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PICList Thread
'Movement sliding on ice etc'
1997\01\10@160431 by Mike

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>For example: How would you detect that the rear end of a car has
> started to slide sideways (on ice) ?  The front wheels are still
> pointed forward (you have not started to turn the wheel to
> compensate).  There are no walls around to bounce a signal off of.
> Assume you have your breaks locked up and therefore cannot use
> comparison of wheel velocities.  Assume also, that you cannot attach
> any sensors to the ground, wheels or be manually activated.  Remember
> that most movement sensors would not be able to tell the difference
> between laterally sliding on ice and a sharp turn.  An optical sensor
> would detect ice but not that your sliding on it.
>
>How would you do it??
>
>Gene

Accelerometer

Gyroscope

Fibre optic loop

Anybody care to add the 'etc'

And you'd need a processor to keep track of:-

1.      Change in direction
2.      Rate of change of direction

And it would need an appropriate decision mechanism, a model of the vehicle's
mass/speed etc would be a realistic starting point.

Rgds


Mike

Socrates once gave the advice to "by all means get married... If you
get a good wife you will become happy, if you get a bad one you will
become a philosopher."

Become an Engineer and avoid making this problematic decision.

1997\01\10@172356 by Brooke

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> >For example: How would you detect that the rear end of a car has
> > started to slide sideways (on ice) ?  The front wheels are still
> > pointed forward (you have not started to turn the wheel to
> > compensate).  There are no walls around to bounce a signal off of.
> > Assume you have your breaks locked up and therefore cannot use
> > comparison of wheel velocities.  Assume also, that you cannot attach
> > any sensors to the ground, wheels or be manually activated.  Remember
> > that most movement sensors would not be able to tell the difference
> > between laterally sliding on ice and a sharp turn.  An optical sensor
> > would detect ice but not that your sliding on it.
> >
> >How would you do it??
> >
> >Gene

I think that the radial velocity as a vehicle goes around any turn is
zero.
(as if there were a string from the vehicle to the center point of the
turn)
A microwave doppler radar could be used to detect radial (side looking)
velocity.  The radar would see through the ice and still work fine.

Have Fun,
Brooke
spam_OUTbrookeTakeThisOuTspampacific.net

1997\01\11@072805 by rgreason

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What is a fibre optic loop - Just interested.

Roy...

{Quote hidden}

------------------------------
Roy Greason....
http://www.jumper.mcc.ac.uk/~royg
------------------------------

1997\01\11@080755 by fastfwd

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Roy Greason <.....rgreasonKILLspamspam@spam@colours.demon.co.uk> wrote:

> What is a fibre optic loop - Just interested.

Roy:

In this context, it's a gyroscope.  The usual name for it is "Ring
Laser Gyro".

It works by splitting a laser beam into two beams, each of which
travels through a fiber optic loop... The beams follow the same
path, but in opposite directions.

The beams are combined after their trip around the loop.  If the gyro
isn't rotating, each beam will have traveled the same distance and
they'll still be in phase at the output detector.  If the gyro IS
rotating, the beams will have traveled DIFFERNT distances and they'll
be out of phase when they're recombined.

Since the amplitude of the output signal is related to the degree of
phase shift, and since the phase shift is related to the rotation
rate, you can calculate rotation rate by carefully measuring the
amplitude of the output signal.

The primary advantage of laser gyros over mechanical gyros is that
lasers don't drift over time... This makes them suitable for use in
aircraft, etc.

For high-precision applications where the total flight time is
relatively short (like, for instance, guiding intercontinental
ballistic missiles), laser gyros are generally NOT used...
Mechanical gyros are preferred because they're more accurate.

At least, they WERE preferred; I don't know whether any recent
advances have been made in laser-gyro technology.

-Andy

=== Andrew Warren - fastfwdspamKILLspamix.netcom.com                 ===
=== Fast Forward Engineering - Vista, California          ===
===                                                       ===
=== Custodian of the PICLIST Fund -- For more info, see:  ===
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1997\01\11@150802 by Hamilton Feltman

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At 05:02 AM 1/11/97 +0800, you wrote:
>>For example: How would you detect that the rear end of a car has
>> started to slide sideways (on ice) ?  The front wheels are still
>> pointed forward (you have not started to turn the wheel to
>> compensate).  There are no walls around to bounce a signal off of.
>> Assume you have your breaks locked up and therefore cannot use
>> comparison of wheel velocities.  Assume also, that you cannot attach
>> any sensors to the ground, wheels or be manually activated.  Remember
>> that most movement sensors would not be able to tell the difference
>> between laterally sliding on ice and a sharp turn.  An optical sensor
>> would detect ice but not that your sliding on it.
>>
>>How would you do it??
>>
>>Gene

       How about those postioning satellites?  With a sensor on the front
and one on the rear of the car the heading (and speed) can be determined,
as well as a host of other info not pertaining to (such as angle of incline.)
I think they are very accurate, at least the military type is so I hear.
But can anyone just `use' these signals for anything they want? Probably
not. For manufacture anyway <g>

       P.s. Why do you ask?



\_\  _ __ o \ \_ _  _      __  _ \    __  _   __
\ \(_\\\\ \ \ \ \_\\ ) @  \__ \  \ . \__ \_\ \\\
http://www.slip.net/~ham         .....hamiltonKILLspamspam.....crl.com

1997\01\11@174000 by Mark A. Corio

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In a message dated 97-01-11 08:08:36 EST, you write:

>The primary advantage of laser gyros over mechanical gyros is that
>lasers don't drift over time... This makes them suitable for use in
>aircraft, etc.

I do not know much about mechanical (or laser) gyros but lasers DO drift with
time, temperature and most other environmental conditions.  To what
degree?.....relative to the application.  A small drift for one application
might be massive for another.  Lasers drift not only in output power
amplitude.  They also drift in wavelength.  Semiconductor lasers (laser
diodes) also drift in their threshold current level, divergence, astigmatism
and even their polarization ratio.  I spent much time investigating these
things for a previous employer whose application was sensitive to all these.
Many applications of laser diodes are digital with a wide margin between 0
and 1 with respect to these conditions so it is possible to ignore most
effects caused by environment.

Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY  14624
Tel:  (716) 328-5850 --- Fax:  (716) 328-1144
http://www.frontiernet.net/~rmi/

***** Designing Electronics For Research & Industry *****

1997\01\11@181605 by Mark A. Corio

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In a message dated 97-01-11 17:47:35 EST, you write:

>        How about those postioning satellites?  With a sensor on the front
>and one on the rear of the car the heading (and speed) can be determined,
>as well as a host of other info not pertaining to (such as angle of
incline.)
>I think they are very accurate, at least the military type is so I hear.
>But can anyone just `use' these signals for anything they want? Probably
>not. For manufacture anyway <g>
>
>

Yes, anyone can use the GPS (global positioning system) signals.  There are
some encrypted military channels that allow the military to correct for
errors intentionally introduced to reduce the resolution of the system for
non-military uses.  Even the military channels provide resolution on the
order of a meter.  A special application method can be used to get ~ 1 cm
resolution but this requires a fixed reciever in a known location nearby to
decode its position from the GPS signals and, knowing where it is, broadcast
a correction factor(s) to nearby recievers.

Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY  14624
Tel:  (716) 328-5850 --- Fax:  (716) 328-1144
http://www.frontiernet.net/~rmi/

***** Designing Electronics For Research & Industry *****

1997\01\11@183922 by fastfwd

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I wrote:

> > The primary advantage of laser gyros over mechanical gyros is
> > that lasers don't drift over time... This makes them suitable
> > for use in aircraft, etc.

and Mark A. Corio <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU> replied

> I do not know much about mechanical (or laser) gyros but lasers DO
> drift with time, temperature and most other environmental
> conditions.

Yeah, ok... After I wrote that, I KNEW that I should have rephrased
it.

What I should have said is, "Laser gyros don't drift AS MUCH as
mechanical gyros, if everything else (including cost and size)
remains equal.  If cost and packaging is no issue, mechanical gyros
perform better than laser gyros."

Other advantages are that laser gyros require no startup time and
consume much less power than mechanical gyros.

Also, before anyone points out the OTHER minor inaccuracy in my last
message... Yes, I know that what I described was an IFOG
(Interferometric Fiber Optoc Gyro), and that IFOG isn't a synonym
for RLG (Ring Laser Gyro).

Just found out, by the way, that there are new technologies that
improve upon certain aspects of the RLG and IFOG... RFOGs (Resonance
Fiber Optic Gyros), for instance, have significant cost, size, and
power advantages over the RLG, IFOG, and mechanical gyros.

-Andy

Andrew Warren - fastfwdspamspam_OUTix.netcom.com
Fast Forward Engineering, Vista, California
http://www.geocities.com/SiliconValley/2499

1997\01\13@044650 by Keith Dowsett

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>
>I think that the radial velocity as a vehicle goes around any turn is
>zero.
>(as if there were a string from the vehicle to the center point of the
>turn)

Hmm. Don't think so. Most road curves are not arcs of circles.

>A microwave doppler radar could be used to detect radial (side looking)
>velocity.  The radar would see through the ice and still work fine.

This is getting some high cost solutions. How about a (slightly damped)
magnetic pendulum and a couple of hall effect sensors. A PIC could monitor
the pendulum position and calculate acceleration from it. Add a simple
steering wheel sensor and look for big deviations between chosen direction
(from steering) and actual direction (from accelerometer).

Keith.
==========================================================
Keith Dowsett         "Variables won't; constants aren't."

E-mail: @spam@kdowsettKILLspamspamrpms.ac.uk
WWW:    http://kd.rpms.ac.uk/index.html

1997\01\13@124702 by Gerald Morrison

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>
> Yes, anyone can use the GPS (global positioning system) signals.  There
are
> some encrypted military channels that allow the military to correct for
> errors intentionally introduced to reduce the resolution of the system
for
> non-military uses.  Even the military channels provide resolution on the
> order of a meter.  A special application method can be used to get ~ 1 cm
> resolution but this requires a fixed reciever in a known location nearby
to
> decode its position from the GPS signals and, knowing where it is,
broadcast
{Quote hidden}

It's called Differential GPS.
-It's expensive
-It's not real time
-It requires a lot of computation
-It requires specific knowledge of the ground station location

No GPS application would have the accuracy required.  Furthermore, GPS is
not real time (not to good for correcting a slide which need real time
feedback).


Gerald Morrison
Smart Technologies Inc.

1997\01\14@120423 by Brooke

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Gerald Morrison wrote:
>
..........
> It's called Differential GPS.
> -It's expensive
> -It's not real time
> -It requires a lot of computation
> -It requires specific knowledge of the ground station location
>
> No GPS application would have the accuracy required.  Furthermore, GPS is
> not real time (not to good for correcting a slide which need real time
> feedback).

Not quite correct.  Differential GPS (DGPS) commonly reffers to the
transmission of corrections by the U.S. Coast Guard (and others) in
real time.  It is based on the CA code signal and has a 2 sigma accuracy
of about 10 meters.  DGPS beacon receivers start at $500.

Postprocessing is the term applied to recording data in the field and at
a base station of known location at the same time and later combining
the
data to determine very accuratley (down to 2 mm) the field locations.
High accuracy postprocessing requires recording a variable called the
carrier phase.

There are systems on the market and more under development that
broadcast
carrier phase based corrections to allow real time kinematic
differential
corrections.  For example see the current issue of "NAVIGATION - Journal
of
the Institute of Navigation" Vol.43 No. 3 page 295. "High-Rate Precise
Real-Time Positioning Using Differential Carrier Phase"

Have Fun,
Brooke

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