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'[PIC]: LPS project'
2001\06\18@170856 by joan

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Hi, PicListers

Now that I have a rover that moves and is able to execute a motion
program, and I have a wonderful LCD terminal to play with, I need
to go one step forward and be able of onboard computing the position and
the orientation of my small monster.

I have thought on a LPS (that is, a Local Positionning System as
opposed to GPS). More specifically I am thinking on using three
ultrasound (or high freq. sound) beacons, all of them emitting
simultanously and periodically  a given signal and compute the
position and orientation of my rover by using the delay of the
signals when reaching two onboard microphones separated a known
distance (1 millisecond <=> 30 cms).

Do you think that this is feasable ? Has someone tried this before ?
Is it too late and I should go to sleep ?

I am somewhat affraid of developing such a project because I am much
more confident on digital electronics than in analog one, but I have
no better (and simpler) idea of getting the data I need.

Any idea will be appreciated

Best regards

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    Joan Ilari                 e-mail : spam_OUTjoanTakeThisOuTspamilari.org
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                                              -Blade Runner-
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2001\06\19@151731 by joan

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>  I have thought on a LPS (that is, a Local Positionning System as
>  opposed to GPS). More specifically I am thinking on using three
>  ultrasound (or high freq. sound) beacons, all of them emitting
>  simultanously and periodically  a given signal and compute the
>  position and orientation of my rover by using the delay of the
>  signals when reaching two onboard microphones separated a known
>  distance (1 millisecond <=> 30 cms).
>
>  Do you think that this is feasable ? Has someone tried this before ?
>  Is it too late and I should go to sleep ?

Some Piclisters have told me off-line that they thought that this was
feasible.
OK. I will trust them. Now, to start building a prototype I have only an
electret microphone, a 8 Ohm loudspeaker, a 555 and a 567 pll (and, of
course,
plenty of PICs !).

Somebody knows the typical (?) cutoff frequency of the microphone and the
loudspeaker ? This one does not seem to have mobile parts. Is it
piezoelectric ?
I am ashamed to admit that I bought both of them two weeks ago and I
don't know what I got for my money :-(. Anyway I think that perhaps the
easiest
thing to do is to emit differenet frequencies with the loudspeaker, get them
with
the micro and make some kind of Bode diagram of the set....

Somebody has done some kind of tone decoder with a 567 ? How long does it
take to
catch a given frequency ? Is this time always the same ? If it is not the
same,
the idea of sending a sound burst and computing distance through sound delay
won't be feasible...

As you can see, I have plenty of questions. If anybody could give me some
clue,
I would be grateful forever !

Cheers

Joan

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2001\06\20@094421 by Roman Black

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Joan Ilari wrote:
>
> >  I have thought on a LPS (that is, a Local Positionning System as
> >  opposed to GPS). More specifically I am thinking on using three
> >  ultrasound (or high freq. sound) beacons, all of them emitting
> >  simultanously and periodically  a given signal and compute the
> >  position and orientation of my rover by using the delay of the
> >  signals when reaching two onboard microphones separated a known
> >  distance (1 millisecond <=> 30 cms).


Hi Joan, you may be re-inventing the wheel. :o)
I also see potential problems with using sonic
beacons due to the high reflectivity of most
indoor surfaces.

Most robot labs are using infrared beacons, these
transmit a simple infrared code like a TV remote
does. The robot just needs a rotating infrared
sensor and can get reliable position sensing with
some simple triangulation calcs.

Infrared beacons are easier to build and will give
more accurate results. :o)

Maybe try a web search for "robot lab" and see
what some of the Uni guys are using.
-Roman

PS. You are probably getting off-list responses
as your "mail to" is set to you.

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2001\06\20@180550 by Andreas Eriksson

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At 23:38 2001-06-20 +1000, you wrote:
>Hi Joan, you may be re-inventing the wheel. :o)
>I also see potential problems with using sonic
>beacons due to the high reflectivity of most
>indoor surfaces.

I'm doing a project which needs the same info(the position in the room) and
I've come up with:
If you use different signals for each transmitter you know the shortest way
will always be a straight line and not a reflection.

>Most robot labs are using infrared beacons, these
>transmit a simple infrared code like a TV remote
>does. The robot just needs a rotating infrared
>sensor and can get reliable position sensing with
>some simple triangulation calcs.

Sounds great, but for my project I wouldn't like to have a rotating
IR-detector on my head(it's a VR-project) and the angles would get all
messed up..

So I need a way to find the local position and it shouldn't give different
results when the "receiver" is tilted or rotated in any way... suggestions?


Regards

Andreas Eriksson

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2001\06\20@190816 by David Venz

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Hey.

Could it be done with a single IR source and rotary encoders on the wheels?  (Not being a roboticist myself, I wonder if you need
rotary encoders if you use stepper motors?)

Cheers,
-Dave.

Roman Black wrote:
{Quote hidden}

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2001\06\20@192931 by David Cary

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Dear Andreas Eriksson,

Andreas Eriksson <KILLspamvulpineKILLspamspamSWIPNET.SE> on 2001-06-20 05:03:26 PM mentioned:
>I'm doing a project which needs the same info(the position in the room) and
>I've come up with:
>If you use different signals for each transmitter you know the shortest way
>will always be a straight line and not a reflection.

Yes, if you use acoustic beacons. (I suspect that photons travel too fast for
you to discriminate between the ``first'' reception and the ``echo'' ... unless
you have a really, really big room :-).

>I wouldn't like to have a rotating
>IR-detector on my head(it's a VR-project) and the angles would get all
>messed up..
>
>So I need a way to find the local position and it shouldn't give different
>results when the "receiver" is tilted or rotated in any way... suggestions?

Hasn't this been done before ?

How about: Put a small camera on your headgear
 small CCD cameras
 TV video transmitters
 http://www.ramseyelectronics.com/hk/hkcam.htm

and carefully put bar code patterns on the walls of the room so you know which
direction it is pointing.

Or:

Put a camera in the North-East corner of the room, and another camera in the
North-West corner of the room, and some bright LEDs in your headgear (so it's
easy to discriminate between the headgear and the other clutter in the room).
Then use binocular vision to figure out where those LEDs are. Um... would a
camera pointed down from the ceiling be helpful ? Maybe blink the LEDs ?

 Robotics Frequently Asked Questions List # Cameras
 http://www.frc.ri.cmu.edu/robotics-faq/10.html#10.1.1

 more about CCDs
 http://rdrop.com/~cary/html/machine_vision.html#CCD

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2001\06\21@093922 by Roman Black

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Sure, that would work fine allowing for some small
errors from wheel traction. Some robot labs do it exactly
that way, especially with the "ants" (tiny group robots).
-Roman



David Venz wrote:

{Quote hidden}

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2001\06\21@094130 by Douglas Butler

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Any driven wheel will slip on any real floor (not laboratory
conditions).  Also any sort of collision will confuse wheel counts.
Encoders on non-driven wheels are a posibility.  I am working on a
system using optical mice for relative tracking, and time of flight
ranging for periodic absolute position corrections.

Sherpa Doug

> {Original Message removed}

2001\06\21@163031 by joan

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Douglas Butler wrote :
>
>  Any driven wheel will slip on any real floor (not laboratory
>  conditions).

You are completely right. I have programmed my rover to describe square
trajectories (begin : advance X m, turn right 90 degrees, goto begin)
and in a few seconds you can see how the square trajectory which
was pointing to the room's door, happens to start pointing to the
window, and then to the table, and then .....

It is absolutely useless to try to implement a dead recknoning
system counting wheel turns. It is like trying to follow a trajectory
in the desert, in the middle of a sand storm by counting paces.
Haven't you seen tons of films where the main character did describe
a circle by implementing this method ? The reason : when we walk, we
never walk exactly straight on, we slightly derive to one side...
We need an external reference to keep our North (the Polar Star, the
magnetic North, a GPS ...)

IMHO dead recknoning is only useful as a rough guide between positioning
processes (as far as theses processes are frequent enough). That is :
compute your position, walk (guiding yourself by dead recknoning),
compute your position again and correct the following piece of trajectory
according to the position error you have got, etc....

>  Also any sort of collision will confuse wheel counts.

This is an added problem !

>  Encoders on non-driven wheels are a posibility.

This only makes the instant error smaller, but the acumulative one
is uncontrolable.

>  I am working on a
>  system using optical mice for relative tracking, and time of flight
>  ranging for periodic absolute position corrections.

I am very interested on this last point. Please, if you make any
progress let me know ...

Joan

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2001\06\21@164523 by steve

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> I have thought on a LPS (that is, a Local Positionning System as
> opposed to GPS). More specifically I am thinking on using three
> ultrasound (or high freq. sound) beacons, all of them emitting
> simultanously and periodically  a given signal and compute the
> position and orientation of my rover by using the delay of the
> signals when reaching two onboard microphones separated a
known
> distance (1 millisecond <=> 30 cms).
>
> Do you think that this is feasable ? Has someone tried this
before ?

I haven't tried either but another approach you could consider is a
single microphone with a rotating parabolic dish. The strength of
the signal would peak when the dish is pointing at a beacon. Have
two identifiable beacons and calculate your position.
Suitable assemblies can be found on top of police cars. Just
replace the bulb with a microphone.
It would certainly look the part. :-)

Steve.


======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: spamBeGonestevebspamBeGonespamtla.co.nz      fax +64 9 820-1929
======================================================

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2001\06\21@164729 by steve

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> I have thought on a LPS (that is, a Local Positionning System as
> opposed to GPS). More specifically I am thinking on using three
> ultrasound (or high freq. sound) beacons, all of them emitting
> simultanously and periodically  a given signal and compute the
> position and orientation of my rover by using the delay of the
> signals when reaching two onboard microphones separated a known
> distance (1 millisecond <=> 30 cms).
>
> Do you think that this is feasable ? Has someone tried this before ?

I haven't tried either but another approach you could consider is a
single microphone with a rotating parabolic dish. The strength of
the signal would peak when the dish is pointing at a beacon. Have
two identifiable beacons and calculate your position.
Suitable assemblies can be found on top of police cars. Just
replace the bulb with a microphone.
It would certainly look the part. :-)

Steve.

======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: TakeThisOuTstevebEraseMEspamspam_OUTtla.co.nz      fax +64 9 820-1929
======================================================

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2001\06\21@170329 by joan

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>  Now, to start building a prototype I have only an
>  electret microphone, a 8 Ohm loudspeaker, a 555 and a 567 pll (and, of
>  course,
>  plenty of PICs !).

I have started with some prior tests, with the 555 as a astable oscillator
feeding the speaker, and looking with a scope the signal driving the
loudspeaker and the signal given by the microphone. One of the few
things that  I can conclude with absolute certainty is that for frequencies
above 10 KHz I am absolutely deaf :-(
The other thing that I can conclude is that my wife does not like 10 KHz
sounds :-)

(Note : Both the speaker and the microphone work for frequencies well above
the audible band. I have not measured yet the cutoff frequency. I have not
tried neither to put the 567 tone decoder to work).

By the way, I have dismantled an ultrasound-based  distance measuring gadget
and I have taken away the emitter and the receiver.
How can I distinguish one from the other ? They look like the same.
The only difference is that one has a white spot painted and the other one a
blue one. Any clues ?

Any simple circuit for driving them ?

Thanks

Joan

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2001\06\21@185850 by David Venz

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Hey, thanks.  Very informative.

So would dead reckoning plus the single IR beacon I suggested do the
trick?  I guess you'd need a rotating detector as suggested for the
audio rig, anyway - to detect "peak" signal & determine direction of
beacon.  A thought - to account for reflections etc (whether audio or
IR), would you have to complete a full 3600 sweep and say that the
highest peak is the true direction of the transmitter?  Also, I guess
that at time of computation of the true direction, you'd have to account
for any movement of the vehicle since the peak was detected?  If the
speed of the vehicle was slow enough and the detector rotated fast
enough, this could be trivialised.

Cheers,
-Dave.

Joan Ilari wrote:
{Quote hidden}

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2001\06\21@201332 by Brandon Fosdick

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The lab I work in (http://www.ssl.umd.edu) has developed a system called
3DAPS (3D Audio Positioning System) for use in our neutral bouyancy
tank. It works very similar to GPS in that there is a set of emitters in
the tank that produce a periodic signal. The vehicles determine their
locations by comparing the time delay between the different received
signals. Such a system could potentially work on land to. I believe the
multipath problem is solved by limiting the periodicity of the signal
such that the alternate path echo is short in comparison. It may even
work for IR too.

You could also use an approach similar to what airplanes have been using
for many years called VOR (VHF Omnidirectional Radio). Instead of a
rotating detector, the transmitter(s) rotate(s). Each time the
transmision direction passes a given direction (north in the aviation
case) a "center beacon" sends a pulse on a slightly different frequency.
The receiver on the vehicle starts a timer when it sees the center
beacon pulse and waits till the sweeping signal is received. Knowing the
rotational speed of the transmitter, the receiver can then find its
bearing from the beacon. By using more than one beacon a complete
position can be triangulated. This might be hard to do with IR unless
you can get IR LED's with dicernable frequency seperations. But it
should be very easy to do with sound. In fact, with sound you don't even
need rotating parts, just use a simple phased array antenna (depending
on how much processing power you have and how much angular resolution
you need).

Hope that helps.
-Brandon

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2001\06\22@025505 by Peter L. Peres

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> Brandon Fosdick's idea of IR VOR

Hm. Nowadays VORs do not rotate, they statically switch the antennas. Why
not switch four LEDs with some lenses using an AM+pulses modulated
signal. The zero could be signalled by a different code or
modulation frequency. There are some optical problems and some hardware
problems with this (implementing controlled current drive for the LEDs).
The beacon would be expensive unless mass manufactured. It would only make
sense when used with many robots.

On the other hand, how about implementing the VOR/DF on the receiver ?
Four sensors, each covering a quadrant, A PIC with four A/D channels doing
the static scanning, no moving parts, presto -> optical direction finding
equipment. If the source does not vary quickly it is possible to use two
four-sensor units and implement binocular 360 degree 'vision' using only a
16F84 and 4051 mux (and a few opamps).

Am I right saying that this system may have troubles with multiple sources
(they would vector add to a false bearing and intensity indication if in
the same semiplane). So it would have to use some sort of modulated
signal on each beacon.

Peter

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2001\06\22@040332 by Peter L. Peres

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This discussion gave me an idea. What if instead of using a revolving
sensor, two sensors were embedded, one in each wheel, excentrically. Since
the wheel already has an encoder you get a spatial resolver that covers
nearly 180 degrees of solid angle.

When the wheel revolves it scans a semispace for IR sources. A mirror
glued at 45 degrees to the wheel could also be used. There may be other,
better arrangements for this.

With two sources guarding a passage in the middle this system could help
robots pass doorways etc without removing any paint. It could also help
navigate labirynths (micromouse ?) by illuminating the walls with a small
bulb or modulated IR (diffuse) and using the explored semispace to detect
walls and openings.

Has any1 done experiments on angular and distance resolution using IR
remote receivers with modulated IR ?

Peter

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2001\06\22@040415 by Lee Jones

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> You could also use an approach similar to what airplanes have
> been using for many years called VOR (VHF Omnidirectional Radio).

It's been decades.  Original transmitter was mechanical and
vacuum tube modulation.  VOR is VHF Omnidirectional Range.
It replaced the older 4 quadrant Radio Range.

> Instead of a rotating detector, the transmitter(s) rotate(s).
> Each time the transmision direction passes a given direction
> (north in the aviation case) a "center beacon" sends a pulse
> on a slightly different frequency.  The receiver on the vehicle
> starts a timer when it sees the center beacon pulse and waits
> till the sweeping signal is received. Knowing the rotational
> speed of the transmitter, the receiver can then find its
> bearing from the beacon.

That sounds more like TACAN, but I'm not familiar enough with
it to be sure.

In the VOR system, the VHF carrier frequency is modulated with
2 audio frequencies, 9600 Hz and 30 Hz (from memory, can't find
the reference book right now).  The phase shift is 0 then the
signal is aimed at magnetic north.  The phase shift varies from
0 to 359 degrees to align with the compass heading _from_ the
transmitter.

Receiver measures the phase difference between the modulating
frequencies.  Older units generate a phase shift based on the
setting of the OBS (Omni Bearing Selector). Then compare the
internally generated phase shift with the received phase shift
and drive a left/center/right needle display in the OBS.  New
VOR receivers have a mode to directly display the radial.

Remember -- this was all technology that was designed, built,
and fielded in the 1950s.

                                               Lee Jones

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2001\06\22@084415 by Roman Black

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Peter L. Peres wrote:
>
> This discussion gave me an idea. What if instead of using a revolving
> sensor, two sensors were embedded, one in each wheel, excentrically. Since
> the wheel already has an encoder you get a spatial resolver that covers
> nearly 180 degrees of solid angle.
>
> When the wheel revolves it scans a semispace for IR sources.



Clever. I haven't seen this. Part of the trouble
would be attaching a IR sensor to the rotating
wheel, would you use brushes??

Maybe could try a rotating mirror fixed to the wheel
and a stationary sensor?
-Roman

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2001\06\22@090528 by Douglas Butler

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> So would dead reckoning plus the single IR beacon I suggested do the
> trick?

I think you will need at least two beacons, more if there are
obstructions that can block the beacons.

>  I guess you'd need a rotating detector as suggested for the
> audio rig, anyway - to detect "peak" signal & determine direction of
> beacon.  A thought - to account for reflections etc (whether audio or
> IR), would you have to complete a full 3600 sweep and say that the
> highest peak is the true direction of the transmitter?

I work with sonar underwater and there are lots of focused reflections.
The strongest signal may not be the direct one.  The first signal is the
direct path, unless the direct path is blocked in which case it is the
shortest reflection.

>  Also, I guess
> that at time of computation of the true direction, you'd have
> to account
> for any movement of the vehicle since the peak was detected?  If the
> speed of the vehicle was slow enough and the detector rotated fast
> enough, this could be trivialised.

That is why my company is mostly engineers and mathematicians.

Sherpa Doug
http://www.imetrix.com

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2001\06\22@123714 by David Minkler

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Hi,
The origin for this technique was probably Loran which worked on a
similar principle.  Lots of advantages to this type of position sensing:
single frequency transmitters and receiver, no rotating parts, multipath
can be overcome,  receive system delays are a constant.  Disadvantage
was that the calculation of position from delay information was
difficult (in the days before micros) as position is at the intersection
of hyperboloids.  Much easier these days.
Regards,
Dave

Brandon Fosdick wrote:
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