez; detomaso at poca.com
>> >> >> Subject: Re: [DeTomaso] Speedhut versus Autometer gauges help
>> >> >>
>> >> >> GPS units have the ability to be incredibly accurate, that's down
>> >> >> to millimeters and micro seconds. The problem is this these levels
>> >> >> of
>> >> accuracy
>> >> >> are limited to miltary GPS units. Civilian GPS units are forced by
>> >> legal
>> >> >> statute to build in varying degrees of error. The governments that
>> >> enforce
>> >> >> theses regulations are trying to prevent GPS units from being used
>> >> >> by terrorist groups .
>> >> >> I don't know the particulars but I was told that GPS units
>> >> >> designed
>> >> for
>> >> >> automotive or marine use are also set up so they can't be used in
>> >> anything
>> >> >> traveling over a particular speed ( like 200 mph). This is
>> >> >> supposed
>> >> to
>> >> >> prevent their use in a home made cruise missel . A few year ago a
>> >> >> guy
>> >> in
>> >> >> New Zeland was offering plans on popular mechanics  to build a
>> >> >> cruise missel power erred by a ram jet that was supposed to be
>> >> >> able to be constructed with all "off the shelf components,GPS,
>> computer, etc"
>> >> With
>> >> a
>> >> >> substantial range and a high speed ( like 500 mph).
>> >> >>
>> >> >> So you can blame all the errors in GPS  on the government and the
>> >> >> terrorists. On a brighter note I had heard that the government
>> >> >> had recently lowered  the required degree of error built in on GPS
>> units.
>> >> >>
>> >> >> Boyd
>> >> >>
>> >> >>
>> >> >> On Friday, January 18, 2013, Roland Jaeckel wrote:
>> >> >>
>> >> >>> In town, they are zero accurate. If they don't have contact to
>> >> >>> all satelites, they can't notice, that youre driving thrue a
>> turn.
>> >> >>> Whatch for it in town and anywhere while changing speed quickly.
>> >> They
>> >> >> can't
>> >> >>> follow as quick as a convetionel speedo can. They work for a
>> >> >>> boat,
>> >> but
>> >> >> that
>> >> >>> is way slower in changing speeds.
>> >> >
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